Aqueous Two-Phase Extraction: Theory and Experiment

当两种水溶性聚合物的水溶液混合在一起时，超过临界浓度，就会发生液-液分离。当聚乙二醇和盐混合在一起时，也会发生类似的情况。添加到两相混合物中的蛋白质或酶往往会在两相之间不均匀地分配，从而允许提取特定的蛋白质。在过去的三年里，在西德朱利希酶技术研究所的库拉教授的合作下，在国家科学基金会的资助下(CBT-872084)，PI一直在开发水相两相分配的统计力学理论，并一直在对聚乙二醇/Dx体系的相行为进行补充实验。实验包括仔细地组合相平衡图，以及确定两相之间的界面张力作为组成的灵敏指示剂。理论上，建立了聚合物-聚合物、聚合物-蛋白质、离子-离子、蛋白质-蛋白质、蛋白质-离子和聚合物-离子相互作用的简单模型，可以用来计算水中的平均作用力势。这项拟议的研究建议按照同样的思路进行额外的理论工作。利用已发展的平均力势，通过积分方程法的闭合假设，求出径向分布函数。从径向分布函数可以得到热力学性质，并识别相分离行为。这些计算将得到相平衡的Gibbs蒙特卡罗计算机模拟的补充。这些模拟将允许验证通过积分方程法获得的平衡，并将提供一种获得积分方程法被证明不适用的相平衡的方法。将进行模拟和积分相平衡计算，以开发能够预测聚合物/聚合物和聚合物/盐混合物中的相平衡的理论，以及蛋白质的分离g，包括多个蛋白质分配，以及可能的与聚合物分子结合的亲和配体的影响。还将进行蛋白质分配的补充实验。

When two aqueous solutions of water soluble polymer such as PEG and dextran are mixed together, above critical concentrations, a liquid-liquid phase separation occurs. A similar situation occurs when PEG and salt are mixed together. Proteins or enzymes added to either of the resulting two phase mixtures will tend to partition unequally between the two phases, thus allowing for the extraction of a particular protein. Over the past three years, in collaboration with Professor Kula of the Institute for Enzymetechnology in Julich, West Germany, and under the auspices of an NSF grant (CBT-872084), the PI has been developing a statistical mechanical theory for aqueous two phase partitioning, and has been undertaking complementary experiments on the phase behavior of the PEG/Dx system. The experimentation involved the careful assemblage of phase equilibria diagrams, and the identification of the interfacial tension between the two phases as a sensitive indicator of composition. Theoretically, simple models of polymer-polymer, polymer-protein, ion-ion, protein-protein, protein-ion and polymer-ion interactions have been developed which can be used to calculate potentials of mean force in water. The proposed research suggests additional theoretical work along the same lines. The mean force potentials which have been developed are to be used to obtain the radial distribution function via the closure postulation of the integral equation technique. From the radial distribution function, thermodynamic properties can be obtained, and phase separations behavior identified. These calculations will be supplemented by Gibbs Monte-Carlo computer simulations of the phase equilibria. These simulations will allow verification of the equilibria obtained by the integral equation route, and will provide a method for obtaining phase equilibria for which the integral equation approach proves inadequate. Simulations and integral phase equilibria calculations will be carried out to develop theories capable of predicting phase equilibria in polymer/polymer and polymer/salt mixtures, and the segregation g of proteins including multiple protein partitioning and possibly the effect of affinity ligands attached to the polymer molecule.. Complementary experiments on protein partitioning will also be undertaken.