Department of Chemistry, University of Utah, 315 South 1400 East, Salt Lake City, Utah 84112, United States.
Langmuir. 2012 Feb 7;28(5):2628-36. doi: 10.1021/la2037444. Epub 2012 Jan 20.
Adsorption of 11-mercaptoundecanoic acid (MUA) on silver from methanol and aqueous solutions was monitored in situ by surface-enhanced Raman scattering (SRES) spectroscopy. While adsorption of MUA from methanol is a one-step formation of a thiol-bound monolayer, SERS spectra reveal that monolayer formation from aqueous solution involves interactions of both carboxylate and thiol groups of MUA with the silver surface. Several Raman scattering bands, including the ν(C-S), ν(s)(COO(-)), and ν(C-C), were used to investigate the evolution of the structure of adsorbed MUA on silver surfaces. The time-dependent profiles of these bands for assembly from aqueous solution indicate a multistep process, which is initiated by the binding of both carboxylate and thiol groups to silver, producing a mixture of gauche and trans conformations. In a subsequent step, the COO-Ag interactions are displaced by stronger S-Ag bonds, leading to ordering of the resulting monolayer with formation of a complete SAM with all-trans conformations. The results also showed that the adsorption process depended strongly on the solution pH and surface potential of the metal. These factors can significantly affect the participation and displacement of -COO(-) during self-assembly of MUA from aqueous solution.
通过表面增强拉曼散射（SRES）光谱原位监测了甲醇和水溶液中 11-巯基十一酸（MUA）在银上的吸附。虽然甲醇中 MUA 的吸附是一个形成硫醇键单层的一步过程，但 SERS 光谱表明，从水溶液中形成单层涉及 MUA 的羧酸根和硫醇基团与银表面的相互作用。几个拉曼散射带，包括ν（C-S）、ν（s）（COO（-））和ν（C-C），被用于研究吸附在银表面上的 MUA 结构的演变。从水溶液中组装的这些带的时变曲线表明是一个多步过程，该过程由羧酸根和硫醇基团与银的结合引发，产生了 gauche 和 trans 构象的混合物。在随后的步骤中，COO-Ag 相互作用被更强的 S-Ag 键取代，导致生成的单层有序，并形成具有全反式构象的完整 SAM。结果还表明，吸附过程强烈依赖于溶液 pH 值和金属的表面电势。这些因素会显著影响 -COO（-）在 MUA 从水溶液中自组装过程中的参与和取代。
