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

In mitochondria, cytochrome c oxidase (C c O) 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 C c O. 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 C c O. 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.