The Formation and Reaction of Methyl Radicals Produced by Direct Photolysis of Aqueous Solutions of N-acetyl Substituted Aliphatic Amino Acids at 77 K

Summary

Photolysis of amino acids, peptides and their derivatives leads to the formation of free radicals in these substances. The electron-spin-resonance spectra obtained directly after irradiation at 77 K are not very well resolved. They are recognizable as the superposition of the spectra of different types of photoproduced radicals. ĊH₃ radicals are formed by U.V. irradiation if methyl groups are present in the molecule. These radicals are easily detectable because of their four line spectrum.

In this paper the formation of methyl radicals and their reaction with undamaged molecules of N-acetyl-substituted amino acids is investigated.

The number of ĊH₃ radicals present after a 30 min U.V. irradiation is higher if preceding U.V. irradiations and heat treatments are performed. The overall concentration of radicals is reduced only partially during this heat-treatment, while the ĊH₃ radicals decay completely. Other experiments show that the rate of and the yield of ĊH₃ radicals by U.V. irradiation increase with the dose of a preceding γ-irradiation.

The results suggest that there are substances present which are responsible for the higher production rate of methyl radicals after a preceding treatment. It is assumed that radicals are precursors of the fast-formed ĊH₃ radicals.