The chemistry of vitamin B12. Part 23. Decomposition of the cobalt(I) cobalamin B12s in aqueous solution; a novel oscillating reaction

Chemaly, Susan M.; Hasty, R. A.; Pratt, J. M.

doi:10.1039/dt9830002223

Cited by 8 publications

(9 citation statements)

References 3 publications

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“…3 x rnol dm-3) of the very reactive and probably 4-coordi-nate13 Col-Cbl (Cbl = cobalamin) were prepared by reducing deoxygenated solutions of aquo-Cbl (B12a) under nitrogen with Naf3H4 in the presence of Co(NO3)2 as catalyst.14 Reactions were studied by UV-VIS spectrophotometry in a 1 cm pathlength cell thermostated at 25 "C; such studies are limited to pH > 3 because of the increasing rate of evolution of H2 bubbles with increasing acidity. 14 Col-Cbl reacts with the PhNMe3+ ion 1 (cf. PhNMe2 pK 5.1) as the chloride to give Me-Cbl,?…”

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confidence: 99%

Methyl transfer from nitrogen to cobalt: model for the B12-dependent methyl transfer enzymes

Pratt¹,

Norris²,

Hamza³

et al. 1994

J. Chem. Soc., Chem. Commun.

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The Co atom can be methylated by reaction of the Col cobalamin with the PhNMe3+ ion in aqueous solution at 25 "C at a pH-independent rate (pH 4-10) with the second-order rate constant k2 = 2 X 10-3 dm3 mol-1 s-1.Methyl transfer is the simplest nucleophilic substitution reaction, as well as one of the most extensively studied and best understood of all organic reactions.' Little is known, however, about the first transfer of a de novo synthesised Me group from the N5 of N-Me-THFA (THFA = tetrahydrofolic acid) to the S of homocysteine to form methionine, for which nature has evolved two families of enzymes.* In the BIZdependent enzymes the mechanism involves the alternate formation of CoI and Me-Co corrinoids; in the less efficient B12-independent enzymes there is no evidence for any prosthetic group. N-Me donors able to methylate thiols nonenzymatically and provide a model for the B12-independent pathway include N-Me-py+ ,334 PhNMe3+ ,4 N5-Me-THFA

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confidence: 99%

Methyl transfer from nitrogen to cobalt: model for the B12-dependent methyl transfer enzymes

Pratt¹,

Norris²,

Hamza³

et al. 1994

J. Chem. Soc., Chem. Commun.

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“…The formed hydride ion could reduce the metal(loid)s and form volatile hydride species. Nevertheless, we suggest another mechanism, as Cob(I) decomposes slowly with a half‐life of 22 min at pH 7 in aqueous solution in the absence of O 2 according to equation (2):

Cob (normalI) + H_{2} O \to Cob (II) +^{-} OH + ½ {normalH}_{2}

…”

Section: Resultsmentioning

confidence: 93%

Mechanism of multi‐metal(loid) methylation and hydride generation by methylcobalamin and cob(I)alamin: a side reaction of methanogenesis

Wuerfel

Thomas

Schulte

et al. 2012

Applied Organom Chemis

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a Metal(loid)s are subject to many transformation processes in the environment, such as oxidation, reduction, methylation and hydride generation, predominantly accomplished by prokaryotes. Since these widespread processes affect the bioavailability and toxicity of metal(loid)s to a large extent, the investigation of their formation is of high relevance. Methanogenic Archaea are capable of methylating and hydrogenating Group 15 and 16 metal(loid)s arsenic, selenium, antimony, tellurium, and bismuth due to side reactions between central methanogenic cofactors, methylcobalamin (CH 3 Cob(III)) and cob(I)alamin (Cob(I)). Here, we present systematic mechanistic studies on methylation and hydride generation of Group 15 and 16 metal(loid)s by CH 3 Cob(III) and Cob(I). Pentavalent arsenical species showed neither methylation nor reduction as determined by using a newly developed oxidation state specific hydride generation technique, which allows direct determination of tri-and pentavalent arsenic species in a single batch. In contrast, efficient methylation of trivalent species without a change in oxidation state indicated that the methyl transfer does not proceed via a Challenger-like oxidative methylation, but via a non-oxidative methylation. Our findings also point towards a similar mechanism for antimony, bismuth, selenium, and tellurium. Overall, we suggest that the transfer of a methyl group does not involve a free reactive species, such as a radical, but instead is transferred either in a concerted nucleophilic substitution or in a caged radical mechanism. For hydride generation, we propose the intermediate formation of hydridocobalamin, transferring a hydride ion to the metal(loid)s.

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“…28 We have now re-examined the electron transfer reactions of the Cbi by uv-vis spectroelectrochemistry 29 and report hysteresis for both couples. Oscillations with a basic periodicity of 4-5 min and independent of pH 2-12 were reported in 1983 for the decomposition of Co(I) to Co(II) Cbl in homogeneous aqueous solution at 35°C 12 and later for Co(I) Cbi, 8b i.e. the nucleotide side-chain is not required for the observation of oscillations.…”

Section: Introductionmentioning

confidence: 93%

“…We focus here, however, on some extraordinary properties of corrinoids such as hysteresis 10 in redox reactions and dual fluorescence in emission, 11 which have both been known but generally ignored for almost 30 years, and on the more recently discovered oscillatory reactions. 12 They all suggest 3c the existence of one or more additional conformations of the corrin structure. Oscillations require a feed-back mechanism and are associated with the occurrence of hysteresis or other more complex forms of multiple stationary states.…”

Section: Introductionmentioning

confidence: 98%

See 1 more Smart Citation

Vitamin B12 as an allosteric cofactor; dual fluorescence, hysteresis, oscillations and the selection of corrin over porphyrinThe chemistry of vitamin B12. Part 32. For part 31, see ref. 1.

et al. 2004

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Studies of the emission spectra of four Co(III) cobinamides (diaquo-, aquohydroxo-, dihydroxo- and dicyano-) show (1) that the excited states corresponding to the alphabeta and epsilon absorption bands behave like the S(1) and S(2) levels in the non-alternant hydrocarbon azulene (with emission from S(2)>> S(1) in violation of Kasha's rule) and (2) that the excited states include a TICT (twisted intramolecular charge transfer) mechanism, as in the simpler cyanines, but where the TICT state gives rise to dual fluorescence instead of cis-trans isomerisation. Combined with the previously reported dual fluorescence from the S(1) level in synthetic metal corrinoids and in the naturally-occurring metal-free corrin, this provides evidence that the existence of an additional (metastable) ground state with a significantly different vibronic splitting and nuclear configuration is an intrinsic property of the basic corrin ligand (irrespective of the nature of the side-chains and the metal ion or even the absence of a metal) which distinguishes it from porphyrin. The occurrence of hysteresis (and its associated oscillations) in redox reactions of the cobinamides involving both the Co(III/II) and Co(II/I) couples indicates that the corrin ligand also has an intrinsic ability to exist in different conformations or "allosteric" forms with differing redox potential, which further distinguishes it from the porphyrin ligand. Possible links between the existence of an additional metastable ground state and of allosteric changes and the likely reasons for the selection of corrin over a porphyrin for the vitamin B(12)-dependent enzymes are discussed.

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The chemistry of vitamin B12. Part 23. Decomposition of the cobalt(I) cobalamin B12s in aqueous solution; a novel oscillating reaction

Cited by 8 publications

References 3 publications

Methyl transfer from nitrogen to cobalt: model for the B12-dependent methyl transfer enzymes

Methyl transfer from nitrogen to cobalt: model for the B12-dependent methyl transfer enzymes

Mechanism of multi‐metal(loid) methylation and hydride generation by methylcobalamin and cob(I)alamin: a side reaction of methanogenesis

Vitamin B12 as an allosteric cofactor; dual fluorescence, hysteresis, oscillations and the selection of corrin over porphyrinThe chemistry of vitamin B12. Part 32. For part 31, see ref. 1.

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