Phase behavior characterization of mixed nonionic surfactant solutions: implications for membrane protein crystallization

The phase behavior of aqueous nonionic surfactant mixtures of n-octyl-b-D-glucopyranoside and triethylene glycol monooctyl ether (C8bG1 and C8E3) has been studied. C8bG1 is widely used for crystallization of membrane proteins, and forms an isotropic liquid phase in aqueous solution at all temperatures up to 60% wt. We explored the effect of the cosurfactant C8E3 on the solubility of C8bG1. Light scattering was used to determine critical micelle concentrations and second virial coefficients for the mixed surfactant systems at various surfactant ratios. The effect of such surfactant solutions on colloidal interparticle interactions was explored by examining the behavior of colloidal silica particles in mixtures near the cloud curve. Particle attractions and aggregation depend on the proximity of the cloud curve, and show how such phase behavior features could influence protein interactions.