Fine tuning of the electronic structure of the dinuclear copper site CuA

A. J. VILA

Encuentro; XVI Brazilian Meeting on Inorganic Chemistry; 2012

CuA is a dinuclear copper site present in the soluble domain of the subunit II of the Cytochrome c oxidase (COX II). This center accepts electrons from reduced Cytochrome c and funnels them to the catalytic site present in subunit I (COX I) where oxygen reduction takes place. These electron transfer reactions are highly efficient despite the long distances and the small driving forces between the redox active centers. This efficiency has been attributed to the unique coordination features of the CuA site, which gives rise to a low reorganization energy and an electronic structure that provides superexchange coupling by means of a high metal-ligand covalency[1]. Two alternative electronic ground states have been established for the CuA center in its oxidized form, a u* and a u level. NMR studies have revealed a fast interconversion between these states which are very close in energy. However u* has been considered as the only redox-active orbital in electron-transfer[2]. Here we show that mutations of the first and second coordination sphere of the CuA center, lead to fine tuning of its electronic structure that favors the population of the u state in the CuA site and, far from being detrimental to the electronic transfer reaction, an alternative pathway compensates the larger reorganization energy of this state.