Thermodynamic Studies of Metal Complexes of Tetracycline and their Application in Drug Analysis

The complexation reactions of Fe3+, Cu2+ and Pd2+ ions with tetracycline HCl (TC) in water or DMF at 15, 25, 35 and 45 +/- 0.1A degrees C were studied by the spectrophotometric method. The complexation process was optimized in terms of pH, temperature, and time. The stoichiometry (metal ion/ligand ratio) of the complexes was found to be 1 : 2 for Pd(II) - TC and Fe(III) - TC and 1 : 1 for Cu(II) - TC. The formation constants of the obtained complexes were determined from computer fitting of the absorbance - molar ratio data and emphasized by the KINFIT program. The values of the thermodynamic parameters for complexation reactions were estimated from the temperature dependence of the stability constants. TC could be determined by measuring the absorbance of each complex at its characteristic wavelength lambda(max).