Structural implications derived from the analysis of electron paramagnetic resonance spectra of natural and artificial copper proteins

An extension of a method relating chemical structure to the EPR parameters A ∥ and g ∥ is presented. For complexes having the same atoms of ligation, a decrease in charge of the metal-ligand complex decreases g ∥ and increases A ∥. From this analysis, one concludes that in artificial copper proteins as well as in the naturally occurring nonblue copper proteins copper is ligated to oxygen and nitrogen but not to sulfur. A method is presented for the interpretation of EPR changes that occur with ligand exchange reactions at the Type 2 (nonblue) copper sites such as occur in laccase.