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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 –
pH 12 based on the calculation from Marvin sketch in
ChemAxon® software.
77
4.15 Macrospecies distribution for the nitrite anion at pH 2 –
pH 12 based on the calculation from Marvin sketch in
ChemAxon® software.
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
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
C2 Fluorescence emission spectra and Stern-Volmer plot for
titration of nitrite anion in Hamilton receptor in aqueous
solution.
113
C3 Fluorescence emission spectra and Stern-Volmer plot for
titration of acetate anion in Hamilton receptor in aqueous
solution.
114
C4 Fluorescence emission spectra and Stern-Volmer plot for
titration of fluoride anion in Hamilton receptor in
aqueous solution.
115
C5 Fluorescence emission spectra and Stern-Volmer plot for
titration of chloride anion in Hamilton receptor in
aqueous solution.
116
C6 Fluorescence emission spectra and Stern-Volmer plot for
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
titration of nitrate anion in Hamilton receptor in aqueous
solution at pH 2.
122
E2 Fluorescence emission spectra and Stern-Volmer plot for
titration of nitrite anion in Hamilton receptor in aqueous
solution at pH 2.
123
E3 Fluorescence emission spectra and Stern-Volmer plot for
titration of nitrate anion in Hamilton receptor in aqueous
solution at pH 4.
124
E4 Fluorescence emission spectra and Stern-Volmer plot for
titration of nitrite anion in Hamilton receptor in aqueous
solution at pH 4.
125
E5 Fluorescence emission spectra and Stern-Volmer plot for
titration of nitrate anion in Hamilton receptor in aqueous
solution at pH 6.
126
E6 Fluorescence emission spectra and Stern-Volmer plot for
titration of nitrite anion in Hamilton receptor in aqueous
solution at pH 6.
127
E7 Fluorescence emission spectra and Stern-Volmer plot for
titration of nitrate anion in Hamilton receptor in aqueous
solution at pH 7.
128
xxiii
E8 Fluorescence emission spectra and Stern-Volmer plot for
titration of nitrite anion in Hamilton receptor in aqueous
solution at pH 7.
129
E9 Fluorescence emission spectra and Stern-Volmer plot for
titration of nitrate anion in Hamilton receptor in aqueous
solution at pH 8.
130
E10 Fluorescence emission spectra and Stern-Volmer plot for
titration of nitrite anion in Hamilton receptor in aqueous
solution at pH 8.
131
E11 Fluorescence emission spectra and Stern-Volmer plot for
titration of nitrate anion in Hamilton receptor in aqueous
solution at pH 10.
132
E12 Fluorescence emission spectra and Stern-Volmer plot for
titration of nitrite anion in Hamilton receptor in aqueous
solution at pH 10.
133
E13 Fluorescence emission spectra and Stern-Volmer plot for
titration of nitrate anion in Hamilton receptor in aqueous
solution at pH 12.
134
E14 Fluorescence emission spectra and Stern-Volmer plot for
titration of nitrite anion in Hamilton receptor in aqueous
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
anion in HR–PAMAM G0.5 in aqueous solution at pH 2.
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
anion in HR–PAMAM G0.5 in aqueous solution at pH 4.
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
F6 Fluorescence emission spectra and Stern-Volmer plot for
titration of nitrite anion in HR–PAMAM G0.5 in aqueous
solution at pH 6.
141
F7 Fluorescence emission spectra and Stern-Volmer plot for
titration of nitrate anion in HR–PAMAM G0.5 in
aqueous solution at pH 7.
142
F8 Fluorescence emission spectra and Stern-Volmer plot for
titration of nitrite anion in HR–PAMAM G0.5 in aqueous
solution at pH 7.
143
F9 Fluorescence emission spectra and Stern-Volmer plot for
titration of nitrate anion in HR–PAMAM G0.5 in
aqueous solution at pH 8.
144
F10 Fluorescence emission spectra and Stern-Volmer plot for
titration of nitrite anion in HR–PAMAM G0.5 in aqueous
solution at pH 8.
145
F11 Fluorescence emission spectra and Stern-Volmer plot for
titration of nitrate anion in HR–PAMAM G0.5 in
aqueous solution at pH 10.
146
F12 Fluorescence emission spectra and Stern-Volmer plot for
titration of nitrite anion in HR–PAMAM G0.5 in aqueous
solution at pH 10.
147
F13 Fluorescence emission spectra and Stern-Volmer plot for
titration of nitrate anion in HR–PAMAM G0.5 in
aqueous solution at pH 12.
148
F14 Fluorescence emission spectra and Stern-Volmer plot for
titration of nitrite anion in HR–PAMAM G0.5 in aqueous
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
G2 Fluorescence emission spectra and Stern-Volmer plot for
titration of nitrite anion in Hamilton receptor in
acetonitrile solution.
151
xxv
G3 Fluorescence emission spectra and Stern-Volmer plot for
titration of nitrate anion in HR–PAMAM G0.5 in
acetonitrile solution.
152
G4 Fluorescence emission spectra and Stern-Volmer plot for
titration of nitrite anion in HR–PAMAM G0.5 in
acetonitrile solution.
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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