van der Waals phase transition in protein solutions

✍ Scribed by Wills, Peter R. ;Winzor, Donald J.

• Publisher: International Union of Crystallography
• Year: 2005
• Tongue: English
• Weight: 94 KB
• Volume: 61
• Category: Article
• ISSN: 0907-4449
• DOI: 10.1107/s0907444905013569

✦ Synopsis

The van der Waals equation of state for imperfect gases is applied to solutions of macromolecules, especially to explain the fluid–fluid phase transition in protein solutions, a phenomenon of much interest in relation to protein crystallization. The van der Waals b parameter corresponds to the total excluded volume per pair of molecules and can be calculated from independently known molecular properties. It is comprised of terms resulting from hard-sphere and net charge–charge interactions. The experimentally determined second virial coefficient B
~2~ can then be used to obtain the equilibrium constant for dimerization K
~2~, a phenomenologically accessible measure of the van der Waals a parameter. Sedimentation equilibrium is recommended as the technique for measuring B
~2~ most accurately. More general results are used to make a minor quantitative correction to the van der Waals prediction concerning the criterion for the fluid–fluid phase transition. Calculations of the effect of inert co-solutes on the phase transition may prove useful in choosing crystallization conditions.