CONFORMATION OF MONO-CARBOXYLIC AND DICARBOXYLIC-ACIDS ADSORBED ON SILVER SURFACES
CONFORMATION OF MONO-CARBOXYLIC AND DICARBOXYLIC-ACIDS ADSORBED ON SILVER SURFACES
复制标题
DOI：
10.1021/ja00310a014
复制
发表时间：
1985-01-01
影响因子：
15
通讯作者：
SUH, JS
中科院分区：
文献类型：
--
作者：
MOSKOVITS, M;SUH, JS
根据表面增强拉曼光谱，推测了吸附在银胶体表面的一元羧酸和二元羧酸离子的几何构型和构象。一元羧酸在银溶胶表面呈全反式构象，在CC骨架伸缩区没有明显的“笨拙”标记，在CCC变形区存在低频“手风琴”模式，不对称的CH 3伸缩振动强度随烷基链中碳原子数的变化而变化.我们推测，这种构象的选择，以避免，尽可能多的，疏水的烷基链和水性环境之间的相互作用。羧酸基团负责表面键合，可能螯合到银表面位点。二羧酸通过两个羧酸基团结合。因此，聚亚甲基链以最佳方式排列以实现这一点。结果，反式“标记”不存在，表明存在大量的gauche或接近gauche键。琥珀酸根离子具有顺式构象，从而“站立”在其两个羧酸根基团的表面上。表面增强拉曼光谱已被用于研究大量分子吸附在特别制备的金属表面1，其中银是最突出的。我们最近表明，金属表面上的分子取向可以推导出从Sers光谱，通过应用简单的参数有关的相对强度的Sers频带或在某些情况下，没有带。2，3 Creighton 4使用类似的论据来推断吡啶在Ag、Au和Cu溶胶颗粒表面的取向。在本文中，我们研究了一些离子的表面几何和构象，
The geometryand conformationof a number of the ions of monocarboxylic and dicarboxylic acids adsorbed on silver colloid surfaces were deduced from their SERSspectra. Monocarboxylic acids adopt an all-trans conformation on the silver sol surface, as evidenced by the absence of gauche markers in the skeletal CC stretching region of the spectrum, the presence of the low-frequency “accordion" mode in the CCC deformation region, and the alternationof the intensityof the asymmetric CH3 stretching vibration with the number of carbons in the alkyl chain. We speculate that this conformation is chosen in order to avoid, as much as possible, hydrophobe interactions between the alkyl chainand the aqueous ambient. The carboxylate group is responsible for the surface bond, probably chelatingto silver surface sites. The dicarboxylate acids bind through both carboxylate groups. The polymethylene chain is therefore arranged in such a way as best to accomplish this. As a result, trans “markers” are absent suggesting the presence of a large number of gauche or nearly gauche bonds. Succinate ion is shown to have a cis conformation so as to “stand” on the surface on its two carboxylate groups.Surface-enhanced Raman spectroscopy has been used to investigate a large number of molecules adsorbed on specially prepared metal surfaces1 among which silver is the most prominent. We have recently shown that molecular orientation upon the metal surface may be deduced from the SERS spectra by applying simple arguments regarding the relative intensities of SERS bands or in some cases the absence of bands. 2, 3 Creighton4 has used similar arguments to deduce the orientationof pyridine on the surface of Ag, Au, and Cu sol particles. In this paper we investigate the surface geometry and conformationof a number of the ions of