VIBRATIONAL SPECTROSCOPIC STUDIES OF A HYDROXO-BRIDGED DINUCLEAR COPPER COMPLEX, A POTENTIAL MODEL FOR MULTICOPPER PROTEINS

Thc copper complex [Cu2(XYL-O-)(OH)]2+, where XYL = m-xylene connected to two bis[2-(2-pyridyl)ethyl]amine ligands, serves as a potential model for the dinuclear copper sites in hemocyanin, tyrosinase, and thc multicopper oxidases. Resonance Raman (RR) and infrared spectra of the complex reveal a nu(s)(Cu-OH-Cu) mode at 465 cm-1 and a nu(as)(Cu-OR-Cu) mode at 603 cm-1. These represent the first such modes to be definitively identified by isotopic shifts and polarization behavior. These two vibrational modes have RR enhancement maxima at 430 and 460 nm, respectively, indicating that they are associated with different phenolate --> Cu charge-transfer bands. Since no RR enhancement of nu(s)(Cu-OH-Cu) was observed for the homologous mu-alkoxo, mu-OH complex, it appears that coupling to a chromophoric ligand such as phenolate may be important for the observation of M-OH vibrations in the RR spectra of such systems.