Heinrich Heine University, Condensed Matter Physics Laboratory, Düsseldorf, Germany.
iNANO Interdisciplinary Nanoscience Center and Department of Chemistry, Aarhus University, DK-8000 Aarhus C, Denmark.
J Chem Phys. 2022 Jun 28;156(24):244903. doi: 10.1063/5.0088601.
Intermolecular interactions in protein solutions, in general, contain many contributions. If short-range attractions dominate, the state diagram exhibits liquid-liquid phase separation (LLPS) that is metastable with respect to crystallization. In this case, the extended law of corresponding states (ELCS) suggests that thermodynamic properties are insensitive to details of the underlying interaction potential. Using lysozyme solutions, we investigate the applicability of the ELCS to the static structure factor and how far effective colloidal interaction models can help to rationalize the phase behavior and interactions of protein solutions in the vicinity of the LLPS binodal. The (effective) structure factor has been determined by small-angle x-ray scattering. It can be described by Baxter's adhesive hard-sphere model, which implies a single fit parameter from which the normalized second virial coefficient b is inferred and found to quantitatively agree with previous results from static light scattering. The b values are independent of protein concentration but systematically vary with temperature and solution composition, i.e., salt and additive content. If plotted as a function of temperature normalized by the critical temperature, the values of b follow a universal behavior. These findings validate the applicability of the ELCS to globular protein solutions and indicate that the ELCS can also be reflected in the structure factor.
蛋白质溶液中的分子间相互作用通常包含许多贡献。如果短程吸引力占主导地位，则状态图表现出相对于结晶的液-液相分离（LLPS），这是亚稳的。在这种情况下，扩展对应状态定律（ELCS）表明热力学性质对潜在相互作用势能的细节不敏感。我们使用溶菌酶溶液研究了 ELCS 对静态结构因子的适用性，以及有效的胶体相互作用模型在多大程度上有助于合理化接近 LLPS 双节点的蛋白质溶液的相行为和相互作用。（有效）结构因子已通过小角 X 射线散射确定。它可以用 Baxter 的粘性硬球模型来描述，这意味着可以从一个拟合参数推断出归一化第二维里系数 b，并且发现它与静态光散射的先前结果定量一致。b 值与蛋白质浓度无关，但会系统地随温度和溶液组成（即盐和添加剂含量）而变化。如果以通过临界温度归一化的温度为函数绘制 b 值，则 b 值遵循通用行为。这些发现验证了 ELCS 对球状蛋白质溶液的适用性，并表明 ELCS 也可以反映在结构因子中。
