international scientific conference book of abstracts · final conference in the framework of the...

“Chemistry Today for Tomorrow”

Final conference in the framework of the project

BG05M2OP001-2.009-0028 funded by operational program "Science and Education for Smart Growth”

1

INTERNATIONAL SCIENTIFIC CONFERENCE

BOOK OF ABSTRACTS

Sofia University “St. Kliment Ohridski”




2

INTERNATIONAL SCIENTIFIC CONFERENCE

BOOK OF ABSTRACTS

Sofia University “St. Kliment Ohridski”

Sofia, Bulgaria, 1st February 2019

Editors

Ivayla Pantcheva

Miroslava Nedyalkova

Hristiyan Alexandrov

Petko Petkov

St. Kliment Ohridski University Press

Sofia ● 2019

ISBN 978-954-07-4584-8




3

Invited presentations




4

IP1. APTAMERS IN ENVIRONMENTAL AND DIAGNOSTIC

APPLICATIONS – CURRENT TRENDS AND DEVELOPMENTS

Błażej Kudłak, Monika Wieczrzak

Department of Analytical Chemistry, Faculty of Chemistry, Gdańsk University of Technology,

Narutowicza Str. 11/12, 80-233 Gdańsk, Poland

[email protected]

Nucleic acids forming aptamers play a constantly growing and significant role in the target

oriented and rapid analysis of environmental sample composition. Unfortunately mostly the

medical analyses are beneficiaries of the aptamers technology. Aptamers are still seem to be

novel development in environmental analytical chemistry, and are often compared to antibodies

for many reasons, just to mention high affinity and specificity toward target molecules.

Nevertheless, the possibility of obtaining aptamers with chemical synthesis provides a ready

benefit over antibodies. Aptamers have an intrinsic potential to become with time a tool of first-

choice for the analysis and detection of a variety of compounds/stressors in any complex

matrices. During the lecture the basic pros and cons of these entities will be given, methods of

aptamers creation as well as future development trends will be given.




5

IP2. NEW DESCRIPTORS FOR PROTEINS: SEPARATION OF

ALLERGENIC FROM NON-ALLERGENIC PROTEINS

Sergio Madurga1, Miroslava Nedyalkova2, Francesc Mas1, Vasil Simeonov2

1 Department of Material Science and Physical Chemistry & Institute of Theoretical and Computational Chemistry

(IQTC), University of Barcelona, C/ Martí i Franquès, 1, 08028-Barcelona (Catalonia, Spain), [email protected],

[email protected] 2 University of Sofia, ”St. Kl. Okhridski", Faculty of Chemistry, J. Bourchier Blvd. 1, 1164 Sofia (Bulgaria),

[email protected], [email protected]

As a result of increased healthcare requirements and the introduction of genetically modified

foods, the problem of allergies is becoming a growing health problem [1]. The identification of

potential allergenic proteins is usually done by scanning a database of allergenic proteins and

locating known allergens with a high sequence similarity [2, 3]. However, this methodology will

fail if a known allergen with similar sequence is not included in the database.

We define a new methodology that does not require to have known allergens with similar amino

acid sequences. A new three-dimensional protein descriptor is calculated based on surface

protein properties. This descriptor takes into account the spatial characteristics of the surface of

the protein using different hydrophobicity scales of amino acids. This approach has not yet been

applied in protein separation into allergenic and non-allergenic classes, and it could be also

applied to separate and classify proteins in different groups. Hierarchical and non-hierarchical

(K-means) Cluster Analysis (CA) are performed in order to classify and separate the groups of

proteins [4].

Acknowledgements:

We acknowledge the financial support from Generalitat de Catalunya (Grants 2017SGR1033, 2017SGR1329 and

XrQTC), and Spanish Structures of Excellence María de Maeztu program through (Grant MDM-2017–0767). F.

Mas and S. Madurga acknowledge the funding of the EU project 8SEWP-HORIZON 2020 (692146).

References:

1. Sampson, H. J. Allergy Clin. Immunol., 115, 2005, 139–41.

2. Radauer, C. Int. Arch. Allergy Immunol. 173, 2017, 1–11.

3. Dimitrov, I., Naneva, L., Doytchinova, I., Bangov, I. Bioinformatics, 30, 2014, 846-851.

4. Simeonov, V. Classification: Encyclopedia of environmetrics. J.Wiley & Sons, New York, 2002.

mailto:[email protected]

mailto:[email protected]




6

IP3. THEORETICAL MODELING OF THE TRANSITION

TEMPERATURE IN SPIN-CROSSOVER MOLECULES

Jordi Cirera

Departament de Química Inorgànica i Orgànica and Institut de Recerca de Química Teòrica i Computacional,

Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain

Due to their inherent technological applications as molecular level switches, Spin-Crossover

systems (SCO) are the focus of intense research both in chemistry and physics. SCO molecules

display two alternative electronic states with similar energies accessible by means of an external

stimulus, most commonly the temperature, which grants access to the manipulation of an

electronic structure property using a macroscopic perturbation. In this presentation, the use of

electronic structure methods at Density Functional Theory (DFT) level to compute the transition

temperature (T1/2), a key parameter in the physical characterization of SCO systems, will be

outlined. After a proper benchmarking of different DFT methods to compute spin-state energies

for first row transition metal systems,[1] several families of SCO systems,[2-5] including

[Fe(stpy)4(NCX)2] (X = S, Se, or BH3), [Mn(CpR)2] (R = Me, iPr or tBu), or the unusual

tetracoordinated [PhB(MesIm)3Fe–N=PR3] SCO family will be analyzed using the reported

methodology, and the experimental trends observed experimentally will be fully rationalized in

terms of the underlying electronic structure using the corresponding molecular orbitals. The

reported methodology not only allows for an accurate calculation of the T1/2, but also allows us

to make some predictions, which in turns enable the use of this computational approach for the

rational design of new SCO molecules with tailored properties.

References:

1. Cirera, J., Via-Nadal, M., Ruiz, E. Inorg. Chem., 57, 2018, 14097

2. Cirera, J., Ruiz, E. Inorg. Chem., 57, 2018, 702

3. Cirera, J., Ruiz, E. J. Mat. Chem. C, 3, 2015, 7954

4. Cirera, J., Paesani, F. Inorg. Chem., 51, 2012, 8194




7

IP4. SPIN TRANSITIONS IN DITHIAZOLYL-BASED

SWITCHABLE MATERIALS

Jordi Ribas-Ariño

Departament de Ciència de Materials i Química Física and IQTCUB, Universitat de Barcelona, Av. Diagonal 645,

08028 Barcelona, Spain. E-mail: [email protected]

Dithiazolyl (DTA)-based radicals have furnished many examples of organic spin-transition

materials, some of them occurring with hysteresis, and thus giving rise to bistable systems [1].

The high-temperature (HT) polymorphs of many examples of this family of switchable

compounds feature regular π-stacks of radicals (A···A···A···A) [2, 3]. In this talk it will be

shown, on the basis of ab initio molecular dynamics results, that some of these regular π-stacking

motifs are not minimum energy structures on the potential energy surface of the system, but

average structures arising from a dynamic inter-conversion between two degenerate dimerized

configurations: (···A-A···A-A···)n (-A···A-A···A-)n [4]. This unique dynamics, whose

activation entails a second-order phase transition [5], plays a key role in defining the magnetic

properties of DTAs [6] and in triggering their spin transitions by virtue of its associated large

vibrational entropy [4].

References:

1. Rawson, J. M., Hayward, J. J. in Spin-Crossover Materials: Properties and Applications (Ed. M.A.

Halcrow), Wiley, 2013.

2. Fujita, W., Awaga, K. Science, 286, 1999, 261.

3. Brusso, J. L., Clements, O. P., Haddon, R. C., Itkis, M. E., Leitch, A. A., Oakley, R. T., Reed, R. W.,

Richardson, J. F., J. Am. Chem. Soc., 126, 2004, 8256.

4. Vela, S., Mota, F., Deumal, M., Suizu, R., Shuku, Y., Mizuno, A., Awaga, K., Shiga, M., Novoa, J. J.,

Ribas-Arino, J., Nat. Commun. 5, 2014, 4411.

5. Vela, S., Reardon, M. B., Jakobsche, C. E., Turnbull, M. M., Ribas-Arino, J., Novoa, J. J. Chem. Eur. J.,

23, 2017, 3479.

6. Vela, S., Deumal, M., Shiga, M., Novoa, J. J., Ribas-Arino, J. Chem. Sci., 6, 2015, 2371.




8

IP5. MODELLING POLYELECTROLYTES: COUPLING OF

CONFORMATIONAL AND IONIZATION EQUILIBRIA IN SOLUTION

Francesc Mas1, Pablo M. Blanco1, Sergio Madurga1, Josep Lluís Garcés2



[email protected], [email protected] 2 Department of Chemistry, University of Lleida, Av. Alcalde Rovira Roure, 191, E-25198-Lleida

(Catalonia, Spain), [email protected]

The conformational and protonation properties of linear polyelectrolytes are studied by means of

accurate Statistical Mechanics models and Monte Carlo Simulations. Statistical Mechanics is a

very useful tool in polymer science, since it allows to connect the polymer chemical structure

with physical properties such as gyration radius, persistence length, end-to-end distance, optical

and elastic properties, etc. A classical technique, the Rotational Isomeric State (RIS) model

proposed by Flory [1], has been used to study a wide range of such physical properties of neutral

polymers. However, many polyelectrolytes of interest are able to regulate their charge depending

on the conformational state. Here it is shown that the RIS model can be coupled with the Site

Binding (SB) model [2]. The resulting combined scheme, the SBRIS model [3], allows analysing

conformational and ionization properties of polyelectrolytes on the same time. This formalism

can be extended to include long-range interactions by introducing a modified free energy

involving only effective short-range interaction parameters [4]. The analytical results are

compared with Semi-Grand Canonical Monte Carlo (SGCMC) simulations, which explicitly

include long range electrostatic interactions [5]. Moreover, SGCMC simulations of the

polyelectrolyte response to an external mechanical force are also presented [6].

Acknowledgements:


XrQTC), and Spanish Structures of Excellence María de Maeztu program through (Grant MDM-2017–0767). J.L.

Garcés also acknowledges the Spanish Ministry of Science and Innovation (project CTM2016-78798-C2-1-P). F.

Mas and S. Madurga acknowledge the funding of the EU project 8SEWP-HORIZON 2020 (692146). P.M. Blanco

also acknowledges the financial support from grant (FI-2017) of Generalitat de Catalunya.

References:

1. Flory, P., “Statistical mechanics of chain molecules”, John Wiley, New York, 1969.

2. Koper, G., Borkovec, M., J. Phys. Chem. B, 105, 2001, 6666.

3. Garcés, J. L, Madurga, S., Borkovec, M., Phys. Chem. Chem. Phys., 16, 2014, 4626.

4. Garcés, J. L, Madurga, S., Rey-Castro, C., Mas, F., J. Polymer Sci. B: Polymer Phys., 55, 2017, 275.

5. Blanco, P. M., Madurga, S., Mas, F., Garcés, J. L., Polymers, 10, 2018, 811.

6. Blanco, P. M., Madurga, S., Mas, F., Garcés, J. L., submitted, 2019




9

Oral presentations




10

OP1. WWTP IMPACT ASSESSMENT BASED ON PHYSICOCHEMICAL

AND ECOTOXICOLOGICAL INDICATORS

Galina Yotova1, Svetlana Lazarova2, Veronika Mihaylova1, Boika Zlateva1, Błażej Kudłak3,

Tony Venelinov2, Vasil Simeonov1, Stefan Tsakovski1

1 Faculty of Chemistry and Pharmacy, University of Sofia “St. Kliment Ohridski”, 1 J. Bourchier Blvd., Sofia 1164,

Bulgaria, [email protected], [email protected], [email protected], [email protected]

sofia.bg, [email protected] 2 Faculty of Hydraulic Engineering, University of Architecture, Civil Engineering and Geodesy, 1 Hr. Smirnenski

blvd., Sofia 1164, Bulgaria, [email protected], [email protected] 3 Faculty of Chemistry, Gdańsk University of Technology, 11/12 Narutowicza Str., Gdańsk 80-233, Poland,

[email protected]

The quality of the underground, surface, drink and waste waters is an extremely relevant

problem in the last decades, especially after publication of Water Framework Directive [1].

Wastewater treatment plants (WWTPs) play crucial role in shaping modern society’s

environmental well-being and awareness, however only well operated and supervised systems

can be considered as environmentally sustainable.

The aim of the study is to assess the impact of Bulgarian WWTPs on the receiving water bodies

by multivariate statistical modeling of physicochemical and ecotoxicological surface water

quality indicators.

Water samples from receiving water bodies were collected in August 2018 by an appropriate

monitoring scheme including water samples prior to and just after wastewater outlets. Both

classical and biological methods (ecotoxicity tests) were utilized to assess environmental impact

of given WWTPs. To assess the ecotoxicity of water samples a battery of selected ecotoxicity

tests (standardized by ISO) [2] was applied. The selected species are of different troffic levels –

producers (Sorghum saccharatum, Lepidium sativum and Sinapis alba), consumers (Daphnia

magna) and reducers (Vibrio fischeri).

Multivariate analysis was performed in order to reveal internal dataset relations and latent factors

controlling surface water quality. The classification of the specific relationships between both

types of indicators is of substantial importance for assessment of the anthropogenic impact and

identification of the factors on which it depends.

References:

1. Directive 2000/60/EC of the European Parliament and of the Council establishing a framework for

Community action in the field of water policy, OJ L, 327, 2000, 1.

2. Kaza, M., Mankiewicz-Boczek, J., Izydorczyk, K., Sawicki, J., Polish J. Environ. Stud., 16, 2007, 81.




11

OP2. FROM METAL ION DIRECTED TEMPLATE SYNTHESIS

TO POLYMERIC DINUCLEAR COMPLEXES -

CRYSTALLOGRAPHIC EVIDENCES

Anife Ahmedova1, Nikola Burdzhiev1, Boris Borisov1, Yanislav Danchovski1, Sonya Zareva1,

Anna Dołęga2

1 University of Sofia, Faculty of Chemistry and Pharmacy, 1, J. Bourchier av. Sofia 1164, Bulgaria

e-mail: [email protected] 2 Department of Inorganic Chemistry, Faculty of Chemistry, Gdansk University of Technology, G. Narutowicza

11/12, 80-233 Gdansk, Poland

In this talk will be presented crystallographic data on two types of metal complexes –

mononuclear Ni(II) complexes and hetero-bimetallic polymeric complexes of Cu(II) and Zn(II).

The former type of complexes were obtained from attempts to exploit the Ni(II)-directed

template synthesis between 2-acetyl-1,3-indandione (2-AID) and ethylenediamine (en). The

crystallographic data revealed the formation of mononuclear complex of partly cyclized

condensation product. Additional synthetic and theoretical studies are in progress in order to

elucidate the structural effects of the reagents used (the triketone and the diamine) and the

reaction conditions needed to accomplish the complete cyclization.

The hetero-bimetallic polymer complex is obtained by mixing Zn-acetate with the Cu(II)

complex of the Schiff base of 2-substituted-1H-imidazol-4(5)-carbaldehyde and 2-(pyridin-2-

yl)ethan-1-amine, which is also obtained with the templating effect of the Cu(II) ion. The

crystallographic data confirmed our expectations that the Cu(II) complex of the imidazole-based

Schiff base can act as a ligand at a proper pH and can coordinate to another metal ion [1].

All these data, we believe, are the seeds of future fruitful research topics that we intend to

pursue.

Acknowledgement:

This collaboration was initiated with the help of the project - BG05M2OP001-2.009-0028 funded by operational

program "Science and Education for Smart Growth.

References:

1. Ahmedova, N. Burdzhiev, S. Ciattini, E. Stanoeva, M. Mitewa, C. R. Chim. 13, 2010, 1269.




12

OP3. ENRICHED WATER PURIFICATION

USED IN 18F CYCLOTRON PRODUCTION

Boyan Todorov1, Iva Belovezhdova1, Anu Airaksinen2, Rumyana Djingova1

1 Department of Analytical Chemistry, Faculty of Chemistry and Pharmacy, University of Sofia, 1, J. Bourchier,

1164, Sofia. Bulgaria, [email protected] 2 Radiopharmaceutical Chemistry, Department of Chemistry, University of Helsinki, POB 55, FI-00014, Finland,

[email protected]

A new method for purification of previously irradiated enriched water for volumes less than 100

ml was developed and characterized by 93% ± 2% of [18O]H2O recovery after the purification.

Organic compounds (99.5% ± 0.1%), radioisotopes (99.7% ± 0.1%) and trace metals (99.8% ±

0.1%) were efficiently eliminated by the high-yield processes included in this method such as co-

precipitation, co-crystallization and distillation. The method demonstrates effective purification

ability in a wide range of concentrations of organic solvent impurities from ppm to percentage.

From practical point of view, the method being a combination of simple techniques, inexpensive

equipment, reagents and minimal radioactive dose exposure of the involved personal, can be

introduced in a typical hospital radiochemical laboratory, commercial production cyclotron and

scientific cyclotron facilities.




13

OP4. COLLOIDAL APPROACH FOR THE PREPARATION OF THE

TEXTURED Mo-, W-, Fe-BASED MATERIALS FOR HER

Borjana Donkova1, Saim Emin2

1 Department of Inorganic Chemistry, Faculty of Chemistry and Pharmacy, University of Sofia, 1 J. Bourchier Blv.,

1164 Sofia, Bulgaria, [email protected] 2 Materials Research Laboratory, University of Nova Gorica, Vipavska Cesta 11c, SI-5270, Slovenia,

[email protected]

In recent years transition metal carbides, phosphides and chalcogenides have drawn great

attention due to their potential application as a cathode material for hydrogen evolution reaction

(HER) through water electrolysis.

The focus of the present study is on the development of synthesis procedures for the preparation

of metal-based thin films on graphite electrodes. Colloidal Mo, W and Fe nanopartiles were

synthesized using wet-chemistry approach. The nanoparticles of the given metal were deposited

on the graphite plates by spin-coating. After heat treatment at elevated temperatures in the

presence of Se or P the obtained materials were characterized by XRD analysis, SEM-EDS and

HRTEM observations.

The activity of the as prepared textured thin films for a hydrogen production was tested.

Electrocatalytic measurements were done in a three-electrode configuration in 0.5 M H2SO4

aqueous electrolyte solution. Graphite and an Ag/AgCl electrode were used as the counter and

reference electrodes, respectively. The overpotential at current density of 10 mA cm−2 (η10) was

estimated and compared.

Based on the results obtained it could be concluded that the colloidal route is a suitable and

simple way for the preparation of electrocatalytic active thin films for HER.




14

OP5. PHOTOCATALYTIC ACTIVITY OF NiFe2O4 AND Zn0.5Ni0.5Fe2O4

MODIFIED BY Eu(III) AND Tb(III)

FOR DECOMPOSITION OF MALACHITE GREEN

Martin Tsvetkov1, Izabela R. Ivanova1, Evgenia P. Valcheva2, Joana Zaharieva1,

Mariya Milanova1

1 Department of Inorganic Chemistry, Faculty of Chemistry and Pharmacy, Sofia University “St. Kliment Ohridski”,

1, J. Bourchier, 1164 Sofia, Bulgaria 2 Department of Solid State Physics, Faculty of Physics, Sofia University

“St. Kliment Ohridski”, 3, J. Bourchier, 1164 Sofia, Bulgaria

email:[email protected]

The mixed metal oxides NiFe2O4 and Zn0.5Ni0.5Fe2O4 with spinel-like structure modified with

the lanthanide ions Eu(III) and Tb(III) by a sol-gel process using propylene oxide as a gelating

agent were tested as photocatalysts. The photocatalytic activity was studied both under UV and

under polychromic visible light irradiation (halogen lamp) for the decomposition of the water

pollutant Malachite Green in model solutions, prepared in laboratory conditions. The modified

samples showed a better activity under visible light than under UV light irradiation. The highest

activity under visible light irradiation was observed for Zn0.5Ni0.5Fe2O4 modified with 5 %

Eu(III) or Tb(III), and by that showing the positive effect of the doping ions. Based on the

cartographic data for the smooth and equal distribution of Tb(III) on the surface of

Zn0.5Ni0.5Fe2O4 particles an influence of the surface processes on the photocatalytic activity can

be suggested. The energy band gap of the samples was calculated, showing values lower than

those for the pure ferrites, influenced by the presence of Eu(III) and Tb(III).

Acknowledgement:

Authors are grateful to Operational programme "Science and education for smart growth", project BG05M2OP001-

2.009-0028




15

OP6. HARDENING OF PARTICLE/WATER/OIL THREE-PHASE

DISPERSIONS DUE TO CAPILLARY BRIDGES WITH

APPLICATIONS FOR NEW PRODUCTS AND MATERIALS

Mihail Georgiev1, Krassimir Danov1, Peter Kralchevsky1, Theodor Gurkov1,

Denitsa Krusteva1, Lyuben Arnaudov2, Simeon Stoyanov2, Eddie Pelan2

1Department of Chemical & Pharmaceutical Engineering, Sofia University, Sofia 1164, Bulgaria 2Unilever Research & Development Vlaardingen, 3133AT Vlaardingen, The Netherlands

The subject of this study is the rheological behavior of three-phase dispersions

particles/water/oil. In this area, there is a vast unexplored concentration gap between the phase

domain of particle networks (particle volume fractions ϕp < 30%) [1] and the domain of wet

granular materials (p > 70%) [2]. The objective of our studies is to experimentally investigate

and theoretically interpret the rheological properties of dispersions in the intermediate region,

30% < ϕp < 70%. They possess the remarkable property that the addition of a minimal amount of

the second (disperse) liquid phase leads to strong solidification of the dispersion owing to the

interconnection of the particles by capillary bridges. The yield stress, Y, of the dispersions is

investigated for various ϕp values. Quantitative theoretical model is developed, which relates Y

with the maximum of the resultant of capillary bridge force as a function of shearing angle. The

model agrees very well with the experimental data. For water-in-oil bridges, Y is systematically

lower than for the respective oil-in-water bridges (Figure 1) because of electrostatic repulsion

between the particles across the oil phase [3], which opposes the capillary-bridge attraction.

The results could have importance for various materials in chemical and food industries,

construction materials and cosmetics, which represent solid/water/oil three-phase dispersions.

Oily capillary bridges in water

Water capillary bridges in oil

References

1. Koos, E., Curr. Opin. Colloid Interface Sci.,19, 2014, 575.

2. Mitarai, N., Nori, F., Adv. Phys., 55, 2006, 1.

3. Kralchevsky, P. A., Danov, K. D., Petkov, P. V., Phil. Trans. R. Soc. A, 374, 2016, 20150130.




16

OP7. INFLUENCE OF THE HYDRODYNAMIC CONDITIONS,

SURFACTANT TYPE AND SURFACTANT CONCENTRATION

ON SOLUTION FOAMINESS

Borislava Petkova, Slavka Tcholakova, Nikolai Denkov

1 Department of Chemical and Pharmaceutical Engineering, Faculty of Chemistry and Pharmacy, Sofia University,

Sofia, Bulgaria, [email protected], [email protected], [email protected]

Surfactants are essential ingredients in many personal and household care products, and in

various technological applications. Major aim of the current study is to clarify the role of the

hydrodynamic conditions, surfactant type and surfactant concentration on the foamability of

solutions. Experiments were performed at low and high surfactant concentrations, below and

above the critical micelle concentration, using one anionic and two nonionic surfactants which

differ in their hydrophilic head-groups and in the length of their hydrophobic tails. We applied

three experimental methods for foam generation which differ significantly in their hydrodynamic

conditions – automatic Bartsch test, foam rise method and a planetary mixer. To explain the

obtained results, the surface properties of the studied solutions were characterized in terms of

their equilibrium and dynamic surface tensions

The foamability of the solutions of ionic surfactants is higher in the Bartsch test, whereas the

nonionic surfactants are much more efficient when the foam is formed in a planetary mixer.

These trends are explained by the very different characteristic times of the foaming process in

these two foaming methods. In the Bartsch test the surfactant adsorption is in the millisecond

range, whereas the properties of the (almost) equilibrium adsorption layers are important for the

foaming in the planetary mixer. All experimental data obtained with different surfactant

solutions from different foaming methods fall around two universal curves (one for ionic and

another one for nonionic surfactants) when the foam volume is presented as a function of the

Gibbs elasticity of the dynamic adsorption layers, formed on the bubble surface in the respective

foaming method.




17

OP8. SURFACE AND FOAM PROPERTIES

OF NONIONIC SURFACTANT SOLUTIONS

AT HIGH SUGAR CONCENTRATION

Fatmegyul Mustan1, Nadya Politova1, Zahari Vinarov1,

Slavka Tcholakova1, Damiano Rosseti2, Pip Rayment2


1 J. Boucher Ave., 1164 Sofia, Bulgaria, [email protected] 2 Unilever R & D, Colworth, UK

Characterization of the surface and foam properties of the amphiphilic molecules which possess

high surface activity is very important from the view point of their practical application in

different formulations. One of such type of molecules is alkyl esters which are a focus point in

our study. Series of esters with different hydrophilic groups in wide range of hydrophilic-

lipophilic balance values are investigated. The surface properties of their aqueous solutions in

presence of high sucrose concentration are studied in terms of adsorption kinetics and surface

elasticity determined upon slow compression of the surface layer. Their foamability and foam

rheology are also studied.

By the optical observations it is found that the hydrophobic esters (hydrophilic-lipophilic

balance <11) form different in shape and in size vesicles inside the solutions depending on the

hydrophilic head group. From the surface properties characterization is obtained that the

presence of vesicles inside the solutions is responsible for the formation of condensed layers

which give very high surface elasticity > 100 mN/m and very high surface stress upon slow

deformation. The values for both surface and foam rheology of the hydrophilic ones, which do

not form any entities inside the solution, are much lower. But foams with very small bubbles in

size and high yield stress are produced with hydrophobic surfactants. The results from both types

of experiments show very good correlation between the rheological behavior of the adsorption

layers and foams stabilized by these layers.

Acknowledgement:

F. Mustan is grateful to Operational Program "Science and Education for Smart Growth", project BG05M2OP001-

2.009-0028




18

OP9. ENCAPSULATION OF OILS AND FRAGRANCES BY CORE-IN-

SHELL STRUCTURES FROM SILICA

PARTICLES, POLYMERS AND SURFACTANTS:

THE BRICK-AND-MORTAR CONCEPT

Gergana Radulova, Tatiana Slavova, Peter Kralchevsky, Elka Basheva, Krastanka Marinova,

Krassimir Danov

Department of Chemical and Pharmaceutical Engineering, Sofia University, Bulgaria

[email protected]

Colloidosomes provide a possibility to encapsulate oily substances in water in the form of core-

in-shell structures. In this study, we produced microcapsules with shell from colloidal particles,

where the interparticle openings are blocked by mixed layers from polymer and surfactant that

prevent the leakage of cargo molecules. In other words, the particles and polymer play the role of

bricks and mortar. For this goal, we used hydrophilic silica particles, which were partially

hydrophobized by the adsorption of potassium oleate to enable them to stabilize Pickering

emulsions. Various polymers were tested to select the most appropriate one. The procedure of

encapsulation is simple and includes single homogenization by ultrasound. The produced

capsules are pH responsive. They are stable in aqueous phase of pH in the range 3 – 6, but at pH

> 6 they are destabilized and their cargo is released. With the optimized formulation of silica

particles, polymer, oleate and NaCl, we were able to encapsulate various oils and fragrances,

such as tetradecane, limonene, benzyl salicylate and citronellol. All of them have a limited and

not too high solubility in water. In contrast, no stable microcapsules were obtained with oils that

either have zero water solubility (mineral and silicone oil) or higher water solubility

(phenoxyethanol and benzyl alcohol). By analysis of results from additional interfacial-tension

and thin-film experiments, we concluded that a key factor for obtaining stable capsules is the

irreversible adsorption of the polymer at the oil/water interface. The hydrophobization of the

particles by surfactant adsorption (instead of silanization) plays an important role for the pH

responsiveness of the produced capsules. The obtained information about the role of various

factors for the stabilization of microcapsules, which are based on the brick-and-mortar concept,

can be further used to achieve better stability; selection of polymers that are appropriate for

different classes of oils, as well as for the production of smaller capsules stabilized by

nanoparticles.




19

OP10. EFFECT OF SURFACTANT-BILE INTERACTIONS

ON THE SOLUBILITY OF HYDROPHOBIC DRUGS

IN BIORELEVANT DISSOLUTION MEDIA

Zahari Vinarov1, Vladimir Katev1, Nikola Burdzhiev2, Slavka Tcholakova1, Nikolai Denkov1

1Department of Chemical and Pharmaceutical Engineering, Faculty of Chemistry and Pharmacy, Sofia University,

1164 Sofia, Bulgaria, [email protected] 2Department of Organic Chemistry and Pharmacognosy, Faculty of Chemistry and Pharmacy, Sofia University,

1164 Sofia, Bulgaria

Biorelevant dissolution media (BDM) methods are commonly employed to investigate the oral

absorption of poorly water-soluble drugs. Despite the significant progress in this area, the effect

of commonly employed pharmaceutical excipients, such as surfactants, on the solubility of drugs

in BDM has not been characterized in detail. The aim of this study is to clarify the impact of

surfactant−bile interactions on drug solubility by using a set of 12 surfactants, 3 model

hydrophobic drugs (fenofibrate, danazol, and progesterone) and two types of BDM (porcine bile

extract and sodium taurodeoxycholate). Drug precipitation and sharp nonlinear decrease in the

solubility of all studied drugs is observed when drug-loaded ionic surfactant micelles are

introduced in solutions of both BDM, whereas the drugs remain solubilized in the mixtures of

nonionic polysorbate surfactants + BDM. One-dimensional and diffusion-ordered 1H NMR

spectroscopy show that mixed bile salt + surfactant micelles with low drug solubilization

capacity are formed for the ionic surfactants. On the other hand, separate surfactant-rich and bile

salt-rich micelles coexist in the nonionic polysorbate surfactant + bile salt mixtures, explaining

the better drug solubility in these systems. The nonionic alcohol ethoxylate surfactants show

intermediate behavior. The large dependence of the drug solubility on surfactant−bile

interactions (in which the drug molecules do not play a major role per se) highlights how the

complex interplay between excipients and bile salts can significantly change one of the key

parameters which governs the oral absorption of poorly water-soluble drugs, viz. the drug

solubility in the intestinal fluids [1].

References:

1. Vinarov, Z., Katev, V., Burdzhiev, N., Tcholakova, S., Denkov, N., Mol. Pharm, 559, 2018. doi:

10.1021/acs.molpharmaceut.8b00884.




20

OP11. ROLE OF THE INTERFACIAL ELASTICITY FOR THE BULK

PROPERTIES OF EMULSIONS, STABILIZED WITH SAPONINS

Sonya Tsibranska1, Konstantin Golemanov1, Slavka Tcholakova1, Nikolai Denkov1,

Simeon Stoyanov2 and Eddie Pelan2

1 Department of Chemical and Pharmaceutical Engineering, Sofia University, Sofia, 1164, Bulgaria 2 Unilever Research & Development Vlaardingen, Vlaardingen, 3133AT, The Netherlands

Saponins are natural surfactants which are widely used in food and pharmaceutical industries. In

our previous study [1] we characterized the surface rheological properties of saponins on air-

water interface, subjected to shear and dilatational deformations. We established that triterpenoid

saponins (such as Escin, Tea saponin, Berry saponin concentrate and Quillaja Dry) formed

adsorption layers with very high surface elasticities and viscosities. In the current study we

measured the rheological response of the adsorption layers formed on hexadecane-water and

sunflower oil-water interfaces under dilatational deformation by using Capillary Pressure

Tensiometry (CPT). We found that the adsorption layers formed from Quillaja Dry and Berry

saponin concentrate solutions behave as a solid shell (see Figure 1). The other studied saponins

have high dilatational elasticity on oil-water interface which allow us to determine the effect of

dilatational surface elasticity on the rheological response of formed emulsions from these

solutions. We prepared emulsions with oil fractions between 65 wt% and 75 wt% and measured

their elastic modulus. The obtained experimental results showed that the dimensionless elasticity

of emulsions depends significantly on the dilatational elasticity of adsorption layers formed on

the drop surface. When dilatational surface elasticity is below 40 mN/m the dimensionless

elasticity is very close to one predicted by theoretical expressions derived by Mason and Princen

[2-3], whereas when the dilatational surface elasticity is above 40 mN/m the dimensionless

elasticity of emulsions becomes higher than theoretically calculated ones, in some cases more

than 3 times.

(A) (B)

Figure 1. Drop of (A) BSC solution in sunflower oil (B) sunflower oil in QD solution. Oil or

solution is pushed into the drop, the whole surface starts moving as a solid body.

References

1. Pagureva, N., Tcholakova, S., Golemanov, K., Denkov, N. D., Pelan, E., Stoyanov, S. D., Coll. Surface A,

491, 2016, 18.

2. Mason, T. G., Lacasse, M-D., Grest, G. S., Levine, D., Bibette, J., Weitz, D. A., Phys. Rev. E., 56, 1997,

3150.

3. Princen, H. M., Kiss, A. D. J., Coll. Interface Sci., 112, 1986, 427.




21

OP12. ROLE OF LYSOLIPIDS ON THE INTERFACIAL AND

LIQUID FILM PROPERTIES OF ENZYMATICALLY MODIFIED

EGG YOLK SOLUTIONS

Dilek F. Gazolu-Rusanova1, Fatmegul Mustan1, Zahari Vinarov1, Slavka Tcholakova1,

Nikolai Denkov1, Simeon Stoyanov2 and Julius de de Folter2


This study aimed to establish the similarities and differences in the behavior of adsorption layers

of native egg yolk (EY) and enzymatically modified egg yolk (MEY) at the oil-water interface.

The properties of adsorption layers were characterized by measuring interfacial tension and

surface dilatational modulus. The interactions between adsorption layers formed on two oil-

water interfaces were evaluated by optical observations of emulsion films formed in the capillary

cell. The chemical composition, electrokinetic properties and rheological properties of the

studied egg yolk solutions were also determined. It was found that the rate of adsorption is faster

and dilatational surface moduli are lower, whereas the equilibrium surface tension is higher for

adsorption layers formed from a solution of MEY. Faster film thinning and thinner films are

formed from modified egg yolk solutions. To explain these differences between EY and MEY, it

was assumed that the interfacial properties of MEY are mainly determined by the

lysophospholipids, which are products of the enzymatic modification of the egg yolk. The

addition of lysolipid even at a relatively low concentration (corresponding to 60 % degree of

conversion) into the solution of EY leads to properties of adsorption layers and emulsion films

which are typical for enzymatically modified egg yolk.




22

OP13. SELF-SHAPING OF SINGLE

AND MULTICOMPONENT EMULSION DROPS

Diana Cholakova1, Nikolai Denkov1, Slavka Tcholakova1, Zhulieta Valkova1,

Ivan Lesov1, Stoyan Smoukov2

1 Department of Chemical and Pharmaceutical Engineering, Faculty of Chemistry and Pharmacy,

Sofia University, Sofia, Bulgaria, e-mail: [email protected] 2 Active and Intelligent Materials Lab, School of Engineering and Materials Science, Queen Mary University of

London, London, UK, e-mail: [email protected]

Linear hydrocarbons are known to pass through a series of stable and metastable rotator phases

before freezing. In our recent studies [1, 2] we showed that, by using appropriate cooling

protocols, we can harness these phase transitions to control the deformation of liquid

hydrocarbon droplets and then freeze them into solid particles, permanently preserving their

shape. Upon cooling, the droplets spontaneously break their shape symmetry several times,

morphing through a series of complex regular shapes owing to the internal phase-transition

processes.The self-shaping phenomenon was observed with alkanes, alkenes, long chain

alcohols, asymmetric alkanes or mixtures of two or more of these substances [3]. The main

factors which can be used to control the drop “self-shaping”, before their freezing into solid

particles, are the surfactant type and chain length, cooling rate, and initial drop size. As a rule,

the smaller drops, stabilized by surfactants with longer chain-length, and subject to slower

cooling, evolve easier to shapes with higher aspect ratio. The mechanism explaining all these

transformations offers insights into achieving complex morphogenesis from a system with a

minimal number of molecular components [4, 5].

Deformed drops from hexadecane: (a) hexagons, Tween 60; (b) triangle with long protrusions,

Brij 58; (c) rods, Tween 60. Scale bars, 20 m. References:

1. Denkov, N., Tcholakova, S., Lesov, I., Cholakova, D., Smoukov, S. Nature, 528, 2015, 392.

2. Cholakova, D., Denkov, N., Tcholakova, S., Lesov, I., Smoukov, S. K. Adv. Coll. Interface Sci., 235,

2016, 90.

3. Cholakova, D., Valkova, Z., Tcholakova, S., Denkov, N., Smoukov, S. K. Langmuir, 33, 2017, 5696.

4. Denkov, N., Cholakova, D., Tcholakova, S., Smoukov, S. K. Langmuir, 32, 2016, 7985.

5. Cholakova, D., Valkova, Z., Tcholakova, S., Denkov, N., Smoukov, S. K. Multilayer formation and

enthalpy effects in self-shaping emulsion droplets, Langmuir, 2019, under revision.




23

OP14. EFFICIENT SELF-EMULSIFICATION VIA COOLING-HEATING

CYCLES – MECHANISMS AND CONTROL OF THE PROCESS

Zhulieta Valkova1, Diana Cholakova 1, Slavka Tcholakova1, Nikolai Denkov1,

Stoyan K. Smoukov 2


Sofia, Bulgaria, [email protected] 2 Active and Intelligent Materials Lab, School of Engineering and Materials Science, Queen Mary University of

London, Mile End Road, London E14NS, UK, [email protected]

Recently it was reported a conceptually new bottom-up approach where internal phase

transitions in oil droplets transform them into micrometer-sized, fluid objects with complex

shapes, such as regular polyhedra, platelets shaped as hexagons, triangles, squares, toroids, and

others [1, 2]. Under appropriate conditions, we observed a spontaneous process of drop bursting

and fragmentation into numerous much smaller emulsion drops [3, 4]. This novel process of self-

emulsification incorporates three new, highly efficient drop breakup mechanisms which

encompass several branches of science: elasto-caapillarity, hydrodynamic jet stability, and

surface wetting [3]. One of these mechanisms includes the remarkable phenomenon of lipid

crystal dewetting from its own melt [3, 4]. The method works with various oil-surfactant

combinations and has several important advantages. It enables low surfactant emulsion

formations with temperature-sensitive compounds, is scalable to industrial emulsification and

applicable to fabricating particulate drug carriers with desired size and shape.

Acknowledgments:

This work was funded by the European Research Council (ERC) grant to Stoyan Smoukov, EMATTER (№

280078). The study falls under the umbrella of European network COST MP 1305 and the Horizon 2020 project

“Materials Networking” (ID: 692146-H2020-eu.4.b).

References:

1. Denkov, N., Tcholakova, S., Lesov, I., et al., Nature, 528, 2015, 392.

2. Cholakova, D., Denkov, N., Tcholakova, S., et al. Adv. Coll. Interface Sci., 235, 2016, 90.

3. Tcholakova, S., Valkova, Z., Cholakova, D., Vinarov, Z., et al., Nature Comm., 8, 2017, 15012.

4. Valkova, Zh., Cholakova, D., Tcholakova, S., Denkov, N., Smoukov, S. K. Langmuir, 33, 2017, 12155.




24

OP15. THE ABIOGENIC ION Ga3+ AND ITS MECHANISM OF

THERAPEUTIC ACTION:

INSIGHT FROM THEORETICAL RESEARCH

Nikoleta Kircheva1, Todor Dudev1, Valia Nikolova1, Silvia Angelova2

1 Faculty of Chemistry and Pharmacy, Sofia University “St. Kl. Ohridski”, 1164 Sofia, Bulgaria,

[email protected], [email protected], [email protected]

Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences,

Sofia, 1113 Bulgaria, [email protected]

Gallium exhibits no known biological function therefore it is categorized as an abiogenic metal.

However, it has been applied as a continuous infusion to treat cancer-related hypercalcemia as

well as in the form of orally available antineoplastic drugs in different stages of clinical trials.

Although there is significant body of information in literature, its mechanism of therapeutic

action is not absolutely clear. Using the methods of the theoretical chemistry we aim to shed

light on the possible ways of gallium's anticancer activity.

References:

1. Nikolova, V., Angelova, S. E., Kircheva, N., Dudev, T. J. Phys. Chem. B, 120, 2016, 2241.

2. Kircheva, N., Dudev, T. Bulg. Chem. Comm.,50(J), 2018, 55.




25

OP16. SMART ZWITTERIONIC HYDROGELS

AS WOUND DRESSINGS IN CHRONIC WOUND THERAPY

Konstans Ruseva1,2, Kristina Ivanova2, Katerina Todorova3, Margarita Gabrashanska3, Tzanko

Tzanov2, ElenaVassileva1

1Laboratory on Structure and Properties of Polymers, Department of Pharmaceutical and Applied Organic

Chemistry, Faculty of Chemistry and Pharmacy, Sofia University ”St. Kl. Ohridski”, 1, J. Bourchier blvd., 1164,

Sofia, Bulgaria 2Group of Molecular and Industrial Biotechnology, Department of Chemical Engineering, Universitat Politechnica

de Catalunya, Rambla Sant Nebridi,22, 0822 Terrassa, Spain 3Institute of Experimental Morphology, Pathology and Anthropology with Museum, Bulgarian Academy of Sciences,

Acad. G. Bonchev Str., Bl. 25, 1113, Sofia, Bulgaria

Polyzwitterions (PZ) comprise an anionic and a cationic group in each monomeric unit which are

covalently bound. This coexistence of an equal amount of oppositely charged moieties in the

polymer structure results into a zero overall charge but at the same time causes strong intra- and

intermolecular interactions. The latter are strongly influenced by external stimulus such as

changes in temperature, pH, salt concentration, etc. As a consequence, zwitterionic polymers

undergo dramatic changes of their properties and are referred to as “smart materials”.

Furthermore, PZ are known to be remarkably resistant to protein adsorption as well as to cell

adhesion which makes them particularly interesting and promising materials for biomedical

applications.

The present work is focused on the development of zwitterionic hydrogels for efficient treatment

of highly exudating and hard-to-heal chronic wounds. To this purpose, two types of

polyzwitterionic netwoks with different crosslinking degree were synthesized - polysulfobetaine

(PSB) and polycarboxybetaine (PCB). They were characterized in terms of their physico-

mechanical properties, e.g. microhardness, swelling ability, smart behaviour. Furthermore, the

potential of PZ to resist biofilm formation towards Staphylococcus aureus and Escherichia coli

was studied. Then, their ability to reduce the high levels of myeloperoxidase and

metalloproteinase, two enzymes that present in chronic wound was revealed. Moreover, the in

vitro cytotoxic assessment of PSB and PCB networks along with their in vivo performance in

rats was also studied to reveal their high biocompatibility.

Acknowledgments:

This work is funded by Project BG05M2OP001-2.009-0028. The financial support of Bulgarian National Science

Foundation, Grant DFNI T-02-15/12.12.2014 is also acknowledged.




26

OP17. ON THE HYDRATION AND COMPLEX FORMATION

OF CYCLODEXTRINS WITH DRUGS

Stiliyana Pereva1, Tsveta Sarafska1, Silvia Angelova2, Valya Nikolova1, Tony Spassov1, Todor

Dudev1, Svetla Bogdanova1

1 Faculty of Chemistry and Pharmacy, Sofia University “St. Kl. Ohridski”, 1164 Sofia, Bulgaria,

[email protected] 2 Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences,


Cyclodextrins (CDs) are natural macrocyclic oligosacharides. They have wide applications when

used as hosts in inclusion complexes with various guests (drugs, food ingredients, cosmetic

compounds, etc). [1, 2]. Natural cyclodextrins – α-, β- and γ-CD have hydrophobic interior and

hydrophilic exterior, thus able to accommodate a guest molecule inside their cavity. Despite

having hydrophobic interior they are also non-defined hydrates – even at ambient conditions they

entrap water molecules. It has been suggested that the entrapped water molecules stabilize their

crystal lattice [3-6]. In our studies we were able to prove, both experimentally and using the

methods of quantum chemistry, that during the complex formation the guest molecule displace

(partially or completely) the water molecules from the host [7-8]. As a model drugs for the

inclusion compounds we used ibuprofen and naproxen.

References:

1. Bilensoy, E. Cyclodextrins in Pharmaceutics, Cosmetics, and Biomedicine: Current and Future Industrial

Applications; John Wiley & Sons, Inc., 2011.

2. Dodziuk, P. D. H. Cyclodextrins and Their Complexes: Chemistry, Analytical Methods, Applications,

Wiley‐VCH Verlag GmbH & Co. KGaA, 2006.

3. Jana, M., Bandyopadhyay, S. J. Phys. Chem. B, 115, 2011, 6347.

4. Nakai, Y., Yamamoto, K., Terada, K., Kajiyama, A., Sasaki, I. Chem. Pharm. Bull., 34, 1986, 2178.

5. Angelova, S., Nikolova, V., Molla, N., Dudev, T. Inorg. Chem., 65, 2017, 1981.

6. Angelova, S., Nikolova, V., Pereva, S., Spassov, T., Dudev, T. J. Phys. Chem. B, 121, 2017, 9260.

7. Pereva, S., Himitliiska, T., Spassov, T., Stoyanov, S. D., Arnaudov, L. N., Dudev, T. J. Agric. Food Chem.,

63, 2015, 6603.

8. Pereva, S., Sarafska, T., Bogdanova, S., Spassov, Т. J. Drug Deliv. Sci. Techn., 35, 2016, 34.




27

OP18. BIOMIMETIC CAVITY-BASED FLUORESCENT DYE PROBES

COMPLEXES PROVED BY DIFFUSION ORDERED SPECTROSCOPY

Vladimira Videva1,2, Aleksey Vasilev1, Snejana Kitova2,

Constantin Haese3, Mihail Mondeshki3

1University of Sofia, Faculty of Chemistry and Pharmacy, 1, J. Bourchier av., 1164 Sofia, Bulgaria,

[email protected], [email protected] 2Institute of Optical Materials and Technologies, Bulgarian Academy of Sciences, Acad. G. Bonchev str. bl. 109,

1113 Sofia, Bulgaria, [email protected] 3Institut für Anorganische Chemie und Analytische Chemie, Johannes Gutenberg Universität, Duesbergweg 10-14,

55128 Mainz, Germany, [email protected]

The development of nano-medicine and mitochondrial medicine is directly related to the creation

of new nanomaterials that carry fluorescence visualization tools to mark specific cellular

organelles. The aim of the present work is to demonstrate "host-guest" interactions using NMR

by measuring the diffusion coefficients between new fluorochromes and cyclodextrins and

confirming the results obtained by using UV-VIS and fluorescence spectrophotometry. The

created new supramolecular complexes will be used as fluorescent nano-molecular

thermometers.

Acknowledments:

We kindly acknowledge to project BG05M2OP001-2.009-0028 for the financial support of the present work.




28

OP19. NEW NAPHTALENE BASED CHROMOPHORES

FOR HIGH-TECH APPLICATIONS

Yulian Zagranyarski1, Stanimir Stoyanov1, Kalina Peneva2

1 Sofia University ‘St. Kliment Ohridski‘, Faculty of Chemistry and Pharmacy, 1 James Bourchier Ave., 1164 Sofia,

Bulgaria, [email protected] 2 Laboratory of Organic and Macromolecular Chemistry, Friedrich Schiller University Jena, Lessingstr 8, 07743

Jena, Germany

The naphthalimide core have proven itself as versatile photoactive structure upon which many

fluorescent compounds can be built. The addition of electron donating substituents to the

electron acceptor already present in the aromatic ring forms а push-pull system with good

photostability and high fluorescence quantum yields. Many of these compounds are excellent

chemosensors for cations and anions, fluorescent cellular imaging agents and DNA intercalators,

switches and logical gates, and used for coating of nanoparticles.

Recently we synthesized and explored the photophysics of new 4-mono- and 4,5-disubstituted

naphthalimides, including representatives in which the donor moiety is part of a fused ring, thus

extending the aromatic system of the native chromophore. The new dyes are promising

candidates for high-tech applications such as OLEDs, visualisation of cellular organelles,

bimodal diagnostic imaging, etc.

References:

1. Kaloyanova, S., Zagranyarski, Y., Ritz, S., Hanulová, M., Koynov, K., Vonderheit, A., Peneva, K., Müllen,

K. J. Am. Chem. Soc., 138, 2016, 2881.

2. Dangalov, M., Yordanova, S., Stoyanova, M., Cheshmedzhieva, D., Petrov, P., Stoyanov, S., J. Mol.

Struct., 1125, 2016, 705.




29

OP20. DFT STUDY OF INTERACTIONS BETWEEN A SERIES OF

HYDROXAMIC ACIDS AND HDAC8 ENZYME

Nikolay Toshev1,2, Diana Cheshmedzhieva1, Todor Dudev 1

University of Sofia “St.Kliment Ohridski”, Faculty of Chemistry and Pharmacy, Department of “Pharmaceutical

and applied organic chemistry, 1164 Sofia, 1 “James Bourchier” Blvd, Bulgaria, e-mail: [email protected],

[email protected]

Institute of Electrochemistry and Energy systems, BAS, 1113 Sofia, Acad. “Georgi Bonchev” Str., Block 10,

Bulgaria, e-mail: [email protected]

Histones, which are the basic structural element of chromatine, can be acetylated and

deacetylated. Disruption of the balance of acetylation and deacetylation of histones is connected

with one of the mechanisms of development of cancer diseases. Inhibitors of histone

deacetylases influence and provoke malignant cell cycle arrest and subsequent apoptosis. A

different type of hydroxamic acids are one of the most promising drugs for treatment of different

types of lymphomas and other cancer diseases. As a Zn-dependent inhibitor of histone

deacetylases (HDACi), hydroxamic acids coordinate to the active site of a HDAC8 enzyme. The

physicochemical and metal binding properties of hydroxamic acids, however, are not well

understood. Using DFT- methods, in this work we investigate the affinity of several hydroxamic

acids with a potential use in oncology to the HDAC8 enzyme. Hydroxamic acids are modeled in

the active site of HDAC8 enzyme. The functional B3LYP and the basis set 6-31+G(d) were

used. Affinity of a series of hydroxamic acids toward HDAC8 enzyme was assessed.

References:

1. Cheshmedzhieva, D., Toshev, N., Gerova, M., Petrov, O., Dudev, T., J. Mol. Model., 24, 2018, 114.

2. Cheshmedzhieva, D., Toshev, N., Gerova, M., Petrov, O., Dudev, T., Bulg. Chem. Comm., 50, 2018, 228.




30

OP21. ILLUSTRATING THE CONCEPT OF A TIMER

WITH RESET AT THE MOLECULAR LEVEL

Vesselin Petrov1, Stoyanka Slavcheva2

1 Sofia University, Faculty Chemistry & Pharmacy, Dept. Phys. Chem., Sofia 1164, Bulgaria 2 Sofia University, Faculty Chemistry & Pharmacy, Lab. Organ. Photochem., Sofia, Bulgaria

The multistate of species regarding 2’-hydroxyflavylium derivatives have a peculiar behavior

due to the formation in moderately basic solutions of a flavanone from the mono-ionized trans-

chalcone. The firmly established theory to account for the thermodynamics and kinetics of the

flavylium based multistate of species in acidic medium was extended to the basic medium. The

key experimental procedure to carry out this study is a sequence of reverse pH jumps from all pH

range to a final pH sufficiently acid to have flavylium cation as the sole species. The reverse pH

jumps can be performed from the equilibrium and pseudo-equilibrium. Acidification of the

flavanone to pH=1 does not give back flavylium cation. In contrast, the di-ionized species trans-

chalcone is obtained in a very fast process from the flavanone at pH > 12. A cycle constituted by

a sequence of pH jumps illustrates the concept of a timer at the molecular level with reset

capacity [1].

References:

1. Slavcheva, S., Mendoza, J., Stanimirov, S., Petkov, I., Basílio, N., Pina, F., Petrov, V., Dyes Pigments,

2018, DOI: 10.1016/j.dyepig.2018.05.066.




31

Poster presentations




32

PP1. THE USE OF BIBLIOMETRIC INDICATORS FOR THE

MEASUREMENT OF IMPACT AND VISIBILITY OF BULGARIAN

RESEARCH PERFORMANCE IN NATURAL SCIENCES

Savina Kirilova

Sofia University “St. Kliment Ohridski”, Faculty of Chemistry and Pharmacy,

1 James Bourchier Blvd., Sofia, Bulgaria, [email protected]

Scientometrics is a discipline that analyzes bibliographic material from a quantitative and

qualitative perspective. Bibliometric indicators are widely used to compare the performance of

the individual researchers, journals, articles, institutions and countries. Two major categories of

bibliometric indicators are (1) quantitative indicators that measure the research productivity of a

researcher and (2) performance indicators that evaluate the quality of publications1. This poster

presents a general overview of Bulgarian publications and individual researchers in the natural

sciences using bibliometric indicators derived from the Web of Science and Scopus such as

journal impact factor, journal impact rank, eigenfactor, h-index and its variants, number of

publications, number of publications in top-ranked journals, etc. The aim is to the measurement

of impact and visibility of Bulgarian research performance in particular in the chemical and

pharmaceutical sciences. The analysis is divided into key sections focused on relevant journals,

authors and institutions in the period 2015-2018. The main advantage is that bibliometric

indicators provide a general picture, identifying some of the most influential journals and

measuring of scientific impact of researchers, thereby supplying a basis for evaluating and

orienting research activity [1].

References:

1. Joshi, M. A. J. Contemp. Dental Pract., 15, 2014, 258-262




33

PP2. CHEMISTRY TEACHERS TRAINING

FROM SKILLS PERSPECTIVE

Vladimir Tzvetkov



Being a great science teacher today is characterised not only by wide multidisciplinary

knowledge and inspirational scientific talks and lab demonstrations, but also by the fluent use of

inquiry-based learning techniques, creative application of modern technologies and development

of exciting project tasks for the students. To achieve that incredible image, a teacher needs to

develop the necessary attitudes to face all challenges and also a set of skills that differ from those

of the teachers of decades ago.

This study is based on a literature review on the science teacher’s role in a constructivist learning

environment from John Dewey’s works to modern articles. Based on the findings of the review,

a model set of skills of the successful teacher is presented, divided in three groups – teaching

skills, interpersonal skills and contextual skills. Following this model, the training of 30 pre-

school science teachers is observed over a period of one academic year, using classroom

observations, interviews, surveys, focus-groups, reflection diaries and other methods. The focus

of the observations is to track the development of the predefined skills for great teaching in the

pre-school practice. The most representative of the observed pre-school teachers are presented as

case-studies, showing that the teacher training programmes are mainly focused on the teaching

skills, neglecting the other two groups. The key findings of the study are that although it is not

realistic to expect having complete professional teachers in the end of the university education,

much more effort needs to be put in development of interpersonal skills and life-long learning

attitudes of the future teachers.




34

PP3. ELECTROCHEMICAL MONITORING OF PLATINUM(II)

COORDINATION REACTIONS IN WATER SOLUTIONS

Borislava Georgieva, Galina Gencheva

1 Sofia University “St. Kl. Ohridski”, Faculty of Chemistry and Pharmacy, 1 James Bouchier blvd., 1164 Sofia,

Bulgaria, [email protected]

Metal complexes possess a diversity of electronic and structural features that can be used in

drug design. Their coordination polyhedra and coordination numbers can be varied as a function

of the metals oxidation state change. The modeling of these specific properties could lead to

fine-tuning of the chemical reactivity, also the rates of ligand exchange, the strengths of metal-

ligand bonds, outer-sphere interactions, etc. Among the factors that determine the chemical

behavior, the metal and ligand based redox potentials deserve a special attention because as a

function of them, the metal complexes can specifically interfere in cellular redox chemistry. In

this regard, there are many advantages if it is achieved construction of transition metals

complexes with properly selected values of the redox potential.

The presented study deals with a directed synthesis of higher oxidation platinum complexes by

redox reactions in water solutions. The choice of the ligands is based on their redox chemistry

and biological activity. Because of the general kinetic inertness of the platinum ions in ligand

substitution reactions the interactions have been monitored by cyclic voltammetry

measurements. The electrochemical experiments of all studied systems were conducted in a

three-electrode cell and recorded at room temperature. During the investigated interactions, the

reduction potentials were measured using a platinum disc and/or a glass carbon disc as a working

electrode until equilibrium was reached. By controlling of the reaction conditions, several new

complexes with formal redox potentials ranging in the interval – 0,2V to 0,5V, have been

reproducibly obtained. The determined values of the formal redox potentials of the new

compounds predict their comparative sustainability to the reducing environment in cancer cells

and also a difference in the ability of cancer cells to cope with changes in the levels of redox-

active species.

Acknowledgements:

Borislava Georgieva is grateful to Operational programme "Science and Education for Smart Growth", project

BG05M2OP001-2.009-0028. We acknowledge also the financial support from the National Science Fund (Project

DN09/16) of Bulgarian Ministry of Education and Science.




35

PP4. ANALYTICAL PROCEDURE FOR SR AND RB ISOTOPES

DETERMINATION IN TRADITIONAL BULGARIAN WINES

Elisaveta Mladenova, Irina Karadjova

1Sofia University, Faculty of Chemistry and Pharmacy, 1, James Bourchier Blvd., 1164 Sofia, Bulgaria,


Consumers around the world are increasingly demanding information on and reassurance of the

origin and content of their food. Determining the authenticity of foods can prevent false

description, substitution of cheaper ingredients, and adulteration, as well as incorrect origin

labeling. The isotope ratio 87Sr/86Sr is proposed in scientific literature as appropriate descriptor

for identification and determination of geographical origin of different foods like wine, rice,

milk, fish. However the significant problem is reliable determination of 87Sr concentrations using

ICP-MS due to isobaric interference from 87Rb. Two main approaches might be used to

overcome this problem: (1) chemical separation of Sr and Rb which is relatively difficult

analytical task and (2) 87Sr instrumental measurement by ICP-MS using specific instrumental

conditions. The aim of the present study is to develop reliable analytical procedure for Sr (86Sr,

87Sr, 88Sr) and Rb (85Rb) isotopes determination in soil extracts and monovarietal Bulgarian

wines with defined geographical and botanical origin by using direct ICP-MS measurement. For

model investigations Sr and Rb isotopes were measured in four white wines from the grape

variety Chardonnay and four red wines from the grape variety Cabernet Sauvignon from

different viticulture regions in Bulgaria. Additionally Sr and Rb isotopes were measured in two

soil extracts from the same region (0.43 mol/L CH3COOH and 0.05 mol/L EDTA (as ammonium

salt). Selective measurement of Sr isotopes was achieved on ICP-MS Triple Quad spectrometer

using reaction cell with oxygen gas. It was concluded that only Sr reacts with the oxygen gas

forming compounds mainly with one O-atom with masses 86Sr→102, 87Sr →103, 88Sr→104,

respectively, Rb does not reacts with the reaction gas and presents in the sample solutions as its

natural isotopes 85Rb and 87Rb. Results obtained shows variation of isotopic ratio 88Sr/86Sr in

wines, acetic acid extract and EDTA extract 8.256662708-8.708593498, 8.346783601-

8.633191996, 8.211823518-8.754735115, respectively, while for 87Sr/86Sr the variation is in the

range 0.71668656-0.791230845, 0.712360781-0.735408866, 0.687491647-0.7343295380,

respectively.

Acknowledgements:

The authors are grateful for financial support of National Bulgarian Science Fund Grant № B02/22. Elisaveta

Mladenova is also grateful to Operational programme “Science and Education for Smart Growth”, project

BG05M2OP001-2.009-0028.




36

PP5. SPECIATION ANALYSIS OF CHROMIUM IN SURFACE WATERS

USING IONIC LIQUID-FUNCTIONALIZED POLYMER GEL

Ivanka Dakova, Tanya Yordanova, Dariya Dimova, Irina Karadjova

Faculty of Chemistry and Pharmacy, Sofia University “St. Kliment Ohridski”, Sofia 1164, Bulgaria

[email protected]

This study is focused on the synthesis and characterization of new ionic liquid-functionalized

polymer gel (P(MIA)) and its application for chromium determination and speciation in surface

waters. P(MIA) was prepared via two-steps synthetic procedure. Firstly, polymer gel (P(GMA))

were synthesized by cross-linking dispersion copolymerization of glycidyl methacrylate (GMA)

and trimethylolpropane trimethacrylate in acetonitrile as a porogen solvent. Then, 1-

methylimidazole (MIA) molecules were covalently attached onto P(GMA) surface by opening of

the epoxy ring. The newly synthesized P(MIA) was characterized using elemental analysis,

Fourier transform infrared spectroscopy, scanning electron microscopy, and nitrogen adsorption–

desorption measurements. The adsorption properties of P(MIA) toward Cr(III) and Cr(VI) were

studied by batch procedure. An excellent separation of Cr(VI), selectively sorbed on the P(MIA),

from Cr(III) was achieved at pH 2−3 for 20 minutes. A freshly prepared mixture of ascorbic acid

and nitric acid was found to be the most efficient eluent for quantitative desorption of the

retained Cr(VI). Experiments performed for selective determination of Cr(VI) in surface waters

showed that the interfering matrix does not influence the extraction efficiency of P(MIA). The

analytical procedure for Cr(VI) determination in surface waters was developed and validated

through analysis of certified reference materials.

Acknowledgments:

The authors gratefully acknowledge the financial support provided by the Bulgarian National Scientific Foundation

(Grant DN 19/10 SmartSpeciation). Ivanka Dakova is grateful to Operational programme "Science and Education

for Smart Growth", project BG05M2OP001-2.009-0028.




37

PP6. SYNTHESIS AND APPLICATION

OF Fe(II)-IMPRINTED POLYMER GELS

FOR Fe(II)/Fe(III) SPECIATION IN SURFACE WATERS

Ivanka Dakova, Mariya Mitreva, Monika Petrova, Violeta Boyadzhieva, Irina Karadjova


[email protected]

The environmental and biological effects of iron depend on its oxidation state, solubility and the

degree of complex formation. Iron is not normally considered a toxic element, but it becomes

toxic when accumulated, especially when present as free ion. Due to changing properties of the

different iron forms, it is highly critical to gain information not only on the total content of the

metal, but also about its speciation.

The aim of the present study was synthesis and characterization of new Fe(II) ion-imprinted

polymer sorbents (Fe(II)-IIPs)) and their application for Fe(II)/Fe(III) speciation in surface

waters. Fe(II)-IIPs were synthesized by precipitation copolymerization of 4-vinylpyridine

(functional monomer), trimethylolpropane trimethacrylate (crosslinking agent) and 2,2'-

azobisisobutyronitrile (initiator) in the presence of different template species – Fe(II) complexes

with 2,2'-bipyridine (BP), 4-(2-pyridylazo)resorcinol (PAR) or salicylic acid (SA). The chemical

structure and morphology of the Fe(II)-IIPs particles are defined using elemental analysis, FTIR,

SEM and BET analyses. Extraction efficiencies of newly synthesized sorbents were studied by

batch procedure. The optimal pH range for the quantitative Fe(II) sorption was between 7-8 for

the all Fe(II)-IIPs synthesized. The loaded Fe(II) ions were easily eluted by 4 mol/L HNO3. The

Fe(II)-BP and Fe(II)-PAR complexes containing copolymer gels had higher capacity and

selectivity than the copolymer gels prepared using Fe(II)-SA complex and the non-imprinted

copolymer gels. It was found that independently of chelating agent used degree of sorption for

both Fe species is between 93-97%. In order to separate them, masking agents (tartrate,

phosphate, F‒) were tested. Selective quantitative sorption of Fe(II) in the presence of Fe(III)

masked as fluoride complex was achieved in the same pH range 7-8. Analytical procedure for

the determination of Fe(II) and Fe(III) in surface waters was developed.

Acknowledgments:


(Grant DN 19/10 SmartSpeciation). Ivanka Dakova is grateful to Operational programme "Science and Education

for Smart Growth", project BG05M2OP001-2.009-0028.




38

PP7. DETERMINATION OF GEOCHEMICAL BACKGROUND AND

THRESHOLD VALUES FOR POTENTIALLY TOXIC ELEMENTS IN

THE BULGARIAN SOIL QUALITY MONITORING NETWORK

Galina Yotova1, Monika Padareva1, Milena Georgieva2, Stefan Tsakovski1

1 Faculty of Chemistry and Pharmacy, University of Sofia “St. Kliment Ohridski”, 1 J. Bourchier Blvd., Sofia 1164,

Bulgaria, [email protected], [email protected], [email protected] 2 Faculty of Geology and Geography, University of Sofia "St. Kliment Ohridski", 15 Tsar Osvoboditel Blvd.,

Sofia 1504, Bulgaria, [email protected]

In environmental geochemistry, the main purpose of threshold values is to discriminate between

background element concentrations and unusually high values caused by local contamination or

natural phenomena [1]. Therefore defining geochemical background and threshold values for

potentially toxic elements (PTEs) in soil is of great importance for environmental management

and decision makers.

Topsoil samples of the Bulgarian soil quality monitoring network were collected and analyzed

for 8 PTEs: As, Cd, Cr, Cu, Hg, Ni, Pb and Zn.

In the present study, median + 2 Median Absolute Deviations (median+2MAD) and Tukey inner

fence (TIF) were used for calculation of national geochemical threshold values of PTEs [2].

Since these methods are sensitive to asymmetric geochemical data, the degree of symmetry was

assessed [3] and PTE data were transformed if required. Additionally a comparison with the

most frequently used percentiles (90th, 95th, and 98th) for the determination of geochemical

background was performed to evaluate different threshold approaches.

The calculated 90th percentile values in combination with the spatial distribution of PTE

concentrations indicate priority areas for further assessment and can be used to reveal reasons for

the higher PTE concentrations. Regions with more than 2 PTEs exceeding the specific threshold

values (2.26% of the Bulgarian territory) are suggested for detailed (eco)toxicological

assessment.

References:

1. Matschullat, J., Ottenstein, R., Reimann, C. Environm. Geol., 39, 2000, 990.

2. Reimann, C., Fabian, K., Birke, M., Filzmoser, P., Demetriades, A., Négrel, P., Oorts, K., Matschullat, J.,

de Caritath, P. Applied Geochem., 88 B, 2018, 302.

3. Ander, E. L., Johnson, C. C., Cave, M. R., Palumbo-Roe, B., Nathanail, C. P., Lark, R. M. Sci. Total

Environm., 454-455, 2013, 604.




39

PP8. COMPARISON OF P-XRF SPECTROMETERS FOR

ARCHAEOLOGICAL RESEARCH: A CASE STUDY FOR ANALYSIS OF

TIN-RICH ARCHAEOLOGICAL BRONZES

Boika Zlateva


In the last 10-15 years, the massive penetration of instrumental analysis techniques in the study

of archaeological objects has led to an increase in archaeometry research, which in turn requires

well-trained specialists in this field. The XRF (X-ray Fluorescence) spectroscopy is a non-

destructive technique of analysis widely used in archaeometry for the identification of chemical

elements in pigments, glass, metal alloys, and other materials. Especially attention in the last two

decades is focused on portable XRF spectrometers, usally used for in the filed nvestigations in

archaeological excavations or in museum collections. However, such analyses have their limits

and not all questions can be answered in this manner [1, 2].

In this paper using three different p-XRF instruments chemical composition of the tin-rich

bronze artefacts form Bronze age in Bulgaria and different standards are obtained. The results for

the standard materials (MBH-33X GM7 J and MBH-33X RB1 A) are in very good coincidense

with the certificated value for all type instruments, despite the results for archaeological objects,

where exist significant differences in the chemical compositions obatined from the different

models of p-XRF.

References:

1. Killick, D. J. Arch. Sci., 56, 2015, 242.

2. Lyubomirova, V., Djingova, R., Kuleff, I. Archaeom., 57, 2015, 677.




40

PP9. MECHANOCHEMICALLY INDUCED SYNTHESIS

OF THERMALLY STABLE U-La MIXED OXIDE

Petya Kovacheva1, Georgi Avdeev2, Nikola Mirchev2

1 University of Sofia “St. Kliment Ohridski”, Faculty of Chemistry and Pharmacy, Sofia, Bulgaria,

[email protected] 2 Bulgarian Academy of Sciences, Institute for Physical Chemistry “Rostislaw Kaishew”, Sofia, Bulgaria

The paper presents the structural characteristics and thermal stability of Lantanium-Uranium

mixed oxide, mechanochemically synthesized from sol-gel obtained precursor. Planetary ball mill

Pulverisette 7 (Fritsch) with stainless steel triboreactors was used for the sample processing.

Crystal structure and phase analysis was made by using X-ray powder diffraction. Quantitative

analysis of the diffraction patterns was performed by PANalytical Highscore +.

The degree of mechanochemical transformation of the initial precursors into Lanthanium-

Uranium mixed oxide was studied after 120 min and 225 min mechanochemical processing in

suspension with toluene. The thermal stability and thermal expansion of the final product were

studied in the temperature range from 25 to 1000 оС in vacuum. The size distribution of the

obtained mixed oxide was determined by dynamic light scattering in distilled water.

Transmission electron microscope equipped with EDX microanalyzer was for observation of the

structure and of the elemental distribution of the mechanochemically synthesized oxide. The

results showed that the mechanochemically synthesized Lantanium-Uranium mixed oxide is

phase homogeneous, nanostructured, thermally stable in vacuum and has submicron particle size.




41

PP10. A CASE STUDY ON THE SOLUTION BEHAVIOR

OF PLATINUM(IV) COMPLEXES DESIGNED

AS POTENTIAL ANTIPROLIFERATIVE AGENTS

Vyara Velcheva, Galina Gencheva

Sofia University “St. Kl. Ohridski”, Faculty of Chemistry and Pharmacy, 1 James Bouchier blvd., 1164 Sofia,

Bulgaria, [email protected]

The potential of platinum (IV) complexes for antitumor drugs design has been known since the

time of the cisplatin discovery, but their clinical application has not yet been realized. The

physicochemical properties of platinum(IV) compounds completely differ from those of their

platinum(II) analogues. In the most cases, the platinum(IV) complexes adopt a octahedral

geometry with six coordinated donor atoms. Thus, the filled inner coordination sphere of

platinum(IV) is kinetically much more inert in the ligand substitution reactions than four-

coordinate platinum(II) centers. Moreover, the two extra ligands afforded by the low-spin d6

configuration could be used for fine-tuning of the desired biological properties such as solubility,

lipophilicity, participation in redox intercations, cancer-cell targeting, improved cellular uptake,

etc. The interpretation of the chemical reactivity of the platinum(IV) drug-candidates in respect

to DNA and other biomolecules in biological milieu requires consideration of the rates of their

substitution and reduction reactions. A stage of these investigations is the précised estimation of

their behavior at dissolution, the kinetic of the processes of solvolysis, the composition and

stability of the solvolitic complex' species.

Here we discuss the chemical behavior of series of platinum(IV) complexes with a polydentate

N,O-containing organic ligand and iodides as monodendante inorganic ligands in water solutions

in a wide pH range, including the physiological pH value. By means of NMR spectroscopy and

mass spectrometry we studied the composition, stability, redox properties and kinetic behavior of

the chemical species, obtained during the hydrolysis processes at dissolving. It has been

established that the factors such as the composition of the inner coordination sphere of the

precursor platinum(IV) compound, the mode of coordination of the organic ligand, the acidity of

the solutions are of crucial meaning for the stability and reactivity of the complex’ species

obtained in solution.

Acknowledgements:

Vyara Velcheva is grateful to Operational programme "Science and Education for Smart Growth", project

BG05M2OP001-2.009-0028. We acknowledge also the financial support from the National Science Fund (Project

DN09/16) of Bulgarian Ministry of Education and Science.




42

PP11. Gd(III) COMPLEX OF MONENSIN: SYNTHESIS, SPECTRAL

CHARACTERIZATION AND BIOLOGICAL ACTIVITY

Radoslava Dimitrova, Ivayla Pantcheva

1 Sofia University “St. Kliment Ohridski”, Faculty of Chemistry and Pharmacy,

1, J. Bourchier blvd., 1164 Sofia, Bulgaria, [email protected]

The study of properties of polyether ionophorous antibiotics (PI) and their metal complexes has

become an important part of research in the biological chemistry field due to diverse activity of

ligands against parasites, Gram-positive microorganisms, fungi, tumor cells, etc. Knowledge on

coordination chemistry of PI, in particular - Monensin and its complexes with mono- and

divalent metal ions, was further extended to the evaluation of ligand ability to bind trivalent

metal ions of gadolinium(III). Depending on metal-to-ligand molar ratio, Monensin forms at

least one neutral and two positively charged complex species. Ligand coordination ability was

studied in solution by means of synchrotron radiation circular dichroism (SRCD). Composition

and coordination mode of Monensin in neutral complex species was evaluated using various (IR,

ESI-MS, EPR) spectral techniques.

Properties of the isolated and structurally characterized neutral complex were studied in a set of

in vitro experiments to provide new experimental data on their activity against Gram-positive

microorganisms and cell cultures of tumor / non-tumor origin.

Acknowledgements:

RD is thankful to Operational programme "Science and Education for Smart Growth", project BG05M2OP001-

2.009-0028. IP acknowledges also the financial support from the National Science Fund (Project KP-06-H29/3) of

Bulgarian Ministry of Education and Science.




43

PP12. NON-CHROMATOGRAPHIC SPECIATION ANALYSIS

OF MERCURY IN SURFACE WATERS

SUPPORTED BY CORE-SHELL NANOCOMPOSITES

Tanya Yordanova1, Petar Ignatov1, Penka Vasileva2, Irina Karadjova1

1Department of Analytical Chemistry, Faculty of Chemistry and Pharmacy, University of Sofia, “St. Kliment

Ohridski”, 1 James Bourchier Blvd., Sofia, Bulgaria, e-mail: [email protected] 2Department of General and Inorganic Chemistry, Faculty of Chemistry and Pharmacy, University of Sofia, “St.

Kliment Ohridski”, 1 James Bourchier Blvd., Sofia, Bulgaria.

In this study we report the preparation of two core-shell materials and their further application as

highly effective sorbents for non-chromatographic speciation analysis of Hg in surface waters.

Nanocomposites consist of submicronsized silica spheres (cores) covered with shells of silver

and gold nanoparticles, respectively. Silica spheres were grown using Stöber method and

functionalized with amine terminal groups by treatment with (3-aminopropyl)-trimethoxysilane.

Silver and gold nanoparticles were synthesized according completely green procedure based on

reduction of AgI and AuIII, respectively, using D-(+) glucose as an environmentally benign

reducing agent and stabilization with soluble starch as a non-toxic capping agent. The colloid

mixing method was applied for deposition of starch-coated silver and gold nanoparticles onto the

amine-functionalized silica spheres. Characterization of morphology, surface properties and

colloidal stability of nanocomposites SiO2/AuNPs and SiO2/AgNPs was realized by SEM, TEM,

zeta potential measurement, UV-Vis spectroscopy. The extraction efficiency and selectivity of

the core-shell sorbents toward Hg species were studied by batch method and the optimal

chemical conditions for selective separation and enrichment of both HgII and methylmercury

were defined: pH 2, 100 µL stock suspension of the sorbents, sample volume – 10 mL, time for

sorption 20 min. Elution of Hg species, retained by AgNPs and AuNPs, was accomplished for 10

minutes by mixture of HNO3 with H2O2 and aqua regia, respectively. A simple analytical

procedure for speciation of Hg in surface waters based on two sequential extraction steps was

proposed.

Acknowledgement:

Authors gratefully acknowledge the financial support of the Bulgarian Scientific Fund, Project DN19/10. Tanya

Yordanova is grateful to Operational programme “Science and Education for Smart Growth”, project

BG05M2OP001-2.009-0028.




44

PP13. ASSESSMENT THE LEVEL OF SELF-CLEANING

OF THE SOILS AROUND THE FORMER METALLURGICAL PLANT –

KREMIKOVTSI, BULGARIA

Tsvetomil Voyslavov, Elisaveta Mladenova

Sofia University, “St. Kl. Ohridski”, Faculty of Chemistry and Pharmacy,


The aim of our research is to study the natural self-cleaning ability of soils around the

metallurgical plant – Kremikovtsi, Bulgaria, closed since 2009. On the basis of results from

previous survey, with soil samples collected nearby operating Kremikovtsi plant, we had

prepared a new sampling plan including sample points of contaminated soils according to the

current Bulgarian soil legislation [1]. The new set of samples was processed and analyzed in

accordance with internationally accepted ISO standards for soils [2-4]. Appropriate analytical

techniques (flame atomic absorption spectrometry and electrothermal atomic absorption

spectrometry) were used for quantification of both pseudo-total concentrations (aqua regia

extraction) and concentrations of selected toxic elements in soil extracts obtained according to

the classical BCR extraction procedure. The content of polycyclic aromatic hydrocarbons

(PAHs) in soil samples was determined by gas chromatography after a Soxhlet extraction.

Comparing the data from the previous studies and the newly obtained results, self-purification

coefficients for the sampling points were calculated with respect to the different analytes (toxic

chemical elements and PAHs).

Acknowledgements

Authors are grateful for the financial support from Operational programme "Science and Education for Smart

Growth", project BG05M2OP001-2.009-0028.

References:

1. Regulation № 3 of the Bulgarian government concerning the maximum allowed content of heavy metals

and metalloids in soils, 2008.

2. ISO 10381-1:2005, Soil quality - Sampling - Part 1: Guidance on the design of sampling programmes.

3. ISO 10381-2:2005, Soil quality - Sampling - Part 2: Guidance on sampling techniques.

4. ISO 11464:2012, Soil quality - Pretreatment of samples for physico-chemical analysis.




45

PP14. QUANTIFICATION STRATEGY

FOR LA-ICP-MS ANALYSIS OF PLANT SAMPLES

Valentina Lyubomirova, Boyan Todorov, Rumyana Djingova

University of Sofia, Faculty of Chemistry and Pharmacy, Trace Analysis Laboratory,

1, J. Bourchier Blvd., 1164 Sofia, Bulgaria, [email protected]

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is a promising

technique for analysis of environmental samples because it has advantages over conventional

digestion techniques such as reduced levels of contamination and shorter sample preparation

time, possibility for spatial distribution analysis of elements, high number of repetitions, etc.

However, when LA-ICP-MS is used for quantitative analysis, many factors may influence the

accuracy of the results. Therefore, the analytical method has to be carefully developed and

optimized in several basic aspects.

The most severe limitation for quantitative analysis is the lack of solid Certified Reference

Material (CRM) in appropriate geometry, necessary for instrument calibration and quality

control. In the present work different procedures for matrix-matched standards preparation from

powdered CRMs are proposed.

Analytical problems, related to the spectral interferences were eliminated by optimization of

Dynamic Reaction Cell parameters (cell gas flow rate and RPq) using O2 and CH4 as reaction

gasses. Correction of molecular overlapping on most of the determined isotopes was achieved

using CH4. For some elements, e.g. As, Se the effectiveness of both reaction gases was tested.

The quantification of the matrix elements has been achieved by the introduction of a rejection

parameter (RPa) to enable the high-mass cut off.

The developed method was applied for simultaneous determination of macro and

microcomponents in plant CRMs and plants samples, previously analyzed by ICP-MS after acid

digestion. The results demonstrate the suitability of LA-ICP-MS for reliable determination of

large number of elements.

References:

1. Lyubomirova, V., Todorov, B., Djingova, R., Compt. Rend. Acad. Bulg. Sci., 69, 2016, 275.

2. Lyubomirova, V., Djingova, R., Compt. Rend. Acad. Bulg. Sci., 68, 2015, 847.




46

PP15. BIOACCESSIBILITY OF ESSENTIAL AND POTENTIALLY TOXIC

ELEMENTS IN APPLES USING ENZYMOLYSIS APPROACH

Veronika Mihaylova, Valentina Lyubomirova, Rumyana Djingova

Faculty of Chemistry and Pharmacy, University of Sofia, 1 J. Bourchier Blvd.,

1164-Sofia, Bulgaria, [email protected]

The main objective of this work was to get information on the content of essential and

potentially toxic elements in apples and their digestion in the human gastrointestinal tract. A

sequential analytical approach was applied to two apples varieties from the commercial network

of Bulgaria (Golden Delicious and Breaburn), focusing on their total element concentrations,

extractability in water, 2% SDS, 50 mM Tris-HCl and 0.1 M HCl. The oral bioaccessibility of

the elements was evaluated using the physiologically-based extraction test (PBET). The element

concentrations were measured using inductively coupled plasma-mass spectrometry (ICP-MS).

The obtained results showed the highest percentage of bioaccessibility for Ca, Cd, Cr, Cu, K, Na,

Mg, Mn and Zn (over 50%) while for Al, Fe, Ni, Pb, Sn and Th only 10÷30% of the total

concentration were bioavailable in human gastrointestinal tract.

Acknowledgements

Authors are grateful to Operational programme "Science and Education for Smart Growth", project

BG05M2OP001-2.009-0028.




47

PP16. CHEMOMETRIC EXPERTISE OF CLINICAL MONITORING

DATA OF PROLACTINOMA PATIENTS

Dimitar Dimitrov, Miroslava Nedyalkova, Boryana Donkova, Vasil Simeonov

Faculty of Chemistry and Pharmacy, University of Sofia “St. Kl. Okhridski”, 1164 Sofia,

J. Bourchier Blvd. 1, Bulgaria

[email protected]

The present investigation indicates hidden relationships between the several clinical parameters

usually monitored on prolactinoma patients using non-hierarchical cluster analysis. The major

goal of the chemometric data mining is to offer a possible mode of optimization of the

monitoring procedure by selecting a reduced number of health status indicators. The intelligent

data analysis reveals the formation of three patterns of prolactinoma patients each one of them

described by a set of clinical parameters. Thus, a better strategies for considering patients with

this diagnosis could be developed and clinically applied.




48

PP17. CHEMOMETRIC ASSESMENT OF ECOTOXICITY

OF SILVER NANOPARTICLES

Dimitar Dimitrov, Miroslava Nedyalkova, Boryana Donkova, Vasil Simeonov

Faculty of Chemistry and Pharmacy, University of Sofia “St. Kl.Ohridski”,

J. Bourchier Blvd. 1, 1164 Sofia, Bulgaria

[email protected]

The major goal of the study is to reveal certain relations between the silver nanoparticles

ecotoxicity, their physicochemical parameters and specific types of organism used as ecotoxicity

tests.

There are many studies dealing with connection between silver nanoparticles acute toxicity but

quite few of them focus on ecotoxicity.

Silver nanopraticles are used especially in medicine (chemotherapy), they have antimicrobial

properties. Some studies claim that silver nanoparticles can provide a means to overcome

multiple drug resistance problems.

The input data set consists 94 different silver nanoparticle systems described by four

physicochemical variables (primary size PS, primary hydrodynamic parameter PHD, DLS

primary hydrodynamic parameter in test media, zeta potential in test media ZP) and additionally,

by the acute ecotoxicity (AT) tested by various organisms. The specimens are organized by their

type or species.

To reveal hidden connections between physicochemical variables of these organisms and

ecotoxicity, we use methods of multivariate statistics such as cluster analysis (hierarchical and

non-hierarchical) and correlation analysis.

The multivariate statistical analysis applied to the data set of silver nanoparticles made it

possible to reveal correlation between acute toxicity and DLS primary hydrodynamic parameter

in test media for each one of the test organisms.




49

PP18. CREATING A MODEL FOR THE PREDICTION OF

ALLERGENIC FOOD PROTEINS USING DISCRIMINANT ANALYSIS

Lyudmila Naneva, Miroslava Nedyalkova, Vasil Simeonov

Faculty of Chemistry and Pharmacy, Sofia”University “’St. Kliment Ohridski”

1, James Bourcher Blvd., Sofia, Bulgaria

e-mail: [email protected]

A group of 1400 food allergen and non-allergenic proteins was studied. A model for predictive

biology activity - allergenicity was produced. The modeling was performed with hemometric

approach PLS – DA [1-8].

Results are evaluated by the Receiver Operating Characteristic (ROC). The model shown has

good predictive ability, recognizing 73% of allergens, 80% of non-allergens or 77% of correctly

recognized allergens and non-allergens in the study group of proteins.

References:

1. Sampson, H. A. J. Allergy Clin. Immunol., 103, 1999, 981.

2. Sampson, H. A. J. Allergy Clin. Immunol., 103, 1999, 717.

3. Sampson, H. J. Allergy Clin. Immunol., 115, 2005, 139.

4. Broadfield, E., McKeever, T. M., Scrivener, S., Venn, A., Lewis, S. A., Britton, J. J. Allergy Clin.

Immunol., 109, 2002, 969.

5. Goodman, R. E., Hefle, S. L., Taylor, S. L., Ree, R. V. Intern. Arch. Allergy Immunol., 137, 2005, 153.

6. Midoro-Horiuti, T, Goldblum, R, Kurosky, A, et al. J. Allergy Clin. Immunol., 104, 1999, 608.

7. Wal, J. M. Ann. Allergy Asthma Immunol., 93, 2004, S2-11.

8. Wulfert, F., Sanyasi, E., Watanabe, L. A. J. Immunolog. Meth., 382, 2012, 48.




50

PP19. MECHANOACTIVATION OF ZnO PHOTOCATALYST

Boryana Donkova1, Nadezhda D. Yakushova2, Igor A. Pronin2, Maxim M. Sachev3,

Vyacheslav A. Moshnikov4

1 Department of Inorganic Chemistry, Faculty of Chemistry and Pharmacy, Sofia University,

str. J. Bourchier 1, Sofia 1126, Bulgaria, [email protected] 2 Department of Nano- and Microelectronics, Penza State University, Penza, 440026, Russia, [email protected];

[email protected] 3 Department of Theoretical Foundations of Materials, Saint-Petersburg State Technological Institute, St.

Petersburg, 190013, Russia, 4 Department of Micro-and Nanoelectronics, Saint-Petersburg Electrotechnical University “LETI”, St. Petersburg,

197376, Russia, [email protected]

The effect of mechanical high-energy grinding on the structural, adsorption and photocatalytic

properties of commercial ZnO powder was investigated. The samples activated for 1, 3 and 5

hours were characterized by XRD, SEM, XPS, UV-Vis and N2 adsorption-desorption. The

concentration of acidic and basic surface sites was determined by adsorption of acid/base

indicators. The photocatalytic activity of the samples was tested in the model reaction of Brilliant

green degradation under UV- and Vis-light irradiation.

The results show that mechanoactivation leads up to two fold increasing of the specific surface

area and microstress, and up to two fold decreasing of the average particle size and size of the

coherent scattering regions. The mechanoactivation changes the nature of the surface active sites

in different manner, depending on the milling duration. The best photocatalytic performance

under UV irradiation is established for ZnO sample, activated for 1 hour, while under visible

light the highest apparent rate constant is estimated for the bare ZnO. Based on the results, a

physicomathematical model of the correlation between the photocatalytic properties of the

samples studied and composition of the surface functional groups was developed.

Acknowledgments:

B. Donkova is grateful to Operational programme "Science and Education for Smart Growth", project

BG05M2OP001-2.009-0028




51

PP20. PREPARATION, CHARACTERIZATION AND ACTIVITY

EVALUATION OF NICKEL OXIDE/G-C3N4 PHOTOCATALYST

Veska Kircheva, Martin Tsvetkov, Toni Spassov, Georgi Tzvetkov

Faculty of Chemistry and Pharmacy, University of Sofia, J. Bourchier 1, 1164, Sofia, Bulgaria, [email protected]

Novel visible light-driven heterostructured NiO/g-C3N4 photocatalyst has been designed and

successfully prepared via ammonia-evaporation-induced method. The as-prepared hybrid

exhibits enhanced photocatalytic activity than pure NiO and g-C3N4 in the degradation of

Malachite Green under visible light irradiation. The enhanced photocatalytic performance of the

composite was mainly attributed to the combination of high adsorption capacity which facilitates

the direct redox reactions of dye and the efficient inhibition of photo-generated electron-hole pair

recombination. Superoxide radicals (•O2−) and photo-generated holes (h+) were found to be the

main active species in the process. The present study provides new insight into the construction

of an efficient visible-light driven 3D composite photocatalyst, which exhibits great potential in

the field of the organic pollutants degradation.




52

PP21. POLYMER-BORATE HYBRIDS FILMS –

THEORETICAL AND EXPERIMENTAL

DЕTERMINATION OF THE STRUCTURE

Hristo Hristov1, Miroslava Nedyalkova1, Sergio Madurga2

1 Faculty of Chemistry and Pharmacy, University of Sofia St. Kl. Okhridski“,

J. Bourchier Blvd. 1, Sofia 1164, Bulgaria, [email protected], [email protected] 2 Department of Material Science and Physical Chemistry,Institute of Theoretical and Computational Chemistry

(IQTCUB) of the University of Barcelona (UB), Barcelona 08028, Catalonia, Spain, [email protected]

Transparent organic-inorganic hybrid films with composition (wt%) PVA(54,5): PEG(40):

B2O3(5,5) are obtained by the sol-gel process and solution casting method at ambient

temperature. Two different precursors of boron aqua solutions of boric acid (H3BO3) and ethanol

solution of trimethyl borate (СН3О)3В) are used for the preparation of hybrid solutions. The

effect of starting boron solution type on the structure of obtained materials are studied by

infrared spectroscopy (IR). It was found that degree of cross-linking and type of bonding in the

hybrid structure are depended on by the functionality of borate units. From experimental and

calculated spectral data it can be concluded that the best cross-linked hybrid structure is obtained

from the aqua solution of H3BO3 at pH 10, with a predominant amount of polyborate ions

involved in the B-O-C ester complexes. We proposed a probable mechanism of boron-containing

organic-inorganic network combining various experimental and computational results.




53

PP22. BOROSILICATE HYBRID MATERIALS AND

NANOCOMPOSITES: SYNTHETIC, STRUCTURAL

AND STATISTICAL APPROACH

Hristo Hristov1, Miroslava Nedyalkova1, Sergio Madurga2, Vasil Simeonov1

1 Faculty of Chemistry and Pharmacy, University of Sofia St. Kl. Okhridski“,

J. Bourchier Blvd. 1, Sofia 1164, Bulgaria, [email protected], [email protected] 2 Department of Material Science and Physical Chemistry,Institute of Theoretical and Computational Chemistry

(IQTCUB) of the University of Barcelona (UB), Barcelona 08028, Catalonia, Spain, [email protected]

Transparent organic-inorganic hybrid films and bulk materials with composition (wt%)

PVA(70):PEG(5):B2O3(5):SiO2(20) (A1) are prepared by sol-gel method. 4 wt % PVA, PEG400,

pre-hydrolyzed TEOS (in a water-alcohol medium) and different precursors of boron are used for

a preparation of hybrid mixtures. The ethanol solution of trimethyl borate (СН3О)3В), aqueous

and glycerol solutions of boric acid (H3BO3) with pH adjustment are sources for cross-linking

borate units. The films and bulk materials were treated at 100, 400, 800 oC for 2 h. The effect of

starting boron solution type on the structure of obtained materials, as well as and structural

changes during a pyrolysis were studied by Fourier transform infrared spectroscopy, X-ray

diffraction, differential thermal analysis, scanning electron microscopy. We found that the

structures of hybrid films and molten materials contain BO3, BO4, SiO4 structural groups and B-

O-Si bonds. The quantities and order of borate structural units as well as residual carbon in the

networks depended on boron precursor type. To access and reveal the impact and hidden patterns

of the experimental conditions on the structural changes of the polymer-borosilicate films and

carbon/borosilicate glass nanocomposites, cluster analysis of the IR-spectral data was used as a

classification method.




54

PP23. TEMPERATURE DEPENDENCE OF LUMINESCENCE

PROPERTIES OF Tb3+ DOPED ZINC ORTHOSILICATE,

SYNTHESIZED BY POLYMERIZED COMPLEX METHOD

Miroslava Getsova

Faculty of Chemistry and Pharmacy, University of Sofia, J. Bourchier 1, 1164, Sofia, Bulgaria,

[email protected]

Qualitative Zn2SiO4·0.025Tb2O3 (mol%) phosphor powder with particles in nanoscale range and

strong green luminescence with emission line at 540 nm was synthesized at relatively low

temperature as 850 °C using a substandard for silica- based materials synthesis- Polymerized

Complex Method. The formation mechanism of the material, its homogeneity and morphology

were characterized by different methods as thermogravimetry, X-ray diffraction, IR, Raman,

UV-vis spectroscopy and SEM measurements. The proper synthesis temperature was established

by investigation of the temperature dependence of the luminescence properties of Zn2SiO4:Tb3+

phosphor. The experiment was conducted in the temperature range 800-1050 °C. No apparent

change in the spectral energy distribution is observed for the samples annealed between 800 and

1050 °C but the intensity of the emitted light considerably reduces with the temperature increase.




55

PP24. POTENTIAL VACCINE ADJUVANTS OF NANOSTRUCTURED

IRON(III) HYDROXYPHOSPHATES: PREPARATION AND

PHYSICOCHEMICAL CHARACTERIZATION

Nadezhda Angelova1, Georgi Yordanov1

1 Sofia University “St Kliment Ohridski”, Sofia, Bulgaria, [email protected]

Vaccine adjuvants are components of inactivated vaccine formulations that potentiate the

immune response against antigens. Widely used adjuvants in routine human vaccinations are

aluminium(III) oxyhydroxide and hydroxyphosphate. However, these adjuvants have certain

limitations (low efficacy for some antigens, selective induction of Th2 type immune response

and ineffective induction of Th1 type cytotoxic immune response, stimulation of eosinophilia,

production of specific and total IgE antibodies, etc.) which is the major motivation for the search

of alternative adjuvants with better efficacy and safety. In our previous work [1] we studied the

physicochemical characteristics of mixed Fe/Al hydroxyphosphates as potential vaccine

adjuvants, because ferric-based adjuvants are known to induce both humoral and cytotoxic T-cell

response [2], which is advantageous compared to aluminium-based adjuvants. Here, we report on

the physicochemical characterisation of nanostructured Fe(III) hydroxyphosphates of various

composition as potential ferric-based alternatives of aluminium adjuvants. We synthesized

various nanostructured iron(III) hydroxyphosphates with different composition. The obtained

materials were characterized for elemental composition, crystal structure, isoelectric points,

protein adsorption, and dissolution rate in sodium citrate solution, which are important

physicochemical characteristics to be studied in the early adjuvant development stages.

Acknowledgments:

Authors are grateful to Operational programme "Science and Education for Smart Growth", project

BG05M2OP001-2.009-0028.

References:

1. Angelova, N., Yordanov, G., Coll. Surfaces A: Physicochei. Engin. Asp., 535, 2017, 184.

2. Leibl, H., Tomasits, R., Brühl, P., Kerschbaum, A., Eibl, M., Mannhalter, J., Vaccine, 17, 1999, 1017.




56

PP25. GREEN SYNTHESIS OF SILVER NANOPARTICLES AND THEIR

ANALYTICAL APPLICATION AS LSPR-BASED OPTICAL SENSORS IN

SPECIATION ANALYSIS OF CHROMIUM AND IRON

Penka Vasileva1, Lyubomir Djerahov2, Irina Karadjova1

1 Faculty of Chemistry and Pharmacy, University of Sofia “St. Kliment Ohridski”,

1164 Sofia, Bulgaria, [email protected], [email protected] 2 Department of Chemistry, University of Mining and Geology “St. Ivan Rilski”,

1700 Sofia, Bulgaria, [email protected]

Green synthesis of silver nanoparticles (Ag NPs) has gained many research interests as a low

cost and eco-friendly approach. This work reported on the use of carbohydrates as reducing and

stabilizing agents for a green production of Ag NPs in aqueous dispersions. The size,

morphology, structure, surface and optical properties of Ag NPs were characterized by

transmission electron microscopy, dynamic light scattering, X-ray diffraction, zeta potential

measurements, FT-IR and UV-vis spectroscopy.

The design and synthesis of ion selective chemical sensors represent an area of current interest

due to their relevance to the development of analytical tools for the detection and monitoring of

ions in various samples. Ag NPs have been already explored as colorimetric probes for metal

ions, but their capabilities for chromium and iron speciation are not reported. In this work,

simple, fast and low cost procedures were developed for highly sensitive and selective

quantitative sensing of Cr(VI) and Fe(III) using aqueous dispersions of raffinose-coated and

starch-coated Ag NPs as optical sensing systems, respectively. Colorimetric probes developed

are based on two different mechanisms: redox interaction of the analyte with silver nanoparticles

in the case of Fe(III) or sorption of the analyte on the surface of Ag NPs followed by NPs

aggregation in the case of Cr(VI). In the latter mechanism, the use of a low weight coating agent

(raffinose) for nanoparticle stabilization leads to a better performance compared to bulkier

polymeric coating (starch).

The sensitivity and selectivity of LSPR-based optical sensors proposed towards interfering

transition-metal ions, alkali metal ions and alkaline earth metal ions were studied. The effect of

the analyte concentrations to the Ag NPs optical response was considered and the LODs for

analyte determination were defined.

Acknowledgements:


(Grant № DFNI-T01/5). P. Vasileva is grateful to Operational programme "Science and Education for Smart

Growth", project BG05M2OP001-2.009-0028.




57

PP26. BERNESSITE AS A STRUCTURAL MATRIX

FOR INTERCALATION OF LITHIUM

Zlatina Zlatanova1, Delyana Marinova1, Radostina Stoyanova2

1 Sofia University, Faculty of Chemistry and Pharmacy 2 Bulgarian Academy of Sciences, Institute of General and Inorganic Chemistry

Since the first clay batteries were used, constant efforts has been mode in searching of new

anode and cathode materials with better properties. The aim is obtaining materials with better

properties suchas energy density, capacity, charge/discharge regimes, satety and of course cost.

Our work is focused on Na – Mn and Mg – Mn oxides of birnesite type as new promising

cathode materials. The results, give us a reason to conclude that replacement Na- ions with Mg-

ions has a positive effect.




58

PP27. KETO-ENOL AND NITRO-ACI-NITRO TAUTOMERISM IN

3,3’,4,4’-TETRAHYDRO-3,3’-DISUBSTITUTED-4,4’-BISCOUMARINS

Ana I. Koleva, Nevena I. Petkova-Yankova, Rositca D. Nikolova


1164, Sofia, 1 J. Bouchier [email protected]

Biscoumarins exhibit properties similar to those of coumarins and act as anticoagulants,

antioxidants, antitumor, and antifungal agents. They are a relatively unexplored class of

compounds, isolated and characterized from different plant species [1].

The current investigations have introduced method for faster and simple preparation of 3,3’,4,4’-

tetrahydro-3,3’-disubstituted-4,4’-biscoumarins under ultrasound irradiation in the presence of

an organozinc reagent. The homodimers are isolated with the highest yields reported in the

literature about such compounds carrying electron-withdrawing groups in third position. The

structures of tetrahydrocoumarins are characterized by IR, NMR and MS spectra and the main

product was assigned to be the meso-stereoisomer.

Analyzing the 2D NMR spectra for the bisproducts of 3-acetyl- and 3-nitrocoumarins enol-forms

and aci-nitro forms were registered due to the small steric hindrance of the substituent and the

adjacency of an alpha-proton to the C=O or NO2 group. The tendency for keto-enol tautomerism

of the products of 3-acetylcoumarin is well known for us from previous investigations [2, 3].

Tautomers of nitro compounds are not frequently detected by spectroscopy or reported in the

literature [4]. Chelation of the enol- and the aci-forms with the C=O from the lactone ring could

additionally stabilize the studied configuration giving us the opportunity to isolate and

characterize them.

References:

1. Pratap, R., Ram, V. J. Chem. Rev., 114, 2014, 10476.

2. Nikolova, R. D., Bojilova, A. G., Rodios, N. A. Tetrahedron, 60, 2004, 10335.

3. Simeonov, M. F., Spassov, S. L., Bojilova, A., Ivanov, C. J. Mol. Struct., 127, 1985, 127.

4. Lammertsma K., Bharatam P. V. J. Org. Chem., 65, 2000, 4662.




59

PP28. SYNTHESIS OF IMIDAZOQUINOLINIUM SALTS

AND THEIR RESPECTIVE PALLADIUM NHC-COMPLEXES

Rumen Lyapchev1, Petar Petrov1, Miroslav Dangalov2, Nikolay G. Vassilev2

1 Department of Organic Chemistry, Faculty of Chemistry and Pharmacy, Sofia University St. Kliment Ohridsky,

1, James Bourchier Blvd., 1164, Sofia, Bulgaria 2 Institute of Organic Chemistry with Center of Phytochemistry, Bulgarian Academy of Sciences,

Acad. G. Bonchev Str. Bl. 9, 1113 Sofia, Bulgaria

Despite the wide variety of different types of NHC structures, there is almost no information for

the catalytic performance of palladium complexes, bearing imidazoquinolinylidene NHC-ligand.

We present the synthesis of imidazoquinolinium salts (1) and two types of their respective NHC-

complexes (2a and 2b) with different nitrogen [1, 2] additional ligands. The catalytic properties

of the complexes were tested in model Suzuki reaction. In order to improve their activity, the

substituents R1 and R2, which influence the electronic and steric properties of the NHC-ligand,

were varied. Selenoureas (3) were synthesized and analyzed by 77Se-NMR spectroscopy to

evaluate the π-acceptor3 ability of the new ligands.

References:

1. O’Brien, C., Kantchev, E., Valente, C., Hadei, N., Chass, G., Lough, A., Hopkinson, A., Organ, M., Chem.

Eur. J., 12, 2006, 4743.

2. Kantchev, E., Peh, G.-P., Zhang, C., Ying, J. Y., Org. Lett., 10, 2008, 3949.

3. Vummaleti, S., Nelson, D., Poater, A., Gomez-Suarez, A., Cordes, D., Slawin, A., Nolan, S., Cavallo, L.,

Chem. Sci., 6, 2015, 1895.




60

PP29. SYNTHESIS AND PHOTOPHYSICAL PROPERTIES OF NOVEL

FLUOROGENIC ASYMMETRIC SQUARILIUM DYES –

NONSPECIFIC PROTEIN BINDERS

Meglena Kandinska1, Alexey Vasilev1, Stanislava Yordanova1, Stanimir Stoyanov1,

Silvia Angelova2

1 Faculty of Chemistry and Pharmacy, Sofia University “St. Kliment Ohridski”, 1164 Sofia, Bulgaria

2 Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences,

Sofia, 1113 Bulgaria

Because of their unique photophysical characteristics – high molar absorptivity in the near UV-

VIS region, remarcable photostability, high fluorescence quantum yields under certain

conditions and photoconductive properties squarilium dyes are one of the most valuable organic

compounds applicable in optoelectronics, xerography, laser technique, optical recording

technologies, design of solar cells and photodynamic therapy of cancer. Here we describe the

synthesis of novel asymmetric squarilium dyes 1a and 2 (Scheme 1) and evaluation of their

protein binding properties.

The investigation of the photophysical behavior of the newly synthesized compounds showed

that they interact with the protein molecule which is evidenced by the change in the fluorescence

properties of the dye and of the bio-object (Fig. 1).

Figure 1. Fluorescence spectra of 1a (increasing concentrations) in the presence of BSA




61

PP30. NAPHTHALIMIDES WITH FUSED N-B-N BRIDGE:

A NEW CLASS OF BORON CONTAINING FLUOROPHORES

Stanimir Stoyanov1, Stanislava Yordanova1, Petar Petrov1, Diana Cheshmedzhieva1,

Miroslav Dangalov2

1 Sofia University ‘St. Kliment Ohridski‘, Faculty of Chemistry and Pharmacy,

1 James Bourchier Ave., 1164 Sofia, Bulgaria, [email protected] 2 Institute of Organic Chemistry, Bulgarian Academy of Sciences, acad. G Bonchev str, Sofia, Bulgaria

In the past decade the chemistry of three-coordinated boron compounds has rapidly developed

and some of these organoboranes were found to be strongly luminescent. N-B-N moieties were

successfully fused to various aromatic systems, and in such surroundings, e.g.

benzodiazaboroles, the boron acted as an electron-donor. Recently we studied the spectral

properties of 3,4-disubstituted 1,8-naphthalimides1 and showed that extending the aromatic

system with a fused imidazole ring leads to dramatic change in the emission of the corresponding

diamino precursors2. The next logical step in our quest for novel push-pull systems with tunable

photophysical properties was to incorporate a three coordinated boron into an N-B-N electron-

donating unit, fused to the classic electron-accepting naphthalimide core. The resulting novel

fluorophores were found to possess bright cyan emission (QY up to 0.9) in non-polar solvents,

which almost disappears in polar media. Various substituents to the boron atom were studied in

order to analyze the potential for fine tuning of the spectral properties.

References:

1. Stoyanov, S., Petrov, P., Stoyanova, M., Dangalov, M., Shivachev, B., Nikolova, R., Petkov, I., J.

Photochem. Photobiol. A: Chem., 250, 2012, 92.

2. Dangalov, M., Yordanova, S., Stoyanova, M., Cheshmedzhieva, D., Petrov, P., Stoyanov, S., J. Mol. Struct.

1125, 2016, 705.




62

PP31. SYNTHESIS, PHOTOPHYSICAL CHARACTERISTIC

AND MICROBIOLOGICAL ACTIVITY

OF NEW PAMAM TRIPOD AND ITS CUPRUM COMPLEX

Stanislava Yordanova1, Stanimir Stoyanov1, Ivo Grabchev2

1Faculty of Chemistry and Pharmacy, Sofia University „St. Kliment Ohridski”

1164 Sofia, 1 James Baurchier Blvd.’ е-mail: [email protected] 2Faculty of medicine, Sofia University „St. Kliment Ohridski” 1407 Sofia, 1 Kozyak Str.

Dendrimers and dendrons have attracted a large amount of interest over the past few decades due

to their utility as molecular scaffolding in a great many applications, e.g. sensors, drug delivery

systems, catalytic nanoreactors and light-harvesting systems. This utility arises from the fact that

dendrimers have the ability to concentrate a high number of end-groups in high concentration in

one molecule. For effective light-harvesting to take place it is necessary for there to be a central

core chromophore (acceptor) which is surrounded by a secondary chromophore (donor).

Dendrons offer such a possibility, specifically PAMAM-type dendrons, as it is possible to

synthesize such dendrons in large quantities with high yields from readily available starting

materials, with minimally need for purification. In this communication we present the synthesis

and photophysical characterization of a new bi-chromphoric 1,8-naphthalimide modified

PAMAM-type dendron, which exhibits a highly efficient energy transfer process from the donor

4-alkoxy-1,8-naphthalimide to the acceptor 4-amino-1,8-naphthalimide. The synthesis,

characterization and microbiological activity of dendron’s cuprum complex have been also

discussed.

Figure 1. Tripod dendrimer chemical structure




63

PP32. WATER-SOLUBLE NIR-ABSORBING RYLENE

CHROMOPHORES FOR VISUALISATION

OF CELLULAR ORGANELLES

Yulian Zagranyarski1, Stefka Kaloyanova2, Kalina Peneva3

1 Sofia University ‘St. Kliment Ohridski‘, Faculty of Chemistry and Pharmacy, 1 James Bourchier Ave., 1164 Sofia,

Bulgaria, [email protected] 2 Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany

3 Laboratory of Organic and Macromolecular Chemistry, Friedrich Schiller University Jena, Lessingstr 8, 07743

Jena, Germany

Biocompatible organic dyes emitting in the near-infrared are highly desirable in fluorescence

imaging techniques. Organic dyes have proven to be highly specific and sensitive molecular

reporters, but usually they suffer from poor hydrophilicity and photostability, low quantum yield,

insufficient stability in biological systems, and low detection sensitivity.

We introduce a novel approach for building small peri-guanidine fused naphthalene monoimide

and perylene monoimide chromophores [1]. The presented structures possess near-infrared

absorption and emission, high photostability, and good water solubility. After a fast cellular

uptake, they selectively stain mitochondria with a low background in live and fixed cells. They

can be additionally modified in a one-step reaction with functional groups for covalent labelling

of proteins. The low cytotoxicity allows a long time exposure of live cells to the dyes without the

necessity of washing. Successful application in localization super-resolution microscopy was

demonstrated in phosphate-buffered saline without any reducing or oxidizing additives.

References:

1. Kaloyanova, S., Zagranyarski, Y., Ritz, S., Hanulová, M., Koynov, K., Vonderheit, A., Peneva, K.,

Müllen, K., J. Am. Chem. Soc., 138, 2016, 2881.




64

PP33. SIMPLE SYNTHESIS OF DIARYL SUBSTITUTED

PYRROLIDINE-2-CARBONITRILES FROM ENONES

Vesela Mihaylova1, Nelly Mateeva2, Ivaylo Ivanov3, Donka Tasheva1

1 Faculty of Chemistry and Pharmacy, Sofia University “St. Kl. Ohridski, 1 James Bourchier blvd, 1164 Sofia,

Bulgaria, [email protected], [email protected] 2 Department of Chemistry, Florida A&M University Tallahassee, FL, USA, [email protected]

3 Department of Chemistry and Biochemistry, Medical University – Sofia, 2 Zdrave str, 1431 Sofia, Bulgaria,

[email protected]

Heterocycles are the largest class of organic compounds. Among them functionalized

pyrroldines continue to attract interest due to their diverse biological properties. For example,

pyrrolidine ring is the central unit of many bioactive natural or synthetic products. Compounds

containing the 2-cyanopyrrolidine scaffold are the most effective inhibitors for postproline

specific petidases.

In this study we present the synthesis of single diastereomers of 3,5-diarylpyrrolidine-2-

carbonitriles. They are obtained by three-step synthesis - Michael addition of

[(diphenylmethylene)amino]acetonitrile to substituted enones; the subsequent cyclization of the

2-amino-5-oxonitriles obtained to the substituted ∆1-pyrroline-5-carbonitriles and their reduction.

2-Amino-5-oxonitriles with a protected amino group, obtained in high yields as mixture of

diastereoisomers in the PTC conditions. They are converted by hydrolytic cyclization in the

presence of acetic acid to ∆1-pyrroline-5-carbonitriles which are isolated as single diastereomers

by column chromatography in high yields. Cis- and trans-isomers of ∆1-pyrroline-5-carbonitriles

are reduced with NaBH4 in the presence of CH3COOH at r.t. Reduction reactions proceed in

good yields and high diastereoselectivity for the short time.

Investigations on the anticancer activity of the pyrrolidine-2-carbonitriles obtained are in

progress.

Acknowledgements:

This work is financially supported by the National Science Fund of the Bulgarian Ministry of Education and

Science, Grant № Т02/25 2014, the Sofia University “St. Kl. Ohridski” Scientific Fund (grant № 80-10-3/2018) and

Project BG05M2OP001-2.009-0028, funded under Operational program “Science and education for smart growth”.




65

PP34. POLYZWITTERIONIC GELS

AS POLYMER ELECTROLYTES FOR LITHIUM ION BATTERIES

Denis Topov1, Konstans Ruseva1, Anton Apostolov1, Latchezar Hristov2, Rumen Tomov3,

Stoyan Smoukov4, Vasant Kumar3, Elena Vassileva1

1Laboratory on Structure and Properties of Polymers, Faculty of Chemistry and Pharmacy, Sofia University,1,

James Bourchier blvd., Sofia, 1164, Bulgaria 1Laboratory of Water Soluble Polymers, Polyelectrolytes and Biopolymers, Faculty of Chemistry and Pharmacy,

Sofia University,1, James Bourchier blvd., Sofia, 1164, Bulgaria 3Materials Chemistry Group, Department of Materials Science & Metallurgy, University of Cambridge, UK, 27

Charles Babbage Road, Cambridge, CB3 0FS 4 Division of Chemical Engineering & Renewable Energy, School of Engineering and Materials Science, Queen

Mary University,UK, London,320 Mile End Rd

Gel polymer electrolytes (GPE) offer many advantages when used in lithium-ion batteries as

they could provide safe and stable operation and an ability to be used in different packaging

formats. Their main advantage is their safety as compared to traditional non-polymer liquid

electrolytes based batteries. The main approach for enhance the ion transport in GPE and thus to

achieve high conductivities is to use large quantities of plasticizers and/or solvents.

The present study aims at the development of polyzwitterionic GPE in order to take advantage of

the polyzwitterions (PZI) well known salt-philicity. PZI are known to swell more upon salt

concentration increase which is a totally opposite behaviour as compared to the polyelectrolytes

which usually shrink as the salt concentration in solution increases. Two types of PZI networks

were synthesized, namely polysulfobetaines and polycarboxybetaines, using poly(ethylene

glycole) diacrylate as crosslinking agent. The PZI networks were characterized in terms of their

swelling capacity in mixed solvent of water: poly(ethylene glycol)=1:1 using LiClO4 as

electrolyte. Two parameters of the solvent’ composition were varied, namely, the molecular

weight of PEG (PEG 300 or PEG400) as well as Li salt concentration (1M and 2M). The PZI

hydrogels swollen in solvents with different composition (PEGs and Li salt concentrations) were

studied for their thermal behaviour by differential scanning calorimetry as well as for their ionic

conductivity. Both PZI types hydrogels showed only bound water inside them for all solvent

compositions. PSB hydrogels showed ionic conductivity ~19 mS/mm while for PCB twice lower

values were determined. PEG molecular weight influenced the PCB behaviour and conductivity

values, but it did not exert any effect on PSB hydrogels behaviour which was explained by the

temperature dependent PSB behaviour.

Acknowledgments:

This study was carried out with the financial support of the Operational Programme "Science and Education for

Smart Growth", project BG05M2OP001-2.009-0028. The financial support of H2020 project Materials Networking,

Contract No 692146 is also acknowledged.




66

PP35. AZEOTROPY IN MULTI-COMPONENT COPOLYMERIZATION:

EXISTENCE AND STABILITY

Latchezar Christov

Department of Chemistry, University of Sofia, 1 James Bourchier Av., Sofia 1164, Bulgaria

[email protected]

While the azeotropy in binary copolymerizing systems is fully investigated and understood, the

more complicated cases of three and even more comonomers are not systematically analyzed yet.

In the frame of the terminal model, a straightforward numerical approach is proposed which

finds easily and fast the full azeotropes (if they exist) for any system, regardless of the number of

comonomers. Furthermore, the problem of the stability of the azeotropes is discussed. It is of

high practical importance as the unstable azeotropic blends do NOT provide constant copolymer

composition for copolymerizations in batch reactors carried out to high conversion. Some

approaches to this problem are outlined [1].

References:

1. Christov, L., J. Univ. Chem. Techn. Metall., XXXVII, 2002, 53.




67

PP36. COPOLYMER HYDROGELS OF POLY(ACRYLIC ACID)

AND POLYACRYLAMIDE: SYNTHESIS, CHARACTERIZATION

AND REVEALING THEIR POTENTIAL

AS TRANSDERMAL DELIVERY SYSTEM FOR QUERCETIN

Marin Simeonov, Christo Tzachev, Elena Vassileva

Faculty of Chemistry and Pharmacy, Sofia University,1, James Bourchier blvd., Sofia, 1164, Bulgaria

([email protected])

The pharmaceutical science has been recently focused on the development of systems for

controlled and prolonged drug delivery. Polymer networks and their hydrogels play an essential

role in solving this challenge. Hydrogels are crosslinked hydrophilic or amphiphilic polymers

able to absorb and retain large amounts of water. They posses excellent biocompatibility,

capacity for drugs and bioactive macromolecules immobilization and ability for their controlled

release. The key factors that could be used to control the drug release are hydrogels composition,

polymer network density, polymer functionality, degradability, etc.

Quercetin is a polyphenol compound of plant origin from the

flavonoid group. Known for its antioxidant and anti-

inflammatory effect, enhancing cell regeneration processes, etc.

its application is parialy limited due to its extremely low

solubility in water. From a pharmacokinetic point of view,

quercetin has a low bioavailability ranging from 0 to 50% and

an extremely short half-life of 1-2 hours after oral administration, both characteristics making it

extremely appropriate for inclusion into prolonged drug release systems.

The present study aims at the development of prolonged-release system of quercetin based on

poly(acrylic acid) and polyacrylamide copolymer hydrogels. The hydrogels were characterized

in terms of their swelling capacity under different environmental conditions - pH, temperature

and ionic strength. The quercetin-loaded hydrogels were characterized by infrared spectroscopy

and differential scanning calorimetry to evaluate the polymer-drug interaction. The quercetin

release profiles were followed in vitro and explained by the hydrogels properties as well as by

the polymer-drug interaction. In summary, a novel patient-friendly system for quercetin

transdermal delivery was developed which ensures prolonged drug release.

Acknowledgments:

This study was carried out with the financial support of the Bulgarian National Scientific Foundation under Contract

DM19/04 and the Operational Programme "Science and Education for Smart Growth", project BG05M2OP001-

2.009-0028.




68

PP37. ENZYMATIC HYDROLYSIS OF MONOMOLECULAR FILM

OF DILAUROYLPHOSPHATIDYLCHOLINE

BY VIPOXIN AND ITS SEPARATED COMPONENTS

Kristina Mircheva1, Svetla Petrova2, Tzvetanka Ivanova1, Ivan Panaiotov1,

Konstantin Balashev1,3*

1Department of Physical Chemistry, Faculty of Chemistry and Pharmacy, St. K. Ohridski University of Sofia, 1

James Bourchier Blvd., 1164 Sofia, Bulgaria 2Department of Biochemistry, Faculty of Biology, St. K. Ohridski University of Sofia, 8 Dragan Tsankov Blvd., 1164

Sofia, Bulgaria 3Life sciences and bioengineering center, Worcester Polytechnic Institute, 60 Prescott St, Worcester, USA

The growing research interest about neurotoxin Vipoxin is inspired by its intriguing

heterodimeric structure and the resulting interactions between Vipoxin’s basic catalytic subunit

and the acidic regulatory subunit.

In this paper, we studied the enzymatic action of Vipoxin and its individual components on

Dilauroylphosphatidylcholine (DLPC) monolayers at air-water interfaces. We applied the

classical surface barostatic method and interpreted our experimental data with an adapted

Michaelis-Menten kinetic model. This approach allowed us to obtain the global kinetic constants

together with the interfacial specific activity of Vipoxin and its subunits. Using reconstituted

Vipoxin complexes formed by incubating the enzymatic VBC-sPLA2 and non-catalytic VAC

subunits in different ratios, we showed that the activity of the reconstituted mixture VAC:VBC-

sPLA2 (1:1), which should correspond to the composition of Vipoxin, is higher than that of the

natural Vipoxin complex. Finally, Vipoxin heterodimers in the DLPC monolayer were imaged

by Atomic force microscope (AFM) and statistically analyzed.




69

PP38. INFLUENCE OF CHARGE REGULATION ON

CONFORMATIONAL, IONIZATION AND STRETCHING PROPERTIES

OF POLYELECTROLYTES

Francesc Mas1, Pablo M. Blanco1, Sergio Madurga1, Josep Lluís Garcés2



[email protected], [email protected] 2 Department of Chemistry, University of Lleida, Av. Alcalde Rovira Roure, 191, E-25198-Lleida (Catalonia,

Spain), [email protected]

Polyelectrolytes are usually modelled using either flexible chains with constant charged groups

or rigid chains with ionisable groups able to regulate their charge. However, in many

polyelectrolytes conformational properties and charge regulation are coupled. A new Statistical

Mechanics model, the Site Binding Rotational Isomeric State (SBRIS) model, has recently been

proposed in order to study the coupling of charge regulation and conformational changes in

polyelectrolytes [1]. This model combines the classical Rotational Isomeric State (RIS) model

developed by Flory [2] with the Site Binding (SB) model [3].

In this work, an extension of SBRIS model to include long range interactions is presented. In this

approach, long range interactions are introduced as a free energy contribution to short ranged

effective parameters [4-5]. The analytical results are compared with Semi-Grand Canonical

Monte Carlo (SGCMC) simulations, which explicitly include long range electrostatic

interactions. Moreover, SGCMC simulations of the polyelectrolyte response to an external

mechanical force are also presented [6]. The role of long range interactions, charge regulation,

ionic strength and pH on polyelectrolyte stretching is discussed.

Acknowledgements:


XrQTC), and Spanish Structures of Excellence María de Maeztu program through (Grant MDM-2017–0767). J.L.

Garcés also acknowledges the Spanish Ministry of Science and Innovation (project CTM2016-78798-C2-1-P). F.

Mas and S. Madurga acknowledge the funding of the EU project 8SEWP-HORIZON 2020 (692146). P.M. Blanco

also acknowledges the financial support from grant (FI-2017) of Generalitat de Catalunya.

References:

7. Garcés, J. L, Madurga, S., Borkovec, M., Phys. Chem. Chem. Phys., 16, 2014, 4626.

8. Flory, P., “Statistical mechanics of chain molecules”, John Wiley, New York, 1969

9. Koper, G., Borkovec, M., J. Phys. Chem. B, 105, 2001, 6666.

10. Garcés, J. L, Madurga, S., Rey-Castro, C., Mas, F., J. Polymer Sci. B: Polymer Phys., 55, 2017, 275.

11. Blanco, P. M., Madurga, S., Mas, F., Garcés, J. L., Polymers, 10, 2018, 811:1-20

12. Blanco, P. M., Madurga, S., Mas, F., Garcés, J. L., submitted, 2019




70

PP39. ALBENDAZOLE SOLUTION FORMULATION

VIA VESICLE-TO-MICELLE TRANSITION

OF PHOSPHOLIPID-SURFACTANT AGGREGATES

Vladimir Katev, Zahari Vinarov, Gabriela Gancheva, Slavka Tcholakova

Sofia University, Faculty of Chemistry and Pharmacy, [email protected]

Objective: To reveal the physicochemical mechanisms governing the solubilization of

albendazole in surfactant and phospholipid-surfactant solutions and, on this basis, to formulate

clinically relevant dose of albendazole in solution suitable for parenteral delivery

Methods: The effect of 17 surfactants and 6 surfactant-phospholipid mixtures on albendazole

solubility was studied. The size of the colloidal aggregates was determined by light-scattering.

The dilution stability of the proposed formulation was assessed by experiments with model

human serum. The solubilization of surfactant and surfactant-phospholipid aggregates was

determined by using High-performance liquid chromatography and then the solubilization

capacity was calculated.

Results: Anionic surfactants increased very strongly drug solubility up to 4 mg/mL at pH = 3

due to strong electrostatic interactions between the oppositely charged (at this pH) drug and

surfactant molecules. This effect was observed with all anionic surfactants studied, including

sodium dodecyl sulfate (SDS), double chain sodium dioctylsulfosuccinate (AOT), and the bile

salt sodium taurodeoxycholate (NaTDC). The phospholipid-surfactant mixture of 40% sodium

dipalmitoyl-phosphatidylglycerol +60% AOT provided highest albendazole solubilization (4.4

mg/mL), smallest colloidal aggregate size (11 nm) and was stable to dilution with model human

serum at (and above) 1:12 ratio [1].

Conclusions: A new albendazole delivery system with high drug load and low toxicity of the

materials used was developed. The high solubility of albendazole was explained with vesicle-to-

micelle transition due to the larger interfacial curvature preferred for albendazole solubilization

locus.

References:

1. Vinarov, Z., Gancheva, G., Katev, V., Tcholakova, S., Drug. Dev. Ind. Pharm., 44., 2018, 1130.




71

PP40. EMULSIFICATION BY ROTOR-STATOR HOMOGENIZER:

COMPARISON OF EXPERIMENTAL AND PREDICTED DROP SIZES

Dilek F. Gazolu-Rusanova1, Bistra Terzieva1, Slavka Tcholakova1, Nikolai Denkov1,

Simeon Stoyanov2, Jo Janssen2


The size distribution of droplets is an important characteristic of every emulsion as it affects its

stability, optical and rheological properties. We studied the main factors affecting the drop size

and polydispersity in oil-in-water emulsions with low weight fraction of the oil phase (ΦOIL =

0.05), prepared by using rotor-stator homogenizer. The obtained results demonstrate that

increasing the viscosity of the aqueous phase, ηC, above a certain critical value, leads to a

transition from inertial to viscous turbulent regime of emulsification. The analysis of the results

showed that the maximum diameter, dV95, of the drops, obtained in the inertial regime, is well

described by the classic Davies model [1], whereas the model of Kolmogorov [2] and Hinze [3]

for emulsification in viscous turbulent regime is not appropriate for description of the maximum

drop diameters obtained at high aqueous phase viscosity. The major aims of the current study

was to carefully analyze the results obtained by the emulsification experiments in viscous

turbulent regime with rotor-stator homogenizer and to find an appropriate equation that

adequately accounts for the contributions of (1) continuous phase viscosity; (2) rotor speed; (3)

interfacial tension on the droplet size. The proposed new equation describes very well the drop

sizes of all emulsions obtained in viscous turbulent regime. To check the validity of the new

equation, we carried out additional experiments at high oil concentrations. We found that the

proposed equation describes very well also the experimental results about the drop size in

emulsions with ΦOIL ≥ 0.6.

References:

1. Davies, J. T. Chem. Eng. Sci., 40, 1985, 839.

2. Kolmogorov, А.Н. Докл. Акад. Наук СССР, 66, 1949, 825.

3. Hinze, J.O. AIChE Journal, 1, 1955, 289.




72

PP41. ROLE OF SURFACE RHEOLOGICAL PROPERTIES

FOR THE KINETICS OF BUBBLE OSTWALD RIPENING

IN SAPONIN-STABILIZED FOAMS

Fatmegyul Mustan1, Slavka Tcholakova1, Nevena Pagureva1,

Konstantin Golemanov2, Nikolai D. Denkov1,

Edward G. Pelan2, Simeon D. Stoyanov2

1Department of Chemical and Pharmaceutical Engineering, Faculty of Chemistry and Pharmacy, Sofia University,

1 J. Boucher Ave., 1164 Sofia, Bulgaria, [email protected] 2 Unilever R&D, Vlaardingen, The Netherlands

Bubble Ostwald ripening (OR) leads to a gradual increase of the mean bubble size in foams with

time. The rate of OR can be reduced significantly or even arrested completely, using appropriate

solid particles and/or surfactants as foam stabilizers. To reveal the reasons for the reduced rate of

OR in saponin-stabilized foams, we performed measurements of the rate of bubble diminishing,

for single air bubbles placed below a solution surface, with a large series of saponin bio-

surfactants. These saponin surfactants form adsorption layers with surface elasticity, spanning a

very wide range – from almost zero up to several thousand mN/m. The measured rate of bubble

OR showed no correlation with the surface elastic modulus (dilatational or shear), as measured at

0.1 Hz frequency of surface oscillations. A reasonable correlation was observed only with the

surface stress (deviation from the equilibrium surface tension), measured at very slow rate of

surface deformation, which mimics much better the actual processes of bubble OR in foams –

higher surface stress corresponds to lower OR rate. New theoretical expression, accounting for

the out-of-equilibrium surface tension during bubble shrinkage and for the gas flux across the

meniscus regions surrounding the foam films, was derived and used to calculate theoretically the

rate of bubble diminishing. The comparison of the theoretical predictions with the experimental

data shows clearly that the main reason for the reduced rate of OR in the studied systems is the

high resistance to gas transfer of the saponin adsorption layers. The deviations from the

equilibrium surface tension, although noticeable, have smaller effect. The complementary

experiments with actual foams showed that the rate of OR is even lower (compared to the rate

measured with single bubbles) which is explained with the thicker non-equilibrium foam films,

formed between the neighboring bubbles in ripening foams [1].

References:

1. Tcholakova, S., Pagureva, N., Mustan, F., Golemanov, K., Denkov, N., Pelan, E., Stoyanov, S., Coll.

Surfaces A, 534, 2017, 16.




73

PP42. SYNERGISTIC MICELLAR GROWTH

IN MIXED SURFACTANT SOLUTIONS:

RHEOLOGY AND CRYO-TEM IMAGING

Gergana S. Georgieva1, Svetoslav E. Anachkov1, Dganit Danino2,

Ludmila Abezgauz2, Ingo Lieberwirth3, Kaloian Koynov3, Peter A. Kralchevsky1

1 Dpt. Chemical and Pharmaceutical Engineering, Sofia University, Sofia, Bulgaria;

[email protected] 2 Dpt. Biotechnology and Food Engineering, Technion - IIT, Haifa, Israel

3 Max Planck Institute for Polymer Research (MPIP), Mainz, Germany

We studied the synergistic growth of giant wormlike micelles in ternary solutions, which contain

a zwitterionic surfactant (CAPB, cocamidopropyl betaine), an anionic surfactant (SLES, sodium

lauryl-ethersulfate) and a fatty acid. For a given fatty acid concentration, the viscosity η0

exhibits a sharp and high peak (Fig. 1), which in the case of octanoic acid (HC8) reaches 41 000

times the viscosity of water [1]. The peak height decreases as a function of the fatty acid

chainlength until it completely disappears for hexadecanoic acid. Experiments with polarized-

light microscopy and NMR showed that all examined solutions are isotropic, rather than liquid-

crystalline. The cryo-TEM imaging revealed complex phase behaviour: (i) growing rod-like

micelles to the left of the peak; (ii) entangled wormlike micelles at the peak (Fig. 1); and (iii)

multi-connected structures for octanoic acid versus shape transition into disc-like micelles for

dodecanoic acid after the peak [1, 2]. The two scenarios in (iii) explain the viscosity reduction by

making a direct correlation between rheology and microstructure.

Figure 1: Viscosity peak and microstructure in the presence of octanoic acid (HC8)

References:

1. Georgieva, G. S., Anachkov, S. E., Lieberwirth, I., Koynov, K., Kralchevsky, P. A. Langmuir, 2016, 32,

12885.

2. Georgieva, G. S., Anachkov, S. E., Abezgauz, L., Danino, D., Kralchevsky,P. A. Langmuir, 2018, 34,

4897.




74

PP43. RHEOLOGY OF ADSORPTION LAYERS FROM THE PROTEIN

HYDROPHOBIN AND ITS MIXTURES WITH OTHER PROTEINS:

EXPERIMENT AND THEORETICAL MODEL

Gergana Radulova1, Krassimir Danov1, Peter Kralchevsky1, Elka Basheva1, Simeon Stoyanov2,

Konstantin Golemanov2

1 Department of Chemical and Pharmaceutical Engineering, Sofia University, Bulgaria

[email protected] 2 Unilever Research & Development, Vlaardingen, The Netherlands

The hydrophobins represent a class of amphiphilic proteins. At air/water and oil/water interfaces

they form adsorption layers with the highest surface elasticity and viscosity among all

investigated proteins. We investigated the surface shear rheology of class II hydrophobin HFBII

layers at liquid interface in two different dynamic regimes – fixed rate of strain and oscillations

[1–3]. The rheological data obtained in both regimes comply with the same viscoelastic

thixotropic model, which is used to determine the surface shear elasticity and viscosity, Esh and

ηsh. The resulting values for the Esh show that the elasticity is insensitive to the rate of strain in a

wide range of the investigated shear rates. The mixing of hydrophobin HFBII with other

conventional proteins could reduce Esh and ηsh proportional to the fraction of the conventional

protein. However, our experiments show that the effect of mixing can be rather different

depending on the nature of the additive. If the additive is a globular protein, like β-lactoglobulin

and ovalbumin, the surface rigidity is preserved, and even enhanced. In contrast, the addition of

the disordered protein β-casein leads to softening of the HFBII adsorption layer. Similar (an even

stronger) effect is produced by the nonionic surfactant Tween 20 [4]. These results could

contribute for quantitative characterization and deeper understanding of the factors that control

the surface rigidity of protein adsorption layers with potential application for the creation of

stable foams and emulsions with fine bubbles or droplets.

References:

1. Radulova, G. M., Golemanov, K., Danov, K. D., Kralchevsky, P. A., Stoyanov, S. D., Arnaudov, L. N.,

Blijdenstein, T. B. J., Pelan, E. G., Lips. A. Langmuir, 28, 2012, 4168.

2. Danov, K. D., Radulova, G. M., Kralchevsky, P. A., Golemanov, K., Stoyanov, S. D. Faraday Discus.,

158, 2012, 195.

3. Radulova, G. M., Danov, K. D., Kralchevsky, P. A., Petkov, J. T., Stoyanov, S. D. Soft Matter, 10, 2014,

5777..

4. Danov, K. D., Kralchevsky, P. A., Radulova, G. M., Basheva, E. S., Stoyanov, S. D., Pelan, E. G.. Adv.

Coll. Interface Sci., 222, 2015, 148.




75

PP44. EFFECTS OF SALT AND FRAGRANCE-LIKE MOLECULES

ON FORMULATION RHEOLOGY

Lidiya M. Dimitrova1, Pamela K. Petrova1, Svetoslav E. Anachkov1, Joanne L. Cook2,

Peter A. Kralchevsky1

1Department of Chemical and Pharmaceutical Engineering, Sofia University,

Sofia, 1164, Bulgaria, [email protected] 2Unilever R&D Port Sunlight, Bebington, CH63 3JW, United Kingdom

Many personal-care formulations contain sodium lauryl ether sulfate (SLES; anionic) and

cocoamidopropyl betaine (CAPB; zwitterionic) as main components. Here, we studied the

effects of salt (NaCl) and fragrance-like molecules (FLMs) on the rheological properties of

SLES-CAPB-containing solutions.

By varying the salt concentration, we constructed the so-called salt-response curve and observed

a viscosity peak at nearly 400-500 mM NaCl; see Figure 1a. The peak position does not seem to

depend on the total surfactant concentration or the weight fraction of SLES. Furthermore, we

found that the zero-shear viscosity, η0, and the relaxation time, τR, pass through a maximum,

whereas the elasticity, G0, increases monotonically as a function of the salt concentration.

We also investigated the effect of small FLMs on the rheological properties of SLES-CAPB-

based micellar solutions. We demonstrated that such FLMs can act as thickeners or thinners

depending on their structure and hydrophobicity; see Figure 1b and also [1]. If hydrophilic FLMs

(log P < 1.5) are added, η0 and G0 remain nearly constant. In the presence of FLMs with

intermediate log P (1.5 < log P < 6.5), η0 and G0 increase. In contrast, hydrophobic FLMs (log P

> 6.5) act as thinning agents and thus η0 and G0 decrease. These rules might be useful for the

design of personal-care formulations that contain perfumes.

(a) (b) Figure 1. Effects of salt (a) and FLMs (b) on the rheology of SLES-CAPB-based formulations

Acknowledgements: The study was supported by Unilever R&D. L.M.D. acknowledges financial support from

project BG05M2OP001-2.009-0028 funded by the EU.

References:

1. X. Tang, X., W. Zou, W., Koenig, P. H., McConaughy, S. D., Weaver, M. R., Eike, D. M., Schmidt, M. J.,

Larson, R. G. J. Phys. Chem. B, 121, 2017, 2468.




76

PP45. ROLE OF PICKERING STABILIZATION AND BULK GELATION

FOR THE PREPARATION AND PROPERTIES OF SOLID SILICA FOAMS

Monika Hristova, Ivan Lesov, Slavka Tcholakova, Nikolai Denkov


Sofia, Bulgaria

E-mail: [email protected]

Foaming of particulate suspensions, followed by foam drying, is developed as an efficient

method for production of highly porous materials with various applications. A key factor for

success is the appropriate choice of surfactants which both modify the particle surface and

stabilize the foam. In our recent work [1] we have compared the efficiency of this method for

silica suspensions containing two surfactants which lead to very different types of foam

stabilization. Cationic TTAB leads to particle-stabilized foams (Pickering stabilization) whereas

zwitterionic CAPB – to surfactant-stabilized foams. Thus we determined the general (common)

features shared between the various surfactant systems: (1) The foaminess is controlled

exclusively by the suspension viscosity under shearing conditions which mimic precisely the

foaming process; (2) The foam stability to drainage and coarsening is controlled exclusively by

the suspension yield stress; (3) The surfactant adsorption on the particle surface should occur in

the time scale of seconds to minutes, thus ensuring appropriate rheological properties of the

foaming suspension. Similar kinetic effects could be of high interest to other colloid systems and

process, e.g. for kinetic control of the internal structure and properties of aerogels produces from

sheared suspensions, and for control of the transient rheological properties and non-Newtonian

flow of particulate gels.

References:

1. Lesov, I., Tcholakova, S., Kovadjieva, M., Saison, T., Lablet, M., Denkov, N., J. Coll. Interface Sci, 504,

2017, 48.




77

PP46. SELF-REGULATION OF FOAM VOLUME AND BUBBLE SIZE

DURING FOAMING VIA SHEAR MIXING

Nadya Politova-Brinkova, Slavka Tcholakova, Zhulieta Valkova,

Konstantin Golemanov, Nikolai D. Denkov

Department of Chemical and Pharmaceutical Engineering,

Faculty of Chemistry and Pharmacy, Sofia University,

1 James Bourchier Ave., 1164 Sofia, Bulgaria

[email protected]

Liquid foams find a variety of applications in everyday life and industry as home and personal

care products, in cosmetics, pharmaceuticals, etc. Here we study the factors affecting the foam

generation in a planetary mixer with a series of surfactant solutions, having different dynamic

surface tensions, surface dilatational moduli and bulk viscosities. The foam generation in this

device consists of three well defined periods: (1) Induction period during which very slow

increase of the foam volume is observed. The duration of this period depends significantly on the

shear rate during foaming and on the volume of the surfactant solution; (2) Fast increase of foam

volume; the rate of this process depends primarily on the shear rate and dynamic surface tension

of the solutions; (3) Plateau region in which the foam volume remains constant. The

experimental results show that the processes of air entrapment ends when a certain critical

(dimensionless) shear stress of the foam is reached. Depending on the bulk and surface

properties of the surfactant solutions, this critical stress is achieved for foams with different air

volume fractions and mean bubble sizes. Thus, when solutions with higher bulk viscosity and/or

higher surface modulus are used, the critical stress is reached at lower air volume fraction and

with smaller bubbles. Power-law equations are shown to describe very well the effects of the

foaming shear rate and solution viscosity on the final foam volume and mean bubble size [1].

References:

1. Politova, N., Tcholakova, S., Valkova, Z., Golemanov, K., D. Denkov, N. D., Coll. Surfaces A 539, 2018,

18.




78

PP47. SULFONATED METHYL ESTERS, LINEAR ALKYLBENZENE

SULFONATES AND THEIR MIXED SOLUTIONS:

MICELLIZATION AND EFFECT OF CАLCIUM IONS

Rumyana D. Stanimirova1, Veronika I. Ivanova1, Krassimir D. Danov1,

Peter A. Kralchevsky1, Jordan T. Petkov2

1 Department of Chemical & Pharmaceutical Engineering, Faculty of Chemistry &Pharmacy, Sofia University,

1164 Sofia, e-mail: [email protected] Bulgaria) 2 KL-Kepong Oleomas SDN BHD, Menara KLK, Jalan PJU 7/6, Mutiara Damansara, 47810 Petaling Jaya,

Selangor Dalur Ehsan, Malaysia

Here, we compare the properties of sulfonated methyl esters of fatty acids (SME) and linear

alkylbenzene sulfonate (LAS) with respect to the effect of calcium ions on their surface tension

and the effect of their mixing on the critical micelle concentration (CMC). The theoretical

interpretation of surface tension isotherms obtained in the presence of NaCl and CaCl2 allowed

us to determine the parameters that characterize the surfactant adsorption layers and counterion

binding. The excluded area per molecule in the adsorption layer is the same for SME and LAS,

and is determined by the cross-sectional area of the sulfonate headgroup. The binding energies of

Na+ ions to the headgroups of SME and LAS are also the same (1). However, the binding energy

of the Ca2+ ion to the headgroup of LAS is considerably greater than that for SME in agreement

with the circumstance that LAS is easily precipitated by hard water. The binding energy of the

Ca2+ ion to the headgroup of SME is smaller even than that of Na+, in accord with the reputation

of SME as one of the most hardness tolerant surfactants. The dependences of the CMC on the

composition of binary mixed surfactant solutions reveal that C14-SME and C16-SME exhibit

ideal mixing; C14-SME and LAS – slightly synergistic mixing, whereas C16-SME and LAS –

antagonistic mixing due to hydrocarbon-chain mismatch. The micellization in mixed solutions of

SME and cocamidopropyl betaine has been also investigated.

The results in the present study allow prediction of the surface tension of solutions of SME and

LAS in the presence of Na+ and Ca2+ ions at various concentrations; contribute for a better

understanding of the different tolerance of SME and LAS to hard water, and quantify the effect

of their mixing on the CMC (2).

References:

1. Danov, K., Stanimirova R., et al. J. Colloid Interface Sci. 457, 2015, 307.

2. Ivanova, V., R. Stanimirova, R., et al. Coll. Surf. A, 519, 2017, 87.




79

PP48. PARTICLE DETACHMENT FROM FLUID INTERFACES:

THEORY VS EXPERIMENTS

Svetoslav E. Anachkov1, Ivan Lesov1, Michele Zanini2, Peter A. Kralchevsky1,

Nikolai D. Denkov1, Lucio Isa2

1Dpt. Chemical and Pharmaceutical Engineering, Sofia University, Sofia, 1164, Bulgaria 2Dpt. Materials, ETH Zurich, Zurich, CH-8093, Switzerland

Presenting author email: [email protected]

Microparticle adsorption and self-assembly at fluid interfaces are strongly affected by the

particle three-phase contact angle θ. On the single-particle level, θ can be determined by several

techniques, including colloidal-probe AFM, the gel-trapping technique (GTT) and the freeze-

fracture shadow-casting (FreSCa) method. While GTT and FreSCa provide contact angle

distributions measured over many particles, colloidal-probe AFM measures the wettability of an

individual (specified) particle attached onto an AFM cantilever. Here, we extract θ for smooth

microparticles through the analysis of force-distance curves upon particle approach and

retraction from the fluid interface; see Figure 1 and Reference [1]. From each retraction curve,

we determine: (i) the maximal force, Fmax; (ii) the detachment distance, Dmax; and (iii) the

work for quasistatic detachment, W. To relate Fmax, Dmax and W to θ, we developed a detailed

theoretical model based on the capillary theory of flotation. The model was validated in three

different ways. First, the contact angles, evaluated from Fmax, Dmax and W, are all close in

value and were used to calculate the entire force-distance curves upon particle retraction without

any adjustable parameters. Second, the model was successfully applied to predict the

experimental force-distance curve of a truncated sphere, whose cut is positioned below the point

of particle detachment from the interface. Third, our theory was confirmed by the excellent

agreement between the particle contact angles obtained from the colloidal-probe AFM data and

the ensemble-average contact angles measured by both GTT and FreSCa. Additionally, we

devised a very accurate closed-form expression for W (representing the energy barrier for

particle detachment), thus extending previous results in the literature [1].

Figure 1. Microparticle at the oil-water interface (left); Comparison of theory vs experiment (right)

Acknowledgements:

I.L. and S.E.A gratefully acknowledge the granted postdoctoral fellowships Sciex 14.081 and Sciex 14.082 at ETH

Zurich. S.E.A. acknowledges financial support from project BG05M2OP001-2.009-0028 funded by the EU.

References:

1. S.E. Anachkov, I. Lesov, M. Zanini, P.A. Kralchevsky, N.D. Denkov and L. Isa, Soft Matter, 12, 2016,

7632.




80

PP49. IMPLEMENTING ATOMIC FORCE MICROSCOPY FOR

CHARACTERIZATION OF SILVER NANOPARTICLES

Silviya Simeonova1, Peter Georgiev1, Lyuben Mihaylov2, Diana Nihtianova3,

Konstantin Balashev1

1 Department of Physical Chemistry, Faculty of Chemistry and Pharmacy, University of Sofia, 1 James Bourchier

Blvd., 1164 Sofia, Bulgaria, [email protected] 2 Department of Applied Inorganic Chemistry, Faculty of Chemistry and Pharmacy, University of Sofia, 1 James

Bourchier Blvd., 1164 Sofia, Bulgaria 3 Institute of Mineralogy and Crystallography, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., bl. 107, 1113

Sofia, Bulgaria

The silver nanoparticles with unique optical, electronic, and antibacterial properties have been

widely used in biosensing, photonics, electronics, and antimicrobial applications. In a novel

experimental approach Atomic Force Microscopy (AFM) was applied as a method for

characterization of silver nanoparticles. The silver nanoparticles were synthesized by classical

citrate synthesis. During the synthesis process AFM images silver nanoparticles are obtained.

From the AFM images silver nanoparticle’s sizes and size distributions can be obtained. The

AFM method is compared with Transmission Electron Microscopy (TEM) method.




81

PP50. IMPLEMENTING ATOMIC FORCE MICROSCOPY FOR

CHARACTERIZATION OF GOLD NANOPARTICLE FILMS

Peter Georgiev, Silviya Simeonova, Konstantin Balashev

Department of Physical Chemistry, Faculty of Chemistry and Pharmacy, University of Sofia, 1 James Bourchier

Blvd., 1164 Sofia, Bulgaria, [email protected]

In a novel experimental approach Atomic Force Microscopy (AFM) was applied as a method for

studying the gold nanoparticle films. The gold nanoparticle films were obtained by spin coating

method during the citrate synthesis. From the analysis of AFM images during the synthesis

process the nanoparticle s’ sizes and surface concentration can be obtained. The AFM method is

compared with Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy

(SEM) data. From the AFM images of gold nanoparticle films, size, shape, number and surface

concentration of nanoparticles are obtained.




82

PP51. DETERMINANTS OF Fe2+ OVER M2+ (M = Mg, Mn, Zn)

SELECTIVITY IN NON-HEME IRON PROTEINS

Todor Dudev, Valia Nikolova

Faculty of Chemistry and Pharmacy, Sofia University “St. Kliment Ohridski”



Iron cations are indispensable players in a number of vital biological processes such as

respiration, cell division, nitrogen fixation, oxygen transport, nucleotide synthesis, oxidant

protection, gene regulation, and protein structure stabilization. The basic mechanisms and factors

governing the competition between Fe2+ and other metal species from the cellular fluids such as

Mg2+, Mn2+ and Zn2+ are, however, not well understood, and several outstanding questions

remain: (i) How does the Fe2+ binding site select the “right” cation and protect itself from attacks

by other biogenic cations present in the surrounding milieu? (ii) Do the iron binding sites employ

different selectivity strategies toward metal cations possessing different ligand affinities and

cytosolic concentrations? (iii) What are the key determinants of metal selectivity in Fe2+

proteins? In this study, by employing density functional theory calculations combined with

polarizable continuum model computations, we endeavor to address these questions by

evaluating the thermodynamic outcome of the competition between Fe2+ and Mg2+ /Mn2+/Zn2+ in

model non-heme mononuclear metal binding sites of various compositions and charge states.

The present calculations, which are in line with available experimental data, shed light on the

mechanism of Fe2+ - Mg2+/Mn2+/Zn2+ competition in non-heme iron proteins and disclose the key

factors governing the process.

Acknowledgement:

Support from the project BG05M2OP001-2.009-0028 is acknowledged.




83

PP52. COMPETITION BETWEEN ABIOGENIC Al3+

AND NATIVE Mg2+, Fe2+ AND Zn2+ IONS IN PROTEIN BINDING SITES:

IMPLICATIONS FOR ALUMINIUM TOXICITY

Sonia Ilieva1, Todor Dudev1, Diana Cheshmedzhieva1, Lyudmila Doudeva2

1Faculty of Chemistry and Pharmacy, Sofia University, Sofia 1164, Bulgaria

e-mail: [email protected] 2Rostislaw Kaischew Institute of Physical Chemistry, Bulgarian Academy of Sciences,

Sofia 1113, Bulgaria

Abiogenic aluminum has been implicated in some health disorders in humans. Protein binding

sites containing essential metals (mostly magnesium) have been detected as targets for the

“alien” Al3+. However, the acute toxicity of aluminium is very low. Although substantial body of

information has been accumulated on the biochemistry of aluminium, still the underlying

mechanisms of its toxicity are not fully understood. Several outstanding questions remain

unanswered: (1) Why is the aluminium toxicity, unlike that of other “alien” metal cations,

relatively low? (2) Apart from Mg2+ active centers in proteins, how vulnerable are other essential

metal binding sites to Al3+ attack? (3) Generally, what factors do govern the competition

between ‘alien” Al3+ and cognate divalent metal cations in metalloproteins under physiologically

relevant conditions? Here, we endeavor to answer these questions by studying the

thermodynamic outcome of the competition between Al3+ and a series of biogenic metal cations,

such as Mg2+, Fe2+ and Zn2+, in model protein binding sites of various structures, compositions,

solvent exposure and charge states. Density functional theory (DFT) calculations in combination

with polarizable continuum model (PCM) computations are employed. For the first time, the

presence of different Al3+ soluble species at physiological pH was properly modeled in

accordance with experimental observations. The results suggest that a combination of

concentration and physicochemical factors renders the Al3+ → M2+ (M = Mg, Fe, Zn)

substitution and subsequent metalloenzyme inhibition a low-occurring event at ambient pH: the

more active aluminum species, [Al(H2O)6]3+, presents in very minute quantities at physiological

conditions, while the more abundant soluble aluminum hydrate, {[Al(OH−)4](H2O)2}−, appears to

be thermodynamically incapable of substituting for the native cation.




84

PP53. HYPERCONJUGATIVE EFFECTS IN Π-HYDROGEN BONDING:

THEORY AND EXPERIMENT

Boris Galabov1, Diana Cheshmedzhieva1, Valia Nikolova1, Boriana Hadjieva1,

Henry F. Schaeffer III2

1Faculty of Chemistry and Pharmacy, University of Sofia, Sofia, Bulgaria.

e-mail: [email protected] 2 Center for Computational Quantum Chemistry, University of Georgia, Athens, United States.

Density functional theory computations with the B3LYP/6-311++G(2df,2p) method and IR

spectroscopy are employed in investigating the properties of twenty π-hydrogen bonded

complexes between substituted phenols and hexamethylbenzene. All complexes possess T-

shaped structures. The methyl hyperconjugative effects on interactions energies and O-H

stretching frequencies are estimated via comparisons with previously reported theoretical and

experimental results for analogous phenol complexes with benzene. The theoretical

computations provide excellent quantitative predictions of the O-H stretching frequency shifts

(ΔOH) resulting from the hydrogen bonding. The ΔOH shifts in the hexamethylbenzene

complexes are approximately twice as large as the corresponding shifts for the benzene

complexes. Hirshfeld charges, electrostatic potential at nuclei (EPN) values, and molecular

electrostatic potential maps are employed in gaining insights into the mechanisms of methyl

hyperconjugative effects on complex formation.




85

PP54. MULTILIPID BILAYER WITH AN EMBEDDED RECEPTOR –

SELECTION OF A THERMODINAMIC ENSEMBLE

Jasmina Petrova, Gergana Gocheva, Nikoleta Ivanova,

Galia Madjarova, Stoyan Iliev, Anela Ivanova

Department of Physical Chemistry, Faculty of Chemistry and Pharmacy, Sofia University “St. Kliment Ohridski”,

1 James Bourchier Blvd., 1164 Sofia, Bulgaria

e-mail: [email protected]

Active targeting is a very promising approach for effective drug delivery to cancer cells, where

the drug carrier uses a ligand specifically recognized by cell surface receptors overexpressed in

neoplastic membranes. Such a protein is the folate receptor-α (FR-α) with folic acid as its natural

ligand. Modelling the targeting process in such a highly complex system faces many problems.

One of the main points in the current stage of the investigation is the selection of an appropriate

thermodynamic ensemble for adequate description of the receptor and membrane properties. The

available experimental data are used for construction of a lipid bilayer mimicking a neoplastic

membrane with FR-α embedded by a GPI anchor [1-3]. The properties of the system are studied

by atomistic molecular dynamics simulations at physiological conditions. Three different

pressure scaling methods - NPT isotropic, NPT semi-isotropic, and NPγT are tested. The results

about mass density profiles of the components, average area per lipid, order parameter of the

lipid tails, shape of the receptor, and size of its pocket are analyzed in the three ensembles. The

shape of FR-α in the three ensembles is similar. The profiles for the membrane characteristics of

interest are analogous in NPT semi-isotropic and in NPγT. The main differences in the three

ensembles are found in the representation of the membrane phase. The membrane is in liquid

disordered state in NPT with isotropic pressure scaling, while in the other two ensembles the

lipid tails adopt partial order corresponding to liquid ordered state. The latter is in

correspondence with the experimentally registered behaviour [4]. Overall, it is found that the

results of NPγT reproduce most closely the experimental values.

Acknowledgements:

The research is funded by the Bulgarian Scientific Fund, contract № DN09/14 from 16.12.2016; computational time

was provided on the HPC facility Aris (application Surf_prop, project “VI-SEEM”, grant number: 675121).

References:

1. Yu, Y., Skočaj, M., Kreft, M. E., Resnik, N., Veranič, P., et al., Mol. Bio Syst., 12, 2016, 3266.

2. Merchant, T. E., Kasimos, J. N., Vroom, T., Bree, E., Iwata, J. L., Graaf, P. W., Glonek, T. Cancer Lett.

176, 2002, 159.

3. Brown, D., Waneck, G. L., J. Am. Soc. Nephrol., 3, 1992, 895.

4. Derek, M., Biochim. Biophys., 1286, 1996, 183.




86

PP55. PREDICTING PARTITION COEFFICIENTS

BY FIRST PRINCIPLES CALCULATIONS OF ORGANIC SOLVENTS

WITH IMPLICIT SOLVENT MODEL

Miroslava Nedyalkova1, Sergio Madurga2, Marek Tobiszewski3, Vasil Simeonov1

1Faculty of Chemistry and Pharmacy, University of Sofia, 1164Sofia, Bulgaria, [email protected]

2 Departament de Ciència de Materials i Química Física & Institut de Química Teòrica i

Computacional (IQTCUB), Universitat de Barcelona, 08028 Barcelona, Catalonia, Spain 3 Department of Analytical Chemistry, Faculty of Chemistry, Gdańsk University of Technology (GUT), 80-233

Gdańsk, Poland

1Analytical Chemistry Department, Faculty of Chemistry and Pharmacy, University of Sofia,


The quantum chemical calculations were examined, and the results imply that SMD continuum

model is like a benchmark and tends to give the best agreement with observed experimental

values in conjunction with three DFT functionals (B3LYP, M06-2X, M11). The highest

correlation with the experimental data for the octanol/water values was reached by the M06-2X

functional. For the second partition coefficient octanol/air, B3LYP functional was observed as

the proper one for this level of theory. Herein, for the first time is presented the computational

approach for the octanol/air partition coefficient revealing predictions accuracy and precision by

the DFT calculations. The last part of the work was focused on the hidden links between

observed partition coefficients and other physicochemical properties like water solubility,

Henry’s Law constants, log BCF and surface tension. The trends of similarities or dissimilarities

were explored through multivariate data analysis using available experimental and calculated

data by computational methods that enable the accurate measurement of properties for the set of

molecules which are in our focus.




87

PP56. MOLECULAR DYNAMIC SIMULATION

OF PROTON TRANSFER IN FUNCTIONALIZED PAF

Petko Petkov1, Thomas Heine2

1 University of Sofia, Faculty of Chemistry and Pharmacy, University of Sofia, J. Bourchier blvd. 1, 1164, Sofia,

Bulgaria, [email protected] 2 Technical University Dresden, Germany

The proton conductivity in water-mediated proton-conducting porous materials as MOFs and

COFs depend on water concentration in their pores, which limits their application at higher

temperatures (T > 300 K). In the case of anhydrous proton conducting COFs and MOFs, the

conductivity of the proton is mediated by guest molecules like imidazole, triazole etc. that

operate at relatively high temperature. The aim of the recent study is the modeling of porous

aromatic polymers that show intrinsic proton conductivity. As a case study, we choose a class of

materials called porous aromatic frameworks (PAFs). PAFs are materials with diamond-like

structure and high surface area. Here we show how the functionalization of PAF with

phosphonic or sulfonic groups could make these materials suitable for membranes with intrinsic

proton conductivity.

Figure 1. Model of a membrane based on PAF, functionalized with phosphonic group

Acknowledgements:

Petko Petkov acknowledge project BG05M2OP001-2.009-0028 for the financial support.




88

international scientific conference book of abstracts · final conference in the framework of the...

Documents