Mass Transfer and Thermodynamics for Biological Production of Chemicals

这一更新项目涉及增加生物过程对特种化学品生产的影响的两个重要领域：使用非水溶剂进行酶催化反应，以及开发基于双水相系统的新分离工艺。第一个方面将集中在超临界溶剂中的酶反应：在之前的赠款期间，已经证明了酶在密集二氧化碳中的稳定性，并获得了胆固醇氧化和三酰甘油酯交换反应的动力学数据。这项研究通过探索超临界二氧化碳与夹带剂的用途，扩大了超临界二氧化碳可能使用的底物浓度范围；它还提供了对所研究的两种酶的动力学和传质影响的更详细的研究。此外，还利用EPR光谱研究了酶在非水介质中的构象。使用氮氧化物自旋标记的胆固醇探针来监测胆固醇氧化酶活性部位的空间坐标。第二个方面将集中于产品回收的双水相体系：这项研究旨在建立双水相体系的基本分子热力学。一个重要的目标是确定哪些聚合物-聚合物系统可能最适合生物处理。为此，PI使用光散射和差蒸汽压继续测量，以获得含有葡聚糖、聚乙二醇组分、蛋白质以及聚合物-聚合物和聚合物蛋白质对组合的水混合物的热力学参数。这些数据与盐分配引起的电势效应信息和基于渗透维里方程的分子热力学模型相结合，使PI能够预测聚合物-聚合物-水相图和蛋白质分配系数，用于工艺设计和优化。

This renewal project is concerned with two areas of importance for increasing the impact of biological processes on production of specialty chemicals: use of non-aqueous solvents for enzyme catalyzed reactions and development of novel separations processes based on aqueous two-phase systems. The first aspect will focus on enzyme reactions in supercritical solvents: In the previous grant period, the stability of enzymes, both free and immobilized in dense carbon dioxide, has been demonstrated, and kinetic data have been obtained for the oxidation of cholesterol and the interesterification of triacylglycerides. This research expands the possible range of substrate concentrations which can be used with supercritical carbon dioxide by exploring its use with entrainers; it also provides a more detailed study of the kinetic and mass transfer effects of importance for both enzymes studied. In addition, the conformation of enzymes in this non-aqueous medium is examined by the use of EPR spectroscopy. A nitroxide spin-labelled cholesterol probe is employed to monitor the spatial coordinates at the active site of cholesterol oxidase. The second aspect will focus on aqueous two-phase systems for product recovery: This research is directed toward establishing the fundamental molecular thermodynamics of aqueous two-phase systems. An important objective is to determine what polymer-polymer systems may be best suited for bioprocessing. Toward that end, the PIs continue their measurements using light scattering and differential vapor pressure to obtain thermodynamic parameters for aqueous mixtures containing dextran, polyethyleneglycol, proteins and combinations of polymer-polymer and polymer protein pairs. These data, combined with information on electrical-potential effects due to salt partitioning and a molecular-thermodynamic model based upon the osmotic virial equation, allow the PI's to predict polymer-polymer-water phase diagrams and protein partition coefficients for process design and optimization.