Spectrophotometric Study of Complexation between Trimethoprim and Sulfamethoxazole and Pd(II) and Cu(II) and the Determination of Thermodynamic Parameters with Kinfit Software

Abstract

The complexation reactions between Cu2+ and Pd2+ ions with trimethoprim (TMP) and sulfamethoxazole (SMX) in N,N-Dimethylformamide (DMF) were studied by the spectrophotometric methods at [(15, 25, 35 and 45±0.1) °C]. The complexation process was optimized in terms of pH, temperature and time. The stoichiometry of the complexes was found to be 1:2 (metal ion/ligand). The formation constants of the resulting complexes were determined from computer fitting absorbance-mole ratio data and emphasized by the KINFIT program. The values of the thermodynamic parameters for complexation reactions were obtained from the temperature dependence of the stability constants. In all cases, the complexes were found to be enthalpy stabilized but entropy destabilized. SMX and TMP could be determined by measuring the absorbance of each complex at its specific λmax. The proposed method was successfully applied for the determination of these compounds in their dosage forms.