Catalysis of the autoxidation of carbon monoxide by cobalt corrins

Bayston, James H.

doi:10.1016/0021-9517(67)90247-3

Cited by 16 publications

(4 citation statements)

References 9 publications

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“…Buffering the solution at pH 7.3 with phosphate did not affect the result. The same poor resolution was observed when Blzr was produced by reduction of aquocobalamin in the pH 7.3 buffer by CO (Bayston and Winfield, 1967), or by HCOOK. A sharper spectrum was obtained from a sample of crystalline B12r in argon ( Figure 1A).…”

Section: Cob(iandlaminmentioning

confidence: 57%

“…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%

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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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Section: Cob(iandlaminmentioning

confidence: 57%

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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“…Wasserstoffdruck wahrend 3 Tagen wurde ebenfalls in 92% Ausbeute (nach Chromatographie) nur der Reaktand 1 isoliert; reduzierte oder isomerisierte Produkte konnten nicht nachgewiesen werden. Die Herstellbarkeit von Cob (1I)alamin ausgehend von Aquocob-(1II)alamin unter einer Wasserstoffatmosphare ohne zusatzlichen Katalysator wurde aber auch in der Literatur in Zweifel gezogen [4]. Bei Zugabe eines Platin-oder Palladium-Katalysators ist die Reduktion zu Cob (1I)alamin rnit elementarem Wasserstoff hingegen gut belegt und mehrfach bestatigt [5-81.…”

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Cob(I)alamin als Katalysator, 5. Mitteilung [1]. Enantioselektive Reduktion α,β‐ungesättigter Carbonylderivate

Fischli

Süß

1979

Helvetica Chimica Acta

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Cob(1)alamin as Catalyst. 5. Communication Ill. Enantioselective Reduction of a,/l-Unsaturated Carbony1 Derivatives SummaryThe cob (1)alamin-catalyzed reduction of an a,B-unsaturated ethyl ester in aqueous acetic acid produced the (S)-configurated saturated derivative 2 with an enantiomeric excess of 21%. The starting material 1 is not reduced at pH= 7.0 in the presence of catalytic amounts of cob(1)alamin (see Scheme 2). It is shown that the attack of cob(1)alamin and not of cob(II)alamin, also present in Zn/CH,COOH/ H,O, accounts for the enantioselective reduction observed. All the (2)-configurated starting materials 1, 3, 5, 7, 9 and 11 have been transformed to the corresponding (S)-configurated saturated derivatives 2,4, 6,8, 10 and 12, respectively. The highest enantiomeric excess revealed to be present in the saturated product 12 (32,7%, S) derived from the (2)-configurated methyl ketone 11 (see Scheme 3 and Table 1). The reduction of the (E)-configurated starting materials led mainly to racemic products. A saturated product having the (R)-configuration with a rather weak enantiomeric excess (5.9%) has been obtained starting from the (a-configurated methyl ketone 23 (see Scheme 5 and Table 2). The allylic alcohols 16 and 24 have been reduced to the saturated racemic derivative 17.

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“…Gas trains for purification of tank argon and carbon monoxide were as described earlier. 13 Spectrometry. When epr measurements and unpaired spin concentrations were required on solutions to be examined spectrophotometrically (for determination of the initial and final concentrations of aquocobalamin) they were performed as described earlier6 in a cell in which a quartz epr sample tube was sealed at right angles to a quartz Thunberg cuvette.…”

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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Catalysis of the autoxidation of carbon monoxide by cobalt corrins

Cited by 16 publications

References 9 publications

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

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

Cob(I)alamin als Katalysator, 5. Mitteilung [1]. Enantioselektive Reduktion α,β‐ungesättigter Carbonylderivate

Superoxocobalamin, the first intermediate in the autoxidation of vitamin B12

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