Predicting the stability constants of metal-ion complexes from first principles

Area of Science:

• Computational Chemistry
• Biophysical Chemistry
• Thermodynamics

Background:

• The stability constant (β) is crucial for understanding metal-ion binding thermodynamics with ligands and biomolecules.
• Calculating β involves complex free-energy changes due to charged species interactions and solvation effects.
• Traditional thermodynamic cycles require subtracting large energy values, leading to potential inaccuracies.

Purpose of the Study:

• To calculate stability constants (β) for various metal-ion complexes using advanced computational methods.
• To assess the accuracy and limitations of current theoretical protocols for predicting metal-ion binding thermodynamics.
• To propose strategies for improving the accuracy of theoretical stability constant predictions.

Main Methods:

• Density Functional Theory (DFT) and Møller-Plesset second-order perturbation theory (MP2) were employed.
• The conductor-like screening model for realistic solvation (COSMO-RS) was used to account for solvation effects.
• Calculations were performed for complexes involving eight divalent metal ions and various inorganic/organic ligands.

Main Results:

• Relative accuracy of 2-4 kcal·mol⁻¹ (1-3 orders of magnitude in β) was achieved using current computational protocols.
• Systematic metal- and ligand-dependent shifts were identified, affecting absolute accuracy.
• Metal-ion selectivity can be computed with an average accuracy of 2 kcal·mol⁻¹, unaffected by ligand-dependent shifts.

Conclusions:

• Theoretical calculations, with proposed corrections for metal-dependent shifts, can accurately predict metal-ion stability constants.
• Computational methods offer a competitive and complementary approach to experimental measurements in studying metal-ion binding.
• Understanding potential caveats in theoretical predictions is crucial for reliable results.