Energetics of interconversion reactions of oxyradicals

Abstract

The energetics of reactions involving oxyradicals are reviewed. Thermodynamic data of radical species containing O and H are presented first, followed by those of metallocomplexes and metalloproteins, halogen containing species and organic radicals. Our approach is to calculate Gibb energy changes with the help of reduction potentials. If a particular potential is unknown, we estimate it by way of a thermodynamic cycle. The number of assumptions and estimates increases with the order of the topics covered. Thus, our calculations regarding reactions involving H and O containing species are quite rigorous, while conclusions related to organic radicals are more tentative. In particular reactions of hydrogen peroxide, metal ions in lower oxidation states, hydroquinones, hypohalide ions and ascorbic acid leading to short-lived species such as superoxide radical, hydroxyl radical and singlet oxygen are discussed. Appendices contain conventions regarding electrode potentials and solubility data of oxygen in water.