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Spectroscopy
Volume 24 (2010), Issue 1-2, Pages 153-158
http://dx.doi.org/10.3233/SPE-2010-0423

Low-frequency dynamics of biological molecules studied by terahertz time-domain spectroscopy

Shintaro Kawaguchi,1 Ohki Kambara,2 Carlito S. Ponseca Jr.,2 Mikihiro Shibata,3 Hideki Kandori,3 and Keisuke Tominaga1,2,4

1Graduate School of Science, Kobe University, Nada, Kobe, Japan
2Molecular Photoscience Research Center, Kobe University, Nada, Kobe, Japan
3Nagoya Institute of Technology, Showa-ku, Nagoya, Japan
4Graduate School of Science, Kobe University, Nada, Kobe, 657-8501, Japan

Copyright © 2010 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

By terahertz (THz) time-domain spectroscopy we have measured low-frequency spectra of amino acid (glycine; Gly), short peptides ((Gly)3 and (Gly)4), six globular proteins and bacteriorhodopsin (BR). From the analysis of the THz spectra we defined and obtained the reduced absorption cross sections for these cases, which are proportional to the vibrational density of states. We observed anharmonic behaviors in the low-frequency modes of the short peptides. The globular proteins we investigated show a universal feature in the low-frequency spectra. BR shows the dynamical transition in the temperature dependence of the THz spectrum when the sample is hydrated.