Excluded volume effect for large and small solutes in water

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Thermodynamics

Background:

• Cavitation, the formation of voids in solvents, is crucial for understanding solute behavior.
• Existing information theory (IT) approaches provide a framework for calculating cavitation free energy.
• Previous models were limited in the range of solute sizes they could accurately describe.

Purpose of the Study:

• To extend the information theory (IT) approach for calculating cavitation free energy across a wide range of cavity sizes.
• To develop a unified model that bridges the gap between small molecular solutes and large biomolecular structures.
• To validate the extended model against molecular simulation data and macroscopic solvent properties.

Main Methods:

• Applied the binomial cell model as the default distribution within the information theory (IT) framework.
• Extended the model to include two distinct binomial peaks representing volume- and surface-dependent free energy contributions.
• Utilized an interpolation procedure to connect small and large cavity regimes, validated with Monte Carlo (MC) simulations.

Main Results:

• The extended model successfully reproduces MC simulation results for spherical solutes up to 10 Å radius.
• The model captures the transition from volume-dominated effects in small cavities to surface-dominated effects in large cavities.
• The large cavity limit accurately reflects macroscopic properties of water, including surface tension and compressibility.

Conclusions:

• The extended IT binomial cell model provides a robust framework for calculating cavitation free energy across diverse solute scales.
• The model's ability to unify small and large cavity descriptions enhances its applicability in solvation studies.
• The approach offers a pathway to understanding solvation thermodynamics for both simple molecules and complex biomolecules.