We performed Molecular Dynamics (MD) simulations on an extensive set of simple ion pairs in explicit water (TIP3P model) to extract their potentials of mean force (PMFs). Solutes were modeled as Lennard-Jones (LJ) spheres bearing a charge of +1 or -1. We simulated all possible combinations with respect to the charge, and for each of those all the combinations with respect to the solute sizes (LJ diameter ranging from 2 to 5.5 A in increments of 0.5 A). From this pre-simulated grid of PMF values, we developed an interpolation scheme capable of predicting PMFs for arbitrary combinations of solute sizes in the range from 2 to 5.5 A. Figure 1. <img src='https://acs-archive-assets2.s3.amazonaws.com/241nm/uploads/70099_figure.jpg' alt='' />The computational cost is negligible compared to determining PMFs via MD simulations. The predicted PMFs agree with the test MD simulation results within the error-bars. From predicted PMFs, we extracted association constants for ion pair formation without running tedious simulations, and the values agreed with the constants calculated from simulated PMFs. This interpolation algorithm may be useful for rapid and accurate calculation of the strengths of salt bridges and bridging waters in biomolecular simulations. In addition, we found that our data is consistent with Collins' `Law of Matching Affinities' of ion solubilities: small-small or large-large ion pairs are insoluble in water, whereas small-large are soluble.

Computing accurate ion-ion potentials of mean force by fast interpolation

248th National Meeting (2014)

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