Thermodynamic Studies of Complexes of Amlodipine Besylate with Ni2+, Mg2+, Co2+ and Ca2+ cations in pure and in mixed binary solvent systems at 303.15, 313.15 and 323.15 K by Conductometric Method

Abstract

The present work relates to the complexation reaction between Amlodipine Besylate[AML] with Ni2+, Mg2+, Co2+ and Ca2+ cation in dimethylsulfoxide (DMSO), pure methanol (MeOH) and their binary mixtures(DMSO-MeOH and DMSO-Water) by conductometric method. The conductance data show that the stoichiometry of the complexes formed between AML with Ni2+, Mg2+, Co2+ and Ca2+ cation in pure DMSO, pure MeOHas well as in the binary solvent mixtures was 1:1. The stability of AML complexes with Ni2+ , Mg2+, Co2+ and Ca2+ metal ion was observed to be sensitive to the nature of the solvent system. In case of DMSO-Water binary solvent systems there was a linear change in LogKf values but in case of DMSO-MeOH binary solvent systems non linear change in LogKf values observed.The negative values of ΔG0 show that the reaction is spontaneous and ability of the AML ligand to form stable complexes. However, the result shows positive value of ΔH0 which indicates that enthalpy is not driving force for the formation of the complexes. Furthermore, the positive value of ΔS0 indicates that entropy is a driving force for the complexation. The values of ΔH0 and ΔS0 for formation of the complexes were obtained from temperature dependence of the stability constants.