Nicotinamide solvation state in aqueous dimethyl sulfoxide

Abstract

The solvation state of biologically active compound vitamin B3, viz., 3-pyridinecarboxamide, in an aqueous-dimethyl sulfoxide solvent of a variable composition was studied by 1H and 13C NMR and IR spectroscopy. Below X DMSO −0.65 molar fraction, the solvation of the N heteroatom due to hydrogen bonds with water molecules weakens. At X DMSO > 0.65 molar fraction, almost no changes are observed in the solvate state of the N heteroatom. The 1H NMR spectra indicate that the degree of conjugation of the carbamide group with the heterocycle increases with an increase in the DMSO concentration. The structures of the dimethyl sulfoxide and mixed aqueous-dimethyl sulfoxide solvates of nicotinamide were optimized by the B3LYP/6311++(DP) method, and their 13C chemical shifts (GIAO) and IR spectra were obtained. According to the IR spectroscopic data, the number of hydrogen bonds involving the carbamide group decreases on going from H2O to DMSO.