CHAPTER - I

INTRODUCTION

1.1. Supramolecular chemistry

Supramolecular chemistry is a highly interdisciplinary field of science covering the

chemical, physical and biological features of certain chemical species of greater complexity

than molecules themselves that are held together and organized by means of intermolecular

(non-covalent) binding interactions [1-3]. Supramolecular species are characterized both by

the spatial arrangement of their components, their architecture or suprastructure, and by the

nature of the intermolecular bonds that holds these components together [3, 4]. Various

types of interactions may be identified, that offers different degrees of strength and

directionality to the supramolecule. They could be electrostatic forces, hydrogen bonding,

van der Waals interactions, donor-acceptor interactions etc. [2, 5].

Natural molecules such as proteins, oligonucleotides, lipids and their multimolecular

complexes have been the major source of inspiration for supramolecular chemists. Design

and synthesis of novel multimolecular supramolecular architectures of similar complexity

and functionality are the dream of many supramolecular scientists. Evidently, synthetic

supramolecular systems were initially rather small and composed of relatively simple

building blocks [6]. However, the increased knowledge over intermolecular interactions and

molecular recognition has culminated in an impressive control over molecular self assembly

[1, 2]. Supramolecular synthesis of multimolecular architectures with diverse shapes,

compositions, and functionalities is now possible in a wide range of conditions in solution

and the solid state. Even though the initial inspiration for supramolecular chemistry came

from biology, most of the current applications of supramolecular chemistry can be found in

the materials sciences. Supramolecular concepts have enabled unprecedented control over

materials organization and properties. This has yielded for example supramolecular

switches, electronics and polymers [7]. Remarkably, most of these supramolecular materials

display their specific properties in the solid or gel state or in organic solvents. This is in

contrast with the biological systems from which their design initially was derived. Proteins,

lipids and sugars assemble and unfold their specific properties in water. The application of

supramolecular chemistry to study biology, supramolecular chemical biology, thus requires

synthetic systems that assemble in water or biological media.

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Supramolecular chemistry can be classified in two broad categories as host-guest

chemistry and self-assembly, in which classification is done in terms of size and shape

comparison among interacting molecules. Host-guest condition occurs for two molecules

which differ from each other in a way that one can host the other one by providing a hole or

can wrap around the guest [4]. However in self-assembly case, building blocks do not differ

in size and shape as one of them can serve as host or guest [4].

1.2. Host-guest chemistry

Host-guest chemistry as being a fruitful branch of supramolecular chemistry,

investigates complexes consisting two or more molecules or ions that are formed through

non-covalent interactions. A complexation event could be considered when a molecule

(host) binds another molecule (guest) to produce a host-guest complex or a supramolecule.

Commonly, the host is large molecule or aggregate such as an enzyme, or synthetic cyclic

compound possessing a sizeable, central hole or cavity and the guest can be either a

monoatomic cation, a simple inorganic anion or even sophisticated molecules like

hormones, pheromones etc [8]. Formally, a host is defined as the molecular entity

possessing convergent binding sites and the guest possesses divergent binding sites. The

resulting host-guest complex composes either of the constituents held together in unique

structural relationships by electrostatic forces other than those of full covalent bonds [6, 9].

A key division within host-guest systems relates to the stability of the host-guest

complex in solution and to the topological relationships between the guest and host.

Cavitands are hosts possessing intramolecular cavities which are strictly an intramolecular

property of the host and exists both in solution and solid state. Conversely, clathrands

possess extramolecular cavities, often a gap between two or more hosts, which are relevant

in crystalline or solid state [6, 10].

The construction of supramolecular systems involves selective molecular

combination of guest and host. Among all potential supramolecular hosts, cyclodextrins

(CDs) seem to be the most important ones, for the following reasons [11]. (i) They are

seminatural products, produced from a renewable natural material, starch, by a relatively

simple enzymic conversion. (ii) They are produced in thousands of tons per year by

environmentally friendly technologies. (iii) High production led to their initially high prices

dropping to levels where they become acceptable for most of the industrial purposes.

(iv) Any of their toxic effect is of secondary relevance and can be eliminated by selecting

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the appropriate CD type or derivative or mode of application. (v) Consequently, CD can be

consumed by humans as ingredients of drugs, foods or cosmetics.

1.3. Self-assembly

Self-assembly is scientifically interesting and technologically important for various

reasons. The first is that it is centrally important in life. The cell contains an astonishing

range of complex structures such as lipid membranes, folded proteins, structured nucleic

acids, protein aggregates, molecular machines and many others that form by self-assembly.

The second is that self-assembly provides routes to a range of materials with regular

structures: molecular crystals, liquid crystals and semicrystalline and phase-separated

polymers are examples. Finally, self-assembly seems to offer one of the most general

strategies now available for generating nanostructures. The richness of such structures

results from the weak ordering due to non-covalent interactions and the consequent

importance of thermal energy, which enables phase transitions with differing degrees of

order.

Many self-assembly processes rely on the self-assembling nature of organic

molecules, including complex species such as DNA; these methods are termed chemical or

molecular self-assembly. Generally molecular self-assembly is the spontaneous organization

of relatively rigid molecules into structurally well defined aggregates, via weak, reversible

interaction such as hydrogen bonds, ionic bonds and van der Waals bonds. The aggregated

structure represents a minimum energy structure or equilibrium phase. Other simpler

methods rely on geometric self organization, in which hard spheres or hard rods will arrange

themselves into two- and three-dimensional structures based on packing considerations.

In the past decades, cyclic compounds have played a key role in self-assembly

chemistry for the creation of ordered and functionalized assemblies [12]. The cyclic

oligomers of glucose known as cyclodextrins (CDs) are ideal candidates to provide various

self-assembled structures and functionalities. CDs are one of the most important members of

the supramolecular family and are used in the food, drug and home-products industry. In

particular, much attention has been focused on CD because of their potential

pharmaceutical, environmental, electrochemical, biological and catalytic applications [11].

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1.4. History of Cyclodextrins

In 1891, A. Villiers published the discovery of a material later known to be a CD

[11, 13]. He described the isolation of about 3 g of a crystalline material from the digestion

of 1000 g starch with Bacillus amylobacter. Villiers named this material ‘cellulosine’ and

determined its composition to be (C6H10O5)2.3H2O [11, 13]. The material was noted for its

similarities to cellulose, namely resistance towards acid hydrolysis and lack of reducing

properties. Scientists today believe that Villiers formed a mixture of α-CD and β-CD in

these digestion procedures [11]. In 1903, Schardinger studying bacteria pertaining to food

poisoning, isolated two separate crystalline compounds during the digestion of potato starch.

Schardinger determined these two compounds to be the ‘cellulosines’ that Villers had

discovered twelve years earlier [11]. He initially renamed these compounds as ‘cystalline

dextrins’, but later changed the names to α- and β-dextrin. The major crystalline product of

these digestion experiments was determined to be α-dextrin. To distinguish between the two

compounds, Schardinger reacted them with iodine. The dry α-dextrin/iodine complex

formed a greenish color and the dry β-dextrin/iodine complex formed a reddish brown color

[11, 13, 14]. Until 1911, Schardinger continued to publish on CDs, discovering that the

materials could be synthesized from several sources of starch and bacteria [11, 14].

Freudenberg et al synthesized γ-CD in 1935. The authors later determined from hydrolysis

and acetolysis techniques that the crystalline dextrins were ringed structures comprised of

α-1,4-glycosidic linkages. The crystalline cyclic dextrins were renamed ‘cyclodextrins’

[11, 15].

During the 1950’s, Cramer et al researched the physical and chemical properties of

α-CD, β-CD and γ-CD, including cavity size, structure and reactivity. It was reported that by

forming inclusion complexes with CD, the solubility and oxidative stability of certain

compounds could be increased [11, 13, 15]. The unique properties of inclusion complexation

led to an increased interest in using CD in drug formulations. However, research on CD

products for human use was stalled for over two decades when French et al reported in 1957

that CD was toxic in animal studies. In this publication, a small population of rats that fed a

diet of β-CD died within a week [11]. It has been postulated that the β-CD used in this study

contained a significant amount of toxic organic impurity. In the decades following this

claim, CDs were deemed safe for human consumption and can be readily found as

ingredients in foods, drugs and cosmetics [15, 16].

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1.5. Structure of Cyclodextrins

Cyclodextrins (CDs) are cyclic molecules consisting of 6, 7 or 8-glucose residue,

designated α-CD, β-CD and γ-CD respectively, and linked by α-1,4-glycosidic bonds

(Fig. 1.1). Cyclodextrin glucanotransferase acts on starch or starch derivatives to produce

CDs which are enzymatically modified starches. α-CD and β-CD are widely used in

industries due to low price, availability, cavity dimensions and suitable to be used in most of

the reactions. However, γ-CDs are not so popular in industries because of low yield and

being expensive.

Studies of CDs in solution are supported by a large number of crystal structure

studies. CDs crystallise in two main types of crystal packing, channel structures and cage

structures, depending on the type of CD and guest molecules. These crystal structures show

that CDs in complexes adopt the expected ‘round’ structure with all glucopyranose units in

the 4C1 chair conformation. Further, studies with linear maltohexaoses, which form an

antiparallel double helix, indicate that α-CD is the form in which the steric strain due to

cyclization is least while γ-CD is most strained [15, 16].

According to Szejtli (1988), the hydrophilic hydroxyl groups are oriented on the

outside of the ring structure which gives aqueous solubility properties of the CDs (Fig. 1.1).

The interior of the cavity contains the hydrophobic CH groups and glycosidic oxygen which

form the electron-dense apolar interior of CDs. The molecular inclusion complexes are

formed through the hydrophobic interior that interacts with organic molecules or the organic

moiety of molecules. According to Szejtli (1988), the ability of forming inclusion complexes

can impart new properties such as prolonged stability and increased water solubility to the

guest molecules.

Both the physical and chemical properties of the CDs are important for the

applications of the molecular inclusion complexes of the CDs and also the ability to form

complexes with various materials. The physical and chemical properties are used to

determine selection of CD for a particular guest and also the conditions under which a

particular complex may or may not be used. The graphical representation of α-CD, β-CD

and γ-CD and their dimensions are shown in Fig. 1.1.

Chemical and physical properties of the four most common CDs are given in

Table 1.1. The diameter of the cavity increases with the increase of the number of glucose

units in the ring. Generally, compounds that are able to form complex inclusion with α-CD

or γ-CD will also form complex with β-CD. α-CD is usually used to form complexes with

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small molecule that contains four or fewer carbon atoms while γ-CD is used to complex with

larger and more bulky guests [15, 16]. CDs are known to be relatively thermal stable. The

water contained within the crystals of CDs evaporates below 100 °C and nothing happens

until approximately 300 °C. The crystals melt as the heat is absorbed and thermal

decomposition of the CDs take place. Both the melting of the crystals and thermal

decomposition of the CDs happen at the same time.

Fig. 1.1. Chemical structures and approximate molecular dimensions of

(a) α-CD, (b) β-CD and (c) γ-CD.

(a)

(b)

(c)

6.5 Å

7.8 Å

15.4 Å

7.8 Å

8.3 Å 17.5 Å

5.3 Å 14.6 Å

7.8 Å

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Table 1.1. Properties of cyclodextrins.

The parent CDs, in particular β-CD, have limited aqueous solubility, and their

complex formation with lipophilic drugs and other compounds with limited aqueous

solubility, frequently gives rise to B-type phase-solubility diagrams as defined by Higuchi

[17]. That is, addition of these unmodified CDs to aqueous drug solutions or drug

suspensions often results in precipitation of solid drug-CD complexes. The aqueous

solubility of the parent CDs is much lower than that of comparable acyclic saccharides and

this could partly be due to relatively strong binding of the CD molecules in the crystal state

(i.e., relatively high crystal lattice energy). In addition, β-CD and γ-CD form intramolecular

hydrogen bonds between secondary OH groups, which detract from hydrogen bond

formation with surrounding water molecules, resulting in less negative heats of hydration

[11, 15, 18]. Thus, intramolecular hydrogen bonding can result in relatively unfavorable

enthalpies of solution and low aqueous solubilities. Substitution of any of the hydrogen bond

forming hydroxyl groups, even by hydrophobic moieties such as methoxy and ethoxy

functions, will result in a dramatic increase in water solubility [11, 15]. For example, the

aqueous solubility of β-CD is only 1.85% (w/v) at room temperature but increases with

increasing degree of methylation. The highest solubility is obtained when two-thirds of the

hydroxyl groups (i.e., 14 of 21) are methylated, but then falls upon more complete

alkylation, i.e., the permethylated derivative has a solubility that is lower than that of,

e.g., heptakis(2,6-O-dimethyl)-β-CD but that is still considerably higher than that of

unsubstituted β-CD [11]. Other common CD derivatives are formed by other types of

Properties α-CD β-CD γ-CD

Number of glucopyranose units 6 7 8

Chemical formula C36H60O30 C42H70O35 C48H80O40

Molecular weight (g/mol) 972 1135 1297

Solubility in water at 25 °C (%, w/v) 14.5 1.85 23.2

Outer diameter (Å) 14.6 15.4 17.5

Cavity diameter (Å) 4.7-5.3 6.0-6.5 7.5-8.3

Height of torus (Å) 7.8 7.8 7.8

Minimum cross section of cavity (Å2) 15 26 43

Cavity volume (Å3) 174 262 427

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alkylation or hydroxy-alkylation of the hydroxyl groups [11, 15]. The main reason for the

solubility enhancement in these derivatives is that chemical manipulation frequently

transforms the crystalline CDs into amorphous mixtures of isomeric derivatives. For

example, (2-hydroxypropyl)-β-CD is obtained by treating a base-solubilized solution of

β-CD with propylene oxide, resulting in an isomeric system that has an aqueous solubility

well in excess of 60% (w/v) [8]. The number of isomers generated based on random

substitution is very large. Statistically, for example, there are about 1,30,000 possible

heptakis(2-O-(hydroxypropyl))-β-CD derivatives, and given that introduction of the

2-hydroxypropyl group also introduced an optically active center, the number of total

isomers, i.e., geometrical and optical, is even much greater.

CDs are frequently used as building blocks. Up to 20 substituents have been linked

to β-CD in a regioselective manner. The synthesis of uniform CD derivatives requires

regioselective reagents, optimisation of reaction conditions and a good separation of

products. The most frequently studied reaction is an electrophilic attack at the OH groups,

the formation of ethers and esters by alkyl halides, epoxides, acyl derivatives, isocyanates

and by inorganic acid derivatives as sulphonic acid chloride cleavage of C−OH bonds has

also been studied frequently, involving a nucleophilic attack by compounds such as azide

ions, halide ions, thiols, thiourea and amines; this requires activation of the oxygen atom by

an electron-withdrawing group [15, 16].

Because of their ability to link covalently or noncovalently specifically to other CD,

CDs can be used as building blocks for the construction of supramolecular complexes. Their

ability to form inclusion complexes with organic host molecules offers possibilities to build

supramolecular threads. In these way molecular architectures such as catenanes, rotaxanes,

polyrotaxanes and tubes, can be constructed. Such building blocks, which cannot be

prepared by other methods, can be employed, for example, for the separation of complex

mixtures of molecules and enantiomers [15, 16].

1.6. Inclusion complexes of CDs with guest molecules

The inclusion complexes are supramolecular assemblies composed of two or more

molecules. The host-guest complexes are held together without covalent bonds. From the

point of view of the formation of inclusion complexes the size and the structure of the guest

are predominant. The fit of the guest in the cavity should be appropriate to form van der

Waals and hydrophobic interactions and hydrogen bonding. A special type of this process is

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the complex formation of CDs. Inclusion complexes can be formed both in solution where a

cosolvent or heating may be required and in the solid state through many standard methods

[15-17].

The inclusion of a guest in a CD cavity consists basically of a substitution of the

included water molecules by the less polar guest (Fig. 1.2). The process is energetically

favoured by the interactions of the guest molecule with the solvated hydrophobic cavity of

the host. In this process entropy and enthalpy changes have an important role.

Fig. 1.2. The 1:1 inclusion complex formation of β-CD with sulfadimethoxine (SDMO) in water.

Complex formation in solution is a dynamic equilibrium process which can be

illustrated by the Eqn. (1.1), where CD is the cyclodextrin, G is the guest molecule and

CD−G is the inclusion complex. The stability of the inclusion complex can be described in

terms of recombination constant (kR) or a dissociation constant (kD):

…(1.1)

K = kR/kD …(1.2)

The larger guest molecule is the slower the formation and decomposition of the

complex. Ionization decreases the rate of complex formation and decomposition. This

recombination-dissociation equilibrium is one of the most important characteristics of this

association. In spite of the fact that the ‘driving force’ of complexation is not yet completely

understood, it seems that it is the result of various effects: (a) Substitution of the

energetically unfavoured polar–apolar interactions (between the included water and the CD

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cavity on the one hand, and between water and the guest on the other) by the more favoured

apolar–apolar interaction (between the guest and the cavity), and the polar–polar interaction

(between bulk water and the released cavity-water molecules), (b) CD-ring strain release on

complexation and (c) van der Waals interactions and hydrogen bonds between the host and

guest molecules.

Depending on the fit inside the CD cavity, guest molecules may form inclusion

complexes with different stoichiometries. Host:guest ratios may be 1:1, 2:1, 1:2, 2:2, etc [11,

19-22]. For example, p-nitrophenol/α-CD has a 1:1 stoichiometry, whereas C60/γ-CD has a

1:2 stoichiometry [20]. The physiochemical properties of the guest molecule are altered once

complexed with CD, especially the aqueous solubility. For example, Montassier et al have

shown that aqueous solubility of tretinoin (8 × 10-3 mg/ml). The acidic form of vitamin A

increases to 2.7 × 103 mg/ml after complexation with β-CD [23]. Other properties that are

altered after complexation include the reactivity of the guest molecules, diffusion/volatility

and spectral information (absorption, fluorescence, FTIR, NMR, etc.) [11, 14, 20].

A variety of organic or inorganic molecules are included in the fairly hydrophobic

cavity of CDs [24]. Equilibrium constants have been directly determined from calorimetric

methods or indirectly from spectroscopic measurements. In the latter case, a spectroscopic

property of the guest or CD has to change when the complex is formed and equilibrium

constant values are obtained by analyzing the magnitude of the changes with CD

concentrations [24]. UV-visible absorption, fluorescence, conductometry and 1H NMR have

been employed in many cases [24]. Some of these techniques can provide additional

information on the structure of the complex. For example, fluorescence can be frequently

related to the polarity of the microenvironment [25] or 1H NMR provides information of the

location of the guest within the CD cavity [26]. CDs can form complexes with different

guest to host stoichiometries. Most frequently the complexes have 1:1 guest/CD

stoichiometries. However, 1:2 and 2:2 complexes have been found, particularly when the

guest is too large and part of it is not completely included in the cavity.

The magnitude of equilibrium constants provides information on the complexation

efficiency. However, they do not provide any information on the entry/exit dynamics for the

guest with the CD. Understanding of this complexation dynamics is important when these

host-guest complexes are designed to perform functions such as catalysis or transport. There

is much less information available on the CD complexation dynamics than on the

complexation efficiency [27]. This situation is probably due to the fact that most entry/exit

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processes are fast and can only be studied with fast kinetic techniques. Furthermore, the

dynamics of complexation cannot be extrapolated from the magnitude of equilibrium

constant values. For example, the observation of small equilibrium constants does not

indicate that the compounds do not interact with CDs but may signal that the entry and exit

processes occur on similar time scales.

The inclusion complexes of CDs have wide application because the physical and

chemical properties of the guest compounds have changed on the effects of complex

formation. For example the pharmaceutical application of CDs is remarkable. The solubility

and the stability of the active ingredients and the permeability of biological membranes can

be improved without any changes in the chemical quality of the compound.

1.7. Application of cyclodextrins

The large interest in CDs and their derivatives lies in their ability to form inclusion

complexes with a wide range of guest molecules, mediated by a hydrophobic cavity

surrounded by a hydrophilic outer surface. The CD can change the physicochemical

properties of a guest. When a guest compound is included in the CD cavity, the guest

becomes surrounded by the atoms in the cavity of CD. Therefore, the hydrophobic groups of

the guest that would be in contact with the solvent in the free-state interact with the atoms of

the cavity of the CD instead. As a result, the solubility of the complex is dictated by the

hydrophilic outer surface of the CD. Thus, CDs can alter the physical properties of guests,

such as increasing water solubility or reducing volatility. The properties imparted to the

guest due to inclusion formation with CDs have been ubiquitously applied in

pharmaceutical, food, cosmetic, and textile industries and in the field of catalysis,

environmental remediation, chemical sensing, and enantiomeric separations [28, 29].

1.7.1. CD application in pharmaceuticals

A drug substance has a certain level of water solubility to be readily delivered to the

cellular membrane, but it needs to be hydrophobic enough to cross the membrane. One of

the unique properties of CDs is their ability to enhance drug delivery through biological

membranes. The CD molecules are relatively large (molecular weight ranging from almost

1000 to over 1500), with a hydrated outer surface and under normal conditions, CD

molecules will only permeate biological membranes with considerable difficulty [14-16]. It

is generally recognised that CDs act as true carriers by keeping the hydrophobic drug

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molecules in solution and delivering them to the surface of the biological membrane. On the

other hand, CDs act as penetration enhancers by increasing drug availability at the surface of

the biological barrier. For example, CDs have been used successfully in aqueous dermal

formulations [30], an aqueous mouth wash solution [31], nasal drug delivery systems [32]

and several eye drop solutions [16, 33]. The majority of pharmaceutical active agents do not

have sufficient solubility in water and traditional formulation systems for insoluble drugs

involve a combination of organic solvents, surfactants and extreme pH conditions, which

often cause irritation or other adverse reactions. CDs are not irritant and offer distinct

advantages such as the stabilization of active compounds, reduction in volatility of drug

molecules and masking of malodours and bitter tastes.

1.7.2. CD application in food preparations

CDs are used in the food industry to disguise the taste of unpalatable compounds or

to prolong their flavor lifetime. Limonin and Naringin are abundantly found in citrus foods.

These compounds impart an undesirable cloudiness and bitterness to the juice of canned

orange slices. Adding β-CD to citrus products masks the bitter taste of limonin and naringin,

thus resulting in more palatable citrus juices [34]. Another common use for CD is in

chewing gum [35]. CDs can form inclusion complexes with flavor inducing compounds. It

has been proven that the duration of flavor, as well as the flavor impact and sensation of

coolness is higher with a CD-methoxypropane-1,2 complex. CDs are also ubiquitously

found in can coatings [36]. Can coatings can produce an off taste in the stored product. The

stale flavor in can-stored foods arises from ketones containing 6-18 carbons; coatings made

with adsorbed CDs are able to form inclusion complexes with the aforementioned ketones.

Therefore, the ketones will bind to the CDs and remain attached to the can coating keeping

the undesirable flavor constituents out of the stored food.

1.7.3. CD application in agricultural and chemical industries

CDs form complexes with a wide variety of agricultural chemicals including

herbicides, insecticides, fungicides, repellents, pheromones and growth regulators. CDs can

be applied to delay germination of seed. In grain treated with β-CD some of the amylases

that degrade the starch supplies of the seeds are inhibited. Initially the plant grows more

slowly, but later on this is largely compensated by an improved plant growth yielding a

20-45% larger harvest [11]. In the chemical industry, CDs are widely used to separate

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isomers and enantiomers, to catalyse reactions, to aid in various processes and to remove or

detoxify waste materials. CDs are widely used in the separation of enantiomers by high

performance liquid chromatography (HPLC) or gas chromatography (GC). The stationary

phases of these columns contain immobilised CDs or derived supramolecular architectures.

Due to their steric effects, CDs also play a significant role in biocatalytic processes by

increasing the enantioselectivity. After the formation of inclusion complex with the

prochiral guest molecule, the preferential attack by the reagent takes place only from one of

the enantioselective faces, resulting in higher enantioselectivity. It was reported by Kamal et

al [37] that the hydrolysis of racemic arylpropionic esters by bovine serum albumin, a

carrier protein, resulted in low enantioselectivity (50-81%), while addition of β-CD to this

reaction not only enhanced the enantioselectivity (80-99%) but also accelerated the rate of

hydrolysis. Rao et al [38] demonstrated that chiral recognition during cycloaddition reaction

of nitriloxides or amines to the C≡C triple bond using baker’s yeast as a chiral catalyst was

improved by the addition of CDs, increasing the enantio selectivity of yeast by up to 70%.

1.8. Nanotechnology

Nanotechnology is generally defined as the study of controlling matter on an atomic

and molecular scale. This cross-disciplinary science is at the intersection of major physical

science and biological disciplines: physics, chemistry, biology and materials science.

Nanotechnology deals with particles and structures between 0.1 and several hundred

nanometers. In the aera of nanotechnology, where properties are dependent on the size of the

structure, prodigious discoveries and applications in multiple areas of science suggest the

importance of understanding a systems structure and its impact on material properties [39,

40]. This great interest is based on the quantum states of these materials, which are size-

dependent, leading to new physical and chemical properties that differ considerably from the

solid and molecular state [40].

1.9. CD and nanotechnology

Nanoencapsulation is a method to enhance bioactivity or bioavailability of natural or

biochemically modified compounds [41-47]. From the wide range of encapsulation matrices,

CDs and liposomes are extensively used in medicine and food fields [41-47]. The specific

architecture of CDs structure (truncated cone with exterior hydroxyl groups and

hydrophobic inner cavity) determine to use them for nanoencapsulation of hydrophobic and

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geometrically compatible bioactive molecules (such as drugs, food additives, odorant and

flavoring compounds etc.) in order to obtain powdery formulations with higher water

solubility, protecting capacity (against air, light, humidity) and controlled release properties

[41, 42, 48, 49]. Various natural antioxidants (such as flavonoids, antocyanins and related

compounds - quercetin, rutin, chlorogenic acid, trans-resveratrol) were encapsulated in

natural and modified CDs in order to enhance their stability and bioactivity [50, 51].

1.9.1. CD based self-assembled nano and microparticles

The interaction between CDs and guest molecules has also been exploited to design

self-assembled nanoparticles or microparticles. Microparticles usually refer to particles with

diameter between 0.1 and 100 µm and nanoparticles are the particles with diameter between

1 and 100 nm although in drug delivery nanoparticles can have diameter up to 1000 nm [52,

53]. Microparticles can be used as formulations for local delivery of drugs and

pharmaceutical proteins e.g. subcutaneous or intramuscular injections. In addition, owing to

the unique size and physical properties of nanomaterials [54], there is enormous current

interest in using spherical nanoparticles for biomedical application, including enzyme

encapsulation [55], DNA transfection [56], biosensors [57] and drug delivery [58].

In the recent years, there has been considerable interest in developing biodegradation

nanoparticles as effective drug delivery carriers. Nanoencapsulation of medicinal drugs

(nanomedicines) has many advantages in the protection of premature degradation,

enhancement of absorption into a selected tissue, bioavailability, retention time and

improvement of intracellular penetration [59]. And the largest advantages of the

nanoparticles are that they can effectively deliver the drug to a specific site and control the

drug release speed [60]. The last decade, many CD-based physically assembled nano and

microparticles have been developed using strategies similar to those discussed for

self-assembling systems. Currently, the biodegradation nanoparticles contenting two

different drugs have been prepared. The results prove that simultaneous administration could

result in better treatment efficacy [61].

Magnetic nanoparticle (MNP) is one of the most popular materials among the

spherical nanoparticles and has been increasingly used in immobilizing proteins, enzymes

and other bioactive agents in analytical biochemistry, medicine and biotechnology [62-64].

Cao et al [65] have fabricated CD-functionalized Fe3O4/(3-aminopropyl)triethoxysilane

nanoparticle. This CD-MNP with superparamagnetism was constructed successfully via a

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layer-by-layer method. The study implies a wide variety of biomedical applications as a very

promising drug carrier and bioseparator.

Vesicles are important self-assembled aggregates in solutions and represent simple

model systems for biological membranes. The native CDs itself cannot assemble into

vesicles according to the literature [11]. Thus, it is significant to find simple driving

molecules complexing with CDs in forming micro-aggregates in this field. Vesicles

assembled by the supramolecular amphiphiles are not only simple and effective but also

more promising in developing responsive drug-carrier systems with targeted-release ability.

In recent papers, some organic molecules have been employed to build CD-based vesicles

[66, 67]. For instance, Zhang and his coworkers found that stable vesicles of 2-O-

carboxymethyl-β-CD incorporated with N-1-decyl-ferrocenylmethylamine could be formed

just through supramolecular assembly [68]. Although they were observed these kind of

supramolecular assemblies by β-CD and N,N'-bis(ferrocenylmethylene)diaminohexane in

water and in a mixed solvent (water/methanol) [69]. Zhang et al [70] also discovered the

double hydrophilic block copolymers with a polyethylene glycol block molecules could also

lead to the formation of vesicles of β-CD in aqueous solutions. Additionally, vesicles

prepared from CD inclusion complexes can be responsive to optical stimuli, [71] which is an

important requirement for ‘smart materials’[72].

1.9.2. CD based self-assembled multidimensional nanoarchitechtures

At the beginning of 1990s, Harada et al reported a meaningful molecular fabrication

method of a molecular necklace and tubular aggregate [73] by threading CD on polymers

accompanied by a covalent cross-link of neighboring CD, which subsequently led to the

design and preparation of a variety of linear supramolecular polymers based on CD [73].

From then on, more and more one, two and three dimensional nanometre-sized

nanoarchitectures constructed from CD as building blocks have attracted increasing

attention owing to their controllable size, unique topological structure and fascinating

potentials to serve as molecular devices, molecular machines and functional materials. As

compared with natural CD and simply modified CD, CD-based nanoarchitectures, which

combine numerous functional substituents that are attached to CD cavities in a single

aggregated structure, can lead to an efficient enlargement of the functions of these groups.

Moreover, the simultaneous interaction of many functional groups and CD cavities in a CD-

based nanoarchitecture with several binding sites for substrates, through an integrative effect

16

of some non-covalent interactions, can mimic the cooperative ‘multimode, multipoint’

binding often observed in biological systems. This makes CD-based nanoarchitectures as

good models of artificial enzymes and drug/gene carriers. Generally, CD-based

nanoarchitectures can be constructed by self-assembly with or without templates. In the

former route, the substituent of one CD derivative is included in the hydrophobic cavity of

an adjacent one to form multi-dimensional nanoarchitectures. In the latter route, the

cooperative binding of two or more CD cavities with a template molecule is the driving

force of the molecular assembly process. It should be noted that the cooperative contribution

of several non-covalent interactions, including van der Waals, hydrophobic, hydrogen bond,

electrostatic, π-stacking interactions, etc., working between CD units and

substituent/template units is usually strong enough to make the multidimensional

nanoarchitectures to achieve a high stability. However, through judicious adjustment of

environmental conditions such as hydrophobicity, pH, temperature, etc. CD-based

multidimensional nanoarchitectures can be degraded to the original building blocks. This

property enables their potential application as recyclable, environmentally friendly

materials. Recently several researchers have made investigations on the construction and

structural characters of CD-based nanostructures, wherein linear or helical assemblies with a

single growth direction, such as helix, pseudopolyrotaxane, polyrotaxane, nanotube or

nanowire are classified as the one-dimensional CD-based nanoarchitectures, while the

topographical nanostructures of self-assembled dendrimers, networks, vesicles, hydrogels,

nanoparticles or cyclodextrin-decorated carbon nanotubes are classified as the

multidimensional assemblies because multidimensional growths are achieved within these

nanostructures.

It is well known that the elucidation of crystal structures is one of the most

convincing methods of unequivocally illustrating the geometrical structure of CD-based

nanoarchitectures, like the crystal structures of pseudopolyrotaxanes formed by β-CD with

polyethylene glycol [74], polypropylene glycol and poly(trimethyleneoxide) [28]. Therein,

β-CD is arranged as tail-to-tail dimers on the axle component to form a one-dimensional

columnar structure in the solid state. Each of the secondary hydroxyl groups of CD are

hydrogen-bonded to secondary hydroxyl groups in the same and/or neighboring molecule in

tail-to-tail CD dimers, thus forming a network of hydrogen bonds, but intermolecular

hydrogen bonds between primary hydroxyl groups are rare. More detailed information about

the morphology of CD-based nanoarchitectures in solution or on a surface can be obtained

17

from electronic microscopy and scanning probe microscopy, particularly scanning electronic

microscopy (SEM), transmission electronic microscopy (TEM), scanning tunneling

microscopy (STM) and atomic force microscopy (AFM). In SEM images, the building

blocks, such as CDs and axle components, always present small or moderate irregular

morphologies. In contrast, the SEM images of CD-based nanoarchitectures are distinct from

those of the building blocks and can be characterized as having a regular morphology. This

phenomenon is always accompanied by obvious differences in the XRD patterns of the

building blocks and the nanoarchitectures due to not only the reorientation of the building

blocks upon construction, but also to the formation of an ordered structure of resulting

nanoarchitectures with an arrangement mode different from that of their precursor building

blocks [75]. Superior to SEM, TEM can give a rough insight into the size and shape of CD-

based nanoarchitectures, while STM and AFM can provide the fine structure of CD-based

nanoarchitectures at the molecular or submolecular level. For example, the STM study of

α-CD/polyethylene glycol polyrotaxane shows that one of the α-CD units in the

polyrotaxane can be mechanically pushed by the STM tip along the polyethylene glycol axle

to make a reversible shuttle movement and it is also possible to move two adjacent α-CD

units simultaneously. Furthermore, even the axle component of the polyrotaxane can be bent

with the STM tip by pushing it laterally in the perpendicular direction [28, 74]. It should be

noted that these structural characterization methods including X-ray crystallography,

circular dichroism spectroscopy, NMR, SEM, TEM, STM, AFM, etc., are widely applied in

determining the topology of not only pseudopolyrotaxanes or polyrotaxanes but also other

CD-based multidimensional nanoarchitectures, which will be described in detail below.

It is interesting to note that nano-technological aspects of the CD-based host/guest

chemistry have been published first on the rotaxane-type structures of unique molar

stoichiometries in the complexes. One of the very first such papers was already published by

Ogino in 1981 [76]. Ogino synthesized a rotaxane structure by threading the host α-CD and

β-CD on α,ω-diamino-alkane-co-ordinated cobalt-II complexes.

In 1991 Shigekawa published the structural arrangements of empty and guest-filled

CDs using STM [29]. These complexes visualized by STM method were still the ‘classical’

1:1 and 1:2 complexes like, for instance β-CD/adamantanol. At the same time, Harada and

coworkers made much more complicated, highly ordered, CD-assisted nanostructures, so

called polyrotaxanes [73, 74]. These polyrotaxanes are a kind of ‘molecular necklaces’

threading up to 23 cylindrical α-CD hosts onto individual polyethylene-glycol polymer

18

chains. The polyrotaxanes are also inclusion complexes but they have rather unusual

stoichiometry (1:20, 1:30 guest:host). Harada’s molecular necklaces have opened the door

for CD technology to the actual nanotechnological field. In fact Harada necklaces can be

considered as real CD-based nanoarchitectures.

In 1991, Li and McGown [77] reported on the preparation and visualization of the

CD based nano-structures in the Science magazine, linking β-CD and γ-CD molecular

nanotubes aggregates by the entrapped diphenyl-hexatrienes. These CD-nanotubes were

successfully visualized by STM and were found to consist of 20 β-CD and 30-35 γ-CD,

respectively, threaded precisely by the rod-like diphenyl-hexatriene guest molecule

entrapped. Until about 1994, not much was reported on the practical aspects (usefulness) of

CD-based nanostructures, except that everybody assumed that such highly ordered

nanostructures would find some day their place in the electronics and in medicine.

The fabrication of monodispersed particles perfectly controlled in size, shape and

internal structure is the main goal for general advanced particulate materials such as

electromagnetic devices, catalysts, sophisticated drug delivery systems, photosensitive

materials, etc. Magnetite nanorods are a good example for such advanced materials.

Kumar et al prepared magnetite nanorods by sonochemical oxidation of aqueous iron-II-

acetate in the presence of β-CD. They found their method applicable to prepare other types

of metal oxide nanorods simply by employing CDs to accommodate metal oxides in a highly

ordered manner, on the nanoscale [78].

Cacialli et al [79] took advantage of the polyrotaxane approach in making such nano-

insulators by entrapping different semiconductor polymers into CD-formed “tunnels”. They

explored the properties of a class of materials that were engineered at a supramolecular level

by threading a conjugated macromolecule (poly-para-phenylene and poly-4,4’-diphenylene-

vinylene or poly-fluorene) through α-CD and β-CD rings, so as to reduce intermolecular

interactions. CD-threaded semi conducting polymer rotaxane structures were used to make a

light-emitting polymer device. The polymers without CD showed a face-to-face stacking

that affected luminescence efficiencies. However, when CD is threaded on them, the

molecular insulator (sugar coating) will protect against such unwanted phenomenon [79].

Self-assembled CD inclusion complexes were visualized by STM by Yasuda et al

[80]. The results on the channel-like methanol/α-CD complex and the three-fold

symmetrically arranged p-nitrophenol/α-CD complex indicate the existence of high potential

for the structural control of the self-assembled α-CD complexes by changing the guest

19

molecules. Moreover, the authors also observed that the arrangement of self-assembled

CD complexes was different from that expected from the crystal structure determined by

X-ray diffraction. By removing the surface CD molecular layer using atom manipulation

technique of the STM, ordering (head to head) of the molecules in the inner layers was

observed (ordered self-assembled structures) [80]. Self-assembling dendritic

supramolecules of molecular nanotubes and starpolymers were synthesized and visualized

by STM by Okumura et al [81]. The molecular nanotube is an organic tubular molecule

with the length of 25 nm made from α-CD and polyethyleneglycol monocetylether.

The Multiwall carbon nanotube β-CD composites have been successfully

synthesized and characterized by Liu et al [82]. J.G. Selbo has reported elastic and

thermodynamic properties of dianin’s inclusion compounds and their guest-host

interactions [83]. Many researchers [84-86] have also reported the inclusion complex

formation of organic compounds with CDs.

Rajendiran and co-workers mainly focused on investigations of various drug

molecules in different solvents, pH and CDs. Recently, they studied many molecules

which contain proton donor groups like ‒NH2, ‒OH etc., and proton acceptor groups like

N=N, =N‒, C=O, etc [87-93]. In their earlier studies, sulfanilamides [88], hydroxy benzoic

acids [89] and amino benzoic acids [90] were investigated. Sulfanilamides such as

sulfadiazine, sulfisomidine, sulfamethoxazole and sulfathiazole formed the inclusion

complexes with β-CD in a 1:1 molar ratio [88]. Recent studies on the complexation

between β-CD and the drugs viz., flutamide [91a], bicalutamide [91b], tramadol [91c],

salbutamol, sotalol, atenolol [92a], dothiepin, doxepin [92b], imipramine, carbamazepine

[92c], labetalol, pseudoephedrine, terbutaline, orciprenaline [93] were reported. In these

above works, we found out, both the electron acceptor and donor groups showed much

more interesting spectral features in different media. Because the C=O group is a better

electron acceptor than SO2–NH, it might facilitate the formation of the twisted

intramolecular charge transfer (TICT) in organic molecules like fast violet B and fast blue

RR [87] than sulphanilamides. These studies also revealed that sulfanilamide drugs

undergo intramolecular charge transfer (ICT) emission and form 1:1 inclusion complex

whereas tramadol, dothiepin, doxepin, imipramine, carbamazepine drugs form 1:2

inclusion complex with β-CD.

20

The quantum of information on the selected drugs available till now is summarized below.

1.10. Important Drugs

Medicinal chemistry is concerned with the understanding of chemical and biological

mechanism by which the action of drug molecules can be explained [94]. It also tries to

establish relations between chemical structure and biological activity and to link the latter to

the physical properties of the drug molecules. The discovery of a new and biologically

important active compound usually gives rise to an extended search for closely related

compounds of similar more effective, more specific or even opposite activity [95]. In many

cases, substitution of one atom or group of atoms in the parent compound (drug) results in

surprising actions.

Norepinephrine or noradrenaline (4-(2-amino-1-hydroxyethyl)benzene-1,2-diol,

NORE) is a catecholamine used to elevate blood pressure, in the case of shock or

haemorrhage and as a peripheral vasoconstrictor. Catecholamines are active amines

containing catechol, which act as neurotransmitters and hormones. Such substances are

biosynthesized from tyrosine. Catecholamines are controllers of the autonomous and central

nervous system [96].

Epinephrine or adrenaline (4-(1-hydroxy-2-(methyl amino)ethyl)benzene1,2-diol,

EPIN) also belongs to the catecholamine family and plays an important role as

neurotransmitters and hormones. It is biosynthesized in the adrenal medulla and sympathetic

nerve terminals, as well as secreted by the suprarenal gland along with norepinephrine. It is

used as medicine in the treatment of heart attack, bronchial asthma and cardiac surgery [97].

Isoprenaline or isoproterenol (4-[1-hydroxy-2-[(1-methylethyl)-amino]ethyl]

benzene-1,2-diol, ISOP) is a catecholamine drug that is widely used in the treatment of

allergic emergencies, status asthmatic, bronchial asthma, ventricular brady cardia, cardiac

arrest, glaucoma and as styptic [98]. The cardiovascular effects of isoprenaline are compared

with the epinephrine and norepinephrine, which can relax almost every kind of the smooth

musculature that contains adrenergic nervous, but this effect is pronounced in the

musculature of bronchus and also in the gastrointestinal tract. The isoprenaline is better

absorbed when dispensed by inhalation [99].

Methyldopa ((S)-2-amino-3-(3,4-dihydroxyphenyl)-2-methyl-propanoic acid,

MDOP) is a catechol derivative (catecholamine) widely used as antihypertensive agent. It is

a centrally acting α-2-adrenoceptor agonist, which reduces sympathetic tone and produces a

21

fall in blood pressure [100]. The spectrum of activity of methyldopa lies between those of

the more potent agents, such as guanethidine, and the milder antihypertensive, such as

reserpine. Methyldopa is a structural analogue of dihydroxyphenyl alanine (dopa); it differs

only due to the presence of methyl group on the α-carbon of the side chain [100].

Methyldopa contains a chiral centre. It can therefore occur either as S- or R-isomer. The

activity of methyldopa as antihypertensive is due to the S-isomer of α-methyldopa.

Procainamide hydrochloride (p-amino-N-(2-(diethylaminoethyl)benzamide

hydrochloride, PCA) is a Class Ia antiarrhythmic agent (cardiac sodium channel blocking)

finds use pharmaceutically as a cardiac depressant, especially as an antiarrhythmic. It is used

in tablet form mixed with various excipients. Its principal metabolic pathway in the liver is

its acetylation under the formation of N-acetylprocainamide (NAPA). The decrease of the

hepatic capacity for N-acetylation of PCA may indicate a genetic defect of a liver enzyme,

polymorphic N-acetyltransferase (NAT). There are about 55-60% of individuals with a

genetic defect of NAT (slow acetylators) and 40-45% of individuals with a normal rate of

acetylation (rapid acetylators) within the European and American population [101, 102].

Propafenone hydrochloride (1-{2-[2-hydroxy-3-(propylamino) propoxy] phenyl}-3-

phenyl propan-1-one, PFO) is a class Ic antiarrhythmic agent with slight β-adrenergic-

antagonist properties, which is effective in the treatment of supraventricular and ventricular

arrhythmias [103]. PFO is administered as a racemic mixture (S-(+)- and R-(−)-PFO). Both

enantiomers are equally potent sodium channel blockers. But only the S-enantiomer exerts a

modest degree of β-blockade [103]. Studies on the metabolism of PFO in man and animals

[104] revealed that PFO is extensively metabolized via phase I and phase II enzymes. The

urinary and biliary metabolites were almost exclusively conjugated. PFO, hydroxylated PFO

derivatives and o-methylated catechol-like derivatives were the main metabolites identified

after enzymatic conjugate cleavage. And the major metabolite, 5-hydroxypropafenone also

possesses antiarrhythmic properties [105]. The stereoselective pharmacokinetics of PFO

have been studied by several investigators [103, 106]. The results showed that, after racemic

PFO is administered, R-PFO is cleared faster than S-PFO, leading to higher plasma levels of

S-PFO.

Local anaesthetics (LA) are a class of medicines widely used to provide pain relief.

They are amphiphilic molecules that act along the axons inhibiting the Na+ influx and thus

the signal transduction [107]. Lidocaine (2-(diethylamino)-N-(2,6-dimethylphenyl)-

acetamide, LC) and Prilocaine ((RS)-N-(2-methylphenyl)-N2-propylalaninamide, PC) are

22

two of the most widely used LA in clinics, belong to the non-cyclic amino-amide class. LC

is a local anesthetic drug with a pronounced antiarythmic and anticonvulsant effect. It is also

a CNS depressant and produces sedative, analgesic and anticonvulsant effects. And PC is

marketed as a racemic mixture of R-(–)- and S-(+)-prilocaine and is used for intravenous

regional nerve block and topical anesthesia [108]. But both drugs are very hydrophobic.

Therefore, it is a need to develop the amorphous state of the above LA drugs with enhanced

solubility related to oral bioavailability. The development of local anesthetic formulations in

carriers such as liposomes, glucose polymers, dextran, hyaluronic acid, biopolymers,

microspheres, among others could offer the possibility of controlling drug delivery in

biological systems, prolonging the anesthetic effect and reducing its toxicity [107].

Non-steroidal anti-inflammatory drugs (NSAIDs) are a group of drugs which possess

diverse chemical composition and different therapeutic potentials having a minimum of

three common features: identical basic pharmacological properties, similar basic mechanism

of action as well as similar adverse effects. Most NSAIDs are metabolized in the liver by

oxidation and conjugation to inactive metabolites which are typically excreted in the urine,

although some drugs are partially excreted in bile. Metabolism may be abnormal in certain

disease states, and accumulation may occur even with normal dosage [109]. Mefenamic acid

(2-[(2,3-dimethylphenyl)amino]benzoic acid, MFA) belongs to a family of NSAIDs with

antipyretic and strong analgesic properties which is a derivative of N-phenylanthranilic acid.

MFA is used for the treatment of joint disorders and various kinds of pain such as headache,

dental pain, post-operative and post-partum pain. It has been widely applied in

pharmaceutical field [110]. It has been reported that mefenamic acid has two polymorphs,

forms I and II, and they showed different solubility and stability. Form II exhibited higher

solubility than form I in several solvents [111]. The dissolution profile of form II showed

supersaturation accompanying the decrease down to the solubility of form I due to the

transformation to form I. Conversely, form I transformed to form II at high temperature

(142.5-150 ◦C) and this transformation followed the zero-order reaction mechanism

(Polany-Winger equation) [112].

Aceclofenac (2-[(2, 6-dichlorophenyl) amine] phenylacetoxyacetic acid, ALF) is an

orally effective non-steroidal anti-inflammatory drug (NSAID) of the phenyl acetic acid

group. It possesses anti-inflammatory, analgesic and anti-pyretic activity [110, 113]. ALF

drug is used for the treatment of rheumatoid arthritis and is selected as a model drug. Short

biological half life (about 4 hrs) and dosing frequency more than one per day make

23

aceclofenac an ideal candidate for sustained release. It is a newer derivative of diclofenac

and has less gastrointestinal complications.

Among the many and different families of organic or inorganic chemicals being

currently investigated because of their applications, sulfonamides and their N-derivatives are

one of the outstanding groups. Sulfonamides were the first effective chemotherapeutic

agents employed systematically for the prevention and cure of bacterial infections in

humans. After the introduction of penicillin and other antibiotics, the popularity of

sulfonamides decreased. However, they are still considered useful in certain therapeutic

fields, especially in the case of ophthalmic infections as well as infections in the urinary and

gastrointestinal tract. Besides, sulfa drugs are still today among the drugs of first selection

(together with ampicillin and gentamycin) as chemotherapeutic agents in bacterial infections

by escherichia coli in humans. The sulfonilamides exert their antibacterial action by the

competitive inhibition of the enzyme dihydropterase synthetase towards the substrate

p-aminobenzoate.

Sulfonamides belong to the group of antibacterial drugs, which are used for human

and animal therapy, to cure infectious diseases of digestive and respiratory systems,

infections of the skin (in the form of ointments) and for prevention or therapy of coccidiosis

of small domestic animals [114]. Quality control of sulfonamide formulations and their

quick systematic monitoring in body fluids are important analytical tasks. A number of

articles have been published concerning the determination of sulfonamides by different

analytical methods.

Sulfadimethoxine (4-amino-N-(2,6-dimethoxy-4-pyrimidynyl)benzenesulfonamide,

SDMO), sulfamerazine (4-amino-N-[4-methyl-2-pyrimidinyl]benzenesulfonamide, SMRZ)

and sulfapyridine (4-amino-N-pyridin-2-ylbenzenesulfonamide, SFP) are the synthetic anti-

microbials having the bioactive p-amino group, generally administered via food to farm

animals such as hen, cow, etc., for the prevention of bacterial infections and coccidiosis with

a broad spectrum activity. Even though, the over drug dosages of sulfa drugs in animal foods

is of great anxiety, because it can produce residue that present in marketed milk, egg and

chicken meat [114b]. European Union (EU) and Republic of Korea have set maximum

residue limit upto 100 μg kg-1 and 10 μg kg-1 respectively, for SDMO in foods of animal

origin to assure the food safety for consumers [114c]. Most of the antibiotics are poorly

absorbed by human and farm animals after intake due to their poor bioavailability.

24

There are a few reports dealing with the analytical determination of sulfonamides by

using CD and they employ, in general, a capillary electrophoresis technique. In the case of

sulfamethoxazole (SMO), Okamoto et al [115a] used dimethyl-β-CD as modifier of the

mobile phase in micellar electro-kinetic chromatography and β-CD is used in capillary

electrophoresis. Mora Diez et al [115b] made fluorescence measurements in pharmaceutical

preparations of the inclusion complex of SMO in β-CD. Longhi and coworkers [116] have

studied the inclusion complexes of sulfamethoxazole and sulfadiazine with β-CD and its

derivatives in aqueous solution and solid state.

The fluorescence characteristics of different sulfonamides have been studied and

proposed for the determination of these compounds. Thus, sulfanilamide can be determined

by reaction with homo phthaldehyde. The analysis of sulfa drugs [117] has been performed

in foods and pharmaceuticals using the fluorescamine reaction. The reaction of

9-chloroacridine with sulfonamides produces a fluorescence quenching which allows the

determination of sulfonamides. Sulfa drugs were determined in milk and pharmaceutical

preparations by photo chemically-induced fluorimetry [118]. Fluorescence has also been

used as HPLC detection for determining sulfa drugs in milk and eggs [119] and recently,

fluorescence after pre-column derivatisation with fluorescamine has been applied as

detection technique [119].

1.11. Scope of the present work

The discussion in the previous section shows the widening scope of the study of

molecular recognition of various drug molecules with α-CD and β-CD both in solution and

solid state, and applications of inclusion complexation by cyclodextrins in different fields.

The main aim of this work is to study the molecular recognition of some selected drug

molecules derivatives with α-CD and β-CD. The objectives of the research are

1. To analyze absorption and fluorescence spectral shifts of different drug molecules in

α-CD, β-CD and different solvents of various polarities.

2. To analyze the dual fluorescence, intramolecular charge transfer (ICT) or twisted

intramolecular charge transfer (TICT), intramolecular proton transfer (IPT) etc.,

characters of the drugs in aqueous, α-CD and β-CD media.

3. To determine the stoichiometry and binding constant of the host-guest complexes.

4. To analyze the first excited singlet state lifetime of the guests in aqueous, α-CD and

β-CD media.

25

5. To characterize the solid state inclusion complexes by using scanning electron

microscopy (SEM), FTIR spectroscopy, differential scanning calorimetry (DSC),

powder X-ray diffraction (XRD) and 1H NMR spectroscopy.

6. To visualize and characterize the self-assembly behaviour of host-guest complexes by

transmission electron microscopy (TEM).

7. To analyze the structure of the inclusion complexes by molecular modeling method.

8. To determine the thermodynamic parameters (energy change, enthalpy change,

entropy change and free energy change) of the inclusion complexes using PM3

method.