PARAMAGNETIC ABSORPTION OF L-CYSTINE DIHYDROCHLORIDE IRRADIATED AT LOW TEMPERATURE,

Abstract : The paramagnetic absorption spectrum of a single crystal of L-cystine dihydrochloride x irradiated at 4.2K is shown. The two principal components of the absorption spectrum, designated alpha and beta, are due to positive and negative ions in which the unpaired electron is localized primarily on the disulfide group. The absorption spectra of these ions are distinguished by the following characteristics: (1) The ions give rise to a single absorption pattern. Since the crystal structure of L-cystine dihydrochloride is such that the two halves of the molecule are related by a twofold axis, the absorption patterns of all other paramagnetic species occur in duplicate related by the twofold axis. (2) There is a large g-value variation due to spin-orbit coupling as expected for sulfur electrons. (3) In the case of the alpha absorption the hyperfine pattern indicates an interaction between the unpaired electron and the protons of the adjacent CH2 groups. Upon warming, the paramagnetic absorption spectrum undergoes a sequence of changes until finally, after several hours at room temperature, the stable absorption reported by Kurita and Gordy is obtained. The stable absorption is presumably due to neutral free radicals. (Extracted)