A water-soluble supramolecular complex that mimics the heme/copper hetero-binuclear site of cytochrome 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. The O 2 adduct of an aqueous synthetic heme/copper model system built on a porphyrin/cyclodextrin supramolecular complex has been characterized.