Dept. of Chemistry
Oregon Graduate Center
The infrared and Raman spectra of the N-coordinated bis(biuretat0)-and bis(oxamidat0)-cuprate(II,III) complexes have been recorded, and normal coordinate analyses have been carried out using a Urey-Bradley force field for the copper complexes. The Cu(II)-biuret system undergoes little change upon oxidation to Cu(III), but is characterized by ring tightening and a general increase in mode frequencies. On copper oxidation, the oxamide system undergoes more drastic structural changes, most notably a strengthening of the C-C bond in the oxamide rings, as shown by a 19% increase in K(C-C), and an increase in electron density in the 0-C-C-0 framework. The Wilson GF matrix method of vibrational frequency calculation was used to investigate various possible active site geometries for the " blue" copper protein azurin. Models representing trigonal bipyramidal, square planar, regular tetrahedral, and distorted tetrahedral active sites were examined, and it was found that a distorted tetrahedral, CuN2S2 model most accurately described the observed resonance Raman spectrum. Various active site geometries for the oxygen-carrying proteins hemerythrin and hemocyanin were also examined by the Wilson GF matrix method. The models examined for hemerythrin were Âµ-monooxygen and Âµ-0x0 bridged active site structures. It was determined that the structure which best described the resonance Raman spectrum of oxyhemerythrin, including the available data on the unsymmetrically labeled dioxygen adduct, was one that had a single oxygen of the 02 molecule bound to both iron atoms. This model exhibited a Fe-0-0 angle of 70Â°, whereas the angle made between the 02 bond and the Fe-0-Fe plane was found to be 11l0Â°. A similar experiment utilizing mixed isotope dioxygen was performed on oxyhemocyanin. The resonance Raman data were interpreted in terms of an active site geometry in which the oxygen atoms occupied spectroscopically equivalent position, such as a Âµ-peroxo bridged structure. Wilson GF matrix calculations confirmed the Âµ-peroxomodel as being favorable, but in addition, the calculations describe other favorable models for the active site of oxyhemocyanin. One such model was a Âµ-monooxygen bridge structure which had a Cu-0-0angle of 80Â° and an O2 bond angle of 110Â° with respect to the Cu-0-Cuplane. Such a structure is very similar to the one determined to be favorable for oxyhemerythrin. Normal coordinate analysis, therefore, does not provide unique structures but drastically restricts those possible from the available experimental data.
Thamann, Thomas J., "Structural investigations of the active sites of azurin, hemerythrin, and hemocyanin, and vibrational analyses of the copper (II) and copper (III) complexes of biuret and oxamide" (1979). Scholar Archive. 337.