Thermophoresis of biological and biocompatible systems

Thermophoresis, or thermodiffusion, is mass transport driven by a temperature gradient. This work focuses on thermodiffusion in a biological context, where there are two major applications for the effect: accumulation of a component in microfluidic devices through a combination of thermodiffusion and convection, and monitoring of protein binding reactions through the sensitivity of thermodiffusion to complex formation.Both applications are investigated, the first as an accumulation process in the context of origin-of-life theories and the second in light of the question what we can learn from the observed changes in thermodiffusion about modifications of the hydration shell upon complex formation. While thermodiffusion in non-polar liquids can be predicted with reasonable accuracy, the description of aqueous systems is complicated as their concentration and temperature dependence is often anomalous. The underlying goal of this work is to gain a better understanding of the interactions between components in an aqueous mixture and how they influence thermodiffusion.We find that the temperature dependence of a solute's thermodiffusion correlates with its hydrophilicity and argue that the temperature sensitivity of hydrogen bonds, which dominate the interactions in aqueous solutions, might induce a temperature dependence of the chemical potential. Such a temperature dependence is as of yet not considered in theoretical descriptions of thermodiffusion. Numerical calculations show that the thermophoretic accumulation process, as of yet only considered for the formation of RNA, can accumulate formamide to high concentrations that would allow the formation of prebiotic molecules. A heuristic model is developed to illuminate the mechanism behind the accumulation. Cyclodextrins and streptavidin were investigated as model systems for biological complexes. It is feasible that the exquisite sensitivity of thermodiffusion to interactions with the surrounding solvent allows inferences about changes in the protein's hydration shell upon complex formation. Preliminary measurements on streptavidin-biotin show a decreased hydrophilicity of the complex, which is in qualitative agreement with increased entropy of the hydration shell upon complex formation calculated from calorimetric and neutron scattering experiments