It is water what matters

Molecular understanding of biological recognition processes is surely a major prerequisite for future drug design. Protein-ligand binding is favorable when the change in free energy G=H-TS is negative. Therefore, calorimetry is a very powerful biochemical tool. Up to now, calorimetric measurements are all based on heat transfer and are thus inherently slow (with relaxation times of typically 1 - 100s, depending on the system and method applied) and restricted to equilibrium conditions, so only either the bound or the unbound state â€" or stationary mixtures of both (determined by the equilibrium constant K) are characterized in terms of Î"G and Î"H.
Terahertz (THz) spectroscopy is a new tool to probe subtle changes in the hydration dynamics. It allows to directly access the collective, (sub-)psec hydrogen bond dynamics of water. [1,2]
We propose that the low frequency THz spectrum of hydration water around solutes provides fingerprints of the hydration bond network, which can be quantitatively be correlated with changes in entropy S [4]. THz calorimetry offers the possibility to map the solvent reorganization. Our scientific vision is to introduce ultrafast “THz-Calorimetry”, i.e. to correlate the THz spectrum with entropy changes of the solvent under non-equilibrium conditions. I will present the results of linear and non-linear THz experiments to probe the change in hydrogen network dynamics in real time with time resolution in the ps or fs range. Future applications include water mapping in enzymatic reactions, upon protein folding or charge transfer reactions in electrochemical cells.

Speaker: Martina Havenith-Newen, Rurh-Universitat Bochum