Thermophoresis of electrolyte solutions and protein-ligand systems

Thermophoresis or thermodiffusion is the mass transport driven by a temperature gradient. This thesis focuses on the thermophoretic motion of ionic compounds in a biological context and is motivated by a practical application, in which thermodiffusion is used to monitor protein-ligand reactions. Proteins are complex molecules containing non-ionic and ionic groups. While recent studies of non-ionic compounds found a strong correlation between thermodiffusion and hydration, it is unclear how this correlation changes when molecules are charged. To separate ionic from non-ionic contributions, it is reasonable to look first into the thermophoretic motion of simple salts without large organic side groups and to study in the next step complex protein-ligand systems, which typically contain hydrophobic and hydrophilic groups. The systematic studies of aqueous solutions of simple salts should reveal differences between ionic and non-ionic systems and should give further information about ion and ion specific effects. Due to the high complexity of protein-ligand systems, complementary methods should be used to gain a better understanding of the interactions between different components that are present in the system. This will help to understand how the thermophoretic behavior of the free protein differs from that of the protein-ligand complex formed. Study of the thermophoretic behavior of ionic systems indicates that several correlations, which were found for aqueous solutions of non-ionic solutes are no longer valid for ionic solutes. For non-ionic solutes hydrogen bonds primarily influence the thermophoretic behavior. In case of ionic solutes, although both electrostatic interactions and hydrogen bonds are present, it is found that thermophoretic behavior is influenced by electrostatic interactions. Focusing on the specific ion effects for ionic systems in the context of the Hofmeister series, a change of the anion is found to influence the thermophoretic behavior more than a change of the cation. Further, a correlation between thermophoretic behavior and hydrophilicity of the ionic solutes is found, which underlines the sensitivity of thermodiffusion to changes in hydration. Based on this sensitivity, a preliminary model is developed for describing the non-monotonous variation of Soret coefficient ST with concentration for aqueous solutions of alkali iodide salts. To study the thermodiffusion of binding reactions, we also use complementary methods such as Isothermal Titration Calorimetry (ITC) and a thermophoretic microfluidic cell. As systems, we have chosen EDTA-CaCl2 and protein-ligand systems (binding of Bovine Carbonic Anhydrase I (BCA I) with two aryl sulfonamide ligands). To gain deeper insight into the complex formation reactions thermophoretic data (non-equilibrium process) are compared with thermodynamic data (equilibrium process) to establish a mathematical relation between ST and Gibb’s free energy ΔG. For EDTA-CaCl2 and protein-ligand systems, the derived relation holds valid, which enables calculation of ΔG at a particular temperature from ST

Occupational respiratory diseases

Shipping list no.: 87-222-P."September 1986."S/N 017-033-00425-1 Item 499-F-2Also available via the World Wide Web.Includes bibliographies and index