Lazzara Matthew J, Deen William M
Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
J Colloid Interface Sci. 2004 Apr 15;272(2):288-97. doi: 10.1016/j.jcis.2003.10.008.
To test the effects of solute concentration on the equilibrium partitioning of single macromolecules and macromolecule mixtures between bulk solutions and gels, the partition coefficient in agarose was measured for BSA and for four narrow fractions of Ficoll with Stokes radii of 30-59 A. Solutions of each test macromolecule were equilibrated with a known volume of gel, final liquid concentrations measured, and partition coefficients (gel concentration divided by bulk concentration) calculated by applying a material balance. The partition coefficient of each macromolecule was measured in 4 and 6% gels under dilute conditions and with BSA present at initial concentrations up to 13.5 g/dl. As expected, the partition coefficients decreased with increasing agarose concentration and with increasing macromolecular size. Moreover, increasing the BSA concentration increased the partition coefficient of BSA itself and that of all four Ficolls. This effect was most pronounced for the largest test solutes. Measurements at two ionic strengths confirmed that electrostatic interactions were negligible under the conditions used. The experimental results were compared with predictions from a previously developed excluded volume theory for the partitioning of mixtures of rigid, spheroidal macromolecules in fibrous media. Agarose was represented as a randomly oriented array of cylindrical fibers, BSA as a prolate spheroid, and Ficoll as a sphere. The quantitative agreement between the model predictions and the data was generally quite good, indicating that steric interactions among solute molecules and between solute molecules and gel fibers could explain the partitioning results. The theory is simple enough computationally to be applied to a variety of processes that are influenced by the equilibrium partitioning of macromolecules.
为了测试溶质浓度对单个大分子以及大分子混合物在本体溶液和凝胶之间平衡分配的影响，我们测量了牛血清白蛋白（BSA）以及四种斯托克斯半径为30 - 59 Å的窄级分聚蔗糖在琼脂糖中的分配系数。将每种测试大分子的溶液与已知体积的凝胶平衡，测量最终液体浓度，并通过物料平衡计算分配系数（凝胶浓度除以本体浓度）。在稀释条件下，于4%和6%的凝胶中测量了每种大分子的分配系数，且初始浓度高达13.5 g/dl的BSA也存在。正如预期的那样，分配系数随着琼脂糖浓度的增加以及大分子尺寸的增大而降低。此外，增加BSA浓度会提高BSA自身以及所有四种聚蔗糖的分配系数。这种效应对于最大的测试溶质最为明显。在两种离子强度下的测量证实，在所使用的条件下静电相互作用可忽略不计。将实验结果与先前开发的关于刚性、球形大分子混合物在纤维介质中分配的排除体积理论的预测进行了比较。琼脂糖被表示为圆柱形纤维的随机取向阵列，BSA被表示为长椭球体，聚蔗糖被表示为球体。模型预测与数据之间的定量一致性总体上相当好，表明溶质分子之间以及溶质分子与凝胶纤维之间的空间相互作用可以解释分配结果。该理论在计算上足够简单，可应用于受大分子平衡分配影响的各种过程。
