A self-consistent phase-field approach to implicit solvation of charged molecules with Poisson-Boltzmann electrostatics

• Published in: The Journal of chemical physics 2015-12, Vol.143 (24), p.243110-243110
• Main Authors: Sun, Hui, Wen, Jiayi, Zhao, Yanxiang, Li, Bo, McCammon, J Andrew
• Format: Article
• Language: English
• Subjects: Dielectrics; Electrostatics; Free energy; Hydrophobic and Hydrophilic Interactions; Hydrophobicity; Interfacial energy; Mathematical analysis; Mathematical models; Molecular Dynamics Simulation; Parallel plates; Physics; Poisson Distribution; Proteins; Proteins - chemistry; Solubility; Solvation; Solvents; Solvents - chemistry; Special Topic: Coarse Graining of Macromolecules, Biopolymers, and Membranes; Static Electricity; Thermodynamics; Water - chemistry
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.4932336

Dielectric boundary based implicit-solvent models provide efficient descriptions of coarse-grained effects, particularly the electrostatic effect, of aqueous solvent. Recent years have seen the initial success of a new such model, variational implicit-solvent model (VISM) [Dzubiella, Swanson, and McCammon Phys. Rev. Lett. 96, 087802 (2006) and J. Chem. Phys. 124, 084905 (2006)], in capturing multiple dry and wet hydration states, describing the subtle electrostatic effect in hydrophobic interactions, and providing qualitatively good estimates of solvation free energies. Here, we develop a phase-field VISM to the solvation of charged molecules in aqueous solvent to include more flexibility. In this approach, a stable equilibrium molecular system is described by a phase field that takes one constant value in the solute region and a different constant value in the solvent region, and smoothly changes its value on a thin transition layer representing a smeared solute-solvent interface or dielectric boundary. Such a phase field minimizes an effective solvation free-energy functional that consists of the solute-solvent interfacial energy, solute-solvent van der Waals interaction energy, and electrostatic free energy described by the Poisson-Boltzmann theory. We apply our model and methods to the solvation of single ions, two parallel plates, and protein complexes BphC and p53/MDM2 to demonstrate the capability and efficiency of our approach at different levels. With a diffuse dielectric boundary, our new approach can describe the dielectric asymmetry in the solute-solvent interfacial region. Our theory is developed based on rigorous mathematical studies and is also connected to the Lum-Chandler-Weeks theory (1999). We discuss these connections and possible extensions of our theory and methods.