Molecular Dynamics in Physiological Solutions: Force Fields, Alkali Metal Ions, and Ionic Strength.

Area of Science:

• Computational Chemistry
• Biophysics
• Physical Chemistry

Background:

• Monovalent ions (Na+, K+, Cl-) are vital in biological systems.
• Excess chemical potential differences of single ions are crucial for ion transport and DNA interactions.

Purpose of the Study:

• To evaluate molecular dynamics (MD) force fields for predicting ion thermodynamic properties.
• To compare MD predictions with experimental data for NaCl and KCl solutions.

Main Methods:

• MD simulations using various ion/water force fields (AMBER, CHARMM, OPLS, Dang95).
• Calculation of excess (electro-)chemical potential differences and ion activities.
• Comparison of simulation results with experimental data.

Main Results:

• The AMBER force field with TIP3P water accurately predicts properties for both KCl and NaCl.
• CHARMM-TIP3P and Dang95-SPC/E showed good agreement for KCl and NaCl, respectively.
• Single cation potentials were similar across force fields; Cl- activity depended on the counterion.

Conclusions:

• MD simulations, particularly with the AMBER force field, can reliably predict ion thermodynamic properties.
• Force field selection is critical for accurate biomolecular simulations involving ions.
• Findings have implications for understanding ion channel function and DNA-protein interactions.