Quantum chemical calculations of the one-electron oxidation potential of nitroxide spin labels in biologically active compounds

摘要

Density functional theory and continuum solvent model have been used to determine standard redox potentials of oxidation of cyclic nitroxide radicals and the nitroxide derivatives of chitosan and fullerene C-60 in water. Inclusion of structural relaxation of solute in water improves correlation between the measured and calculated oxidation potentials. The underlying limitations of the thermodynamic cycle model have been discussed. The computed oxidation potential of the piperidine-N-oxide derivative of chitosan is several tens mV higher than of the separate radical while the opposite trend was found for the pyrroline-N-oxide derivative of chitosan. The calculations of fullerene C-60-TEMPO have shown that the 6,6-methanofullerene is more stable that the 5,6-fulleroid structure. The determined redox potential of oxidation of fullerene C-60-TEMPO is significantly higher than of TEMPO in water.