Absolute Hydration Free Energy Scale for Alkali and Halide Ions Established from Simulations with a Polarizable Force Field

• Published in: The journal of physical chemistry. B 2006-02, Vol.110 (7), p.3308-3322
• Main Authors: Lamoureux, Guillaume, Roux, Benoît
• Format: Article
• Language: English
• Subjects: Air; Anions; Cations; Chemistry, Physical - methods; Computer Simulation; Ions; Models, Molecular; Models, Statistical; Static Electricity; Thermodynamics; Water - chemistry
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp056043p

A polarizable potential function for the hydration of alkali and halide ions is developed on the basis of the recent SWM4-DP water model [Lamoureux, G.; MacKerell, A. D., Jr.; Roux, B. J. Chem. Phys. 2003, 119, 5185]. Induced polarization is incorporated using classical Drude oscillators that are treated as auxiliary dynamical degrees of freedom. The ions are represented as polarizable Lennard-Jones centers, whose parameters are optimized to reproduce the binding energies of gas-phase monohydrates and the hydration free energies in the bulk liquid. Systematic exploration of the parameters shows that the monohydrate binding energies can be consistent with a unique hydration free energy scale if the computed hydration free energies incorporate the contribution from the air/water interfacial electrostatic potential (−540 mV for SWM4-DP). The final model, which can satisfyingly reproduce both gas and bulk-phase properties, corresponds to an absolute scale in which the intrinsic hydration free energy of the proton is −247 kcal/mol.