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Abstract: This review deals with results from crystallographic studies on proteins that interact with the essential micronutrient cobalamin (vitamin B12). Both B12-dependent enzymes and B12-transport proteins are described with an emphasis on structural aspects of cobalamin and its protein environment. [Copyright &y& Elsevier]

Redox potentials of a series of complexes of cobalt(II) and organocobalt(III) with tetraazamacrocyclic (N) and NO-noncyclic polychelate ligands have been determined by cyclic voltammetry. Introduction of an o-phenylene fragment instead of an ethylene fragment into an equatorial ligand and/or exchange of an N-coordination chromophore for the NO-analog has been shown to result in the anodic shift of redox potentials of MeCo(IV)L/ MeCo(III)L, MeCo(III)L/MeCo(II)L, and Co(II)L/Co(I)L pairs. It has been established that the solvent effect on redox potential is larger for Co(III)L/Co(II)L than for other pairs. Apparently, this is the first case when quasi-reversible stages of oxidation of MeCo(III)L to MeCo(IV)L and MeCo(IV)L to [MeCo(IV)L] can be simultaneously observed. A. relatively stable complex of methylcobalt(IV) with a long lifetime at ∼20 °C has been registered by the ESR method. [ABSTRACT FROM AUTHOR]

Bioorganometallic structure found in coenzyme B 12 is a key component in B 12 -dependent enzymatic reactions in natural enzymes. Cleavage of a cobalt-carbon bond in organometallic B 12 compound provide reactive intermediate for molecular transformations. Application of the bioorganometallic B 12 in organic synthesis have been developed using natural vitamin B 12 as well as synthetic vitamin B 12 derivatives as a bioinspired catalyst in organic solvent. Vitamin B 12 derivatives composed of corrinoid structure should form stable organometallic compound having a cobalt-carbon bond. Using the unique property of the organometallic vitamin B 12 derivatives, various catalytic reactions have been developed in synthetic organic chemistry. The dual catalytic system of vitamin B 12 derivatives and photocatalyst, such as Ru(II) polypyridyl complex or titanium oxide, could construct light-driven molecular transformations. The B 12 -dependent enzymes mimic reactions, such as the dechlorination of organic halides and the radical mediated isomerization reactions, catalytically proceed in the dual catalyst system. Electroorganic syntheses mediated by the vitamin B 12 derivatives have been developed as green molecular transformations. The redox active vitamin B 12 derivatives shows a unique catalysis in the electroorganic synthesis, such as alkene and alkyne reductions., (Copyright © 2022 Elsevier Inc. All rights reserved.)