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PHOTOLYSIS AND INTERACTION OF THIAMINE HYDROCHLORIDE WITH RIBOFLAVIN IN AQUEOUS SOLUTION

Vaid, Faiyaz Hussain Madani (1997) PHOTOLYSIS AND INTERACTION OF THIAMINE HYDROCHLORIDE WITH RIBOFLAVIN IN AQUEOUS SOLUTION. PhD thesis, University of Karachi, Karachi.

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Abstract

A detailed review of the literature on chemical, biochemical, pharmacological, analytical and degradation studies of thiamine HCl (vitamin B1) has been presented and an investigation of the photolysis of thiamine HCL solutions in the presence absence of riboflavin has been made Thiamine HCl solutions on UV irradiation at pH 1.0-12.0 give rise to a number of hydrolytic (2-methyl-4-amino-5-hydroxymethylpyrimidine and 4-methyl-5-β-hydroxyethylthiazole) and oxidation (2-methyl-4-amino-5-amino-methylpyrimidine, α-aceto-γ-mercaptopanol and thiochrome) products both in the presence and absence characteristics. A RP-HOLC method with isocratic elution has been developed for the simultaneous determination of thiamine HCl, its photoproducts and riboflavin The photolysis of thiamine HCl follows an apparent first-order kinetics and the rate constants (kobs) vary from 1.38X10-2 min-1 (pH 1.0) to 0.95 min-1 (pH 12.0) with a maximum value of 2.70X10-2 min-1 (pH 4.0). The second-order rate constants (k2) for the bimolecular interaction of thiamine HCl and riboflavin range from 1.60X10-2 M-1 min-1 (pH 1.0) to 1.62X10-2 M-1 (pH 10.0) with a maximum value of 12.86X10-2 M-1 min-1 (pH 4.0). Thus thiamine HCl exhibits maximum degradation around pH 4.0 both in the presence and absence of riboflavin The pH-rate profiles for the photolysis of thiamine alone, and that in the presence of riboflavin have been determined and the behavior of various ionic and nonionic species involved in the reaction have been explained. The profiles follow bell shaped curves with pHmax around 4.0 and may represent two dissociations in the reacting species. Kinetic equations for the reactions of the species involved (protonated thiamine, non-protonated quaternary thiamine, neutral thiamine and thiol thiamine) have been presented The kinetic data on the photolysis of thiamine HCl alone and that in the present of riboflavin clearly demonstrate that the reaction is inhibited by riboflavin. However, in the presence of divalent phosphate ions, the influence of riboflavin is diminished due to its complexation with phosphate species. The second-order rate constant for this reaction has been determined as 6.24X10-3 M-1 min-1 In water and alcoholic solutions (methanol, ethanol, 1-propanol and 1-butanol) the rate of photolysis of thiamine HCl is dependent upon the solvent dielectric constant and viscosity. An increase in solvent dielectric results in an increase in the rate of photolysis implying the participation of a polar intermediate in the reaction. On the contrary an increase in solvent viscosity leads to a decrease in the rate of photolysis indicating that the reaction is diffusion controlled The kinetic of UV photolysis of 4-methyl-5-β-hydroxyethylthiazole (a hydrolytic product of thiamine) at pH 1.0-12.0 has also been studied and the pH-rate profile has been prepared indicating that pHmax (2.0) lies near the pKa of thiazoles Reaction schemes for the photolysis of thiamine HCl in aqueous solutions have been proposed and the role of riboflavin as a photoinhibitor in the reaction has been elucidated

Item Type:Thesis (PhD)
Uncontrolled Keywords:thiamine hydrochloride, riboflavin, aqueous solution, vitamin b1, thiamine deficiency, hypervitaminosis, thiamine hcl solution
Subjects:Biological & Medical Sciences (c) > Medical Sciences (c2) > Pharmacy(c2.5)
ID Code:1330
Deposited By:Mr. Muhammad Asif
Deposited On:27 Jan 2007
Last Modified:04 Oct 2007 21:05

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