莽草酸FTIR,FT-Raman光谱及SERS研究

FTIR,FT-Raman and Surface Enhanced Raman Study of Shikimic Acid

报道了莽草酸的FTIR,固态及饱和液态的FT-Raman光谱,归属并分析了莽草酸分子内各基团的振动峰位及其相应基团在两种振动光谱中的振动峰位变化规律。利用表面增强拉曼散射(SERS)光谱及表面吸附选择定律研究了莽草酸在以银粒子为活性基底表面的吸附状态及其不同浓度变化对其SERS的影响,探讨了莽草酸在银粒子表面的吸附机理和规律。实验结果表明,红外与拉曼光谱结合较为全面地解析了莽草酸的分子结构中各基团的振动情况;获得了莽草酸在银粒子表面的最佳SERS效应的浓度范围,莽草酸浓度小于1×10-3mol·L-1时,其SERS明显趋好;根据SERS作用机制,莽草酸的分子在银粒子表面的吸附主要是通过其羟基、羧基的电荷转移机制及其亚甲基、次甲基的电磁作用机制共同作用;其环内双键没有明显SERS表明其未能在银粒子表面产生有效吸附理。

The authors reported the FF-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 shikirnic 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× 10^1 to 1.0× 10^-5 mol · 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× 10^-3mol· 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.