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

The reaction of Cu(SR) or [Cu(SR)][ClO(4)] derivatives (SR = p-nitrobenzenethiolate or O-ethylcysteinate) with potassium hydrotris(3,5-dimethyl-1-pyrazolyl)borate produces redox pairs of the stoichiometry Cu(I)N(3)(SR) and Cu(II)N(3)(SR). These complexes are well-defined synthetic approximations to the proposed N(3)S binding sites of blue (type 1) copper electron transfer proteins. The compounds were investigated by a variety of chemical and spectral (optical, resonance Raman, and electron paramagnetic resonance) techniques; the complex K[Cu(hydrotris(3,5-dimethyl-1-pyrazolyl)borate)(p- NO(2)C(6)H(4)S]-2 acetone was also studied by single-crystal x-ray diffraction methods. The spectrochemical characteristics of the Cu(II)N(3)(SR) species are in large part similar to the native system and thus provide some perspective regarding the origin of the unique type 1 spectral parameters and electron transfer properties.