Investigation of self-association, optical transition probability and hetero-association with chlorogenic acid of nicotinamide using UV-Vis spectroscopy

The self-association, optical transition probabilities, and hetero-association with chlorogenic acid of nicotinamide were obtained from UV-Vis spectroscopy in aqueous solution at room temperature (293K). The dimerization constant of nicotinamide ( ) was obtained using dimer model by nonlinear curve fitting technique. The hetero-association constant  in the system of molecules of nicotinamide with chlorogenic acid were obtained in aqueous solution using a Benesi-Hildebrand equation. In order to characterize the binding system of the dimerization reactions for the self and hetero-association of the compound, the thermodynamic parameters were investigated using Vant’s Hoff equation at the temperature range (293 to 299K). As a result, the change of enthalpy obtained for the self and hetero-association is and respectively. The values of change in the thermodynamic parameters indicated that the hydrophobic interaction and electrostatic forces subsequently plays the major role in the binding reaction between the molecules of nicotinamide and its complexes with chlorogenic acid, respectively. In addition, the optical transition probabilities of nicotinamide were also calculated in the wavenumber regions  by using integrated absorption coefficient techniques. Finally, the results of this study are very important for understanding the binding reaction in biological system, nature and strength of the transition in molecular interaction, absorption spectral interpretation, and in providing stringent test of atomic and molecular structure calculations in theoretical work of the compounds. Key words: Nicotinamide, chlorogenic acid, self-association, hetero-association, optical transition probabilities, thermodynamic properties, UV-Vis spectroscopy.