The self-association of amoxicillin (AMX) and its hetero-association with biologically active compound, chlorogenic acid (CGA) were investigated at room temperature (295°K). The dimerization constant of amoxicillin and thiamine (THIA) analyzed using the dimer model at the wavelength of 278 and 256 nm were found to be   1 3 10 2. 3 438. 5    M and 1 2 10 991. 8   M , respectively. The hetero-association constant of amoxicillin and chlorogenic acid analyzed using Benesi-Hildebrand approach were 1 3 10 18. 1   M. Thermodynamic parameters such as Gibbs free energy, enthalpy and entropy of dimerization reactions for the self-association and hetero-association of the compounds were also investigated using Vant's Hoff equation at the temperature ranges (295 to 305°K). The change of enthalpy calculated for amoxicillin, thiamine and the complexes of amoxicillin-chlorogenic acid are 34.73±2.17, 54.1±4.585, and 6.988±0.493 1.  mol kJ at the temperature of 305°K, respectively. The values of change in enthalpy and entropy indicate that the hydrophobic interaction play the major role in the interaction between the molecules.

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 (1 4  cm 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.

The optical transition probabilities and hetero-association of caffeine with norfloxacin were obtained using UV-Vis spectroscopy in aqueous solution at room temperature (295K). The heter-association constant of norfloxacin-caffeine complexes (6.67×10 3 M -1) was obtained using Benesi-Hildebrand approach by linear curve fitting to the experimental data. In order to characterize the binding system of the compounds, the thermodynamic parameters were investigated using Vant's Hoff equation at the temperature ranges (295 to 304K) with a change in enthalpy value (-1.277±0.103 kJ.mol ) by using integrated absorption coefficient techniques. This study is very important for understanding the binding reaction in biological system, nature and strength of the transition, absorption spectral interpretation, and in providing stringent test of atomic and molecular structure calculations for theoretical work of the compounds.