Blue copper proteins: Synthesis, spectra, and structures of Cu I N 3 (SR) and Cu II N 3 (SR) active site analogues

Abstract

The reaction of Cu(SR) or [Cu(SR)][ClO4] derivatives (SR = p-nitrobenzenethiolate or O-ethylcysteinate) with potassium hydrotris(3,5-dimethyl-1-pyrazolyl)borate produces redox pairs of the stoichiometry CuIN3(SR) and CuIIN3(SR). These complexes are well-defined synthetic approximations to the proposed N3S binding sites of blue (type I) copper electron transfer proteins. The compounds were investigated by a variety of chemical and spectral (optical, resonamce Raman and EPR) techniques; the complex K[Cu(hydrotris(3,5-dimethyl-1-pyrazolyl)borate)(p-NO2C6H4S)].cntdot.2 acetone was also studied by single-crystal X-ray diffraction methods. The spectrochemical characteristics of the CuIIN3(SR) species are in large part similar to the native system and provide some perspective regarding the origin of the unique type I spectral parameters and electron transfer properties.