Cobalamins observational studies

Among the other soft ionization techniques is laser microprobe mass spectrometry (LAMMA) in which a laser pulse is used to vaporize a small amount of sample, as discussed in a 1982 review (108). Of interest to us is the application to the study of some cobalamins (109). (M + H) and (M - H) ions were observed in the positive and negative ion modes, respectively. However, there were few other high-mass fragments that could be used to impart structural information. 

Simple alkylcobalt complexes (i.e. those without heteroatomic substituents on the alkyl ligand) are also known to undergo eliminations of cobalt(I) species. Thus Grate and Schrauzer [42] have studied the decomposition of unstable, sterically strained secondary alkyl- and cycloalkyl-cobalamins to form olefins and hydridocobalamin in neutral and acidic solution. In this case the formation of hydridocobalamin was inferred from the observation of monodeuteriohydrogen gas when undeuterated alkylcobalamins were decomposed in DCl/DjO, presumably via Eqns. 42 and 43. 

Three crystal structures of DD [20,217,219] and two of GD [215,220] have been studied, confirming the base-on nature of the boimd corrinoid. Analysis of the crystal structure of DD reconstituted with the coenzyme B12 analogue 5-adeninyl-pentyl-cobalamin (53) [217] helped identify an adenine-binding pocket in the substrate-binding a-subunit. The observed mode of adenine binding allowed the inference of a build-up of strain in the bound adenosyl-cobamide cofactor and activation towards homolysis of the Co - C bond. 

Vitamins Bg, B12 and folate have specific and vital functions in the metabolism a deficiency (or excess) causes specific diseases such as hyperlipidemia, hypertension, obesity or cardiovascular diseases, which are related to a modern lifestyle and common in industrialized countries. As observed in several studies, cobalamin (B12) deficiency in most cases coincides with an insufficient folate status (Ball 2006 Howard et al. 1998 Morris et al. 2007). 

Computational chemistry analysis appears to be helpful as an additional tool to explain the lack of separation between different forms of cobalamins. Recent theoretical studies of the group deal with the electronic and vibrational spectra of some corrins, obtained using density functional theory (DFT) calculations (Andriuniow et al. 2005). The results indicated that, for all the structures used in the calculations, the same electrostatic potential on the molecule was obtained, which supports the observed simultaneous detection of cobalamins, irrespective of the axial ligand (cyano, adenosyl and methyl group). The lack of separation between different forms of cobalamins can be explained by analysis of molecular electrostatic potential (Andriuniow et al. 2005 Lebiedzihska et al. 2007). 

Dioximato-complexes. Studies of dioximato-complexes continue to be extensive probably because of their close similarity to the cobalamins and vitamin B12. Dissociative (often Z>) mechanisms are most commonly observed for the aquation reactions as well as for formations and for ligand exchange. Since these reactions are so similar most of the results will be collected together in this section. References to kinetic studies of aquation,ligand-exchange, and anation reactionsof neutral and anionic complexes of the type /ra 5-[Co(dioxime)2AX] dioxime = [HON=C(R )C(R )=NO] where R and R are alkyl groups are collected in Table 7. 

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