Electronic structure of the oxidized and reduced blue copper sites: Contributions to the electron transfer pathway, reduction potential, and geometry

This is a review of our group's studies on the electronic structure of the blue copper site and its contribution to function. It starts with the known crystallographic results and demonstrates how spectroscopy allows these results to be extended to obtain fundamental insight into reactivity. These studies: (1) demonstrate that the unique spectral features associated with the oxidized blue copper site reflect a novel ground state wavefunction with high anisotropic covalency which plays a key role in activating specific electron transfer pathways; (2) provide the first description of the electronic structure of the reduced blue copper site obtained using variable energy photoelectron spectroscopy as a new method of bioinorganic spectroscopy and (3) determine the change in electronic structure on oxidation which allows for an evaluation of the Jahn-Teller distorting forces present in the oxidized blue copper site. The last result provides insight into whether the reduced geometry is in fact imposed on the oxidized site by the protein (i.e. the 'entatic' or 'rack' state).