Paramagnetic Products of the Oxidation of Cyanocobaltate(II)

Bayston, JH; Looney, FD; Winfield, ME

doi:10.1071/ch9630557

Cited by 35 publications

(21 citation statements)

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“…This spectrum is typical of many Co(II)-oxygen adducts studied in recent years (see, e.g. Bayston et al, 1969;Cockle et al, 1970;Hoffman et al, 1970) (Bayston et al, 1963). The same signal was of course generated in enzymecyanide solutions prepared aerobically, but it should be emphasized that the process giving rise to it was quite irreversible.…”

Section: Complexsupporting

confidence: 57%

“…These and other considerations (Hoffman et al, 1970) indicate that the unpaired spin now resides mainly on the 02 ligand, with cobalt formally oxidized to Co(III). The fact that irreversible oxidation does not occur, as for example with [Co(CN)5]3-, is due in part to the impossibility of obtaining a peroxo-bridged dicobalt species, which is usually the next intermediate (Bayston et al, 1963).…”

Section: Discussionmentioning

confidence: 99%

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Electron-paramagnetic-resonance studies on cobalt(II) carbonic anhydrase. Low-spin cyanide complexes

Cockle

1974

Biochemical Journal

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The low-spin cyanide complexes of three Co(II) carbonic anhydrases were investigated by electron paramagnetic resonance (e.p.r.) at 9 and 35GHz. Well-defined and closely axial spectra were obtained only in the absence of oxygen. Several mole equivalents of cyanide were required for complete formation of the complexes in frozen solution, although large excesses caused abstraction of the cobalt. Experiments with [(13)C]cyanide showed that the low-spin complexes contained two CN(-) groups in an environment similar to that of the in-plane ligands in [Co(CN)(5)](3-). A combined e.p.r. and spectrophotometric titration confirmed the presence of two CN(-) ligands. A 5-co-ordinate square pyramidal structure involving three protein ligands was proposed. The dicyanide complex could be oxygenated reversibly, producing a characteristic new e.p.r. spectrum. The O(2) molecule was thought to occupy the remaining octahedral metal site in a formally Co(III) species. The optical spectrum of the dicyanide lacked the prominent d-d bands of the high-spin monocyanide. Both e.p.r. and optical data indicated that the low-spin complex was formed much more fully in frozen solution than at room temperature. Differences in behaviour between the high- and low-activity enzymes suggested some variation in conformational flexibility at the metal binding site.

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Section: Complexsupporting

confidence: 57%

Section: Discussionmentioning

confidence: 99%

Electron-paramagnetic-resonance studies on cobalt(II) carbonic anhydrase. Low-spin cyanide complexes

Cockle

1974

Biochemical Journal

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“…The techniques used for obtaining electron paramagnetic resonance spectra of cobaltous complexes in an atmosphere of argon, including gas purification, have been dealt with in published papers (Bayston and Winfield, 1967;Bayston et al, 1963Bayston et al, , 1969. Coupling constants and g values were also determined as before (Bayston et al, 1969).…”

Section: Methodsmentioning

confidence: 99%

Electron paramagnetic resonance studies of cob(II)alamin and cob(II)inamides

Bayston¹,

Looney²,

Pilbrow³

et al. 1970

Biochemistry

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Although the water molecule in the fifth coordination position of diaquocob(II1)inamide is easily replaced by imidazole-or pyridine-like molecules, the other aquo group is replaced less readily. On reduction to the cobaltous state the group in the sixth coordination position detaches. The bond to the fifth ligand is weakened, so that in general there is some replacement by solvent, but ligands such as imidazole

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“…Elsewhere we have listed eight conceivable ways in which activation by the metal may commence1 2345and have, together with other groups of investigators (see, for example, references 2-4), provided some experimental evidence for the reality of four of them. 1,[5][6][7][8] Pauling9 and many later investigators have studied the reversible complexing of 02 to give a diamagnetic mono-nuclear product such as oxymyoglobin. Neither partner behaves as a free radical.…”

mentioning

confidence: 99%

Superoxocobalamin, the first intermediate in the autoxidation of vitamin B12

Bayston¹,

King²,

Fd³

et al. 1969

J. Am. Chem. Soc.

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Crystalline cob(II)alamin (vitamin B12r) and its solutions in various liquids react reversibly with 02 to yield a complex which is shown by epr spectroscopy to be mononuclear. In accord with the known shielding of the cobalt atom of the cobalamin against collision with large molecules, the mononuclear product of oxygenation does not combine with a second cob(II)alamin molecule to give a dicobalt complex. Eight hyperfine lines are found in the spectrum of methanolic solutions of oxygenated cob(II)alamin at temperatures close to the melting point. The coupling constant due to the cobalt nucleus is 12 G. At about 159°K there is a transition attributed to cessation of tumbling to give a spectrum different in over-all shape and in having an additional set of eight hyperfine lines. Superhyperfine structure due to the coordinated nitrogen atom of dimethylbenzimidazole is lost on oxygenation. Comparison with the hyperfine coupling constants of related binuclear complexes indicates that oxygenated cob(II)alamin may be regarded as superoxocobalamin, most of the unpaired spin density being concentrated at the coordinated 02 •" group. Detection of a reversibly formed mononuclear product of oxygenation establishes the first reaction step in the autoxidation of Bi2r and indicates the likelihood of transient occurrence of mononuclear superoxo complexes during autoxidation of hemoproteins. When cob(II)inamides are oxygenated the epr signals obtained resemble those from superoxocobalamin at temperatures below 159°K. The hyperfine coupling constants may be larger or smaller than for superoxocobalamin, depending upon whether the strength of bonding of the fifth ligand is less or greater than that for the nucleotide in the cobalamin.

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Paramagnetic Products of the Oxidation of Cyanocobaltate(II)

Cited by 35 publications

References 0 publications

Electron-paramagnetic-resonance studies on cobalt(II) carbonic anhydrase. Low-spin cyanide complexes

Electron-paramagnetic-resonance studies on cobalt(II) carbonic anhydrase. Low-spin cyanide complexes

Electron paramagnetic resonance studies of cob(II)alamin and cob(II)inamides

Superoxocobalamin, the first intermediate in the autoxidation of vitamin B12

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