A systematic study on hydrogen bond interactions in sulfabenzamide: DFT calculations of the N-14, O-17, and H-2 NQR parameters.

A systematic computational study was carried out to characterize the hydrogen bond, HB, interactions of sulfabenzamide crystal structure by DFT calculations of electric field gradient, EFG, tensors at the sites of 14N, 17O, and 2H nuclei. The computations were performed with the B3LYP and B3PW91 DFT methods and 6-311+G and 6-311++G* standard basis sets using the Gaussian 98 package. To perform the calculations, a hydrogen-bonded heptameric cluster of sulfabenzamide was created by X-ray coordinates where the hydrogen atom positions were optimized and the EFG tensors were calculated for the target molecule. Additional optimization and EFG calculations were also performed for crystalline monomer and an isolated gas-phase sulfabenzamide. The calculated EFG tensors were converted to the experimentally measurable nuclear quadrupole resonance, NQR, parameters: quadrupole coupling constant, C(Q), and asymmetry parameter, eta(Q). The results reveal that the geometrical and NQR parameters of the optimized isolated gas-phase and crystalline phase are different. In addition, the difference between the calculated NQR parameters of the monomer and the target molecule shows how much H-bonding interactions affect the EFG tensors of each nucleus. The evaluated NQR parameters reveal that due to the contribution of the target molecule to N-H...O and C-H...O hydrogen bond interactions, the EFG tensors at the sites of N1, O3 and H1 undergo significant changes from monomer to the target molecule in cluster. These features reveal the major role of N-H...O type intermolecular HBs in cluster model of sulfabenzamide which the presence of these interactions can lead to polymorphism directly related to the drug activity and related properties.