The Carbonate Radical: Its Reactivity with Oxygen, Ammonia, Amino Acids, and Melanins

The carbonate radical (CO3•−) is of importance in biology and chemistry. We used pulse radiolysis to generate the CO3•− radical and show there is no reaction with oxygen. However, in the presence of ammonia the CO3•− radical is removed by NO•, which itself arises from the scavenging of NH2• by oxygen, and the mechanism of this process is reported. The CO3•− radical shows complex decay patterns in the presence of ammonia, which can be understood as a balance between the radical−radical reaction CO3•− + CO3•− and CO3•− + NH2• (the amino radical). Also, we report reactivity with glycine and alanine and with melanin models. The CO3•− reacts with both dopa-melanin (DM, a model of black eumelanin) and with cysteinyl-dopa-melanin (CDM, a model of red/blond phaeomelanin). However, the reaction rate constant is much higher with CDM than with DM.