pH Metric Study of Complexe Formation of Some Alkali and Alkaline Earth Metal with two Dicarboxylic Acid Ligands

Abstract

The stability constants of two dicarboxylic acid ligands (1,7-Bis (2′-benzoic acid)-1,4,7-trioxaheptane (L1) and 1,10-Bis(2′-benzoic acid)-1,4,7,10-tetraoxadecane(L2) ) with Na +, K + , Ca 2+ and Mg 2+ in ethanol -water solvent mixtures were determined. The ratio of ligand / metal in these complexes is 1/1, and the stability constants of K + with L1 and L2 are higher than Na + and the stability constants of Ca 2+ with L1 and L2 are higher than Mg 2+ complexes. These studies also showed that the stability constants of Na + and K + complexes with L1 and L2 increases by an increase in the mole fraction of ethanol in the solvent mixtures. IntroductionAlkali and alkaline earth cations play diverse vital roles[1-4 ] in biological systems. The important biological implications of Na + , K + , Mg 2+ and Ca 2+ especially with respect to their membrane transport phenomena [5][6][7][8] causes much attention in study of complexes of these cations. Ederson [9] in 1967 discovered that these cations undergoes complexation with the crown ethers to produce crystalline products. Several acyclic polyethers were found to dissolve small quantities of potassium metal and sodium-potassium alloy [10]. Studies on other acyclic multidentates such as poly(oxyethylene) derivatves [11][12] have also been carried out with these cations. In 1985, pentaethyleneglycol diethyl ethers complexation of M + ions was studied using low temperature 1 H.N.M.R spectroscopy by Raban et al [13].A synthetic acyclic ionophore with a single benzoic acid terminal group has been used[14] to study the transport of Na + and K + ions through a dichloroethane liquid membrane. The results showed that this ionophore has a higher selectivity for K + ions than any other alkali ions.Using calorimetric titration the thermodynamic parameters and stability constants for complex formation between a series of acyclic polyethers and alkali or alkaline earth cations have been determined in CH 3 OH [15].The complexing properties of the naturally occurring acyclic ionophores, lysocellin[16] and monesin [17] have been studied using potentiometric and calorimetric methods, respectively. In complexation of M + (M = Na, K) by lysocelline selectivity favors K + , whereas its Mg 2+ /Ca 2+ selectivity favors Calcium ion [16].