Catalysis by Haemin of some Molybdenum (VI) Oxidations

Abstract

WE report a novel series of oxidations by molybdenum (VI) in acid solution, catalysed by trace amounts of biologically important ferric complexes. These systems extend our knowledge of the catalytic action of haem centres in redox processes and, because of the remarkable specificity involved, may help to investigate isopolyanion equilibria. Catalysts include haemin (ferric protoporphyrin IX), catalase, methaemoglobin and metmyoglobin, although free haemin may be the active catalytic species in each case because the proteins are degraded in acid medium. Reducing substrates include iodide and cuprous, ferrous and thiosulphate ions. None of these species is oxidized at a significant rate in the absence of catalyst. The reduced molybdenum species is deep blue and is probably the molybdenum blue readily formed in the absence of catalyst by the action of powerful reducing agents on molybdenum (VI).