The thermodynamics of solvent exchange

Area of Science:

• Thermodynamics
• Physical Chemistry
• Biophysics

Background:

• A previously developed model for solvation in mixed solvents focused on free energy and preferential interaction.
• This model requires extension to accurately describe thermal properties like enthalpy, entropy, and heat capacity.

Purpose of the Study:

• To extend the existing solvation model to incorporate thermal properties (enthalpy, entropy, heat capacity).
• To analyze the behavior of enthalpy of solvation in relation to site occupation.
• To develop equations for interpreting experimental binding data for heterogeneous systems using homogeneous models.

Main Methods:

• Extension of a mixed solvent solvation model.
• Analysis of enthalpy, entropy, and heat capacity responses to solvent composition.
• Development of equations for heterogeneous binding data interpretation.

Main Results:

• Enthalpy of solvation (H(ex)2) directly correlates with site occupation fraction, differing from free energy and preferential interaction.
• Solvation heat capacity (Cpex2) includes intrinsic and composition-change terms.
• Experimental binding parameters (nexp, Kexp, delta hexp) are functions of equilibrium constant distribution moments for heterogeneous binding.

Conclusions:

• The extended model provides insights into the thermal properties of solvation in mixed solvents.
• The study offers a framework for reconciling homogeneous binding models with heterogeneous biological systems.
• The findings highlight differences in how enthalpy and free energy respond to solvent interactions and binding heterogeneity.