New method to estimate stability of chelate complexes

TL;DR

This paper introduces a novel two-stage quantum chemical method to estimate the stability of Mg2+ chelate complexes in water, emphasizing ligand transfer and bond disruption processes, with results aligning well with experimental data.

Contribution

The paper presents a new computational approach combining ligand transfer and bond disruption modeling to predict chelate complex stability, improving accuracy over previous methods.

Findings

Main contribution from bond disruption and electrostatics to free energy

Achieved agreement within 2 kcal/mol of experimental values

Method applicable to various Mg2+ chelate complexes

Abstract

A new method allowing calculation of the stability of chelate complexes with Mg2+ ion in water have been developed. The method is based on two-stage scheme for the complex formation. The first stage is the ligand transfer from an arbitrary point of the solution to the second solvation shell of the Mg2+ ion. At this stage the ligand is considered as a charged or neutral rigid body. The second stage takes into account disruption of coordinate bonds between Mg2+ and water molecules from the first solvation shell and formation of the bonds between the ligand and the Mg2+ ion. This effect is considered using the quantum chemical modeling. It has been revealed that the main contribution to the free energy of the complex formation is caused by the disruption/formation of the coordinate bonds between Mg2+, water molecules and the ligand. Another important contribution to the complex formation energy is change of electrostatic interactions in water solvent upon the ligand binding with Mg2+ ion. For all complexes under investigation the reasonable (in frame of 2 kcal/mol) agreement between calculated and experimental values are achieved.