9 February 2012 Long-range hydration state of lipid bilayer studied by THz spectroscopy
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Although the importance of water for bio-materials have been believed, even the amount of hydration water have not been defined. Despite picosecond time scale of the collective dynamics of bulk water, past studies for the hydration state of solute with using NMR or neutron scattering have measured water dynamics only in nanosecond time scale and have defined only the strongly perturbed water as the hydration water. However, it is expected that much more slightly perturbed water exist near the solute surfaces. To define precisely the hydration state of lipid bilayer, which is the basic structure of biomembrane, including slightly perturbed water, we have used terahertz time-domain spectroscopy, with which picosecond dynamics of water can be measured. By comparing the terahertz results with the structural information of the lipid/water system obtained by X-ray scattering, it is concluded that there is a long-range hydration layer on the surface of lipid membrane on up to 4-5 water layers (1 nm) [1], which is 5 time as much as that in the previous reports by NMR or neutron scattering. Our results indicates that the hydration water is important for the self-assembly of biomolecules because its length scale is comparable to that of some interactions such as van der Waals interaction.
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Mafumi Hishida, Koichiro Tanaka, "Long-range hydration state of lipid bilayer studied by THz spectroscopy", Proc. SPIE 8221, Optical Interactions with Tissue and Cells XXIII, 82210T (9 February 2012); doi: 10.1117/12.907655; https://doi.org/10.1117/12.907655

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