Nitroxyl Radicals: Electrochemical Approach to Structure-Activity Relationships

Cyclic nitroxyl radicals (NRs) are well known as a spin label, superoxide dismutase (SOD) mimic, and antioxidant. The redox property of NRs play lead role to control their reactivity. The redox electrochemistry, i.e., electrochemically forced removal or addition of an electron, is affected by the structure and stereochemistry of the compounds, solvents used for the electrochemical analysis, and also the various experimental parameter settings. So it is quite important to find out the structure-activity relationships of structurally different NRs by keeping constant all other parameters affecting reactivity of NRs. This allows the selection of most suitable NRs among the present NRs and also allows finding out the way for structural modification of NRs towards the better reactivity. In this study, one-electron redox potentials of five nitroxyl radicals with different substituents at the beta-position were measured in two different solvents, methanol and aqueous phosphate buffer (0.1 M, pH 7.4), by cyclic voltammetry and second-harmonic alternating current voltammetry. Evaluations of obtained data revealed the direct correlation between one-electron redox potentials and electronegativities of the beta-substituent on the ring. beta-Substituent with electron-donating effect caused negative shift in the one-electron redox potentials of the NRs and beta-substituents with electron-withdrawing effect behaved reversely.第22回日本酸化ストレス学会関東支部