I= A STUDY OF PHOTOCHEMICAL INTERACTION OF CYANOCOBALAMIN WITH THIAMINE AND PYRIDOXINE
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Title of Thesis
A STUDY OF PHOTOCHEMICAL INTERACTION OF CYANOCOBALAMIN WITH THIAMINE AND PYRIDOXINE

Author(s)
Masroor Ahmad
Institute/University/Department Details
University of Karachi/ Department of Pharmaceutical chemistry
Session
1996
Subject
Pharmacy
Number of Pages
343
Keywords (Extracted from title, table of contents and abstract of thesis)
cyanocobalamin, thiamine, pyridoxine, vitamin b12, vitamin b1, vitamin b6, thiazole

Abstract
The present investigation is based on a study of the photolysis of cyanocobalamin (vitamin B12) in the presence of thiamine HCI (vitamin B1), its hydrolytic product, 4-methyl-5-(β-hydroxyethyl) thiazole and pyridoxine HCI (vitamin B6) at pH 1-12 using a 125W visible radiation source. The light intensity of the radiation source has been measured by potassium ferrioxalate actinometry during the reactions

Cyanocobalamin is photolysed to hydroxocobalamin and other unknown degradation products both in the presence and absence of thiamine HCI, thiazole and pyridoxine HCI. Hydroxocobalamin as a photoproduct in this reaction has been identified by TLC and spectral characteristics. The assay of cyanocobalamin and hydroxocobalamin in photolysed solutions in the presence and absence of thiamine HCI, thiazole and pyridoxine HCI, has been carried out by a newly reported two-component spectrophotometer method by absorbance measurements at 525 and550 nm (pH 4.0), at which there is no interference from other components present in the solution. The method is specific and has a precision of the order of±3%

Cyanocobalamin photolysed in aqueous solutions in the presence of thiamine HCI, thiazole and pyridoxine HCI follows first-order kinetics and the apparent first-order rate constants (Kobs) show a gradual increase with bimolecular interaction of cyanocobalamin with thiamine HCI, thiazole and pyridoxine HCI range in the decreasing order from 5.0m-1 min-1 (pH 1) to 0.71 m-1 min-1 (pH 1), 3.5 m-1 min-1 (pH 1) to 0.48 m-1 min -1 (pH 7) and 5.0 m-1 min-1 (pH 1) to o.87 m-1 min-1 )pH 7) respectively indicating that the rate of photolysis is accelerated by the presence of these compounds and cyanocobalamin is most stable in the pH range 6-8

The log K2-pH profiles for these reactions in the acid pH range may be represented by a sigmoid curve indicating the involvement of protonated cyanocobalamin species (pka 3.3), followed by a flat portion in the pH range 6-8 and then a gradual increase in the rate in the alkaline pH range. Thus the reaction appears to involve both acid and base catalysis

An increase in citro-phosphate buffer concentration from 0.05M to 0.20M in the pH range 2.5-8.0 results in an increase in the rates of photolysis indicating a catalytic effect of the buffer salts. A comparison of the second-order rate constants of anion catalysed photolysis of cynocobalamin in the presence of equimolar concentrations of thiamine HCI, thaizole and pyridoxine HCI at pH 4.0 in bhosphate (0.80X10-3 M-1 min-1, 0.60X10-3 M-1 min-1, 0.70X10-3 M-1 min-1) and citro-phosphate buffer (1.02X10-3 M-1 min-1, 0.80X10-3 M-1 min-1, 0.80X10-3 M-1 min-1) indicates that citrate ion has a prominent effect on the rate of reaction

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3101.85 KB
S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents 0
84.73 KB
2 1 Introduction 1
103.72 KB
  1.1 Discovery Of Cyanocobalamin 1
  1.2 Biological Function Of Cyanocobalamin 1
  1.3 Nomenclature, Chemical Structure And Physicochemical Characteristics 2
  1.4 Physicochemcial Action 4
  1.5 Pharmacookinetics 7
  1.6 Toxicity 8
  1.7 Hypervitaminosis, Dosage And Side Effects 8
  1.8 Preparations 9
  1.9 Pharamaceurical Importance 9
  1.10 Literature On Cyanocobalamin 10
3 2 Analytical Techniques Used In The Study Of Cyanocobalamin And Related Compounds 11
197.43 KB
  2.1 Chromatographic And Electrophoretic Techniques 11
  2.2 Spectroscopic Techniques 19
  2.3 Electrochemical Techniques 26
  2.4 Radioassay Techniques 27
  2.5 Microbiological Techniques 28
4 3 Degration Reactions, Interactions And Stabilization Of Cyanocobalamin 29
249.06 KB
  3.1 Stability Of Cyanocobalamin 29
  3.2 Modes Of Degradation 29
  3.3 Object Of Present Investigation 50
5 4 Experimental Work 53
169.33 KB
  4.1 Materials 53
  4.2 Methods 56
  4.3 Plan Work 68
6 5 Results And Discussion Photolysis Studies Of Cyanocobalamin-1 And Assay Methods 70
1324.5 KB
  5.1 Photolytic Reactions 70
  5.2 Spectral Characteristics Of Cyanocobalamin , Thiamine HCI, Pyridoxine HCI And 4-Methyl-5-(Β- Hydroxyethyl ) Thiazole 71
  5.3 Colour Changes In Photolysed Solutions 77
  5.4 Nature Of Photoproducts 79
  5.5 Assay Of Cyanocobalamin In Photolysed Solutions 79
  5.6 Analytical Data 82
7 6 Photolysis Studies Of Cyanocobaalamin-2 Kinetics Of Photolysis, Ph And Buffer Effects And Reactions Pathways 171
1382.51 KB
  6.1 Kinetics Of Photolysis 171
  6.2 Buffer Effect 292
  6.3 Reaction Pathways 310
  6.4 Conclusions And Suggestions 314
  6.5 References 317