Sajan D, Fischer Andreas, Joe I Hubert, Jayakumar V S
Centre for Molecular and Biophysics Research, Department of Physics, Mar Ivanios College, Thiruvananthapuram 695 015, Kerala, India.
Spectrochim Acta A Mol Biomol Spectrosc. 2006 Jun;64(3):580-5. doi: 10.1016/j.saa.2005.07.079. Epub 2006 Feb 2.
The surface geometry of (RS)-phenylsuccinic acid molecule was studied by analysis of the SERS spectra of aromatic dicarboxylic acid adsorbed on silver colloid surfaces. For a reliable analysis of the SERS spectrum, we also performed density functional theoretical calculations. The SERS spectral features indicated that the RSPSA molecules should bound to the silver as dicarboxylate, with a strongly tilted orientation with respect to the normal to the surface. Such a tilted orientation was presumed to occur by the simultaneous sigma and pi-type coordination of carboxylate groups to silver surface caused by the steric hindrance and electrostatic repulsion between the two carboxylate groups, and thereby RSPSA on silver was easily displaced with aromatic carboxylic acids. A sigma-type coordination therefore seemed to be more important than a pi-type coordination for aromatic carboxylic acid derivatives to assemble on a silver surface. The large enhancement of in-plane bending, out of plane bending and ring breathing modes in the surface-enhanced Raman scattering spectrum indicates that the molecule is adsorbed on the silver surface in a 'at least vertical' configuration, with the ring perpendicular to the silver surface.
通过分析吸附在银胶体表面的芳香族二羧酸的表面增强拉曼散射（SERS）光谱，研究了（RS）-苯基琥珀酸分子的表面几何结构。为了对SERS光谱进行可靠分析，我们还进行了密度泛函理论计算。SERS光谱特征表明，RSPSA分子应以二羧酸盐形式与银结合，相对于表面法线呈强烈倾斜取向。这种倾斜取向被认为是由于两个羧酸盐基团之间的空间位阻和静电排斥，导致羧酸盐基团与银表面同时发生σ型和π型配位，从而使银上的RSPSA很容易被芳香族羧酸取代。因此，对于芳香族羧酸衍生物在银表面的组装，σ型配位似乎比π型配位更重要。表面增强拉曼散射光谱中面内弯曲、面外弯曲和环呼吸模式的大幅增强表明，该分子以“至少垂直”的构型吸附在银表面，环垂直于银表面。
