A water-soluble supramolecular complex that mimics the heme/copper hetero-binuclear site of cytochrome c oxidase

In mitochondria, cytochrome c oxidase (CcO) catalyses the reduction of oxygen (O(2)) to water by using a heme/copper hetero-binuclear active site. Here we report a highly efficient supramolecular approach for the construction of a water-soluble biomimetic model for the active site of CcO. A tridentate copper(ii) complex was fixed onto 5,10,15,20-tetrakis(4-sulfonatophenyl)porphinatoiron(iii) (Fe(III)TPPS) through supramolecular complexation between Fe(III)TPPS and a per-O-methylated β-cyclodextrin dimer linked by a (2,2′:6′,2′′-terpyridyl)copper(ii) complex (Cu(II)TerpyCD(2)). The reduced Fe(II)TPPS/Cu(I)TerpyCD(2) complex reacted with O(2) in an aqueous solution at pH 7 and 25 °C to form a superoxo-type Fe(III)–O(2)(–)/Cu(I) complex in a manner similar to CcO. The pH-dependent autoxidation of the O(2) complex suggests that water molecules gathered at the distal Cu site are possibly involved in the Fe(III)–O(2)(–)/Cu(I) superoxo complex in an aqueous solution. Electrochemical analysis using a rotating disk electrode demonstrated the role of the FeTPPS/CuTerpyCD(2) hetero-binuclear structure in the catalytic O(2) reduction reaction.