Multiple four-coordinate forms in a nickel hydrocorphinate related to cofactor F430 of methylreductase
| Autor: | John A. Shelnutt |
|---|---|
| Rok vydání: | 1989 |
| Předmět: |
Cofactor F430
Absorption spectroscopy Stereochemistry Resonance Raman spectroscopy General Engineering Analytical chemistry Resonance chemistry.chemical_element chemistry.chemical_compound symbols.namesake Nickel chemistry symbols Physical and Theoretical Chemistry Spectroscopy Raman spectroscopy Raman scattering |
| Zdroj: | The Journal of Physical Chemistry. 93:6283-6290 |
| ISSN: | 1541-5740 0022-3654 |
| Popis: | Four- and 6-coordinate forms of a nickel(II) hydrocorphinate model of cofactor F{sub 430} of the methyl-coenzyme M methylreductase were investigated by using resonance Raman spectroscopy. The 6-coordinate complexes have Raman spectra showing only a single species at room temperature and at 77 K in frozen solutions. The 6-coordinate complexes are characterized by the two highest frequency, strong lines in the 1550-1560- and 1620-1630-cm{sup {minus}1} regions. There is a variation in the frequencies of these two marker lines with the particular axial ligand, but the separation of the lines remains relatively constant at 67-74 cm{sup {minus}1}. The separation of these two lines is an indicator of the nickel coordination number for the hydrocorphinate. The separation for a 5-coordinate complex is 81 cm{sup {minus}1}, and for the major 4-coordinate form the separation is about 93 cm{sup {minus}1}. Raman spectra of 4-coordinate nickel hydrocorphinates show evidence of multiple species both at room temperature and at 77 K. Besides the previously identified 4-coordinate form, we have now identified two other forms. One of the newly identified species is detected in room temperature Raman spectra taken with preresonance excitation and is observed also in frozen solutions. The other new 4-coordinate form is positively detected onlymore » in frozen samples. The new room temperature form has a red-shifted absorption spectrum based on resonance enhancement of its Raman scattering with excitation to the red of the absorption maximum. This red shift is consistent with the observed 20-nm red shift in the absorbance maximum upon freezing at 77 K, under which conditions the new species dominate. A structural interpretation of the 4-coordinate forms is proposed based on molecular mechanics calculations for the nickel hydrocorphinate enantiomers.« less |
| Databáze: | OpenAIRE |
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