THz spectroscopy of compatible solutes at HHP conditions probing changes in the hydration water network

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The central goal of this proposal is to record and analyze in detail the low frequency spectra of solvated compatible biomolecules and cosolutes under high hydrostatic pressure (HHP). In the first funding period, we were successfully implementing a HHP diamond anvil cell into a THz FT spectrometer. This new set-up allowed us to record the first low frequency spectra of bulk water and solvated TMAO at HHP conditions (up to 13 kbar). We observed systematic pressure dependent changes of the librational and H-bond stretch modes. In combination with ab initio MD simulations of D. Marx these low frequency HPP spectra provide detailed new insights into changes of the water network dynamics.In the second funding period we will focus on the effects of HPP on the low frequency hydrogen network modes when adding relevant solutes. Thus, we will systematically study cosolute urea/TMAO mixtures for the pressure perturbation of water. Pressure dependent changes of the low frequency spectrum of solvated salts, amino acids, Ac-Gly-NH2 under HHP conditions will yield new insights into pressure induced changes of the intramolecular large amplitude modes, and correlated and anticorrelated solute-water network modes. As a high risk project we will try to study water under supercritical conditions. Experimentally, the frequency range will be extended to include the frequency range below 50 cm-1 using THz time domain spectroscopy.