van der Waals phase transition in protein solutions.

Area of Science:

• Physical Chemistry
• Biophysics
• Macromolecular Science

Background:

• The van der Waals equation of state is crucial for understanding imperfect gases.
• Fluid-fluid phase transitions in protein solutions are key to protein crystallization.
• Molecular interactions significantly influence the behavior of macromolecular solutions.

Purpose of the Study:

• To apply the van der Waals equation of state to macromolecular solutions, specifically protein solutions.
• To elucidate the phenomenon of fluid-fluid phase transition in proteins.
• To provide insights into protein crystallization by understanding phase behavior.

Main Methods:

• Application of the van der Waals equation of state to protein solutions.
• Calculation of the van der Waals 'b' parameter from molecular properties (hard-sphere and charge interactions).
• Determination of the second virial coefficient (B2) and its relation to the dimerization constant (K2) and van der Waals 'a' parameter.
• Recommendation of sedimentation equilibrium for accurate B2 measurement.

Main Results:

• The van der Waals 'b' parameter is shown to be a function of excluded volume from hard-sphere and net charge-charge interactions.
• The second virial coefficient (B2) provides a measure of the van der Waals 'a' parameter via the dimerization constant (K2).
• A minor quantitative correction to the van der Waals prediction for the fluid-fluid phase transition criterion was derived.
• The influence of inert co-solutes on phase transitions was considered.

Conclusions:

• The van der Waals framework offers a valuable approach to understanding protein solution phase behavior and crystallization.
• Molecular properties, including excluded volume and charge interactions, directly impact phase transitions.
• Accurate measurement of B2 and understanding co-solute effects can aid in optimizing protein crystallization conditions.