Raman Study of Hydrogen Bonding and Long-Wavelength Lattice Modes in an L-Alanine Single Crystal

Abstract

This paper presents a detailed polarization study of the Raman scattering spectrum from the lattice phonons of a single L-alanine crystal, with and without the presence of an external de electric field from 120 to 350°K. The scattering experiments were made with the incident Ar ion laser beam propagating along the 〈100〉, 〈010〉, and 〈001〉 directions of the crystal. The Raman spectra of four different scattering configurations associated with each crystal orientation were measured. The experimental results have shown the presence of a large orientational anisotropy as well as polarization anomalies in the lattice Raman spectrum of the L-alanine single crystal. By means of several different experiments (light transmission measurement, different excitation laser frequencies, temperature variations of the crystal, and de electric field study), several existing possibilities that might be associated with the polarization anomalies have been ruled out. To account for the observed effect, a picture of dynamic disorder due to the proton motion that exists within the hydrogen bond has been proposed. In addition to the spectral features associated with the lattice modes, the spectral bandwidth studies of the – NH 3 + libration and the –N–H stretching also give a result consistent with the proposed picture. Due to the nature of charge fluctuations present in a hydrogen bond, it is suggested that this phenomena should be present in all hydrogen-bonded molecular systems.

Temperature‐dependent Raman study of taurine single crystal

“…With temperature variation, a few amino acid and aminosulfonic compounds were investigated in a search of phase transitions, in particular, by vibrational techniques. In the L-methionine crystal, for example, by using infrared and Raman spectroscopy, a phase transition was observed at 307 K. 13 For the most studied crystal, L-alanine, 14,15 no strong evidence of a phase transition was obtained (nevertheless, we should remark that phonon echo measurements suggested the possibility of a structural modification at 178 K 16 ). In order to study the low-temperature stability of the monoclinic C 2h 5 phase of taurine crystal we obtained the lowwavenumber spectrum at various temperatures.…”

The behavior of NH3 torsional vibration of l-alanine, l-threonine and taurine crystals under high pressure: A Raman spectroscopic study

“…There are many reasons for this: a detailed characterization of the interactions between polar and nonpolar molecules is fundamental for our understanding of biological functions; the Raman polarizability tensor can give informations about the charge-transfer mechanism and intermolecular interactions; Raman and infrared vibrational spectroscopies help in the understanding of the molecular conformation and the nature of hydrogen bonding in proteins [1][2][3][4][5] as well as to provide an indirect way of estimating some thermodynamic parameters, such as enthalpy, associated with the hydrogen bond in the crystals [6].…”

First principles investigation of L-alanine in terahertz region

“…Among amino acids, of particular interest is L-alanine due to its simple molecular structure. Much work has been carried out on the spectral properties of L-alanine, including Raman scattering (25-175 cm −1 ) [19], farinfrared absorption spectra (20-600 cm −1 ) [20], and THz absorption spectra [21][22][23][24][25]. Up to now, some work dealt with the THz spectrum of L-alanine only in terms of experiment [21][22][23].…”