Effects of gamma radiation on vitamin B12 systems

Abstract

Cyanocobalamin and hydroxocobalamin react with both the oxidizing and reducing species produced by radiolysis of water. Reaction with ·OH radicals produces permanent degradation to yield a brown organocobalt compound. Reduction to vitamin B12r occurs by reaction with e^–_aq, and this change can be reversed by the presence of oxygen. When ·OH radicals are scavenged by formate ion, the reducing species CO^–₂ yields vitamin B12r. Oxygen and formate (10^–1 M), therefore, protect the vitamin from permanent damage. The use of similar systems would allow the vitamin to be effectively sterilized in aqueous solution by ionizing radiation without accompanying chemical change. Otherwise, the more radiation resistant solid state should be employed, when G(–cyanocobalamin)∼0.6.