Oxyhemocyanin peroxide bridging

Figure 13. Electronic structures of end-on and side-on peroxide bridged models of oxyhemocyanin. Comparison of experimentally determined peroxide a-donor and w-acceptor abilities.

Fig. 35. Diagrammatic explanation of the transition dipole vector coupling treatment for two possible peroxide bridging geometries, /<-dioxo and ft-monooxo, and comparison to oxyhemocyanin (see text for explanation)...

Baldwin MJ, Root DE, Pate JE, Fujisawa K, Kitajima N, Solomon EL 1992. Spectroscopic studies of side-on peroxide-bridged binuclear copper(II) model complexes of relevance to oxyhemocyanin and oxytyrosinase. JAm Chem Soc 114 10421-10431. 

Many investigators reported that the two copper ions are bridged by the peroxide dianion in oxyhemocyanin (6, 7, 8). We also observed a similar O—O stretching vibration at around 750 cm-1 in the resonance Raman spectrum ofS. lessoniana oxyhemocyanin, as illustrated in Figure 3 (Curve A). The purple hemocyanin also exhibits the charac-... 

The fact that three peroxide-to-copper charge-transfer transitions are observed in oxyhemocyanin and oxytyrosinase led us to consider the spectral effects of bridging peroxide between two Cu(II) ions. A transition-dipole vector-coupling (TDVC) model was developed that predicts that each charge-transfer state in a Cu-peroxide monomer... 

It was of critical importance to evaluate experimentally this unusual electronic structure description for the side-on bridged peroxide and its relation to the spectral features of the p-rt2 rj2 model complex and oxyhemocyanin. This evaluation was accomplished through a series of... 

The structure of oxyhemocyanin has recently been determined.It presents yet a third mode of binding between oxygen-carrying metal atoms and the dioxygen molecule. The latter oxidizes each copper(I) to copper(Il) and is in turn reduced to the peroxide ion (O ). The two copper(ll) atoms are bridged by the peroxide ion with unusual ix-jf-.T] bonds, i.e., each oxygen atom is bonded to both copper atoms. 

Thamann, Loehr and Loehr73) continued to examine the 0—0 stretch using unsymmetrically labelled 02 (1602 + 1802 + 160 180) by the resonance Raman method. They found three Raman peaks at 749,728 and 708 cm-1 for the labelled molluscan oxyhemocyanin and the peak intensities were the same as observed for the 02 gas mixture used. That requires that both oxygen atoms be equivalent in the bound form and strongly supports a bridging peroxide between the two Cu (II) ions. A terminal symmetrical peroxide (a) would be expected to have an... 

Scatter diagram showing the distribution of O — O stretching frequencies and separations in ionic superoxides and peroxides (A) and in coordination compounds. An open circle denotes O2 coordinated to one metal a filled circle denotes O2 bridging two metals. The O — O stretching frequencies of oxyhemoglobin, oxyhemocyanin, and oxyhemerythrin are marked by dashed lines. 

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