[FTIR, FT-Raman and surface enhanced Raman study of shikimic acid].

ABSTRACT

The authors reported the FT-infrared, and FT-Raman spectra of shikimic acid in solid state and in saturated liquid state in the present article. The vibrational peaks of each group in the molecular structure of shikimic acid were obtained and assigned, and furthermore, the Raman and IR vibrational shifts of the corresponding groups in the molecular structure of shikimic acid were analyzed and speculated especially. As shikimic acid mixed with silver nanoparticle the SERS-active substrate, and was adsorbed on the surface of the silver nanoparticle, we also obtained the surface enhanced Raman scattering (SERS) spectra of shikimic acid at different concentrations from 1.0 x 10(-1) to 1.0 x 10(-5) mol x L(-1), further more the adsorption state and the adsorption characteristics of shikimic acid, adsorbed on the surface of the silver nanoparticle, were studied and speculated with the SERS method and the surface selective rule together. Strong Raman signals were detected in the experiments and each group's vibrations in the molecular structure of shikimic acid were resolved with the combination of FT-infrared and FT-Raman spectroscopy. From the experiment data, the ideal optimized concentrations range is lower than 1 x 10(-3) mol x L, among which we could obtain better SERS spectra. Still, the experimental results suggested that the groups in the molecule structure of shikimic acid, such as COO-, OH-, CH2 and so on, can interact and be absorbed tightly with the surface of silver nanoparticle, and this interaction and absorption were mainly through the SERS charge transfer process mechanism of hydroxyl and carboxyl, and SERS electromagnetic process mechanism of methylene and hypomethyl together with the surface of silver nanopartical. The vibrations of alkene's C=C bond on the ring of cyclohexene in the molecule structure of shikimic showed no obvious enhancement in SERS spectra, which indicated that alkene's C=C bond on the ring of cyclohexene in the molecule structure of shikimic acid had no effective interaction and adsorption on the surface of silver nanoparticle according to the surface selective rule.