Thermophoresis or thermodiffusion is a mass transport process driven by a temperature gradient. In the biological context, there are two main applications: first, the accumulation of a component in a microfluidic system through a combination of thermodiffusion and convection, and second, the characterization of protein binding reactions, since thermodiffusion is very sensitive to complex formation. We are investigating both topics: The accumulation process is examined in the context of theories about the “origin-of-life”, and the second topic is examined with regard to the question of what we can learn from the altered thermodiffusion behaviour about changes in the hydration shell during complex formation, e.g. in a protein-ligand binding process. For non-ionic compounds, we find a clear correlation between hydrophilicity and temperature sensitivity of the thermophoretic behaviour.

The thermophoretic investigation of ions reveals ion-specific hydration effects that are crucial for biological information processes. Through systematic thermophoretic measurements combined with neutron scattering experiments, dichroism and isothermal titration experiments, we gain a deeper insight into the entropic, enthalpic and structural changes of the protein, the protein-ligand complex and the accompanying hydration layer. In quantifying biomolecular bonding, we have found a correlation between the energy released during a reaction and the concentration difference generated by a temperature gradient. This is an important step towards understanding non-equilibrium processes as they occur in the human body.