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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 [1].
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 [2]. 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.
[1] G. Niehues, A. L. Kaledin, J. M. Bowman, and M. Havenith, J. Phys. Chem. B (2012),
116(33), 10020.
[2] G. Niehues, M. Heyden, D. A. Schmidt, and M. Havenith, Faraday Discussions (2011),
150, 193-207.
[3] J. L. Cornette, K. B. Cease, H. Margalit, J. L. Spouge, J. A. Berzofsky, and C. DeLisi, J.
Mol. Biol. (1987), 195, 659.
[4] G. D. Rose, L. M. Gierasch, and J. A. Smith, Advan. Prot. Chem. (1985), 37, 1.