anion recognition properties of poly(amidoamine)...

ANION RECOGNITION PROPERTIES OF POLY(AMIDOAMINE)

DENDRIMER FUNCTIONALIZED WITH HAMILTON RECEPTOR MOIETY

IN AQUEOUS SOLUTIONS CONTAINING NITRATE AND NITRITE IONS

ROSLIANA BINTI RUSLI

UNIVERSITI TEKNOLOGI MALAYSIA

ANION RECOGNITION PROPERTIES OF POLY(AMIDOAMINE)

DENDRIMER FUNCTIONALIZED WITH HAMILTON RECEPTOR MOIETY

IN AQUEOUS SOLUTIONS CONTAINING NITRATE AND NITRITE IONS

ROSLIANA BINTI RUSLI

A thesis in fulfillment of the

requirements for the award of the degree of

Master of Science (Chemistry)

Faculty of Science

University Teknologi Malaysia

DECEMBER 2013

iv

Specially dedicated to my parent, Rusli bin Mohd Zain and Zainab Binti Ismail,

brothers, sisters and dearest friends.

v

ACKNOWLEDGEMENT

First and foremost, I would like to acknowledge the lessons, support and

guidance of my supervisor, Prof. Dr. Salasiah Endud. Her continuous commitments

to research studies ensure not only consistent results but also granted her the respect

of all her students. I thank her for giving me the opportunity to carry out this research

in the field of dendrimers. I am also thankful to Dr. Hendrik Oktendy Lintang and

Dr. Srinivasa Budagumpi for comments and opinion in this research.

My words of gratitude also go to all the lecturers, laboratory officers and

research officers from the Department of Chemistry and Ibnu Sina Institute for

Fundamental Science Studies, Universiti Teknologi Malaysia (UTM). I am also

thankful to UTM for the Research University Grant Q.J130000.7113.02H23 and

Ministry of Science, Technology and Innovation (MOSTI) for the National

Nanotechnology Directorate Top-Down Grant R.J130000.7926.4H007.

My sincere appreciation also extends to my parents, Rusli Bin Mohd Zain and

Zainab Binti Ismail, my brothers and sisters for their support, encouragement, care

and love. Besides, I would like to thank to all my friends, especially Ms. Nur Izzatie

Hannah Razman, Ms. Noorulsyahidaini Golbaha, Mrs. Norsahika Basir, Ms. Siti

Haslina Ahmad Rusmili, Ms. Norfariha Hassan, Ms. Nurliana Roslan, Ms. Nurafiqah

Saadon, Ms. Nurul Hanisah Hamidon, Ms. Wong Wen Yee and Mrs. Chong Mun

Hwa for their valuable experience, time and opinions throughout this study.

Moreover, for my special friend, Roslan Abdullah, thanks for the encouragement and

support in helping me move on this research journey until it is complete.

Last but not least, for anyone I may have forgotten, that has involved directly

or indirectly in completing this project, thank you.

vi

PREFACE

This thesis is the results of my work carried out in the Department of Chemistry,

Faculty of Science, Universiti Teknologi Malaysia, between September 2010 to

January 2013 under supervision of Prof. Dr. Salasiah Endud. Parts of my work

described in this thesis have been reported in the following publications or

presentations:

1. Endud, S. and Rusli, R., “Synthesis of Poly(amidoamine)-Dendrimer-Silver

Nanocomposites for Application as Bacteriocides”, Proceedings International

Conference on the Advancement of Materials and Nanotechnology II

(ICAMN II), Prince Hotel & Residence, Kuala Lumpur, 29th

Nov – 2nd

Dec

2010.

2. Endud, S., Chien, L. S., Mohd Nesfu, N. Z., Othman, A. S., Golbaha, N. and

Rusli, R., “DENs-P, Polyfunctional Dendrimer Encapsulated Nanoparticles”,

Silver Medal Winner at the Industrial Art and Technology Exhibition 2011

(INATEX 2011), Universiti Teknologi Malaysia, 16th

– 18th

Nov. 2011.

3. Endud, S., Ramli, Z. and Rusli, R., “Synthetic Macrocylic Hamilton Receptor

Derivative Comprising Amide Group”. Oral presentation at the 24th

Regional

Symposium of Malaysia Analytical Sciences (SKAM 24th

). One Helang Hotel,

Langkawi, organized by Universiti Teknologi MARA and Malaysian

Analytical Sciences Society (ANALIS), 21st – 23

rd November 2011.

vii

4. Endud, S., Chien, L., S., Mohd Nesfu, N., Z., Othman, A. S., Golbaha, N. and

Rusli, R., “Dendrimer Engineered Nanoparticles”, Gold Medal Winner, Seoul

International Invention Fair 2011 (SIIF 2011), Seoul, Korea, 1st – 4

th Dec

2011.

5. Endud, S., Mohd Nesfu, N. Z., Rusli, R. and Othman, A. S., “DENs-P,

Polyfunctional Dendrimer Encapsulated Nanoparticles with Antibacterial

Activity”, Silver Medal Winner, at Malaysia Technology Expo 2012, (MTE

2012), Kuala Lumpur, 16th

– 18th

Feb. 2012.

viii

ABSTRACT

Poly(amidoamine) generation 0.5 (PAMAM G0.5) was functionalized at the

peripheral with N1,N

3-bis(6-(3,3-dimethylbutanamido)pyridine-2-1yl)-5-amino

benzene-1,3-diamide, denoted as Hamilton receptor, for anion recognition studies of

nitrate and nitrite ions in aqueous solutions. The PAMAM dendrimers were prepared

by divergent method using ethylenediamine and methyl acrylate via Michael addition

process. The four amino end groups of 2,6-diaminopyridine were used as precursors

that bind the Hamilton receptor moieties which subsequently were conjugated to the

ester terminal groups of PAMAM G0.5 at a 4:1 molar ratio to give Hamilton-

receptor-functionalized PAMAM G0.5, HR-PAMAM G0.5. All the materials were

characterized by Fourier transform infrared (FTIR) and proton nuclear magnetic

resonance (1H NMR) spectroscopies. Fluorescence spectroscopy together with

fluorescence quenching method were used to estimate the binding association

constants (Kass) of HR-PAMAM G0.5 towards specific anions such as monoanions

(i.e. F-, Br

-, Cl

-) and oxyanions (i.e. NO3

-, NO2

-, AcO

-) in aqueous solutions. As

anion recognition material, HR-PAMAM G0.5 was able to discriminate between the

anions as shown by fluorescence spectra. The results of binding constant

measurements indicate that it did not form hydrogen bonds with halide or acetate

anion but exhibited excellent selectivity for trigonal planar oxyanions such as nitrate

(NO3-) or nitrite (NO2

-). The HR-PAMAM G0.5 receptor demonstrated substantially

higher affinity for NO3- than NO2

- anion suggesting much stronger multiple hydrogen

bonding interactions occurred between the Hamilton receptor and nitro groups (-NO)

of nitrate anion. In addition, the Kass measured at various pH (2 – 12) showed higher

values in basic environment compared to acidic due to deprotonation of amine

groups of HR-PAMAM G0.5 receptor. More significantly, the HR-PAMAM G0.5

also showed binding affinity for nitrate anion in aprotic solvent such as acetonitrile

by hydrogen bonding through π-electron acceptor group of the nitrile. The limit of

detection of HR-PAMAM G0.5 for NO2- (2.85 x 10

-5 M) was relatively lower than

NO3-

(4.06 x 10-5

M) signifying greater sensitivity for the latter anion. The use of

dendrimer molecule as host is advantageous for it has the ability to concentrate anion

substrates which amplify the resulting fluorescent signal, as well as to provide the

optimal binding conformation for hydrogen bonding with various target anions.

ix

ABSTRAK

Poli(amidoamina) generasi 0.5 (PAMAM G0.5) telah difungsikan pada

bahagian luar dengan N1, N

3-bis(6-(3,3-dimetilbutanamido)piridin-2-lil)-5-

aminobenzena-1,3-diamida dikenali sebagai reseptor Hamilton, bagi kajian

pengenalan anion nitrat dan nitrit dalam larutan akueus. Dendrimer PAMAM telah

disintesis dengan kaedah pencapahan menggunakan etilenadiamina dan metil akrilat

melalui proses penambahan Michael. Keempat-empat kumpulan hujung 2,6-

diaminopiridina telah digunakan sebagai pemula bagi mengikat gugusan reseptor

Hamilton yang kemudian berkonjugat dengan kumpulan ester terminal PAMAM

G0.5 dalam nisbah molar 4:1 bagi menghasilkan reseptor Hamilton-berfungsikan

PAMAM G0.5, HR-PAMAM G0.5. Kesemua bahan telah dicirikan menggunakan

spektroskopi inframerah transformasi Fourier (FTIR) dan spektroskopi resonans

magnet nukleus bagi proton (1H RMN). Spektroskopi pendarfluor yang diiringi

dengan kaedah pelindapkejutan pendarfluor telah digunakan untuk menganggar

pemalar pengikatan bersekutu, Kass, HR-PAMAM G0.5 terhadap anion tertentu

seperti monoanion (i.e. F-, Br

-, Cl

-) dan oksianion (i.e. NO3

-, NO2

-, AcO

- ). Sebagai

suatu bahan pengenalan anion, HR-PAMAM G0.5 berupaya membezakan sifat optik

anion yang dikaji berdasarkan spektrum pendarfluor masing-masing. Keputusan

pengukuran Kass menunjukkan ia tidak membentuk ikatan hidrogen dengan anion

halida atau asetat tetapi memperlihatkan kepilihan tinggi terhadap oksianion trigonal

bersatah seperti nitrat (NO3-) atau nitrit (NO2

-). Reseptor HR-PAMAM G0.5

menunjukkan afiniti yang jauh lebih tinggi terhadap NO3-

berbanding NO2-,

mencadangkan terdapat pengikatan hidrogen berganda antara reseptor Hamilton dan

kumpulan nitro (-NO) anion nitrat. Tambahan lagi, Kass yang diukur pada pelbagai

pH (2-12) menunjukkan nilai yang pada umumnya lebih tinggi dalam persekitaran

bes berbanding keadaan berasid yang disebabkan oleh nyahproton kumpulan amina

dari reseptor HR-PAMAM G0.5. Lebih penting lagi, HR-PAMAM G0.5 juga

didapati mempunyai afiniti pengikatan terhadap anion nitrat dalam pelarut aprotik

seperti asetonitril melalui pembentukan ikatan hidrogen yang melibatkan kumpulan

penerima elektron-π iaitu nitril. Had pengesanan bagi HR-PAMAM G0.5 untuk NO2-

(2.85 x 10-5

M) secara relatif lebih rendah daripada NO3- (4.06 x 10

-5 M),

menunjukkan bahawa bahan tersebut lebih sensitif terhadap pengesanan anion NO2-.

Penggunaan molekul dendrimer sebagai perumah mempunyai kelebihan dari segi

keupayaan menumpu substrat anion dalam larutan akueus sehingga menguatkan

signal pendafluor yang dihasilkan. Di samping itu, struktur dendrimer yang unik juga

menyediakan komformasi pengikatan hidrogen yang optimum dengan pelbagai anion

sasaran.

x

TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION iv

ACKNOWLEDGEMNET v

PREFACE vi

ABSTRACT viii

ABSTRAK ix

TABLE OF CONTENTS x

LIST OF TABLES xiii

LIST OF FIGURES xv

LIST OF ABBREVIATIONS xix

LIST OF SYMBOLS xx

LIST OF APPENDICES xxi

1 INTRODUCTION

1.1 Research Background

1.2 Statement of Problem

1.3 Objectives of Study

1.4 Scope of Study

1.5 Significance of Study

1.6 Outline of Research

1.7 Outline of Thesis

1

4

5

6

6

7

8

xi

2 LITERATURE REVIEW

2.1 Dendrimers.

2.2 Hamilton Receptor.

2.3 Health Concern of Nitrate and Nitrite

Anions.

2.4 Recognition and Sensing of Nitrate and

Nitrite Anions.

2.5 Intermolecular Bonding.

9

12

14

18

36

3 EXPERIMENTAL

3.1 Materials.

3.2 Chemicals.

3.3 Preparation of Poly(amidoamine)

PAMAM G0.5 Dendrimer.

3.4 Preparation of Hamilton Receptor.

3.5 Preparation of HR-PAMAM G0.5.

3.6 Anion Recognition Test.

3.7 Characterization Methods.

3.7.1 Fourier Transform Infrared

(FTIR) Spectroscopy.

3.7.2 Proton Nuclear Magnetic

Resonance (1H NMR)

Spectroscopy.

3.7.3 Fluorescence Spectroscopy.

44

44

45

45

48

51

52

53

54

54

4 RESULTS AND DISCUSSION

4.1 Synthesis and Characterization of

PAMAM G0.5 Dendrimer, Hamilton

Receptor and HR-PAMAM G0.5.

56

xii

4.2 Anion Recognition Test.

4.2.1 Effect of pH on the Binding

Constant, Kass.

4.2.2 Effect of Solvent on the Binding

Constant, Kass.

4.2.3 Limit of Detections and Limit of

Quantifications for the Binding

of Receptors with Anions.

65

73

86

89

5 CONCLUSIONS AND RECOMMENDATIONS

5.1 Conclusion

5.2 Recommendations

91

92

REFERENCES

93

APPENDICES 102

xiii

LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 Electron donor groups and examples. 40

2.2 Electron acceptor group and examples. 41

2.3 Classification of molecules according to Pimentel and

McClellan.

42

2.4 Strength of hydrogen bonding donor and acceptor. 43

4.1 FTIR bands of PAMAM G0.5 dendrimer. 58

4.2 FTIR bands of N1, N

3-bis/(6-(3,3-dimethylbutanamido)

pyridine-2-1yl)-5-aminobenzene-1,3-diamide (Hamilton

receptor).

61

4.3 FTIR bands of HR–PAMAM G0.5. 63

4.4 Prominent 1H NMR band assignment of PAMAM G0.5,

Hamilton receptor and HR–PAMAM G0.5.

64

4.5 Radius, structure, geometry and the dissociation constant

of the ions.

67

4.6 Binding constant, Kass and Stern-Volmer quenching

constant, Ksv for the titration of various anions in Hamilton

receptor solution.

68

4.7 Binding constant, Kass and Stern-Volmer quenching

constant, Ksv for the titration of various anions in HR–

PAMAM G0.5 solution.

70

4.8 Binding constant, Kass (M-1

) for the titration of nitrate and

nitrite anions in Hamilton receptor and HR–PAMAM G0.5

solutions at different pH.

79

xiv

4.9 Comparison of binding constant, Kass, for titration of

nitrate and nitrite anions in Hamilton receptor and HR–

PAMAM G0.5 solutions of acetonitrile and deionized

water.

87

4.10 LOD and LOQ for the detection of anions using Hamilton

receptor.

89

4.11 LOD and LOQ for the detection of anions using HR–

PAMAM G0.5.

90

xv

LIST OF FIGURES

FIGURE NO. TITLE PAGE

1.1 PAMAM dendrimer (generation 3.0). 3

1.2 Hamilton receptor for barbital molecule. 4

1.3 Outline of research. 7

2.1 Divergent method. 11

2.2 Convergent method. 11

2.3 The nitrogen cycle in human body. 15

2.4 Nitrite physiology, chemistry and therapeutics. 16

2.5 Bilayer of nitrate biosensor. 19

2.6 The structure of tris(2-aminoethyl)amine. 20

2.7 Chemical reaction between tetramethyl ammonium salt of

anion with tris(2-aminoethyl)amine.

21

2.8 Heteromacrocycle [3.3.3.3]oxazane. 22

2.9 Structure of HNOPH. 22

2.10 Structure of N,N’-bis-succinamide-based dendritic

molecule.

24

2.11 Binding position of anion and cation in the cavity of

ditopic macrobicyclic receptor.

25

2.12 Hydrogen bonding with nitrate lone pair electrons is

favored over hydrogen bonding with π-electrons.

26

2.13 1,3,5-tris(benzimidazol-1-ylmethyl)-2,4,6-trimethyl-

benzene (L).

27

2.14 Possible structural topology of supramolecular complexes

formed between protonated tripodal receptor and counter

anions.

28

2.15 Macrocyclic of polyazapyridinophane. 29

xvi

2.16 Proposed binding interaction of nitrate anion with the

tweezer-type receptor.

30

2.17 Porphyrin host (host 1) designed to fit the bent anions

such as acetate and nitrite.

31

2.18 The proposed mechanism and interaction of host 2 with

nitrate anion.

31

2.19 The proposed reaction between indole molecules and

nitrite anion.

33

2.20 The proposed chemical reaction of nitrite anion with

Rhodamine 110 in acidic medium.

34

2.21 Proposed binding of nitrate anion with tripodal podands

receptor.

36

3.1 Reaction between ethylenediamine and methyl acrylate to

form PAMAM G0.5 dendrimer.

45

3.2 Synthesis of 5-aminoisophthalate. 47

3.3 Synthesis of N-(6-aminopyridin-2-yl)-3,3-

dimethylbutanamide.

47

3.4 The reaction scheme for synthesis of Hamilton receptor. 49

3.5 The reaction scheme for synthesis of HR–PAMAM G0.5. 50

3.6 Jablonski diagram for the fluorescent molecules. 55

4.1 Structure of PAMAM G0.5 dendrimer. 56

4.2 Liquid of PAMAM G0.5. 57

4.3 FTIR spectra of PAMAM G0.5 molecules. 57

4.4 The structures of 5-aminoisophthalate and N-(6-

aminopyridin-2-yl)-3,3-dimethylbutanamide.

58

4.5 The structure of N1, N

3-bis/(6-(3,3-dimethylbutanamido)

pyridine-2-1yl)-5-aminobenzene-1,3-diamide (Hamilton

receptor).

59

4.6 The FTIR spectra of (a) 5-aminoisophthalate,

(b) N-(6-aminopyridin-2-yl)-3,3-dimethylbutanamide and

(c) Hamilton receptor.

60

xvii

4.7 The structure of HR–PAMAM G0.5. 61

4.8 The FTIR spectra of (a) PAMAM G0.5, (b) Hamilton

receptor and (c) HR–PAMAM G0.5.

62

4.9 The sites for hydrogen bonding donor and acceptor in the

HR–PAMAM G0.5 structure.

66

4.10 pKa of amine group in Hamilton receptor based on the

calculation from Marvin sketch in ChemAxon® software.

73

4.11 Macrospecies percentage of Hamilton receptor at pH 2 –

pH 12 based on the calculation from Marvin sketch in

ChemAxon® software.

74

4.12 pKa of amine group in HR–PAMAM G0.5 based on the

calculation from Marvin sketch in ChemAxon® software.

75

4.13 Macrospecies percentage of HR–PAMAM G0.5 at pH 2

untill pH 12 based on the calculation from Marvin sketch

in ChemAxon® software.

76

4.14 Macrospecies distribution for the nitrate anion at pH 2 –



77

4.15 Macrospecies distribution for the nitrite anion at pH 2 –



78

4.16 The effect of the pH on the conformations of dendrimer

structure.

80

4.17 Proposed interaction and binding between nitrate anion

and protonated HR–PAMAM G0.5 at pH 2.

81

4.18 Proposed interaction and binding between nitrate anion

and HR–PAMAM G0.5 at pH 10.

82

4.19 The structure of HR–PAMAM G0.5 with the negative

fourteen charges.

83

4.20 The electric double layer on the HR–PAMAM G0.5

molecule.

84

4.21 Relationship between intermolecular interaction and the

distance of interacting objects.

84

xviii

4.22 Electrostatic attraction forces between the nitrite anions

with the electric double layer at the HR–PAMAM G0.5

molecules.

85

xix

LIST OF ABBREVIATIONS

1H NMR Proton Nuclear Magnetic Resonance

BRB Britton-Robinson buffer

cm-1

Centimeter

DMF Dimethylformamide

DMSO Dimethyl sulfoxide

EDA Ethylenediamine

FTIR Fourier Transformer Infrared

g Gram

G Generation

h Hour

LOD Limit of detection

LOQ Limit of quantification

M Molar

MA Methyl acrylate

ml Milliliter

mol Mole

nm Nanometer

PAMAM Poly(amidoamine)

rt Room temperature.

THF Tetrahydrofuran

TBA Tetrabutylammonium

xx

LIST OF SYMBOLS

λ Wavelength

% Percent

o Degree

xxi

LIST OF APPENDICES

APPENDIX TITLE PAGE

A1 1H NMR spectra of (a) PAMAM G0.5,

(b) Hamilton receptor and (c) HR–PAMAM G0.5.

102

B1 Example of calculation on the values of binding

association constant, Kass and Stern-Volmer constant,

Ksv.

104

B2 Example of calculation on the values of LOD and LOQ. 109

C1 Fluorescence emission spectra and Stern-Volmer plot for

titration of nitrate anion in Hamilton receptor in aqueous

solution.

112


titration of nitrite anion in Hamilton receptor in aqueous

solution.

113


titration of acetate anion in Hamilton receptor in aqueous

solution.

114


titration of fluoride anion in Hamilton receptor in

aqueous solution.

115


titration of chloride anion in Hamilton receptor in

aqueous solution.

116


titration of bromide anion in Hamilton receptor in

aqueous solution.

117

xxii

D1 Fluorescence emission spectra and Stern-Volmer plot for

titration of nitrate anion in HR–PAMAM G0.5 in

aqueous solution.

118

D2 Fluorescence emission spectra and Stern-Volmer plot for

titration of nitrite anion in HR–PAMAM G0.5 in aqueous

solution.

119

D3 Fluorescence emission spectra for titration of (a) acetate

anion, (b) fluoride anion, (c) chloride anion and (d)

bromide anion in HR–PAMAM G0.5 in aqueous

solution.

120

E1 Fluorescence emission spectra and Stern-Volmer plot for


solution at pH 2.

122



solution at pH 2.

123



solution at pH 4.

124



solution at pH 4.

125



solution at pH 6.

126



solution at pH 6.

127



solution at pH 7.

128

xxiii



solution at pH 7.

129



solution at pH 8.

130



solution at pH 8.

131



solution at pH 10.

132



solution at pH 10.

133



solution at pH 12.

134



solution at pH 12.

135

F1 Fluorescence emission spectra for titration of nitrate

anion in HR–PAMAM G0.5 in aqueous solution at pH 2.

136

F2 Fluorescence emission spectra for titration of nitrite


137

F3 Fluorescence emission spectra for titration of nitrate

anion in HR–PAMAMG 0.5 in aqueous solution at pH 4.

138

F4 Fluorescence emission spectra for titration of nitrite


139

F5 Fluorescence emission spectra and Stern-Volmer plot for

titration of nitrate anion in HR–PAMAMG 0.5 in

aqueous solution at pH 6.

140

xxiv



solution at pH 6.

141




142



solution at pH 7.

143




144



solution at pH 8.

145




146



solution at pH 10.

147




148



solution at pH 12.

149

G1 Fluorescence emission spectra and Stern-Volmer plot for

titration of nitrate anion in Hamilton receptor in

acetonitrile solution.

150


titration of nitrite anion in Hamilton receptor in


151

xxv




152


titration of nitrite anion in HR–PAMAM G0.5 in


153

CHAPTER 1

INTRODUCTION

1.1 Research Background

Anions such as nitrate and phosphate play critical roles in a wide range of

biological processes and environmental pollutants from the use of fertilizers in the

agriculture industry (Newkome et al., 1985). Anions are atoms or groups of atoms

that have gained electrons and they are negatively charged. Fertilizers are soil

amendments applied to promote plant growth and the main nutrients present in

fertilizer are nitrogen, phosphorus, and potassium. High application rates of

inorganic fertilizers such as nitrogen in order to maximize crop yields combined with

the high solubilities of these fertilizers leads to increased run off into surface water as

well as leaching into groundwater. This condition promotes the increase of nitrate

levels above 10 mg/L (10 ppm) in groundwater and leads to the 'blue baby syndrome'

(acquired methemoglobinemia), leading to hypoxia (which can lead to coma and

death if not treated). Because of this, anions especially nitrate and nitrite are needed

to be recognized in order to effectively monitor their presence and remove them from

the aqueous media.

The study of anion recognition has been a critical part in the most recent

research in the area of host-guest chemistry (Reinhoudt 1995). In order to

differentiate a target anion from others, the host molecule must be carefully

designed, considering not only the structural complementary interaction between the

ion-molecule pair, but also interactions with solvent molecules. The host molecules

2

for anion recognition comprise at least one interaction site that improves the selective

interaction for the target anion and overcomes the solvation energy of the target

anion in the aqueous phase. Examples of host molecule are, polyaza receptors,

cationic cyclophanes, porphyrin and guanidium-based receptors (Tomalia et al.,

1985). Among these host molecules, dendrimers are of considerable interest as anion

recognition material due to their fascinating structure and unique catalytic, optical,

chemical, sensor and electrochemical properties (Klajnert and Bryszewska, 2001).

Dendrimer is a branched polymer having core, internal cavities, interior

group and surface groups that can be modified (Dirksen et al., 2004). Other than that,

dendrimer had been proven to be a good host material for metal nanoparticles as well

as other stabilizing agents such as citrates, organic solvents (THF or THF/MeOH),

long chain alcohols, surfactants, and organometals in organic solvents (Zakaria et.

al., 2009). These characteristics, along with water solubility, are some of the features

that make them attractive for environmental remediation (Newkome et al., 1985).

Nowadays, there are more than fifty families of dendrimer with their own unique

properties were invented for various applications (Bosman et al., 1999). Therefore,

many possible researches could be done based on the different specific properties

offered by various dendrimers. The dendrimers has been widely developed in drugs

delivery research (Li et al., 2003), catalyst (Delort et al., 2003), low electric

materials (Lee et al., 2005), sensor (Mynar et al., 2006), single-wall carbon

nanotubes (Amama et al. 2006), light harvesting materials (Lo and Burn, 2007) and

host-guest chemistry (Hu et al., 2010).

Therefore poly(amidoamine) (PAMAM) dendrimer is proposed to be used in

this anion recognition study (Figure 1.1). This type of dendrimer having amide group

in the interior cavity and amine (full generation) or ester (half generation) at the

terminal, are easily modified and can form hydrogen bonding with other molecule.

This characteristic is suitable to trap the anions that have either oxygen, hydrogen,

nitrogen and fluorine atom.

3

Figure 1.1: PAMAM dendrimer (generation 3.0)

Besides, addition of receptor at the periphery of dendrimer is expected to

increase the complexation ability and the selectivity of anion recognition. Receptor is

a molecule that can binding tightly with other molecule and act as a host guest for the

molecule. In this study, the Hamilton receptor is highly encouraged to be the

functional group at the periphery of the PAMAM dendrimer because its have six

nitrogen atoms that can be proton donors for anions to form a covalent bonding

(Klajnert and Bryszewska, 2001).

The early model of Hamilton receptor with propane group at the terminal

arms is designed by Hamilton and Chang (1988) especially for the barbital

recognition. This receptor is successful in interactions and recognizing the barbital in

chloroform solution through its six hydrogen bonding sites with binding constant,

2.08 x 104 M

-1. Moreover, the proton nuclear magnetic resonance (

1H NMR)

spectroscopy is used to calculate the binding constant from the downfield shift of

proton. Figure 1.2 illustrates the structure of Hamilton receptor with two pyridine

group and four amides at the arms of the receptor.

4

Figure 1.2: Hamilton receptor for barbital molecule.

1.2 Statement of Problem

An important source of elements such as phosphorus, sulphur and nitrogen

are contained in both organic fertilizer and inorganic fertilizer (Babatunde and

Ajibola, 2009). Other than that, the nitrogen element, is also widely used in the

drinking water and food preservative. Nitrate and nitrite are compounds that contain

a nitrogen atom joined to oxygen atoms, with nitrate containing three oxygen atoms

and nitrite containing two oxygen atoms. In nature, nitrates are readily converted to

nitrites and vice versa. Both are anions, or ions with a negative charge. They tend to

associate with cations, or ions with a positive charge, to achieve a neutral charge

balance. Nitrates are used primarily to make fertilizer, but they are also used to make

glass and explosives. These compounds also are used in various chemical production

and separation processes. Nitrites are manufactured mainly for use as a food

preservative, and both nitrates and nitrites are used extensively to enhance the color

and extend the shelf life of processed meats.

Nitrate and nitrite compounds are very soluble in water and quite mobile in

the environment. They have a high potential for entering surface water when it rains,

as nitrates in applied fertilizers can dissolve in run off that flows into streams or

5

lakes. They also have a high potential for entering groundwater through leaching.

The concentration of anions associated with soil particles has been estimated to be

about half the concentration in interstitial water (the water in the pore spaces between

the soil particles). Nitrates themselves are relatively nontoxic. However, when

swallowed, they are converted to nitrites that can react with hemoglobin in the blood,

oxidizing its divalent iron to the trivalent form and creating methemoglobin. This

methemoglobin cannot bind oxygen, which decreases the capacity of the blood to

transport oxygen so less oxygen is transported from the lungs to the body tissues,

thus causing a condition known as methemoglobinemia.

In recent research (Albretch et al., (2008), Singh and Sun (2012), Weinkers et

al., (2012)), nitrate and nitrite anions are successfully recognized using the hydrogen

bonding strategy. However, all these researches were conducted in non aqueous

solutions which are chloroform, dichloromethane and dimethylsulfoxide. As a

consequence, the methods adapted in those studies are generally unsuitable for

detecting nitrates and nitrites in water samples. The use of the highly water soluble of

PAMAM dendrimer is anticipated to assist the poor solubility of Hamilton receptor

in detection of nitrate and nitrite anions in aqueous solution.

1.3 Objectives of Study

The main objectives of this study are to:

1. Synthesis PAMAM dendrimer modified with Hamilton receptor as a

periphery functional group.

2. Investigate the bonding and selectivity of Hamilton receptors,

PAMAM dendrimer and Hamilton receptors-PAMAM dendrimer

towards various anions especially nitrate and nitrite anions.

3. Evaluate the selectivity of Hamilton receptors-PAMAM dendrimer

and the effect of pH and solvents towards the binding constant (Kass)

of selective anions.

6

4. Calculate the Limit of detection (LOD) of Hamilton receptors-

PAMAM dendrimer.

1.4 Scope of Study

There are three stages in this study, first is synthesizing generation 0.5 (G0.5)

PAMAM dendrimer. In the second stage, the Hamilton receptor is prepared and

attached to the periphery of the PAMAM dendrimer. Lastly, the modified PAMAM

dendrimers are reacted with inorganic anions and the binding affinity is determined.

The PAMAM dendrimer, Hamilton receptor and Hamilton recepto-PAMAM

dendrimer are synthesized and characterized using FTIR and 1H NMR spectroscopy

prior further modifications. For the anion recognition studies, the fluorescence

quenching method is used to explore the binding affinity of the Hamilton receptor-

PAMAM dendrimer towards various anions in aqueous solutions. Moreover, the

effect of parameters such as solvent and pH on the anion binding ability is also

investigated using fluorescence spectroscopy. .

1.5 Significance of Study

This study developed a new compound of Hamilton receptor-PAMAM G0.5

dendrimer as anions recognition material especially for the nitrate and nitrite ions

from the usage of inorganic fertilizer. Moreover, this study also develops an

alternative way to prevent the various diseases from the effect of nitrate and nitrite

anions level in water. Other than that, this study is expected to solve many problems

especially in the groundwater treatment and environmental pollution.

7

1.6 Outline of Research

The outline of the research activities is shown in the Figure 1.3. They include

synthesis, characterization and application of HR-PAMAM G0.5 as anion

recognition material.

Figure 1.3: Outline of research.

Synthesis of

Hamilton receptor

Synthesis of

PAMAM dendrimer

G 0.5

Characterization of HR-PAMAM

dendrimer using FTIR, 1H NMR and

fluorescence spectroscopy.

Conjugation of the Hamilton

receptor to PAMAM dendrimer

Anions recognition process

using Fluorescence quenching method in

aqueous solution for nitrate, nitrite, acetate,

fluoride, bromide, chloride anion.

Study of the effect of solvent using

acetonitrile (MeCN) and effect of pH from

pH (2-12) using Britton-Robinson buffer.

8

1.7 Outline of Thesis

This thesis focuses on the synthesis and characterization of PAMAM

dendrimer, Hamilton receptor and HR–PAMAM dendrimer. Moreover, this thesis

presents the research on the capability of HR-PAMAM dendrimer to detect

selectively the nitrate and nitrite anions in aqueous solutions. This thesis is arranged

into five chapters as follow.

Chapter 1 describes the research background, statement of problem,

objectives of study, scope of study, significance of study, outline of research and

outline of thesis.

Chapter 2 discusses some literature reviews on the background dendrimers,

Hamilton receptor, anion recognition of nitrate and nitrite anions and intermolecular

bonding.

Chapter 3 demonstrates the materials and methods to synthesis the PAMAM

dendrimer and Hamilton receptor.

Chapter 4 converses the results on synthesis and characterization of PAMAM

dendrimer, Hamilton receptor and HR-PAMAM dendrimer. Additionally, it

discusses the anion recognition properties of various types of anions using Hamilton

receptor and Hamilton receptor-PAMAM G0.5 dendrimer in different types of

solvent and at various pH.

Chapter 5 summarizes the conclusions from this research and provides some

recommendation for further research.

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