• Raman;
  • surface-enhanced Raman scattering;
  • l-proline;
  • trans-4-hydroxy- l-proline;
  • theoretical calculations

The Raman and surface-enhanced Raman scattering (SERS) spectra of l-proline (Pro) and trans-4-hydroxy- l-proline (Hyp) were recorded. SERS spectra were obtained on colloidal Ag prepared by reduction with hydroxylamine. Allowing sufficient time for Pro and Hyp to adjust in the colloidal solution resulted fundamentally in obtaining unique and reproducible SERS spectra. Hyp stabilizes on the surface more rapidly than Pro. The spectral analysis indicates that Pro interacts with the Ag surface through the carboxylate group. The interaction of Hyp with the metal surface occurs through the amino, methylene and carboxylate moieties of the molecule. The spectroscopic results are supported by quantum chemical calculations, performed using extended Hückel theory (EHT) of the title compounds interacting with an Ag cluster model. The assignment of the Raman bands was supported by a normal coordinate analysis performed through Becke, three-parameter, Lee–Yang–Parr/6-311 G* + calculations. Copyright © 2011 John Wiley & Sons, Ltd.