Reduction of Hydrogen Peroxide by Glutathione Peroxidase Mimics: Reaction Mechanism and Energetics

The reaction mechanism for the reduction of hydrogen peroxide by N,N-dimethylbenzylamine diselenide, its selenol analogue, and the charged analogues of the diselenide and selenol are elucidated using reliable electronic structure techniques. It is found that the reaction using the diselenide has a large Gibbs energy barrier of 173.5 kJ/mol. The cationic diselenide, with both amines protonated, shows a lower barrier of 103.5 kJ/mol. Both diselenide species show significant Se-Se bond lengthening upon oxidation. An unusual two-step mechanism is found for the selenol with barriers of 136.3 and 141.9 kJ/mol, respectively, showing that it is unlikely that the selenol is the active form. The zwitterion, selenolate, and protonated amine analogues of the selenol show one-step reactions with energy barriers of 82.7, 92.7, and 102.3 kJ/mol, respectively. The zwitterion of the selenol shows the most favorable reaction energies, which is in good agreement with proposed mechanisms for this reaction.