H/D Kinetic Isotope Effect as a Tool to Elucidate the Reaction Mechanism of Methyl Radicals with Glycine in Aqueous Solutions

Guy Yardeni, Chemistry dept., NRCN and Ben Gurion University, Beer Sheva, Israel
Israel Zilbermann, Chemistry dept., NRCN and Ben Gurion University, Beer Sheva, Israel
Eric Maimon, Chemistry dept., NRCN and Ben Gurion University, Beer Sheva, Israel
Lioubov Kats, Chemistry dept., Ben Gurion University, Beer Sheva, Israel
Ronen Bar Ziv, Chemistry dept., NRCN and Ben Gurion University, Beer Sheva, Israel
Dan Meyerstein, Biological Chemistry dept., Ben Gurion University and Ariel University, Ariel, Israel

The reactions of alkyl radicals and alkyl-peroxyl radicals with organic substrates are key steps in a variety of catalytic and physiological processes. The latter are usually initiated by hydroxyl radicals, which react in very fast reactions with most components of biological systems. The rate constants of the reactions of hydroxyl radicals with ammines and amino acids are pH depended.

The H/D kinetic isotope effect, KIE, for the reaction of methyl radicals with glycine in aqueous solutions at pH 10.6 equals 16+-3. This result proves that the methyl radical abstracts a hydrogen atom from the methylene group of glycine and not an electron from the unpaired couple on the nitrogen atom. The rate constant of the reaction of methyl radicals with glycine at pH 7.0 is orders of magnitude smaller than at pH 10.6.

Detailed experimental results and reaction mechanisms will be presented.