Authors: V. Sonois, A. Estève, A. Zwick, P. Faller, W. Bacsa
Affilation: CEMES CNRS Univ Toulouse, France
Pages: 352 - 355
Keywords: Raman spectroscopy, amino acids, density functional calculations, scanning electron microscopy, nanogram detection
Previously we reported intense and narrow vibrational Raman bands of the amino acid histidine grown from droplets of aqueous histidine on silica (Sonois et al., 2007, Chem. Phys. Lett., 439, 360-363). In the present communication we show results on the amino acids glycine and valine. Intense Raman signals were observed of nano gram quantities using visible laser excitation (488nm) at relatively low laser power (5mW) and short acquisition time (2min). Considerable variations in the Raman signal were observed when changing the pH of the amino acid solution. Scanning electron microscopy reveals considerable differences in the crystallite structure of histidine, valine and glycine and as a function of pH. Narrow vibrational bands are correlated with formation of crystallites. H/D substitution and variation of pH were used to identify vibrational bands associated with functional groups which exchange protons. The observed spectral bands are directly compared with density functional calculations to assign the vibrational bands in histidine, valine and glycine. The effect of hydration is studied at neutral pH in the theoretical calculations. We will report periminary results on proteins.