Cyanocobalamin reduction

Many of these cobalt complexes will catalyze the reduction of organic compounds by borohydride, hydrazine, thiols, etc. Cobalt cyanide complexes will catalyze the reduction of a,j8-unsaturated acids by borohydride (105) DMG complexes the reduction of butadiene and isoprene by borohydride, but not by H2 (124) Co(II) salen, the reduction of CHCI3 and CH3CCI3 to the dichloro compounds by borohydride (116) and cyanocobalamin, the selective reduction of -CCI2- by borohydride to -CHCl- in compounds such as aldrin, isodrin, dieldrin, and endrin without... 

Nijenhuis 1,1 Andert, K Beck, M Kastner, G Diekert, H-H Richow (2005) Stable isotope fractionation of tetrachloroethene during reductive dechlorination by Sulfospirillum multivorans and Desulfitobac-terium sp. strain PCE-S and abiotic reactions with cyanocobalamin. Appl Environ Microbiol 71 3413-3419. 

The reduction of cyanocobalamin gives three possible oxidation states for the cobalt atom (Fig. 2). Electron spin resonance studies with Bi2-r reveals that this molecule is the only paramagnetic species giving a spectrum expected for a tetragonal low spin Co(II) complex. Controlled potential reduction of cyanocobalamin to Bi2-r proves that this reduction involves one electron, and further reduction of Bi2-r to B12-S requires a second single electron (16—19). At one time B12-S was considered to be a hydride of Co(III), but controlled potential coulometry experiments provided evidence against a stable hydride species (16). However, these experimental data do not exclude the possibility of a stable Co(III) hydride as the functional species in enzyme catalyzed oxidation reduction reactions. 

Acid is important in releasing vitamin B12 from food. A minor reduction in oral cyanocobalamin absorption occurs during proton pump inhibition, potentially leading to subnormal Bi2 levels with prolonged therapy. Acid also promotes absorption of food-bound minerals (iron, calcium, zinc) however, no mineral deficiencies have been reported with proton pump inhibitor therapy. 

The quantitative reduction, or photodecomposition by illumination with a powerful light source, of cyanocobalamin liberates hydrogen cyanide, and this may be used to precede the assay stage in pharmaceutical preparations [406] with a cyanide ion-selective electrode at pH 11. 

Some forms of MMA may be responsive to vitamin Bjj. Responsiveness can be determined by administration of 1.0 mg hydroxocobalamin (IM or IV) for 5 days. A reduction in serum methylmalonic acid concentrations of 50 % or greater suggests responsiveness [14]. For those with cobalamin-responsive forms of MMA, intramuscular (IM) hydroxocobalamin injections of 1.0-2.0 mg are often administered daily. A decreased frequency of IM injections or use of oral supplements may be appropriate for older individuals. The hydroxocobalamin form rather than the standard cyanocobalamin form must be used [15]. 

Nykong et al. have also smdied a variety of cobalt containing macrocycles. The electrocatalytic properties of cyanocobalamin adsorbed onto GCEs in aqueous solution was examined Along with adsorbed cobalt(II) tetrasulfonated ph-thalocyanine (Co(TSPc)) ", adsorbed cobalt phthalocyanine is examined (CoPc) in DMSO ". The proposed mechanism invokes both a ring- and metal-centered reduction during NO catalysis, Eqs. (4.35)-(4.39). 

Cyanocobalamin adsorbed onto GCEs also readily reduces NO (nitrite as well), giving sequential reduction peaks associated with the effect of NO ligation onto the Co / and NO reduction Co couples ". ... 

The reduction of cyanocobalamin (b, R=CN) occurs in two one-electron steps, through Bj2r cobalt(II) species which exhibits radical character, to an anionic strongly nucleophilic species. Reduction of the model cobaloxime [Co(dmgH)2Clpy] proceeds similarly. The best route to alkyl derivatives is to react (Cb) with an alkyl halide or tosylate. These (Cb) species are very strong nucleophiles to saturated carbon centres. With tosylates substitution occurs with inversion at carbon, indicating an Sj, 2 mechanism. 

It has traditionally been considered that removal of a cyanide molecule from cyanocobalamin is mediated by the formation of glutathionylcobalamin. However, Rosenblatt s group recently reported that direct reduction by NADPH and fiavoprotein in the presence of a cyanocobalamin trafficking chaperone is more important (Lerner-Ellis et al. 2006). This chaperone was named MMACHC, but Rosenblatt and colleagues have proposed calling it cyanocobalamin decyanase (Figure 47.1). 

Cyanocohalamin tracking chaperone. Cyanocobalamin trafficking chaperone is a molecule which removes a cyanide molecule from cyanocobalamin mediated by a direct reduction by NADPH and fiavoprotein. 

Reduction of cyanocobalamin (Figure 54(a) R = CN) with sodium borohydride affords a diamagnetic grey-green product (Vitamin 6x2 which reacts with acyl or alkyl halides and with olefins to give cobalamin o-organo derivatives. There has been some discussion whether Vitamin 6x2. is a cobaltCO anion or whether it is cobalamin hydride. Some of the... 

In the presence of excess vanadium(v), the third process may be identified as the formation of the dinuclear complex [Ti V, the rate again being directly dependent on hydrogen-ion concentration. Studies have been reported on the reduction of cyanocobalamin (Bja) by titanium(in) in HCl-KCl media, the rate being pseudo-first-order in the presence of excess reductant. 

Reduction of cyanocobalamin with sodium borohydride or zinc and acetic acid affords a diamagnetic, grey-green product (Vitamin B12,) which reacts with acyls, alkyl halides and with olefins to ve cobalamin-[Pg.248]

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