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Electron spin resonance studies on the oxidation of rifamycin SV catalyzed by metal ions.

The formation of Mn2+- or Cu2+-rifamycin SV complex and the semiquinone radical of rifamycin SV was studied by electron spin resonance spectroscopy. The results indicate that: (1) the complexes Mn2+-rifamycin SV (g parallel = 2.265, g perpendicular = 2.087, A parallel = 177 x 10(-4) cm-1) were formed; (2) in Cu2+-rifamycin SV, Cu2+ was of square-planar type and was ligated to oxygen atoms; (3) the semiquinone radical of rifamycin SV (g = 2.0031) was formed only under aerobic conditions and its formation was inhibited by superoxide dismutase. The formation of hydroxyl radicals during the autoxidation of rifamycin SV was detected by the spin trapping method using N-t-butyl-alpha-phenylnitrone. Superoxide dismutase, mannitol and EDTA inhibited the development of the signal of the spin adduct, indicating that the hydroxyl radical is formed in via the Fenton-type reaction.