Probing the thermodynamics of competitive ion binding using minimum energy structures

Area of Science:

• Computational Chemistry
• Biophysics
• Biochemistry

Background:

• Ion binding significantly impacts biomolecular properties and biochemical pathways.
• Quantum mechanical treatment is ideal for understanding ion binding energetics in polar biological environments.
• Computational costs often necessitate approximations in quantum mechanical studies, challenging validity assessment.

Purpose of the Study:

• To develop a theoretical framework for modeling competitive ion binding using quantum mechanics.
• To build intuitive models from simplified ion-ligand binding sites.
• To unify existing viewpoints on ion selectivity into a single, explicit theory.

Main Methods:

• Utilized thermodynamic cycles to construct models from isolated ion-ligand binding geometries.
• Calculated intrinsic ion selectivities from ion binding free energies of minimum energy structures.
• Analyzed local interaction energies and external environmental influences (dispersive, electrostatic).

Main Results:

• Developed a theory unifying field-strength, topological control, and phase activation.
• Demonstrated that conformational contributions are crucial for accurate Na(+) → K(+) selectivity prediction.
• Identified rigid/mechanical and disordered/entropic selectivity mechanisms in Na(+)- and K(+)-water clusters.

Conclusions:

• The solute coordination state plays a critical role in overall reaction energetics for ion binding.
• The developed theory provides explicit insights into the factors governing ion selectivity.
• Accurate prediction of experimental ion properties in biological systems relies on understanding coordination structure.