title: Communication: modeling charge-sign asymmetric solvation free energies with nonlinear boundary conditions.
abstract: We show that charge-sign-dependent asymmetric hydration can be modeled accurately using linear Poisson theory after replacing the standard electric-displacement boundary condition with a simple nonlinear boundary condition. Using a single multiplicative scaling factor to determine atomic radii from molecular dynamics Lennard-Jones parameters, the new model accurately reproduces MD free-energy calculations of hydration asymmetries for: (i) monatomic ions, (ii) titratable amino acids in both their protonated and unprotonated states, and (iii) the Mobley "bracelet" and "rod" test problems [D. L. Mobley, A. E. Barber II, C. J. Fennell, and K. A. Dill, "Charge asymmetries in hydration of polar solutes," J. Phys. Chem. B 112, 2405-2414 (2008)]. Remarkably, the model also justifies the use of linear response expressions for charging free energies. Our boundary-element method implementation demonstrates the ease with which other continuum-electrostatic solvers can be extended to include asymmetry.
authors.affiliation: Department of Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts 02115, USA.
authors.forename: Jaydeep P
authors.initials: JP
authors.lastname: Bardhan
authors.affiliation: Computation Institute, The University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Matthew G
authors.initials: MG
authors.lastname: Knepley
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D007477:Ions / Q000737:chemistry*; D008956:Models, Chemical; D056004:Molecular Dynamics Simulation; D011522:Protons; D012996:Solutions; D055672:Static Electricity; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
chemical_list: D000596:Amino Acids; D007477:Ions; D011522:Protons; D012996:Solutions; D014867:Water