Quantitative determination of vitamin b12 by cyan dosage, with infrared absorption spectrophotometry

Goldstein, Sandu; Ciupitoiu, A.; Vasilescu, V.; Duca, Al.

doi:10.1007/bf01271528

Cited by 5 publications

(2 citation statements)

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“…Comparison of the bond length of the CN bond in the free cyano ligand (CN − ) and CNCbl, both obtained by geometry optimization at the same level of theory, reveals a shortening of about 0.01 Å in CNCbl (1.174 Å compared to 1.186 Å in CN − ) which is contradictory to the π-backdonation. Furthermore, the CN-stretch frequency νCN of vitamin B 12 is found to be slightly shifted to higher energies as compared to the free cyanid anion (2137 cm −1 in CNCbl compared to 2080 cm −1 in KCN) . However, in a NMR study of cobaloximes, evidence for cobalt-to-cyanide π-bonding was made, so we believe that the value of the νCN frequency is not a sufficient criterion for the exclusion/confirmation of π-backdonation from the metal to the cyano ligand.…”

Section: Resultsmentioning

confidence: 89%

“…Furthermore, the CNstretch frequency νCN of vitamin B 12 is found to be slightly shifted to higher energies as compared to the free cyanid anion (2137 cm -1 in CNCbl compared to 2080 cm -1 in KCN). 89 However, in a NMR study of cobaloximes, evidence for cobaltto-cyanide π-bonding was made, 90 so we believe that the value of the νCN frequency is not a sufficient criterion for the exclusion/confirmation of π-backdonation from the metal to the cyano ligand. The reason is that the orbital energies of the C atom shift to lower values in the process of building the Co-C bond, coming closer to the values of the N atom.…”

Section: Resultsmentioning

confidence: 99%

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Electron Densities of Three B₁₂ Vitamins

et al. 2009

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The electron densities of the three natural B(12)-vitamins, two of them being essential cofactors for animal life, were determined in a procedure combining high-order X-ray data collection at low to very low temperatures with high-level density functional calculations. In a series of extensive experimental attempts, a high-order data set of adenosylcobalamin (AdoCbl) could be collected to a resolution of sin theta/lambda = 1.00 A(-1) at 25 K. This modification contains only minor disorder at the solvent bulk. For methylcobalamin (MeCbl), only a severely disordered modification was found (sin theta/lambda = 1.00 A(-1), 100 K, measured with synchrotron radiation). The already published data set of cyanocobalamin (CNCbl) (sin theta/lambda = 1.25 A(-1), 100 K) was reintegrated to guarantee similar treatment of the three compounds and cut to sin theta/lambda = 1.11 A(-1) to obtain a higher degree of completeness and redundancy. On the basis of these accurate experimental geometries of AdoCbl, MeCbl, and CNCbl, state-of-the-art density functional calculations, single-point calculations, and geometry optimizations were performed on model compounds at the BP86/TZVP level of theory to evaluate the electronic differences of the three compounds. AdoCbl and MeCbl are known to undergo different reaction paths in the body. Thus, the focus was directed toward the characterization of the dative Co-C(ax) and Co-N(ax) bonds, which were quantifed by topological parameters, including energy densities; the source function including local source; and the electron localizability indicator (ELI-D), respectively. The source function reveals the existence of delocalized interactions between the corrin macrocycle and the axial ligands. The ELI-D indicates unsaturated Co-C(ax) bonding basins for the two biochemically active cofactors, but not for CNCbl, where a population of 2.2e is found. This may be related to significant pi-backbonding, which is supported by the delocalization index, delta, of 0.15 between the Co atom and the N atom of the cyano ligand. Considering all results, the inherent electronic differences between AdoCbl and MeCbl are found to be small thus, supporting earlier findings that the interaction with the protein site mainly controls the type of Co-C(ax) bond cleavage.

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Section: Resultsmentioning

confidence: 89%

Section: Resultsmentioning

confidence: 99%