Determination of Stability Constants and Thermodynamic Parameters for Ciprofloxacin-HCl With Some Transition Metal Ions by Potentiometric Titration Technique

Abstract

This study included calculating the stability constants and stoichiometries of some binary complexes formed from the interaction of seven of metal ions (Cr+3,Mn+2,Co+2,Ni+2,Cu+2,Zn+2 and Cd+2) with Ciprofloxacin-HCl. This study was carried out using Potentiometric Titration Technique at different concentrations of the drug and the metal ion and at temperatures (288,298,310,318 and 328 K±0.1) in aqueous solution. Although, there are many methods available to study the stability of metal-ligand complexes, pH-metric is most frequently used to determine the stability constants. Hence, (Calvin - Bjerrum pH-metric titration technique) as adopted by Irving–Rossotti was used to calculate of stability constants. The results of the concentration effect study showed that the formation of complexes were more stable in dilute solutions, and through study of the temperature effect it was concluded that the stability of the complexes can be increased with raising temperature, and the stability constants value obtained were used in the calculation of thermodynamic parameters . The results of this study also showed that the ciprofloxacin tends to form two types of metal complexes in the solution (ML1),(ML2) and this indicates that the reaction ratio between the drug and the metal ion was (1:1) and (1:2)(M:L) respectively for all metal ions. These ratios depended on the nature of the ligand or the metal ion, and the stability of the complexes formed increases according to the following arrangement (Mn+ 2< Co+ 2< Ni+ 2< Cu+ 2> Zn+ 2) and this arrangement is compatible with Irving Williams’s arrangement for the stability of the elements.