Solvation of nicotinamide nitrogen heteroatom in aqueous ethanol according to 15N and 13C NMR data

The solvation state of 3-pyridinecarboxamide (nicotinamide) is studied at different temperatures and compositions of mixed water-ethanol solvent using 13C NMR spectroscopy. Basing on the dependences of temperature coefficients of nicotinamide carbon chemical shifts on alcohol concentration, the main change in solvation of nicotinamide pyridine cycle is observed at the mole fraction of ethanol less than 0.2. This change consists in the transition from hydrogen bonded complex of nitrogen heteroatom with water molecule to that with ethanol. It is shown that carbamide group solvation is mainly determined by specific interactions with solvent molecules at XEtOH < 0.2. The thermodynamics of nitrogen heteroatom transfer (ΔG, ΔH and TΔS) is determined from 13C NMR data. The quantum chemical modeling of H-complexes of nicotinamide with water and ethanol is performed.