Date

2-1-1997

Document Type

Dissertation

Degree Name

Ph.D.

Department

Dept. of Chemistry

Institution

Oregon Graduate Institute of Science & Technology

Abstract

Four different redox-active metal clusters with unusual properties were studied by resonance Raman (RR) spectroscopy. Two dizirconium compounds, {[(Pr[superscript i][subscript 2]PCH[subscript 2]SiMe[subscript 2])[subscript 2]N]Zr(η[superscript 5]-C[superscript 5]H[subscript 5])}[subscript 2](µ-η1:η1-N2) and {[Pr[superscript i]2PCH2SiMe2)xN]ZrCl}2(µ-η²:η²-N2) serve as spectroscopic models for nitrogen activation. Resonance Raman spectra of these compounds reveal ν(N-N) modes at 1211 and 731 cm-1, respectively. These frequencies imply N-N bond orders of ~1 and less than 1, respectively. The high degree of N2 activation in these compounds suggests that N2 activation by nitrogenase is possible with N2 bound with either "end-on" or "side-on" geometry to two or more metal atoms. Resonance Raman spectra of [Fe2O(Ph3CCOO)2(Me3tacn)2]X (X = CF3SO3 or BPh4) show that the intensity of ν23(Fe-O-Fe) at ~702 cm[superscript -1] is unusually high. This is ascribed to structural asymmetry, thereby providing evidence for a trapped-valence (Fe²+/Fe³+) species. Retention of the µ-[superscript 18]O ligand during the oxidation of [Fe2(18OH)(PH3CCOO)2(ME3tacn)2]X by O2, H2O2, or R3NO, proves that electron transfer proceeds via an outer-sphere mechanism. This is in contrast to the inner-sphere mechanism proposed for ribonucleotide reductase and Fe2(O2CH)4(BIPhMe)2. Cellobiose dehydrogenase from Phanerochaete chrysosporium contains a flavin adenine dinucleotide and a b-type heme on separate domains of the monomeric protein. Raman excitation of the oxidized holoprotein at 413.1 nm results in photoreduction of the heme, displaying ν4 at ~1362 cm[superscript -1] However, excitation of deflavoCDH or the isolated heme domain under identical conditions did not cause photoreduction. These observations suggest that electron transfer proceeds from the flavin to the heme, as in flavocytochrome b2 from Saccharomyces cerevisiae. A transient iron-tyrosinate intermediate forms upon addition of Fe²+ and O2 to wild type and mutant frog H-chain apoferritin. The half-life of decay of this intermediate recorded by electronic or RR spectroscopy is very similar, indicating that the two analytes are the same. Studies on H-, M- and L-chain mutants imply that a specific tyrosine (probably Tyr136 or Tyr147) is responsible for color formation in frog FTN-H but a different residue (probably Tyr30) is responsible for rapid ferroxidation in human FTN-H and frog FTN-M. Ferroxidase activity could be due to a stable diiron cluster that catalyzes electron transfer or to a mobile cluster that is autocatalytic.

Identifier

doi:10.6083/M4MC8X0D

Share

COinS
 
 

To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.