Electrochemical and structural studies of transition metal complexes as models for oxygen binding and electron transfer hemoproteins

Thesis/Dissertation · Tue Jan 01 04:00:00 EST 1985

OSTI ID:7170818

Srivatsa, G S

The low-temperature (77K) EPR spectrum for the /sup 57/Fe enriched complex of the one-electron reduction product of Fe(II) tetraphenyl porphyrin, (Fe(TPP))/sup -/ exhibits hyperfine structure on the g/sub parallel/ = 1.93 signal, but no hyperfine structure on the g/sub perpendicular/ = 2.28 signal. In the presence of pyridine the g/sub parallel/ signal of the (/sup 56/Fe(TPP))/sup -/ exhibits well resolved /sup 14/N hyperfine structure, due to axial ligation of a signal nitrogen base, consistent with a low-spin d/sup 7/Fe(I) formulation for (Fe(TPP))/sup -/ with little or no porphyrin ..pi..-anion character. At room temperature, the resonance Raman vibrational frequencies of (Fe(TPP))/sup -/ are within 2 cm/sup -1/ of those for Fe/sup parallel/(TPP), again consistent with an Fe(I) formulation. In Me/sub 2/SO, addition of OH/sup -/ to (Fe/sup III/(TPP))/sup +/, results in a negative shift of the Fe(III)/Fe(II) redox couple from E/sub pc/ = -0.14 V to E/sub pc/ = -0.74 V vs. SCE. Under basic conditions, oxidation of tetrakis (3,5-di-tert-duryl-4-hydroxyphenyl)porphine (TDPH/sub 2/) and its Zinc(II) derivative, (ZnTDP) resulting in a stable semiquinone anion species. Both TDPH/sub 2/ and ZnTDP cause the catalytic electroreduction of O/sub 2/ by promoting the disproportionation of superoxide ion. In aprotic media, the combination of the dianion of toluene-3,4-dithiol (TDT/sup 2 -/) with divalent transition metals yields a stable, but oxygen-sensitive complex (M(II)(TDT)/sub 2/)/sup 2 -/. The site of electron transfer in the oxidation of (M(II)(TDT)/sub 2/)/sup 2 -/ to (M(TDT)/sub 2/)/sup -/ has been assigned to a bound sulfide group which spin pairs with an unpaired electron of the transition metal to yield a stable d/sup n/.SR covalent bond on the basis of the observed redox potentials, optical spectra and magnetic properties.

• Research Organization: California Univ., Riverside (USA)
• OSTI ID: 7170818
• Country of Publication: United States
• Language: English

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
CARBOXYLIC ACIDS
COMPLEXES
ELECTRON SPECTRA
ELECTRON SPIN RESONANCE
ELECTRON TRANSFER
ELEMENTS
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
INTERMEDIATE MASS NUCLEI
IRON 56
IRON 57
IRON COMPLEXES
IRON ISOTOPES
ISOTOPES
LASER SPECTROSCOPY
MAGNETIC RESONANCE
MOLECULAR STRUCTURE
NONMETALS
NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXYGEN
PORPHYRINS
RAMAN SPECTROSCOPY
RESONANCE
SPECTRA
SPECTROSCOPY
STABLE ISOTOPES
TRANSITION ELEMENT COMPLEXES