A Molecular Mechanics Force Field for Alkylcobaloximes, a Model of Vitamin B12 Coenzyme – Implications of Steric and Electronic Factors in the Co–C Bond Cleavage
✍ Scribed by Silvano Geremia; Mario Calligaris; Lucio Randaccio
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 441 KB
- Volume
- 1999
- Category
- Article
- ISSN
- 1434-1948
No coin nor oath required. For personal study only.
✦ Synopsis
Molecular mechanics force field constants have been derived correlated with their calculated cone angles. The force field has been used to analyse some conformational features of for alkylcobaloximes, (alkyl)Co(DH) 2 L (DH = monoanion of dimethylglyoxime and L = planar N-donor ligand), these compounds, such as the influence of the rotation of the axial ligands on their coordination geometry. The calculated implementing the AMBER force field. Atomic charges have been calculated by the semiempirical ZINDO/1 method. energy for the Co-N rotational barrier agrees well with the experimetal ones derived from dynamic and saturation 1 H-Stretching and bending constants have been calculated by the Badger and Halgren equations, with the introduction of NMR spectroscopy in (alkyl)Co(DH) 2 (2-NH 2 -py). In order to have more experimental data for this analysis, the crystal simple functions for the description of the electronic influence of the axial ligands on the coordination geometry.
structures of two new cobaloximes, (CH 2 Cl)Co(DH) 2 L with L = py, 1, and 1-Me-Im, 2) have been determined. The results 26 parameters have been optimized, by the Simplex method, to fit 4523 bond lengths and angles of 52 alkylcobaloxime of a conformational analysis on ribosyl-imidazole derivatives, taken as a suitable vitamin B 12 coenzyme model, suggest that accurate crystal structures. In spite of the oversimplification of the adopted method for the description of the electronic the 1-Me-imidazole-like ligands have a significantly greater rotation freedom with respect to the benzimidazole-like ones, effects, this approach provides a good description of the metal coordination geometries. The root-mean-square but cause similar stretchings of the Co-C bond, and a significantly less stretching of the Co-N one. Implications for deviations of the calculated bond lengths and angles from the experimental values average to 0.023 A ˚and 1.4°, the recent findings on the binding mode of the coenzyme B 12 in the enzyme active site are discussed. respectively. The molecular mechanics results are discussed in terms of the steric properties of the axial ligands and lengthening of the CoϪL bond by up to 0.15 A ˚as the σ-CoϪC bond is not so apparent. [10] On the other hand, Hal-Supporting information for this article is available on the pern has found that the CoϪC BDE increases with the in-WWW under http://www.wiley-vch.de/home/eurjic or from the author. crease of the pKa of 4-substituted pyridines in the series