Solvation-free energy of uncharged and charged water-soluble synthetic polymer using adaptive Poisson-Boltzmann solver: poly(acrylic acid)

Abstract

ABSTRACT Implicit solvent based on the Poisson-Boltzmann model of electrostatics provides a faster approach to the calculation of solvation and conformations of polymers compared to explicit solvents in molecular dynamics simulations. While PB-based methods have been used extensively for biological macromolecules, here we present the use of the Adaptive Poisson-Boltzmann Solver (APBS) approach for the solvation of synthetic polymer in water. Stereo-specific (isotactic) poly(acrylic acid) of different chain lengths (20–55 for uncharged and 15–50 for charged) are sampled from atomistic molecular dynamic simulations in explicit water followed by APBS in implicit water. The hydration energy of uncharged and charged polymers varies linearly with the number of units (N). The variation of total solvation energy for SASA (Solvent Accessible Surface Area) and SAV (Solvent Accessible Volume) shows a crossover from one scaling to the other. While such a transition is known for small hydrophobic solutes, we report this for a dilute solution of polymer at uncharged and fully charged conditions and in implicit solvent.