Metal ion catalyzed oxidation of the antibiotic rifampicin.

The metal ions Cu++, Mn++ and Co+++, but not Ca++, Fe+++, K+, La+++, Mg++, Na+, Sr++ or Zn++ catalyzed the oxidation of rifampicin from the naphthohydroquinone to the naphthoquinone form. This reaction was pH dependent, and occurred at neutral or basic pH more rapidly than at acidic pH. Mn++ catalyzed the most rapid oxidation, followed by Cu++ and then Co+++. Rifampicin oxidation was metal ion dependent and complete oxidation occurred at metal ion concentrations below stoichiometric values. Initial rate studies suggest that the oxidation mechanism is complex.