Department of Chemical and Geological Sciences, University of Cagliari, Cittadella Universitaria, S.S. 554 bivio Sestu, 09042 Monserrato (CA), Italy.
Murdoch University, Discipline of Physics, Chemistry and Mathematics, 90 South St, Murdoch, WA, 6150, Australia.
Phys Chem Chem Phys. 2022 Mar 16;24(11):6544-6551. doi: 10.1039/d2cp00223j.
Buffer solutions do not simply regulate pH, but also change the properties of protein molecules. The zeta potential of lysozyme varies significantly at the same buffer concentration, in the order Tris > phosphate > citrate, with citrate even inverting the zeta potential, usually positive at pH 7.15, to a negative value. This buffer-specific effect is a special case of the Hofmeister effect. Here we present a theoretical model of these buffer-specific effects using a Poisson-Boltzmann description of the buffer solution, modified to include dispersion forces of all ions interacting with the lysozyme surface. Dispersion coefficients are determined from quantum chemical polarizabilites calculated for each ion for tris, phosphate, and citrate buffer solutions. The lysozyme surface charge is controlled by charge regulation of carboxylate and amine sites of the component amino acids. The theoretical model satisfactorily reproduces experimental zeta potentials, including change of sign with citrate, when hydration of small cosmotropic ions (Na, H, OH) is included.
缓冲溶液不仅能调节 pH 值，还能改变蛋白质分子的性质。溶菌酶在同一缓冲浓度下的 ζ 电位变化显著，按 Tris > 磷酸盐 > 柠檬酸盐的顺序变化，甚至柠檬酸会使 ζ 电位反转，通常在 pH 值为 7.15 时为正，变为负值。这种缓冲特定的效应是豪夫迈斯特效应的一个特例。在这里，我们使用缓冲溶液的泊松-玻尔兹曼描述，提出了一个理论模型，该模型对所有与溶菌酶表面相互作用的离子的色散力进行了修正。色散系数是根据每种离子的量子化学极化率计算得出的，用于 tris、磷酸盐和柠檬酸盐缓冲溶液。溶菌酶表面电荷由组成氨基酸的羧酸盐和胺基位点的电荷调节控制。当包括小的亲水分子（Na、H、OH）的水合作用时，理论模型可以很好地再现实验 ζ 电位，包括与柠檬酸一起变化的符号。
