A contribution to the theory of preferential interaction coefficients

Area of Science:

• Thermodynamics
• Physical Chemistry
• Biophysical Chemistry

Background:

• Preferential interaction coefficients quantify solute interactions in solutions.
• Understanding these interactions is crucial for macromolecular behavior in biological systems.
• Existing models have limitations in fully explaining these coefficients.

Purpose of the Study:

• To provide a complete derivation of concentration-based preferential interaction coefficients from pair correlation functions.
• To address omissions in previous treatments of pair correlation functions in multicomponent thermodynamics.
• To connect concentration-based coefficients with molality-based ones and analyze experimental data.

Main Methods:

• Derivation of relationships between preferential interaction coefficients and pair correlation functions.
• Heuristic analysis of contributions to these coefficients from excluded volume and exchange reactions.
• Application of the derived formulation to experimental data of osmolytes with bovine serum albumin.

Main Results:

• A simple and complete derivation is presented for the first time.
• Excluded volume effects are shown to be larger than exchange reaction contributions.
• Preferential interaction coefficients exhibit predicted dependence on osmolyte concentration.
• Analysis of experimental data indicates slight deviations from random occupation near macromolecular surfaces.

Conclusions:

• The study provides a robust theoretical framework for understanding preferential interactions.
• Excluded volume and exchange reactions play distinct roles in osmolyte-macromolecule interactions.
• A mechanism for osmolyte identity concealment in ordered water layers is proposed.