We apply an extension of the Baxter sticky-sphere model to mixtures of highly concentrated aqueous solutions of the bovine eye lens proteins gamma-B crystallin and alpha crystallin, which show enhanced phase separation[1] likely due in part to their effective radius ratio of close to 4.5. Gamma-B crystallin is smaller and is modeled with a temperature-dependent stickiness parameter that reproduces static light scattering near its upper consolute point[2], and small-angle neutron scattering at scattering vector magnitudes below 2 inverse nanometers[3]. Alpha crystallin is modeled as a larger, hard sphere, consistent with its scattering properties. With these choices together with hard-sphere gamma-B-alpha crystallin interactions, the Barboy-Tenne mixture extension of the Baxter model[4] predicts considerably higher phase separation temperatures than are observed. This is consistent with recent findings from molecular dynamics simulations applied to model small-angle neutron scattering data, that hard-sphere gamma-B-alpha interactions would lead to mixture instability[5]. We examine the consequences of alternative gammaB-alpha interactions for phase separation and scattering.

[1] Thurston GM, J. Chem. Phys., 124, 134909 (2006) [2] Fine B.M., Lomakin A, Ogun OO, et al. J. Chem. Phys., 104(1):326-335 (1996) [3] Stradner A, Thurston GM, and Schurtenberger P, J. Phys. Cond. Matt. 17:1-12 (2005) [4] Barboy B and Tenne R, Chem. Phys. 38(3):369-387 (1979) [5] Stradner A, Foffi G, Dorsaz N, et al, to be submitted.