Electronic Properties of the Axial Co−C and Co−S Bonds in B12 Systems − A Density Functional Study

Abstract

The numerous accurate structural data of cobalamins now available allows us to optimize the geometry of these systems, based on a simplified model by using density functional theory (DFT) calculations. This approach, which reproduces the trend of the experimental distances derived from EXAFS and X-ray crystal structures in the corrin macrocycle, permit us to interpret the electronic properties in the NB3−Co−X axial system. In particular, the results are analyzed for cobalamins containing a sulfur ligand which exhibits a ''regular'' trans influence, i.e., when the Co−S bond shortens, the trans Co−NB3 bond lengthens. This feature appears in contrast with an anomalous effect (''inverse'' trans

A simple, convenient method to synthesize cobalamins: synthesis of homocysteinylcobalamin, N-acetylcysteinylcobalamin, 2-N-acetylamino-2-carbomethoxyethanethiolatocobalamin, sulfitocobalamin and nitrocobalamin

“…4B), with a Co-S bond distance of 2.250(3) Å, similar to the bond lengths observed in other Co-S containing cobalamin structures determined previously (Table 3). 43,59,69,88 Furthermore, the four in-plane CoN bonds and the axial base Co-N bond are all very similar to those reported elsewhere. Comparison of the Na[NACCbl]·18H 2 O structure with that of γ-GluCysCbl is rather interesting, in that whereas the upward corrin fold in the latter was found to be the largest yet observed in a cobalamin structure (24.2°), the corrin fold angle in Na [NACCbl]·18H 2 O of 17.5° is significantly less, although still slightly larger than some of the other Co-S containing cobalamins.…”

“…Although both are isolable from biological samples, [11][12][13][14][15][16][17]20 and are well studied and structurally characterized, 23,29,38,43,[59][60][61][62][63][64][65][66][67][68][69] neither are commercially available. NO 2 Cbl is also of interest, since if nitrosylcobalamin (NOCbl) is formed in biological systems to any appreciable extent, NO 2 Cbl rather than NOCbl will be isolated after typical (aerobic) isolation and purification procedures.…”

DFT Analysis of Co−Alkyl and Co−Adenosyl Vibrational Modes in B12-Cofactors

“…37 Changing the alkyl group to ethyl lengthens the Co-C bond, to 1.99 Å, due to a combination of electronic and nonbonded ethyl-corrin interactions, while increasing the steric bulk further, to propyl, lengthens the Co-C bond to 2.03 Å. Interestingly, the Co-imidazole bond lengthens in the same order, to 2.26 and 2.32 Å, illustrating what has become known as the 'inverse trans influence'. [38][39][40][41][42][43] The computed frequencies fall in the same order, as expected. The Co-C stretching frequencies are in excellent agreement with reported values for MeCbl and EtCbl; no data are available for isopropyl derivatives.…”

Vitamin B12 Transport Proteins: Crystallographic Analysis of β‐axial Ligand Substitutions in Cobalamin Bound to Transcobalamin

“…Model rebuilding was carried out with COOT v0.3.1 (35). Geometric restraints for CN-Cbl were taken from the Cambridge Structural Database entry WIKXUJ (36) and for SO 3 -Cbl from entry NOJKIG (37). Table 1 compiles processing and refinement statistics.…”