Calculation of Nuclear Quadrupole Parameters in Imidazole Derivatives and Extrapolation to Coenzyme B12. A Theoretical Study

Abstract

The 14N nuclear quadrupole coupling (NQC) constants (χ) and asymmetry parameters (η) for a series of small nitrogen-containing imidazole derivatives are investigated, by using density functional theory (DFT), in three clearly distinct environments: as free molecules, in the solid state, and in solution. The spectroscopic characterization is also extended to coenzyme B12 and cob(II)alamin systems. The main findings can be summarized as follows: (i) Deviations in the calculated χ for the two nitrogen sites in the free imidazole molecule are small enough to allow quantitatively accurate predictions for isolated molecules of substituted benzimidazole compounds. (ii) Asymmetry parameters, however, are difficult to reproduce with accuracy; only trends along a series of compounds can be taken as informative. (iii) Shifts of the NQC parameters on going from gas phase to solid state are reasonably well reproduced at a qualitative level by using a trimer model; to reach similar levels of accuracy in the case of η...