Radical cations of some water-soluble organoselenium compounds: Insights from pulse radiolysis studies

Radical cations of three water-soluble organoselenium compounds, viz., selenourea, selenomethionine, and selenocystine, were produced and their reactions in the pH range 1–7 were studied using nanosecond pulse radiolysis technique. The radical cations, centered on the selenium atom, were generated by one-electron oxidation using hydroxyl (OH) radicals and Cl2− and Br2− radicals. The radical cations of selenourea were converted to dimer radical cations in the entire pH range, which in presence of oxygen released elemental selenium as one of the products. The monomer radical cations of selenomethionine are stabilized at neutral pH by the lone pair of electrons on the N atom of the amino group and undergo partial decarboxylation to produce α-amino selenyl radicals, which are reducing in nature. At highly acidic conditions, when the lone pair is not available due to protonation, they were converted to dimer radical cations. Selenocystine, being a diselenide, produced monomer radical cations on one-electron oxidation in the entire pH range and acquires stability by sharing the electrons between the two adjacent selenium atoms.