MECHANISTIC INVESTIGATIONS OF OXIDATION OF PURINE AND PYRIMIDINE BASE COMPONENTS OF NUCLEIC ACIDS BY BROMAMINE-B IN AQUEOUS ALKALINE MEDIUM : A KINETIC APPROACH

摘要

Mechanism of oxidation of purine bases (adenine and guanine) and pyrimidine bases (uracil, thymine and cytosine) in presence of NaOH by bromamine-B(BAB) has been investigated. The reactions follow identical kinetics for all the bases, being first order dependence on [BAB]_o and fractional order each in [substrate]_o and [NaOH]. Addition of the reaction product retards the rate and the dielectric effect is positive. Variation of ionic strength and addition of halide ions had no effect on the rate. Proton inventory studies were made in H_2O-D_2O mixtures for adenine and cytosine. Oxidation products were identified and activation parameters were evaluated. An isokinetic relationship is observed with β = 336 K indicated that enthalpy factors control the rate. The rate of oxidation of purines is in the order: guanine > adenine while in case of pyrimidines the order is thymine > uracil > cytosine. A suitable mechanism is proposed and discussed.