Comparative EPR study of the radical species formed during the radiolysis in polycrystalline solid state of monohydrated (L-ASN.H2O) and deuterated asparagine (L-ASN.D2O)

Abstract

L-asparagine monohydrate (L-Asn•H 2 O) and L-asparagine deuterated (L-Asn•D 2 O), gamma irradiated were investigated in polycrystalline state, by means of the EPR spectroscopy. The recorded spectra of L-Asn•H 2 O are due to the overlapping radicals spectra, having the structures R 1 , R 2 and R 3 in various ratios. The water participation at the radiolysis mechanism via the H and OH radicals formed by ionizing radiations was highlighted. The kinetic study was performed at temperatures beyond and above dehydration temperature. The high value of the preexponential factor and the positive one of the activation entropy proves that the bonds of the transition complex involving the radicals are weaker after dehydration, the rate of the radical's disappearance reaction being fast. For L-Asn•D 2 O, a different behaviour was found, the recorded spectra are different from L-Asn•H 2 O, due to the increasing energy of the deuterium bonds. The radicalic entities ratio depends on crystalisation time after dissolution in D 2 O.