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FIR CENTER SEMINAR Title: THz Spectroscopy and Simulation of Aqueous Solutions: Hydrophobicity and Phase Transitions in Hydrogen Bond Networks Speaker: Dr. Gudrun Niehues (Researcher of FIR Center) Date: 16:40~17:40, December 25th (Tue), 2012 Place: Colloquium room, 5F, FIR FU Organizer: FIR FU, University of Fukui Host: M. Tani Phone: 0776-27-8659 (Ext. 2724) THz Spectroscopy and Simulation of Aqueous Solutions: Hydrophobicity and Phase Transitions in Hydrogen Bond Networks The role of the water for biological relevant processes such, as protein folding or enzymatic function, is still a matter of debate. THz absorption spectroscopy can address open questions in this field, which we demonstrate by simulating the driving of a solute in the THz regime . Applying the “Driven Molecular Dynamics” approach, we watch the energy flow from solute to water. We find much larger and faster energy flow from the solute to the water when exciting THz modes compared to IR modes. This indicates a strong coupling of solute and water dynamics in the THz regime. Furthermore, we present a study on solvated amino acids using terahertz (THz) absorption spectroscopy measurements . Although hydrophobicity is a commonly used concept, its microscopic nature, particularly in the context of hydration, is not well understood. The literature gives a large number of hydrophobicity scales [3,4], which are based various experimental and empirical data. Here, we investigated several solvated amino acids and some small peptides using our high-power p-Germanium laser spectrometer (2.3-2.8 THz). We are able to correlate the concentration dependent absorption coefficient of the aqueous solutions with specific properties of the solute such as polarity and hydrophobicity. Expanding the studies to amphiphilic molecules, which consist of a hydrophobic and a hydrophilic part, we investigate lyotropic liquid crystals. Due to the amphiphilic character of the solutes, micelles are formed in aqueous solution. These build up different phases dependent on temperature, pressure and concentration of the solute. In a temperature dependent study using FT-THz spectroscopy, we are able to identify and quantify chances in the THz spectrum of a lyotropic liquid crystal during phase transitions.  G. Niehues, A. L. Kaledin, J. M. Bowman, and M. Havenith, J. Phys. Chem. B (2012), 116(33), 10020.  G. Niehues, M. Heyden, D. A. Schmidt, and M. Havenith, Faraday Discussions (2011), 150, 193-207.  J. L. Cornette, K. B. Cease, H. Margalit, J. L. Spouge, J. A. Berzofsky, and C. DeLisi, J. Mol. Biol. (1987), 195, 659.  G. D. Rose, L. M. Gierasch, and J. A. Smith, Advan. Prot. Chem. (1985), 37, 1.