ABSTRACT
A simple and sensitive spectrophotometric method is described for the assay of the
drugs; niacin, glibenclamide, erythromycin, thiamine and 4-aminobenzoic acid. The
method is based on charge transfer complexation (CT) reaction of niacin, glibenclamide,
erythromycin, thiamine and 4-aminobenzoic acid as n-electron donors with 2,3-
dichloro-5,6-dicyno-1,4-benzoquinone(DDQ) as л-electron acceptor in methanol.
Intensely coloured charge transfer complexes with niacin (reddish brown, lmax ;464 nm;
εmax, 1.02×103 dm3mol-1cm-1) thiamine (reddish brown ,lmax ;474 nm; εmax, 1.08×103
dm3mol-1cm-1), glibenclamide (reddish brown , lmax ;474 nm; εmax,0.99×103 dm3mol-
1cm-1) erythromycin(reddish brown , lmax ;464 nm; εmax, 1.27×103 dm3mol-1cm-1) 4-
aminobenzoic acid(reddish brown, lmax ;474nm; εmax, 1.06×103 dm3mol-1cm-1) all in a
1:1 stoichiometric ratio. Condition for complete reactions and optimum stability of
complexes were niacin (70 min, 60 OC) thiamine (25 min, 40 OC), glibenclamide (35
min, 40 OC), erythromycin (15 min, 60 OC) and 4-aminobenzoic acid (15 min, 60 OC) as
absorbances of the complexes remained invariant within these conditions. Formation
and stability of the complexes of niacin, thiamine, 4-aminobenzoic acid and
erythromycin were optimum at pH 8. For glibenclamide pH 2.0 favoured optimum
stability and formation. The bands distinguished for the donors to donor-acceptor CT
complexes displayed small changes in band intensities and frequency values in the IR
spectra ,The –NH2 group vibration occurring at 3609 cm-1 shifted to 3610 cm-1 in
thiamine, PABA (3222 cm-1 to 3183 cm-1), ѵ (N-H) occurring at 3331cm-1 shifted to
3371 cm-1 in glibenclamide, ѵ(C= N) occurring at 2936 cm-1 shifted to 2944 cm-1 in
niacin, ѵ (CH3-N) occurring at 2948 cm-1 shifted to 2939 cm-1 in erythromycin. The
vi
vibration ѵ (C= O) of DDQ observed at 1665 cm-1 shifted to 1669 cm-1 in the CT
complex for thiamine, PABA(1665 cm-1 to 1670 cm-1), glibenclamide(1675 cm-1 to
1676 cm-1), erythromycin(1665 cm-1 to 1674 cm-1), niacin(1665 cm-1 to 1655 cm-1)
respectively. Adherence to Beer’s Law was within the concentration range for niacin (5-
130 μg/cm3), thiamine (5-80 μg/cm3), glibenclamide (9-100 μg/cm3), erythromycin
(5-150 μg/cm3), 4-aminobenzoic acid(5-90 μg/cm3). Limit of detection and
quantification of the drugs based on this method is niacin (1.78 and 5.4), thiamine (1.23
and 3.37), glibenclamide (3.47 and 10.5), erythromycin (2.11 and 6.40), 4-aminobenzoic
acid (0.55 and 1.67) respectively. Evaluation of the degree of interference by excipients
used in the drugs manufactured indicates tolerance to certain concentrations. A detailed
study on the interference of different excipients was made. No significant interference
was observed in magnesium stearate (30 μg/cm3), Talc (15-25μg/cm3, 35-40 μg/cm3)
with thiamine-DDQ complex. There were no significant interference in stearic acid (35
μg/cm3) but tolerable interference was seen in magnesium stearate (20 μg/cm3) and
calcium phosphate (15 μg/cm3) with niacin-DDQ complex. For glibenclamide – DDQ
complex, no significant interference was seen with calcium phosphate (30 μg/cm3) but
there were tolerable interference present in stearic acid (40 μg/cm3). In 4-aminobenzoic
acid, no significant interference was observed with magnesium stearate (30 μg/cm3) and
talc (35 -40μg/cm3) but tolerable interference was observed in corn starch (15 μg/cm3).
Also no significant interference was seen in corn starch (35 μg/cm3) with erythromycin-
DDQ complex but there was tolerable interference in talc (10 μg/cm3). The Pearson
correlation coefficient for the compliance of the method as regards the pure and
commercial forms of niacin, thiamine, glibenclamide, erythromycin and 4-aminobenzoic
vii
acids are 0.993, 0.977, 0.987, 0.998 and 0.993 respectively which shows significance
with p < 0.01. The analysis of variance test revealed the non-significance of niacin,
thiamine, glibenclamide, erythromycin and 4-aminobenzoic acid with p > 0.01. The
mean percentage recoveries were 98.94 ± 0.016, 96.2 ± 0.016, 98.24 ± 0.011, 107.4
± 0.023 and 102.35 ± 0.014 for niacin, thiamine, glibenclamide, erythromycin and 4-
aminobenzoic acid respectively. Kinetics of the reactions infer that the rate of formation
of the CT complexes did not vary significantly with increase in concentration of
glibenclamide, erythromycin, thiamine, niacin and 4-aminobenzoic acid indicating
likely zeroth order dependence of the rate with respect to concentration of the drugs.
However, the linearity of the pseudo-first order plot points to first order dependence of
rate on [DDQ].The overall rate equation for the reactions can be given as
− ı[ııı]
ıı = ıııı [ııı]
Based on the limit of detection and quantification, adherence to Beer-Lambert’s
law and low degree of interference, the method is recommended for the analysis of these
drugs.
TABLE OF CONTENTS
Title page – – – – – – – – – – i
Declaration – – – – – – – – – – ii
Certification page – – – – – – – – iii
Dedication – – – – – – – – – iv
Acknowledgement – – – – – – – – v
Abstract – – – – – – – – – iv
Table of Contents – – – – – – – – ix
List of Figures – – – – – – – – – xxii
List of Tables – – – – – – – – – xxvii
Abbreviations– – – – – – – – – xxxiv
Chapter One
1.0 Introduction – – – – – – – 1
1.1 Charge transfer complexation- – – – – – 1
1.1.2 Analysis of Drugs – – – – – – 2
1.1.3 Justification of the study – – – – – – 6
1.1.4 Problem of the study – – – – – – – 6
1.1.5 Aims and Objectives- – – – – – – – 7
1.1.6 Scope of study- – – – – – – – 8
Chapter Two
2.0 Literature Review – – – – – – – 9
2.1 Charge transfer complex – – – – – 9
2.1.1 Marcus theory- – – – – – – – – 11
ix
2.1.2 The one electron redox reaction – – – – – 11
2.1.3 The outer sphere electron transfer- – – – – – 12
2.2 Charge transfer transition energy – – – – – 13
2.3 Identification of CT bands – – – – – – 13
2.4 Spectroscopy – – – – – – – – 14
2.4.1 Different spectroscopic techniques – – – – – 14
2.4.2 Spectrophotometry – – – – – – 15
2.4.3 Major classes of spectrophotometer – – – – – 16
2.4.4 Terms used in U.V spectroscopy – – – – – 16
2.5 Absorption laws – – – – – – – 17
2.6 2,3- dichloro-5,6- dicyano-1, 4- benzoquinone – – – 18
2.6.1 Previous studies on DDQ- – – – – – – 20
2.7 Niacin (Pyridine – 3 – Carboxylic acid) – – – – 20
2.7.1 Previous studies on niacin – – – – – 21
2.8 Vitamin B1 (Thiamine Hydrochloride) – – – 22
2.8.1 Previous studies on thiamine hydrochloride- – – – 23
2.9 Glibenclamide – – – – – – – – 24
2.9.1 Previous studies on glibenclamide – – – – – 25
2.10 Erythromycin – – – – – – – – 26
2.10.1 Previous studies on erythromycin – — – – – 26
2.11 Para Aminobenzoic acid (PABA) – – – – – 28
2.11.1 Previous studies on PABA — – – – – – 28
x
Chapter Three
3.0 Experimental – – – – – – – – 30
3.1 Materials and Methods – – – – – – 30
3.1.1 Drugs used and their sources – – – – – – 30
3.2 Preparation of reagents and standard solutions – – – 32
3.2.1 Preparation of 2, 3-dichloro-5, 6- dicyano 1,
4- benzoquinone – – – – – – – 32
3.2.2 Preparation of Standard solution of erythromycin – – – 32
3.2.3 Preparation of standard solution of glibenclamide – – – 32
3.2.4 Preparation of Standard solution of niacin – – – 32
3.2.5 Preparation of standard solutions of paraminobenzoic
acid (PABA) – – – – – – – – 33
3.2.6 Preparation of standard solutions of thiamine
hydrochloride – – – – – – – 33
3.3 Absorption spectra – – – – – – – – 33
3.3.1. Absorption spectra of 2,3- dichloro -5,6- dicyano -1,
4-benzoquinone – – – – – – – 33
3.3.2. Absorption spectra of erythromycin – – – – 33
3.3.3 Absorption spectra of glibenclamide – – – – 34
3.3.4 Absorption spectra of thiamine hydrochloride – – – 34
3.3.5 Absorption spectra of niacin – – – – – – 34
3.3.6 Absorption spectra of paraminobenzoic acid – – – 34
3.4.1 Absorption spectra of erythromycin-DDQ complex – – – 34
xi
3.4.2 Absorption spectra of glibenclamide-DDQ complex – – – 34
3.4.3 Absorption spectra of thiamine hydrochloride-DDQ
Complex – – – – – – — – 35
3.4.4 Absorption spectra of niacin-DDQ complex – – – 35
3.4.5 Absorption spectra of paraminobenzoic acid–DDQ
Complex – – – – – – – – 35
3.5 Stoichiometry of complexes – – – – – – 35
3.5.1 Stoichiometry of Erythromycin–DDQ Reaction – – – 35
3.5.2 Stoichiometry of Glibenclamide – DDQ Reaction – – – 36
3.5.3 Stoichiometry of Thiamine Hydrochloride – DDQ Reaction- – 36
3.5.4 Stoichiometry of Niacin-DDQ Reaction – – – – 36
3.5.5 Stoichiometry of PABA- DDQ Reaction – – – – 37
3.6 Effect of time on the formations of complexes- – – – 37
3.6.1 Effect of time on the formations of erythromycin–DDQ complex – 37
3.6.2 Effect of time on the formation of glibenclamide-DDQ complex – 37
3.6.3 Effect of time on the formation of thiamine
hydrochloride-DDQ complex – – – – – 38
3.6.4 Effect of time on the formation of PABA- DDQ Complex – – 38
3.6.5 Effect of time on the formation of niacin- DDQ complex — – 38
3.7 Effect of solvents on formation of complexes- – – – 38
3.7.1 Effect of solvents on erythromycin -DDQ complex – – – 38
3.7.2 Effect of solvents on glibenclamide – DDQ complex – – 39
3.7.3 Effect of solvents on complex formation of thiamine hydrochloride – 39
xii
3.7.4 Effect of solvents on niacin – DDQ complex – – – – 39
3.7.5 Effect of solvents on PABA- DDQ complex – – – – 40
3.8 Effect of temperature on formation complexes – – – 40
3.8.1 Effect of temperature on erythromycin-DDQ complex – – 40
3.8.2 Effect of temperature on glibenclamide-DDQ complex – – 40
3.8.3 Effect of temperature on thiamine- DDQ complex – – 40
3.8.4 Effect of temperature on niacin- DDQ complex – – – 41
3.8.5 Effect of temperature on PABA- DDQ complex – – – 41
3.9 pH study on formation of complexes – – – – – 41
3.9.1 pH study on erythromycin –DDQ complex – – – 41
3.9.3 pH study on glibenclamide-DDQ complex – – – – 41
3.9.4 pH study on thiamine hydrochloride-DDQ complex – – 41
3.9.5 pH study on niacin- DDQ complex – – — – – 42
3.9.6 pH study on PABA-DDQ complex – – — – – 42
3.10 Determination of association constant, molar absorptivity,
Free energy and Benesi- Hildebrand plot of the complexes- – 42
3.10.1 Benesi–Hildebrand plot of erythromycin-DDQ complex – – 42
3.10.2 Benesi- Hildebrand plot of glibenclamide- DDQ complex – – 42
3.10.3 Benesi – Hildebrand plot of thiamine hydrochloride-
DDQ complex – – – – – — – – 43
3.10.4 Benesi – Hildebrand plot of niacin –DDQ complex – – 43
3.10.5 Benesi-Hildebrand plot of PABA-DDQ complex – – – 44
3.2 Beer’s calibration plot for the formation of complexes – – 44
xiii
3.21 Beer’s calibration plot of erythromycin –DDQ complex – – 44
3.22 Beer’s calibration plot of glibenclamide –DDQ complex- – – 44
3.23 Beer’s calibration plot of PABA –DDQ complex – – – 45
3.24 Beer’s calibration plot of niacin-DDQ complex – – – 45
3.25 Beer’s calibration plot of thiamine–DDQ complex – – – 45
3.30 Interference studies on complex formation – – – – 46
3.31 Interference studies of erythromycin-DDQ complex – – – 46
3.32 Interference studies of thiamine hydrochloride-DDQ Complex – 46
3.33 Interference studies of niacin –DDQ complex – – – 46
3.34 Interference studies of PABA-DDQ complex – – – 47
3.35 Interference studies of glibenclamide-DDQ complex – – 47
3.40 Assay of dosage forms of drug samples – – – – – 47
3.41 Assay of dosage form of erythromycin drug – – – – 48
3.42 Assay of dosage form of glibenclamide drug – – – – 48
3.43 Assay of dosage form of thiamine drug- – – – – 48
3.44 Assay of dosage form of niacin drug – – – – 49
3.45 Assay of dosage form of PABA drug – – – – – 49
3.5 Kinetic measurements- – – – – – – 50
Chapter Four
4.1.1 Results – – – – – – – – – 52
4.1.2 Absorption spectra of the complex – – – – – 52
4.20 Stoichiometric relationship of erythromycin-DDQ Complex- – 81
4.21 Stoichiometric relation of glibenclamide –DDQ complex – – 81
xiv
4.22 Stoichiometric relationship of thiamine hydrochloride-DDQ complex – 81
4.23 Stoichiometric relationship of niacin-DDQ complex – – – 81
4.24 Stoichiometric relationship of PABA- DDQ complex- – – 81
4.30 Effect of time on the formation of complex – – – – 95
4.31 Maximum time for the formation of erythromycin-DDQ Complex – 95
4.32 Effects of time on glibenclamide-DDQ complex – – – 95
4.33 Effect of time on thiamine-DDQ complex – — – – 95
4.34 Effects of time on niacin-DDQ complex – — – – 95
4.35 Effects of time on PABA- DDQ complex – — – – 95
4.40 Effect of temperature on complexation- – – – – 108
4.41 Effect of temperature on the erythromycin-DDQ Complex – – 108
4.42 Effect of temperature on glibenclamide-DDQ Complex – – 108
4.43 Effects of temperature on thiamine hydrochloride-DDQ complex – 108
4.44 Effects of temperature on niacin-DDQ complex – – – 108
4.45 Effect of temperature on PABA- DDQ complex- – – – 109
4.50 pH studies of the complexes – – — – – – 120
4.51 pH study of erythromycin-DDQ complex — – – – 120
4.52 pH study of glibenclamide -DDQ complex – – – – 120
4.53 pH study of thiamine hydrochloride-DDQ complex – – – 120
4.54 pH study of niacin-DDQ complex – – – – – 120
4.55 pH study of PABA-DDQ complex – – – – – 120
4.6 Association constant, molar absorptivity, free gibb’s
energy, enthalpy and entropy changes of the complexes – – 131
xv
4.6.1 Association constant, molar absorptivity, free energy,
enthalpy and entropy changes of the erythromycin-DDQ complex – 131
4.6.2 Association constant, molar absorptivity, free energy,
enthalpy and entropy changes of the glibenclamide-DDQ complex – 142
4.6.3 Association constant, molar absorptivity, free energy,
enthalpy and entropy changes of the thiamine- DDQ complex – 152
4.6.4 Association constant, molar absorptivity, free energy,
enthalpy and entropy changes of the niacin- DDQ complex – 162
4.6.5 Association constant, molar absorptivity, free energy,
enthalpy and entropy changes of the PABA- DDQ complex – – 172
4.7 Beer’s calibration plots of the complexes – – 182
4.7.1 Beer’s calibration plot for erythromycin-DDQ Complex – – 182
4.7.2 Beer’s calibration plot for glibenclamide – – – – 184
4.7.3 Beer’s calibration plot of thiamine –DDQ complex – – – 186
4.7.4 Beer’s calibration plot for niacin-DDQ complex – – 188
4.7.5 Beer’s calibration plot for PABA-DDQ complex – – – 190
4.8.1 Recovery experiment of erythromycin-DDQ complex – – 192
4.8.2 Recovery experiment of glibenclamide-DDQ complex – – 195
4.8.3 Recovery experiment of thiamine-DDQ complex – – – 197
4.8.4 Recovery experiment of niacin-DDQ complex – – – – 199
4.8.5 Recovery experiment of PABA-DDQ complex – – – 201
4.9.1 Pharmaceutical interference studies on thiamine–DDQ complex – 203
4.9.2 Pharmaceutical interference studies on niacin –DDQ complex – 204
xvi
4.9.3 Pharmaceutical interference studies on glibenclamide–DDQ complex – 205
4.9.4 Pharmaceutical interference studies on PABA–DDQ Complex – 206
4.9.5 Pharmaceutical interference studies on erythromycin-DDQ complex 207
4.10 Determination of order of reactions – – – – – 208
4.10.1 Reaction of glibenclamide with DDQ – – – – 208
4.10.2 Reaction of erythromycin with DDQ- – – – – 211
4.10.3 Reaction of niacin with DDQ – – – – – 213
4.10.4 Reaction of PABA with DDQ – – – – – 216
4.10.5 Reaction of thiamine with DDQ – – – – – 219
4.10.6 Effect of temperatures on reaction rate of erythromycin-DDQ complex 222
4.10.7 Effect of temperatures on reaction rate of glibenclamide-DDQ complex 227
4.10.8 Effect of temperatures on reaction rate of niacin-DDQ Complex – 232
4.10.9 Effect of temperatures on reaction rate of PABA-DDQ Complex – 237
4.10.10 Effect of temperatures on reaction rate of thiamine-DDQ Complex 242
4.10.11 Effect of pH1-pH13 on reaction rate of erythromycin-DDQ Complex 248
4.10.12 Effect of pH1-pH13 on reaction rate of glibenclamide-DDQ complex 250
4.10.13 Effect of pH1-pH13 on reaction rate of niacin-DDQ complex – 252
4.10.14 Effect of pH1-pH13 on reaction rate of PABA-DDQ complex – 254
4.10.15 Effect of pH1-pH13 on reaction rate of thiamine – DDQ complex – 256
4.10.16 Effect of hydrogen ion concentration on reaction rate of – – 258
4.10.17 Effect of hydrogen ion concentration on reaction rate of PABA complex- 260
4.10.18 Effect of hydrogen ion concentration on reaction rate of niacin complex – 262
10.19 Effect of hydrogen ion concentration on reaction rate of
xvii
thiamine complex – – – – – – – – 264
4.10.20 Effect of hydrogen ion concentration on reaction rate of
erythromycin complex– – – – – – – 266
4.10.21 Effect of ionic strength on erythromycin-DDQ Complex – 268
4.10.22 Effect of ionic strength glibenclamide-DDQ Complex- – – 270
4.10.23 Effect of ionic strength on niacin-DDQ Complex– – — 272
4.10.24 Effect of ionic strength on PABA-DDQ Complex- – – 274
4.10.25 Effect of ionic strength on thiamine-DDQ Complex- – – 276
4.10.26 Rate determining Steps of drugs-DDQ complex – – – 278
4.10.27 Infrared frequencies and tentative assignments for drugs and reagent – 282
Chapter Five
5.0 .1 Discussion- – – – – – – – 287
5.0.2 Absorption Spectra- – – – – – – – 287
5.0.3 Absorption spectra of erythromycin complex- – – – 288
5.0.4 Absorption spectra of erythromycin in different solvent- – – 299
5.0.5 Absorption spectra of glibenclamide complex- – – – 290
5.0.6 Absorption spectra of glibenclamide in different solvent – – 291
5.0.7 Absorption spectra of thiamine complex- – – – – 292
5.0.8 Absorption spectra of thiamine in different solvent- – – – 293
5.0.9 Absorption spectra of niacin complex- – – – – 293
5.0.10 Absorption spectra of niacin in different solvent- – – – 294
5.0.11 Absorption spectra of PABA complex- – – – 294
5.0.12 Absorption spectra of PABA in different solvent- – – – 295
xviii
5.1 Stoichiometric relationship of erythromycin-DDQ Complex- – 296
5.1.1 Stoichiometric relation of glibenclamide –DDQ complex – – 296
5.1.2 Stoichiometric relationship of thiamine hydrochloride-DDQ complex 296
5.1.3 Stoichiometric relationship of niacin-DDQ complex — – – 297
5.1.4 Stoichiometric relationship of PABA- DDQ complex – – 297
5.2 Effect of time on the formation of complex – – – – 297
5.2.1 Maximum time for the formation of erythromycin-DDQ Complex – 297
5.2.2 Effects of time on glibenclamide-DDQ complex – – – 297
5.2.3 Effect of time on thiamine-DDQ complex – – – – 298
5.2.4 Effects of time on niacin-DDQ complex – – – – 298
5.2.5 Effects of time on PABA- DDQ complex – – – – 298
5.3 Effect of temperature on complexation – – – – 298
5.3.1 Effect of temperature on the erythromycin-DDQ Complex – – 298
5.3.2 Effect of temperature on glibenclamide-DDQ Complex- – – 299
5.3.3 Effects of temperature on thiamine hydrochloride- DDQ complex – 299
5.3.4 Effects of temperature on niacin-DDQ complex – – – 300
5.3.5 Effect of temperature on PABA- DDQ complex – – – 300
5.4 pH studies of the complexes – – – – – – 301
5.4.1 pH study of erythromycin-DDQ complex – – – – 301
5.4.2 pH study of glibenclamide -DDQ complex – – – – 301
5.4.3 pH study of thiamine hydrochloride-DDQ complex – – – 301
5.4.4 pH study of niacin-DDQ complex – – – – – 301
5.4.5 Effect of pH medium on the formation of PABA-DDQ complex – 302
xix
5.5 Association constant, molar absorptivity, free Gibb’s energy, enthalpy
and entropy changes for the formation of the complexes – – 302
5.5.1 Association constant, molar absorptivity, free energy,
enthalpy and entropy changes of the erythromycin-DDQ complex – 302
5.5.2 Association constant, molar absorptivity, free energy,
enthalpy and entropy changes of the glibenclamide-DDQ complex – 303
5.5.3 Association constant, molar absorptivity, free energy,
enthalpy and entropy changes of the thiamine- DDQ complex – 304
5.5.4 Association constant, molar absorptivity, free energy,
enthalpy and entropy changes of the niacin- DDQ complex – 305
5.5.5 Association constant, molar absorptivity, free energy, enthalpy and
entropy changes of the PABA- DDQ complex – – – 305
5.6 Beer’s calibration plots for the formation of the complexes – – 306
5.6.1 Beer’s calibration plot for the formation of erythromycin – DDQ complex – 306
5.6.2 Beer’s calibration plot for the formation of glibenclamide-DDQ complex – 306
5.6.3 Beer’s calibration plot for the formation of thiamine – DDQ complex – 306
5.6.4 Beer’s calibration plot for the formation of niacin – DDQ complex – 307
5.6.5 Beer’s calibration plot for the formation of PABA – DDQ complex – 307
5.7.1 Recovery studies on the formation of erythromycin-DDQ reaction – 307
5.7.2 Recovery studies on the formation of glibenclamide-DDQ reaction- 307
5.7.3 Recovery studies on the formation of thiamine-DDQ reaction – 308
5.7.4 Recovery studies on the formation of niacin-DDQ reaction – – 308
5.7.5 Recovery studies on the formation of PABA-DDQ reaction- – 308
xx
5.8.1 Interference studies on the formation of thiamine–DDQ complex – 308
5.8.2 Interference studies on the formation of niacin – DDQ complex – 309
5.8.3 Interference studies on the formation of PABA –DDQ complex 311
5.8.4 Interference studies on the formation of PABA –DDQ complex – 313
5.8.5 Interference studies on the formation of erythromycin -DDQ complex 313
5.8.6 Kinetics measurement – – – – – – 315
5.8.7 Determination of order of reactions – – – – – 315
5.8.8 Determination of order of reactions – – – – – 317
5.8.9 Determination of order of reactions – – – – – 318
5.8.10 Determination of order of reactions – – – – – 320
5.8.11 Determination of order of reactions – – – – – 321
5.8.12 FTIR characterization of the complexes – – – – 322
Chapter Six
6.0. Conclusion and Recommendation- – – – – – 323
References – – – – – – – – – 326
Appendix – – – – – – – – – – 339
CHAPTER ONE
1.0 Introduction
1.1 Charge Transfer Complexation
Acceptors are aromatic systems containing electron withdrawing substituents
such as nitro, cyano and halogen groups (Foster, 1967). Electron donors are systems
that are electron rich (Ajali and Chukwurah, 2001). The interaction between electron
donor and electron acceptor results in formation of charge transfer complex (Ajali et al,
2008). The term charge transfer denotes a certain type of complex which results from
interaction of an electron acceptor and an electron donor with the formation of weak
bonds (Hassib and Issa, 1996). However the nature of the interaction in a charge
transfer complex is not a stable chemical bond and is much weaker than covalent
forces. It is better characterized as a weak electron resonance. As a result, the excitation
energy of this resonance occurs very frequently in the visible region of the
electromagnetic spectrum. This produces the usually intense colour characteristic for
these complexes. These optical absorption bands are often referred to as charge transfer
bands. Molecular interactions between electron donors and acceptors are generally
associated with the formation of intensely coloured charge transfer complexes which
absorb radiation in the visible region.Charge transfer (CT) complexes have been widely
studied (Ezeanokete et al, 2013; Hala et al, 2013; Frag et al, 2011; Ramzin et al, 2012;
Farha, 2013). Charge transfer complexes are known to take part in many chemical
reactions like addition, substitution and condensation reactions (Van et al, 2006).
Donor acceptor properties are prerequisites for the formation of charge transfer
complexes. Most drugs have –NH or –NH2 groups which behave as bases (electron
donors) and could form complexes with acids (electron acceptor).Various cases have
been reported. The charge-transfer complexes formed between the ephedrine (Eph)
2
drug as a donor with picric acid (Pi) and quinol (QL) as ı–acceptors have been
synthesized in methanol as a solvent at room temperature and spectroscopically studied
as shown in scheme 1:
HO
N
CH3
O
H2
CH3
OH
[(EPh) (QL)] Complex
HO
OH
HO
N
CH3
H
CH3
Quinol Ephedrine
+
Scheme 1: Interaction of Ephedrine with Quinol to form the charge transfer
complex
Spectrophotometry is widely used to monitor the progress of reactions and the position
of equilibrium. Its measurement is often straight forward to make and the technique is
sensitive and precise provided that relevant limitations (such as the regions over which
Beer’s law is valid) are recognized. Spectrophotometric technique continues to be the
most preferred methods for routine analytical work due to their simplicity and
reasonable sensitivity with significant economical advantages (Raza, 2006).
1.1.2: Analysis of Drugs
A spectrophotometric method has been employed for the determination of
allopuriol using DDQ through charge transfer formation. The absorption spectra of
allopuriol-DDQ complex in acetonitrile solvent showed three maxima at (ʎmax = 450
nm; ε1 = 1.95 x103 Lmol-1cm-1), 540 nm (ε2 = 0.80 x 103 Lmol-1cm-1) and 580 nm
3
(ε3 = 0.69 x 103 Lmol-1cm-1) with a 1:1 stoichiometric ratio between allopuriol and
DDQ. The charge transfer complex formation is shown in scheme 2:
Cl
O
NC
NC
O
Cl
N
N
NH
O
H
Allopurinol
DDQ
O O
Cl Cl
HN
N
N N
N
NH
O
Allopurinol -DDQ Charge Transfer Complex
+ +
Scheme 2: Interaction of Allopurinol with DDQ to form the charge transfer complex
DDQ (2,3 – dichloro – 5, 6 – dicyano -p- benzoquinone) acts as an oxidizing
(Braude et al, 1956) as well as dehydrating agent in synthetic organic chemistry. It is
known for its interaction with drugs having donor sites in their structures and form Ion-
Pair charge transfer complexes which offers a basis for quantification of drugs
(Ghabsha et al, 2007; Vmsi and Gowri, 2008; Rehman et al, 2008; Rahman and Kashif,
2005; Khaled, 2008; Walash, 2004; El-Ragehy et al, 1997). DDQ as π-electron
acceptors often forms highly coloured electron-donor, electron-acceptor or CT
complexes with various donors which provide the possibility of determination of drugs
by spectrophotometric methods.
Vitamin B1 (Thiamine) has its chemical name as 2-[3-[(4-Amino-2-methyl- pyrimidin-
5-yl) methyl] -4-methyl – thiazol – 5 – yl] ethanol. Vitamin B1 is a water soluble
vitamin. It plays an important biological role in the metabolic process of the
carbohydrate in the human body (Khaled, 2008). Previous studies have utilized
different techniques for the estimation of thiamine hydrochloride which includes:
4
normal flow injection (Mouayed, 2012), electrochemical analysis method (Akyilmaz
and Dinckaya, 2006) high performance liquid chromato graphy (Ghasemi, 2005)
spectrofluorimetry (Hassan, 2001) polarimetry. Also direct spectrophotometric method
has been described for the determination of thiamine hydrochloride in the presence of
its degradation products (Wahbi et al, 1981).
Vitamin B3 (Niacin) chemically designated as [pyridine -3- carboxylic acid] is one of
the water soluble vitamins of the B-complex. It is an essential vitamin that is widely
available in drug and health food stores. Niacin is sometimes prescribed in high
dosages to lower cholesterol. People also take niacin supplements because they think
niacin helps ease gastrointestinal disturbances. It is widely distributed among plants
and animals. Some analytical methods have been developed for determination of niacin
which includes HPLC, flow injection TLC (Sarangi et al, 1985) HPTLC (Tiwari, 2010;
Zarzycki et al, 1995; Hsieh, 2005).
Furthermore, Spectrophotometric methods have been reported for the
simultaneous estimation of Atorvastation and niacin based on simultaneous equation
and absorbance ratio method (Sawart et al, 2012).
PABA [4-aminobenzoic acid] was used as a component of some medicines e.g
analgesic or anesthetic preparations, sunscreen agents and bentiromide (Imondi et al,
1972; Cyr et al, 1976; Charles et al, 1977).
It is an essential factor for the growth of bacteria. It is possessed of an antisulfanilamide
activity (Zhang et al, 2005). Various methods used for the analysis of
PABA include HPLC (Zhang et al, 2005) GC (Zhou and Zhang, 1998; Schmidt et al,
1997; Lambropoulon, 2002). Spectrophotometric methods have been used for the
determination of PABA; most of the methods are based on diazotization of PABA and
coupling the corresponding agent such as Braton Marshall reagent (Othaman and
5
Mansor, 2005), 4–dimethylaminobenzaldehyde (Yamato and Kinoshita, 1979), N-(Inapthyl)
ethylediamine dihydrochloride (Fister and Drazin, 1973) and phyloroglucinol
(Othaman and Mansor, 2005).Indirect spectrophotometric method for the determination
of PABA has been reported (Salvandor et al, 2003).A flow injection
spectrophotometric determination of propoxur with diazotized- 4-aminobenzoic acid
oxidation (Mirick, 1943) methods has been reported.
Erythromycin (3R, 4S, 5S, 6R, 7R, 9R, 11R, 12R, 13S, 14R) – 4-[(2,6-dideoxy -3- Cmethyl-
3-o-methyl-a-L-ribo-hexopy-ransoyl) oxy] – 14 – ethyl – 7 , 12 , 13 –
trihydroxy -3,5,7,9,11,13-hexamethyl- 6 – [ ( 3 , 4 , 6 – trideoxy – 3 – dimethylamino–β-
D-xylo-hexopyranosyl)-oxy]oxa cyclotetradecane -2, 10- dione is a macrolide
antibiotic that has an antimicrobial spectrum similar to or slightly wider than that of
penicillin. It has better coverage of a typical organism and occasional used as a
prokinetic agent. It inhibits bacterial reproduction but does not kill bacterial cells.
Literature revealed different techniques for the analysis of the studied macrolides.
The British Pharmacopeia stated the liquid chromatography method for the assay of
erythromycin. Other method of analysis includes spectrofluormetry (Pakinaz, 2002)
and (Nawal et al, 2006) capillary electrophoresis HPLC (Maria and Britt, 1995;
Dubois et al, 2001; Ramakrishna et al, 2005) voltametry (Faryhaly and Mohammed,
2004) microbiological method (Bernabaeu et al, 1999), spectrophotometry (Tasmin et
al, 2008; Carlos et al, 2010; Safwan Roula, 2012; Magar et al, 2012).
Glibenclamide chemically known as 5-chloro-n-[2-[4[(cyclohexylamino)
carbonyl] -amino] sulphonyl] phenyl] –ethyl] -2-methoxy benzamide is a second
generation sulphonyl ureas drug widely used in treatment of type 2 diabetic patient
(Parmeswararo et al, 2012). The literature survey shows that spectrophotometric
methods have been employed for the determination of glibenclamide based on
6
derivatization technique or coupling with another reagent (Nalwaya, 2008), (Bediar et
al, 1990; Lopez et al, 2005; Goweri et al, 2005; Martins, et al, 2007; Gianotto et
al,2007) High pressure liquid chromatography methods are the most commonly used
for the determination of glibenclamide and different methods coupled with UV
detection. Fluorescence (Khtri et al, 2001) detection or mass spectrometry (Smgh and
Taylor, 1996) .Thin layer chromatography has been employed for the detection of
glibenclamide (Kumasak et al, 2005), voltametric method (Radi, 2004).
Spectrofluorimetric method have all been reported. Erythromycin, thiamine, niacin,
p-Aminobenzoic acid, and glibenclamide are all bases with –NH2 or –NH groups
which have donor sites and can form charge transfer complexes.
1.1.3 Justification of the Study
In order to solve the problem of fake drugs which is rampart in Nigeria, there is
need for a method of drug analysis which is simple, fast and cost effective. However,
this new method of analysis will bring about easier analysis of drugs that is simple, fast
and of low cost which will invariably reduce importation and manufacture of
substandard drugs in Nigeria.
Secondly, the new method will solve the problem of interferences caused by
drug excipients.
1.1.4: Problem of the Study
These drugs are easily adulterated due to their nature and their high demand. This
requires that their degree of purity be certified before usage. Also the methods used in
determining these drugs like the flow injection spectrophotometric method , High
performance liquid chromatography, voltammetry, polarimetry and spectrofluorimetry
all require costly equipment, laborious, involve rigid pH control and use large amounts
7
of organic solvents which are expensive, hazardous to health and harmful to the
environment. Methods like spectrophotometry based on charge transfer complexation,
which are fast, less laborious and economical, are required for the assay of these drugs.
1.1.5 Aims and Objectives
The aim of this research was to determine a method based on formation of CT
complex between the drugs and DDQ that is simple, fast, economical and less
laborious. The objectives of this research are to:
(i) establish the degree of CT complex formation between the drugs and DDQ
(ii) determine the stability of the CT complexes with respect to time, temperature
and pH.
(iii) apply the CT complexes in spectrophotometric determinations of the drug
(iv) determine the average recoveries of the drugs in pure and commercial forms
(v) validate the proposed method using International Conference on
Harmonization Guideline.
(vi) determination of the kinetic model for the charge transfer complexation
reactions.
(vii) characterization of the CT complex using Fourier transformer infra red
spectrometer.
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1.1.6: Scope of Study
• U.V Absorption spectra
• I.R Absorption spectra
• Establishment of ı-max
• Stoichiometric relationships
• Optimum conditions(time , temperature , pH)
• Establishment of standard curves
• Applying the charge transfer complex in the spectrophotometric determination
of the drugs
• Validation of the proposed method using international conference on
harmonization guidelines
• Statistical analysis (One-way analysis of variance and Pearson correlation
coefficient)
• Determination of order of reactions (zero and 1st order)
• Characterization of charge transfer complexes using Fourier transformer infra
red spectrometer.
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