Nonsymmetric substitution of salen (1(R1,R2)) and reduced salen (2(R1,R2)) Cu-II-phenoxyl complexes with a combination of -Bu-t, -(SPr)-Pr-i, and -OMe substituents leads to dramatic differences in their redox and spectroscopic properties, providing insight into the influence of the cysteine-modified tyrosine cofactor in the enzyme galactose oxidase (GO). Using a modified Marcus-Hush analysis, the oxidized copper complexes are characterized as Class II mixed-valent due to the electronic differentiation between the two substituted phenolates. Sulfur K-edge X-ray absorption spectroscopy (XAS) assesses the degree of radical delocalization onto the single sulfur atom of nonsymmetric [1(tBu,SMe)](+) at 7%, consistent with other spectroscopic and electrochemical results that suggest preferential oxidation of the -SMe bearing phenolate. Estimates of the thermodynamic free energy difference between the two localized states (Delta G degrees) and reorganizational energies (lambda(R1R2)) of [1(R1,R2)](+) and [2(R1,R2)](+) lead to accurate predictions of the spectroscopically observed IVCT transition energies. Application of the modified Marcus-Hush analysis to GO using parameters determined for [2(R1,R2)](+) predicts a nu(max) of similar to 43600 cm(-1), well within the energy range of the broad Vis-NIR band displayed by the enzyme.