Computational Prediction of Molecular Hydration Entropy
with Hybrid Scaled Particle Theory and Free-Energy Perturbation Method
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Abstract
Despite the importance of the knowledge
of molecular hydration
entropy (Δ<i>S</i><sub>hyd</sub>) in chemical and
biological processes, the exact calculation of Δ<i><i>S</i></i><sub>hyd</sub> is very difficult, because of the
complexity in solute–water interactions. Although free-energy
perturbation (FEP) methods have been employed quite widely in the
literature, the poor convergent behavior of the van der Waals interaction
term in the potential function limited the accuracy and robustness.
In this study, we propose a new method for estimating Δ<i><i>S</i></i><sub>hyd</sub> by means of combining the
FEP approach and the scaled particle theory (or information theory)
to separately calculate the electrostatic solute–water interaction
term (Δ<i><i>S</i></i><sub>elec</sub>) and
the hydrophobic contribution approximated by the cavity formation
entropy (Δ<i><i>S</i></i><sub>cav</sub>),
respectively. Decomposition of Δ<i><i>S</i></i><sub>hyd</sub> into Δ<i><i>S</i></i><sub>cav</sub> and Δ<i><i>S</i></i><sub>elec</sub> terms is found to be very effective with a substantial accuracy
enhancement in Δ<i><i>S</i></i><sub>hyd</sub> estimation, when compared to the conventional full FEP calculations.
Δ<i><i>S</i></i><sub>cav</sub> appears to
dominate over Δ<i><i>S</i></i><sub>elec</sub> in magnitude, even in the case of polar solutes, implying that the
major contribution to the entropic cost for hydration comes from the
formation of a solvent-excluded volume. Our hybrid scaled particle
theory and FEP method is thus found to enhance the accuracy of Δ<i><i>S</i></i><sub>hyd</sub> prediction by effectively
complementing the conventional full FEP method