Analysis of Solvent Effect on Formation Constants and Speciation of Cobalt(II), Copper(II) and Lead(II) Complexes of L-Methionine and Uracil

Abstract

The analysis of coordination of chelating agents to metal ions in the formation of complexes under different experimental conditions provide information on the effects of the conditions on the extent of the coordination of the ligands to the metal ions for potential applications in bioinorganic and environmental Inorganic Chemistry. The effect of solvent on the coordination of L-methionine (primary ligand) and uracil (secondary ligand) to Co(II), Cu(II) and Pb(II) ions in the formation of binary and ternary complexes have been potentiometrically investigated in water and 40% (v/v) ethanol-water media at 27 °C and ionic strength of 0.02 mol dm-3was maintained by using NaNO3. The proton-ligand stability constants and formation constants of the binary and ternary systems were established under the experimental conditions. The formation constants of the ternary complexes were numerically compared with the corresponding binary complexes in terms of Δ log K and percentage relative stabilization (%RS). Speciation of the metal ions, binary and ternary complexes as a function of pH in the solutions was investigated by using HYSS program. The ligands were observed to form more stable ternary complexes than binary complexes. The proton-ligand stability constants the ligands and the formation constants of the metal complexes were found to be higher in 40% (v/v) ethanol-water than water. The distribution of the species revealed a decrease in the metal ion concentrations with increase in the concentrations of the binary and ternary as pH increased. The chelating agents interacted strongly with the metal ions and showed different selectivity towards the metals ions. These properties can be exploited in combating metal poisoning, separating the metals and expounding the bioinorganic chemistry of the metal ions and the ligands.