The Thermodynamics of Lanthanide-Pipecolinate Complexation in an Aqueous Solution

Abstract

The need to understand and develop novel complexes based on lanthanide ions with biologically active ligands has increased interest in them. The thermodynamics for the complexation and coordination environment of the complexes in solution are of utmost important in these systems to explain the biological activity of the species. For example, the coordination number and the presence of coordinated water molecules in complexes can affect the stability of the resulting complexes and the interaction between the lanthanide ions and ligands in an aqueous solution. With this in mind, we reported the thermodynamics of the complexation of trivalent lanthanide ions with cyclopentanecarboxlate, L-proline and substituted L-proline ligands. Based on the measured thermodynamic parameters, we proposed that lanthanide ions could be used in the resolution of racemic α-aminoacids. In this work, we have extended these studies to pipecolinate complexes in order to investigate the effect of the heterocyclohexyl ring in pipecolinate ligand on complexation in an aqueous solution. Potential and calorimetric titration were used to determine the stability and the enthalpy changes on complexation, and the nature of the binding behaviour was explained in terms of enthalpy and entropy changes.