Structural Changes Induced in Solid Dextran by Irradiation with Gamma Rays.

Abstract

Dextran samples with various molecular properties were irradiated in air and in vacuum by gamma rays. Degradation occurs as ls evidenced from changes in molecular weight. The rate of degradation is faster in oxygen but less reproducible. The energy per broken bond is in vacuum the same for all samples (19 ev) and it does not change with lncreasing dosage up to 18 Mrad. Gel filtration experiments have shown that irradiation in oxygen gives a molecular weight distribution which contains a larger weight fraction of low molecular material. Electron spin resonance data show that very stable free radicals are formed. A hypothesis is put forward that primarily a radical ion is formed which then dissociates into a positive ion and an alkoxy radical. The change in branching during the degradation indicates that simultaneous bond scission and rearrangements of the molecules occur. An increase in branching is typical for molecules having an initially low degree of branching, while a high number of branches originally will lead to the formation of less branched molecules. This is explained as due to the spatial conditions along the chain. In all cases the polymolecularity of the samples increases during the degradation. (auth)