Thermodynamic characteristics of reagents and reaction of Ag+-nicotinamide complex formation in water-ethanol media

The influence of water-ethanol solvent (H2O-EtOH) composition on the stability of complexes between nicotinamide (NicNH2) and Ag+ ions was studied by means of potentiometry. Ionic strength and temperature were kept constant at I = 0.25 M NaClO4 and T = 25 °C, respectively. The data on solubility of Ag+-nicotinamide perchlorate ([AgNicNH2]ClO4) and partition coefficients of NicNH2 between H2O-EtOH and hexane (Hex) were obtained in a wide concentration range of H2O-EtOH to yield the values of Gibbs free energy of NicNH2 and AgNicNH2+ transfer from water to H2O-EtOH mixtures. It has been found that the increase of ethanol concentration leads to more stable Ag+-nicotinamide complexes. The thermodynamic approach was used to analyze the experimental results taking into account the peculiarities of ligand molecule electronic structure and its contributions to solvation. Complex formation equilibrium was discussed from the point of view of the contributions of the reagents to solvation.