An ESR Study of Amino Acid and Protein Free Radicals in Solution. Part . An ESR of Gamma-Irradiated Lysozyme in Frozen Aqueous Solutions

摘要

An electron spin resonance study has been made on lysozyme in frozen aqueous solutions irradiated With 60Co ￥?-rays in air at 77?￡K. Water resonances are dominant when the concentration and the temperature are both below 20% and 130?￡K respectively. More solute radicals are produced in the solution of higher concentration. Majority of the solute radicals results from direct hit of the radiation. The same types of radicals are induced at 77?￡K whether the substances are irradiated in the dry state or in frozen aqueous solution. Based on these results, it is assumed that the number of ESR centers produced by the secondary intermolecular radical reactions and stabilized in aqueous solutions may depend on the concentration of the solution, and the presence of water may facilitate the secondary radical reactions occurring in the solute molecules after heat treatment. Majority of the solute radicals above around 193?￡K are believed to react with oxygen to form peroxy-type radicals. However, when the solution is subjected to heat-treatment at 265?￡K after irradiation at 195?￡K the peroxy-type resonance was not observed, suggesting that an appreciable amount of oxygen is condensed into the ice, at 77?￡K, in addition to the oxygen that has already been dissolved in solution and react with solute free radicals during the process of heat-treatment. When the solution contains H2O2, no water resonance but HO2?¤type resonance was observed probably indicating that the radiation-induced OH radicals are trapped in H2O2aggregates and react readily with H2O2 molecules to produce HO2?¤type radicals even at 77?￡K.