TEMPERATURE-DEPENDENCE OF KINETIC ISOTOPE EFFECTS DURING OXIDATION OF BNAH QUINONES

On oxidation of N-benzyl-1,4-dihydronicotiamide (BNAH) by p-quinones (0.02 M phosphate, pH 7.0) the logarithms of rate constants linearly depend on the single electron reduction potential (E7(1)) of quinones. The reactivity of o-quinones is almost 2 orders higher. In the oxidation of /4,4-H-2(2)/BNAH the kinetic isotope effects decrease with increasing E7(1) of quinones. The equal activation energies of the oxidation of BNAH and /4,4-H-2(2)BNAH by p-quinones show strong evidence for a "parallel" transition state. In the reaction with o-quinones the activation energy of /4,4-H-2(2)/BNAH oxidation is higher than that of BNAH, which indicates a different transition state geometry or tunnelling effects.