Radiation Damage in L-Histidine·HCl Monohydrate

Summary

The radiation-induced radicals in L-Histidine·HCl monohydrate have been studied with e.s.r. spectroscopy. In the temperature region 170–185 K, an intermediate radical is formed with the unpaired electron located in a π-orbital on the C_α arbon atom, interacting with one α- and two β-protons. The principal values for the α-proton coupling are −11·1, −19·4 and −31·8 gauss. The isotropic splitting constants for the β-protons were 44·3 and 7·0 gauss. The g-value was almost isotropic around 2·0036. The intermediate radical is proposed formed by a deamination process. The formation of the radical is described by first-order kinetics. The activation energy for the process is calculated to 15·9 kcal/mole.