Charged patchy particle models in explicit salt: Ion distributions, electrostatic potentials, and effective interactions.
We introduce a set of charged patchy particle models (CPPMs) in order to systematically study the influence of electrostatic charge patchiness and multipolarity on macromolecular interactions by means of implicit-solvent, explicit-ion Langevin dynamics simulations employing the Gromacs software. We consider well-defined zero-, one-, and two-patched spherical globules each of the same net charge and (nanometer) size which are composed of discrete atoms. The studied mono- and multipole moments of the CPPMs are comparable to those of globular proteins with similar size. We first characterize ion distributions and electrostatic potentials around a single CPPM. Although angle-resolved radial distribution functions reveal the expected local accumulation and depletion of counter- and co-ions around the patches, respectively, the orientation-averaged electrostatic potential shows only a small variation among the various CPPMs due to space charge cancellations. Furthermore, we study the orientation-averaged potential of mean force (PMF), the number of accumulated ions on the patches, as well as the CPPM orientations along the center-to-center distance of a pair of CPPMs. We compare the PMFs to the classical Derjaguin-Verwey-Landau-Overbeek theory and previously introduced orientation-averaged Debye-Hückel pair potentials including dipolar interactions. Our simulations confirm the adequacy of the theories in their respective regimes of validity, while low salt concentrations and large multipolar interactions remain a challenge for tractable theoretical descriptions.
Soft Matter and Functional Materials, Helmholtz-Zentrum Berlin, 14109 Berlin, Germany.
Cemil
C
Yigit
Department of Physical Chemistry, University of Chemistry and Technology, Prague, 166 28 Praha 6, Czech Republic.
Jan
J
Heyda
Soft Matter and Functional Materials, Helmholtz-Zentrum Berlin, 14109 Berlin, Germany.
Joachim
J
Dzubiella
D003198:Computer Simulation; D007477:Ions / Q000737:chemistry*; D008956:Models, Chemical; D011506:Proteins / Q000737:chemistry; D012492:Salts / Q000737:chemistry*; D012984:Software; D012997:Solvents / Q000737:chemistry*; D055672:Static Electricity; D013499:Surface Properties
D007477:Ions; D011506:Proteins; D012492:Salts; D012997:Solvents