Abstract

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 (6.67×10³ 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^-1.K^-1). The values of change in the thermodynamic parameters indicated that the electrostatic forces play the major role in the binding reaction between the molecules of norfloxacin-caffeine complexes. In addition, the optical transition probabilities of norfloxacin were also calculated in the wavenumber regions from (20000 to 40000 cm^-1) 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.

Key words: Norfloxacin, caffeine, hetero-association, optical transition, thermodynamics, UV-Vis spectroscopy.