Intramolecular vibrations in low-frequency normal modes of amino acids: L-alanine in the neat solid state.
This paper presents a theoretical analysis of the low-frequency phonons of L-alanine by using the solid-state density functional theory at the Γ point. We are particularly interested in the intramolecular vibrations accessing low-frequency phonons via harmonic coupling with intermolecular vibrations. A new mode-analysis method is introduced to quantify the vibrational characteristics of such intramolecular vibrations. We find that the torsional motions of COO(-) are involved in low-frequency phonons, although COO(-) is conventionally assumed to undergo localized torsion. We also find the broad distributions of intramolecular vibrations relevant to important functional groups of amino acids, e.g., the COO(-) and NH3(+) torsions, in the low-frequency phonons. The latter finding is illustrated by the concept of frequency distribution of vibrations. These findings may lead to immediate implications in other amino acid systems.
†Molecular Photoscience Research Center, Kobe University, Kobe 657-8501, Japan.
Feng
F
Zhang
‡Center for Condensed Matter Sciences, National Taiwan University, 1 Roosevelt Road, Section 4, Taipei 10617, Taiwan.
Houng-Wei
HW
Wang
†Molecular Photoscience Research Center, Kobe University, Kobe 657-8501, Japan.
Keisuke
K
Tominaga
‡Center for Condensed Matter Sciences, National Taiwan University, 1 Roosevelt Road, Section 4, Taipei 10617, Taiwan.
Michitoshi
M
Hayashi
D000409:Alanine / Q000737:chemistry*; D011789:Quantum Theory; D014732:Vibration
D000409:Alanine