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SPECTROPHOTOMETRIC DETERMINATION OF NIACIN, THIAMINE, GLIBENCLAMIDE, ERYTHROMYCIN AND PARA AMINO BENZO IC ACID USING 2, 3 – DICHLORO – 5, 6 – DICYANO – 1, 4 – BENZOQUINONE

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, max ;464 nm; εmax, 1.02×103 dm3mol-1cm-1) thiamine (reddish brown ,max ;474 nm; εmax, 1.08×103 dm3mol-1cm-1), glibenclamide (reddish brown , max ;474 nm; εmax,0.99×103 dm3mol-1cm-1) erythromycin(reddish brown , max ;464 nm; εmax, 1.27×103 dm3mol-1cm-1) 4-aminobenzoic acid(reddish brown, max ;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 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 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

-(d[DDQ])/dt=k_(obs ) [DDQ]

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
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

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
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
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
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
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
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
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
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
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
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
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

LIST OF FIGURES
2.0 2,3-dichloro-5,6- dicyano -1,4 – benzoquinone – – – – 18
2.1 Structure of nicotinic acid- – – – – – – 20
2.2 Structure of thiamine- – – – – – – – 22
2.3 Structure of glibenclamide- – – – – – – 24
2.4 Structure of erythromycin- – – — – – 26
2.5 Structure of PABA- – – – – – – – 28
4.1 Absorption spectra of DDQ in methanol medium – – 54
4.2 Absorption spectra of erythromycin in methanol – – 55
4.3 Absorption spectra of thiamine in methanol – – – 56
4.4 Absorption spectra of glibenclamide in methanol – – 57
4.5 Absorption spectra of niacin in methanol – – – – 58
4.6 Absorption spectra of PABA in methanol medium – – 59
4.7 Absorption of spectra of erythromycin–DDQ complex – – 61
4.8 Absorption of spectra of erythromycin in
ethanol-DDQ in methanol – – – – 62
4.9 Absorption of spectra of erythromycin in
chloromethane- DDQ in methanol complex – – – – 63
4.10 Absorption of spectra of erythromycin in ethylacetate-
DDQ in methanol complex. – – – – – – 64
4.11 Absorption spectra of glibenclamide in methanol –DDQ
in methanol complex – – – – – – – 65
4.12 Absorption spectra of glibenclamide in ethanol –DDQ
in methanol complex – – – – – – – 66
4.13 Absorption spectra of glibenclamide in chloromethane-DDQ
in methanol complex – – – – – – – 67
4.14 Absorption spectra of glibenclamide in ethylacetate–
DDQ in methanol complex – – – – – – 68
4.15 Absorption spectra of thiamine hydrochloride in methanol–
DDQ in methanol complex – – – – – – 69
4.16 Absorption spectra of thiamine hydrochloride in ethanol–
DDQ in methanol complex – – – – – – 70
4.17 Absorption spectra of thiamine hydrochloride
chloromethane –DDQ in methanol complex – – – – 71
4.18 Absorption spectra of thiamine hydrochloride in
ethylacetate-DDQ in the methanol. – – – – – 72
4.19 Absorption spectra of niacin in methanol–DDQ methanol – – 73
4.20 Absorption spectra of niacin in ethanol –DDQ in methanol complex – 74
4.21 Absorption spectra of niacin in chloromethane –DDQ in complex – 75
4.22 Absorption spectra of niacin in ethylacetate –DDQ methanol complex- 76
4.23 Absorption spectra of PABA in methanol medium – – – 77
4.24 Absorption spectra of PABA in ethanol-DDQ in methanol Medium 78
4.25 Absorption spectra of PABA in chloromethane-DDQ in methanol – 79
4.26 Absorption spectra of PABA in ethylacetate-DDQ in Methanol – 80
4.27 Job’s plot of erythromycin- DDQ complex – – – – 82
4.28 Stoichiometric ratio of glibenclamide –DDQ complex – – 85
4.29 Stoichiometric ratio of thiamine hydrochloride-DDQ Complex – 88
4.30 Stoichiometric ratio of niacin-DDQ complex – – – – 91
4.31 Stoichiometric relationship of PABA –DDQ complex – – 94
4.32 Time of complex formation of erythromycin-DDQ Complex – 98
4.33 Glibenclamide-DDQ complex – – – – – 100
4.34 Effect of time on thiamine complex – – – – – 102
4.35 Effects of time on niacin-DDQ complex – – – – 104
4.36 Effects of time on PABA-DDQ complex – – – – 106
4.37 Effects of temperature on erythromycin-DDQ complex – – 110
4.38 Effects of temperature on glibenclamide-DDQ complex – – 112
4.39 Effects of temperature on thiamine hydrochloride-DDQ Complex – 114
4.40 Effects of temperature on niacin-DDQ complex – – – 116
4.41 Effects of temperature on DDQ complex – – – – 118
4.42 Effects ph study of erythromycin- DC complex – – – 121
4.43 Study of glibenclamide-DDQ complex – – – – 123
4.44 pH study of thiamine hydrochloride-DDQ complex – – 125
4.45 pH study of PABA-DDQ complex – – – – – 127
4.46 Effect of pH on formation of PABA-DDQ complex – – – 129
4.47 Benesi plot of erythromycin-DDQ complex – – – – 132
4.48 Benesi plot for the formation of erythromycin-DDQ complex – – 133
4.49 Benesi plot for the formation of erythromycin-DDQ complex- – 134
4.50 Benesi plot for the formation of erythromycin-DDQ complex – – 135
4.51 Log k plot of erythromycin-DDQ complex – – – – 140
4.52 Benesi plot of glibenclamide – – – – – – 143
4.56 Log k plot of glibenclamide-DDQ complex – – – – 150
4.57 Benesi plot of thiamine-DDQ complex – – – 153
4.61 Log k plot of thiamine-DDQ complex- – – – – 160
4.62 Benesi plot of niacin-DDQ complex – – – – – 163
4.66 Log k of plot niacin-DDQ complex – – – – – 170
4.67 Benesi plot of PABA-DDQ complex – – – – – 173
4.71 Log k of PABA-DDQ complex – — – – – – 180
4.72 Beer’s plot of erythromycin-DDQ complex — – – – 182
4.73 Beer’s plot of glibenclamide-DDQ complex- – – – – 184
4.74 Beer’s plot of thiamine-DDQ complex- – – – – 186
4.75 Beer’s plot of niacin-DDQ complex- – – – – – 188
4.76 Beer’s plot of PABA-DDQ complex- – – – – – 190
4.77 Pseudo-first order plot of glibenclamide-DDQ reaction – – 209
4.83 Pseudo-first order plot of erythromycin –DDQ reaction – – 211
4.89 Pseudo-first order plot of niacin-DDQ reaction – – – – 214
4.95 Pseudo-first order plot of PABA-DDQ reaction – – – – 217
4.96 Pseudo-first order plot of thiamine-DDQ reaction – – – 220
4.97 Plot of log A∞-At for the formation of erythromycin-DDQ complex – 222
4.101 Plot of log A∞-At for the formation of glibenclamide-DDQ complex – 227
4.105 Plot of log A∞-At for the formation of complex niacin-DDQ complex – 232
4.109 Plot of log A∞-At for the formation of PABA-DDQ complex – – 237
4.113 Plot of log A∞-At for the formation of thiamine-DDQ complex – – 242
4.118 Representative plot of the effect of pH on erythromycin-DDQ reaction – 248
4.119 Representative plot of the effect of pH on glibenclamide-DDQ complex- 250
4.120 Representative plot of the effect of pH on niacin-DDQ complex- – 252
4.121 Representative plot of the effect of pH on PABA-DDQ complex- – 254
4.122 Representative plot of the effect of pH on thiamine-DDQ complex- – 256
4.123 Representative plot of the effect of HClO4 on the rate
glibenclamide-DDQ complex- – – – – 258
4.125 Representative plot of the effect of HClO4 on the rate PABA-DDQ
Complex- – – – – – – – – 260
4.126 Representative plot of the effect of HClO4 on the rate niacin-DDQ
complex – – – – – – – – 262
4.127 Representative plot of the effect of HClO4 on the rate thiamine-DDQ
complex- – – – – – – – – 264
4.128 Representative plot of the effect of HClO4 on the rate
erythromycin-DDQ complex- – – – – – – 266
4.129 Representative plot of the effect of ionic strength on the rate on
erythromycin DDQ complex- – – – – – – 268
4.130 Representative plot of the effect of ionic strength on the rate on
glibenclamide-DDQ complex- – – – – 270
4.131 Representative plot of the effect of ionic strength on the rate on
niacin-DDQ complex- – – – – – 272
4.132 Representative plot of the effect of ionic strength on the rate on
PABA-DDQ complex- – – — – – 274
4.133 Representative plot of the effect of ionic strength on the rate on
thiamine-DDQ complex- – – – – – 276

LIST OF TABLES
3.1.1 Equipments, their brand and uses – – – – – – 31
4.1 The molar absorptivity of drugs with DDQ reagent in different solvent – 60
4.2 Absorbances of reaction mixtures for erythromycin-DDQ system – 83
4.3 Absorbance of reaction mixtures for glibenclamide-DDQ system – – 86
4.4 Absorbance of reaction mixtures for thiamine-DDQ system – 89
4.5 Absorbance of reaction mixtures for niacin-DDQ system – – 93
4.6 Absorbance of reaction mixtures for PABA-DDQ system – – 95
4.7 Effect of time on formation of erythromycin –DDQ complex – – 99
4.8 Effect of time on formation of glibenclamide – DDQ complex – 101
4.9 Effect of time on formation of thiamine – DDQ complex – – 103
4.10 Effect of time on the formation of niacin –DDQ complex – – 105
4.11 Effect of time on the formation of PABA–DDQ complex – – 107
4.12 Temperature-Absorbance relationship for the formation of
erythromycin – DDQ complex – – – – – 111
4.13 Temperature-Absorbance relationship for the formation of
glibenclamide -DDQ complex – – – – – 113
4.14 Temperature-Absorbance relationship for the formation of
thiamine- DDQ complex – – – – – – 115
4.15 Temperature-Absorbance relationship for the formation of
niacin-DDQ complex – – – – – – 117
4.16 Temperature-Absorbance relationship for the formation of
PABA DDQ complex – – – – – – 119
4.17 Effect of pH on formation of erythromycin-DDQ complex – – 122
4.18 Effect of pH on formation of glibenclamide – DDQ complex – – 124
4.19 Effect of pH on formation of thiamine -DDQ complex – – 126
4.20 Effect of pH on formation of niacin -DDQ complex – – – 128
4.21 Effect of pH on formation of PABA -DDQ complex – – 130
4.23a Benesi- Hildebrand values for the formation of
Erythromycin–DDQ Complex – – – – – 137
4.23b Benesi- Hildebrand values for the formation erythromycin –
DDQ complex – – – – – – – 138
4.24 Association constant, molar absorptivity, free energy, enthalpy and
entropy changes for the formation of the erythromycin-DDQ complex – 141
4.25a Benesi-Hildebrand values for the formation of glibenclamide –
DDQ complex – – – – – – – 147
4.25b Benesi- Hildebrand values for the formation of
glibenclamide – DDQ complex – – – – – – 148
4.27 Association constant, molar absorptivity, free energy, enthalpy and
entropy changes for the formation of the glibenclamide-DDQ complex – 151
4.28a Benesi- Hildebrand values for the formation of thiamine-DDQ
Complex – – – – – – – – – 157
4.30 Association constant, molar absorptivity, free energy, enthalpy and entropy changes for the formation of the thiamine-DDQ complex – – 161
4.31 Benesi-Hildebrand values for the formation of niacin –DDQ complex – 167
4.32 Benesi-Hildebrand values for the formation of niacin –DDQ complex – 168

4.33 Association constant, molar absorptivity, free energy, enthalpy and entropy changes for the formation of the niacin-DDQ complex – – 171
4.34 Benesi – Hildebrand values for the formation of PABA –DDQ
Complex – – – – – – – – 177
4.35 Benesi – Hildebrand values for the formation of PABA –DDQ complex – 178
4.36 Association constant, molar absorptivity, free energy, enthalpy and entropy changes for the formation of the PABA-DDQ complex – – 181
4.37 Absorbance-concentration values for the formation of
erythromycin- DDQ reaction – – – – – 183
4.38 Absorbance-concentration values for the formation of
glibenclamide – DDQ complex – – – – – – 185
4.39 Absorbance-concentration values for the formation of thiamine
DDQ reaction – – – – – – – 187
4.40 Absorbance-concentration values for the formation of
niacin-DDQ reaction – – – – – – – 189
4.41 Absorbance-concentration values for the formation of
PABA-DDQ reaction – – – – – – – 191
4.42 Results of recovery studies from erythromycin-DDQ reaction – 193
4.43 Results of recovery studies from glibenclamide-DDQ reaction – 195
4.44 Results of recovery studies from thiamine-DDQ reaction – – 197
4.45 Results of recovery studies from niacin-DDQ reaction – – 199
4.46 Results of recovery studies from PABA-DDQ reaction – – 201
4.47 Pharmaceutical excipients used in the formulation of thiamine drug – 203
4.48 Pharmaceutical excipients used in the formulation of niacin drug – 204
4.49 Pharmaceutical excipients used in the formulation of
glibenclamide drug – – – – – – – 205
4.49 Pharmaceutical excipients used in the formulation of PABA drug – 206
4.50 Pharmaceutical excipients used in the formulation of erythromycin drug
– – – – – – – – – – 207
4.51 Values of pseudo-first order and second order rate constants for
glibenclamide – DDQ reaction with buffer 2, [DDQ] =10-3M- – 210
4.52 Values of pseudo-first order and second order rate constants for the
formation of erythromycin-DDQ reaction, [DDQ] =10-3M at 30 oC – 212
4.53 Values of pseudo- first order and second order rate constants for
the formation niacin reaction, [DDQ] =10-3M at 30 oC – – 215
4.54 Values of pseudo – first order and second order rate constants for the
formation of PABA reaction, [DDQ] =10-3M at 30 oC – – 218
4.55 Values of pseudo – first order and second order rate constants for the
formation of thiamine-DDQ reaction, [DDQ] =10-3M at 30 oC – – 221
4.56 Effect of temperature on the pseudo-first order rate constant and
activation parameters for the formation of erythromycin-DDQ complex
at ʎmax = 464 nm, [Erythromycin] = 10-2M, [DDQ] = 10-3 M – – 225
4.57 Effect of temperature on the pseudo-first order rate constant and
activation parameters for the formation of glibenclamide-DDQ complex at ʎmax = 464 nm, [Glibenclamide] = 10-2M, [DDQ] = 10-3 – – 230
4.58 Effect of temperature on the pseudo-first order rate constant
and activation parameters for the formation of niacin-DDQ complex
at ʎmax = 464 nm, [Niacin] = 10-2M, [DDQ] = 10-3 M – – – 235
4.59 Effect of temperature on the pseudo-first order rate constant
and activation parameters for the formation of PABA-DDQ complex
at ʎmax = 474 nm, [PABA] = 10-2M, [DDQ] = 10-3 M – – 241
4.60 Effect of temperature on the pseudo-first order rate constant
and activation parameters for the formation of thiamine-DDQ complex
at ʎmax = 474 nm, [Thiamine] = 10-2M, [DDQ] = 10-3 M – – 246
4.61 pH medium on the pseudo-first order rate constant with respect to
the formation of erythromycin-DDQ complex at ʎmax = 464 nm,
[Erythromycin] =10-3M, [DDQ] = 10-4 M – – – – 249
4.62 pH medium on the pseudo-first order rate constant with respect
to the formation of glibenclamide-DDQ complex
at ʎmax = 474 nm, [glibenclamide] =10-3M, [DDQ] = 10-4 M – – 251
4.63 pH medium on the pseudo-first order rate constant with respect
to the formation of niacin-DDQ complex at ʎmax = 464 nm,
[Niacin] =10-3M, [DDQ] = 10-4 M – – – – – 253
4.64 pH medium on the pseudo-first order rate constant with respect
to the formation of PABA-DDQ complex at ʎmax = 474 nm,
[PABA] =10-3M, [DDQ] = 10-4 M – – – – – 255
4.65 pH medium on the pseudo-first order rate constant with respect
to the formation of thiamine-DDQ complex at ʎmax = 474 nm,
[Thiamine] =10-3M, [DDQ] = 10-4 M – – – – 257
4.66 Acid values for the pseudo-first order and second order rate
constant of glibenclamide-DDQ complex at ʎmax = 474 nm, T =
30 oCNaClO4 = 1.02M, [gli]=2.0×10-5 M,[DDQ]=1 x 10-6 M – 259
4.67 Acid values for the pseudo-first order and second order rate
constant of PABA-DDQ complex at ʎmax = 474 nm, T = 30 oC
NaClO4 = 1.02M, [PABA]=2.0×10-5 M,[DDQ]=1 x 10-6 M – – 261
4.68 Acid values for the pseudo-first order and second order rate
constant of niacin-DDQ complex at ʎmax = 474 nm, T = 30 oC
NaClO4 = 1.02M, [Niacin]=2.0×10-5 M,[DDQ]=1 x 10-6 M – – 263
4.69 Acid values for the pseudo-first order and second order rate
constant of thiamine-DDQ complex at ʎmax = 474 nm, T = 30 oC
NaClO4 = 1.02M, [Thiamine]=2.0×10-5 M,[DDQ]=1 x 10-6 M – 265
4.70 Acid values for the pseudo-first order and second order rate constant
of erythromycin-DDQ complex at ʎmax = 474 nm, T = 30 oC NaClO4 =
1.02M, [Erythromycin]=2.0×10-5 M,[DDQ]=1 x 10-6 M – – 267
4.71 Effect of ionic strength on the rate of erythromycin-DDQ reaction
at ʎmax = 464 nm, T = 30 oC ,NaClO4 = 0.1M, [Erythromycin]
= 2.0×10-5 M, [DDQ] =1 x 10-6 M – – – – – 269
4.72 Effect of ionic strength on the rate of glibenclamide-DDQ
reaction at ʎmax = 474 nm, T = 30 oC, NaClO4 = 0.1M, [gli]
=2.0×10-5 M, [DDQ] =1 x 10-6 M – – – – – 271
4.73 Effect of ionic strength on the rate of niacin-DDQ reaction
at ʎmax = 464 nm, T = 30 oC, NaClO4 = 0.1M, [NIA] =2.0×10-5 M,
[DDQ] =1 x 10-6 M – – – – – – – 273
4.74 Effect of ionic strength on the rate of PABA-DDQ reaction
at ʎmax = 474 nm, T = 30 oC, NaClO4 = 0.1M, [PABA] =2.0×10-5 M,
[DDQ] =1 x 10-6 M – – – – – – – 275
4.75 Effect of ionic strength on the rate of thiamine-DDQ reaction at
ʎmax = 474 nm, T = 30 oC, NaClO4 = 0.1M, [THIA] =2.0×10-5 M,
[DDQ] =1 x 10-6 M – – – – – – – 277
4.76 FTIR characterization of glibenclamide-DDQ complex – – – 282
4.77 FTIR characterization of erythromycin-DDQ complex – – 283
4.78 FTIR characterization of PABA-DDQ complex – – – 284
4.79 FTIR characterization of thiamine-DDQ complex – – – 285
4.80 FTIR characterization of thiamine-DDQ complex – – – 286

ABBREVIATIONS

Abbreviation Name
ANOVA Analysis of variance
CT Charge transfer
DDQ 2,3-dichloro-5,6-dicyano-1,4 benzoquinone
ERY Erythromycin
FTIR Fourier transformer infra red
GC Gas chromatography
GLI Glibenclamide
HPLC High performance liquid chromatography
PABA p-aminobenzoic acid or 4-aminobenzoic acid
NIA Niacin
NMR Nuclear magnetic resonance
THF Tetrahydrofuran
THIA Thiamine
TLC Thin layer chromatography
UV-VIS Ultraviolet/visible

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) drug as a donor with picric acid (Pi) and quinol (QL) as π–acceptors have been synthesized in methanol as a solvent at room temperature and spectroscopically studied as shown in scheme 1:

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