Kinetics and Mechanism of Protection of Thiamine from Phosphate Radical

The rates of photo oxidation of thiamine in presence of peroxydiphosphate (PDP) has been determined by measuring the absorbance of thiamine at 264 nm spectre metrically. The rates and quantum yields of oxidation. Of thiamine by phosphate radical anion have been determined in the presence of different concentrations of caffecic acid. Increase in (caffeic acid) is found to decrease the rate of oxidation of thiamine suggesting that caffecic acid acts as an efficient scavenger of PO4-2 and protects thiamine from it. Phosphate radical anion compacts for thiamine as well as caffeic acid the rate constant for phosphate radical anion with caffeic acid has been calculated to be 1.3059 X 10-8 litres mol-1.s-1. The quantum yields of photo oxidation of thiamine have been calculated from the rates of oxidation of thiamine and the light intensity absorbed by PDP at 264 nm. The wave length at which PDP is activated to phosphate radical anion. From the results of experimentally determined quantum yields (exp+) and the quantum yields calculated (cal) assuming caffeic acid concentration and corrected for PO.-4. Scavenging by caffeic acid are also found to be greater than experiment values. These observations suggest that thiamine radicals are repaired by caffeic acid in addition to scavenging of phosphate radical anions. Bansal and Fessenden have used sulphate radical anion (So4) a strong electro phillic radical to create radical cation in uracil and substituted uracils. In the paper we report the results on the protection of thiamine from phosphate radical anion by caffeic acid the rate constant of PO.-4 reaction with caffeic acid has been evaluated. Further an attempt has also been made to evaluate the extent of repair of thiamine radicals by caffeic acid.