Terahertz Time-Domain Spectroscopy of Amino Acids and Polypeptides

¹ Molecular Photoscience Research Center, Kobe University
² Graduate School of Science and Technology, Kobe University
³ Institute for Molecular Science

^* To whom correspondence should be addressed. E-mail: tominaga{at}kobe-u.ac.jp.

Submitted on May 26, 2005
Revised on June 16, 2005
Accepted on 6 July 2005

	Abstract

Frequency-dependent absorption coefficients and refractive indices of amino-acids (glycine and L-alanine) and polypeptides (polyglycine and poly-L-alanine) in the wavenumber region from 7 cm^-1 to 55 cm^-1 were measured by terahertz time-domain spectroscopy. A vibrational band was observed at 45.5 cm^-1 for polyglycine, which was assigned as an interchain mode. The reduced absorption cross sections of the amino acids and polypeptides show power law behavior. The exponents are different between the monomers and polymers, and those of the two polypeptides suggest that the time dependences of the total dipole moments are similar in the time scale of subpico- to picoseconds.

Key Words: amino acid, low-frequency spectrum, polypeptide, spectroscopy, terahertz region

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