Electronic structure of the perturbed blue copper site in nitrite reductase: Spectroscopic properties, bonding, and implications for the entatic/rack state
- Stanford Univ., CA (United States)
- Univ. of Virginia, Charlottesville, VA (United States)
Low-temperature optical absorption, circular dichroism, magnetic circular dichroism, and sulfur K-edge X-ray absorption spectra have been measured for the green `blue` copper center (type 1) in Achromobacter cycloclastes nitrite reductase. Combined with density functional calculations, the results of these spectroscopies have been used to define the extremely `perturbed` electronic structure of this site relative to that of the prototypical `classic` site found in plastocyanin. Experimentally calibrated density functional calculations have been further used to determine the specific geometric distortions which generate the perturbed electronic structure. These studies indicate that the principal electronic structure changes in nitrite reductase, relative to plastocyanin, are a rotation of the Cu d{sub x(2)-y(2)} half-filled, highest occupied molecular orbital (HOMO) and an increase in the ligand field strength at the Cu center. These changes in Cu-ligand interactions result in the redistribution of absorption intensity in the charge transfer and ligand field transitions. Additionally, the new S(Met)-Cu interaction accounts for the unexpectedly high sulfur covalency in the HOMO. The increase in ligand field strength shifts all the d {yields} d transitions in nitrite reductase to nearly 1000 cm{sup -1} higher energy than their counterparts in plastocyanin, which accounts for the EPR spectral differences between the type 1 sites in these complexes. 97 refs., 7 figs., 3 tabs.
- OSTI ID:
- 374502
- Journal Information:
- Journal of the American Chemical Society, Vol. 118, Issue 33; Other Information: PBD: 21 Aug 1996
- Country of Publication:
- United States
- Language:
- English
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