Raman and electrochemical characterization of 2-mercaptoethanesulfonate monolayers on silver: A comparison with monolayers of 3-mercaptopropionic acid

The influence of various electrolytes on the structure of a 2 -mercaptoethanesulfon ate (MES) monolayer on silver was studied using surface-enhanced Raman scattering. Raman measurements revealed that in the MES layers almost all molecules were able to adopt a trans conformation and that the structure of MES monolayers is practically insensitive to the presence of relatively diluted solutions of electrolytes. This seems to be very promising for possible applications. The portion of trans conformers could be further increased by soaking of the monolayer in concentrated solutions of various metal salts. MES monolayers soaked in solutions containing various metal cations reveal two components of the symmetric v(s)(SO3) band: at the wavenumber typical for the crystalline sodium salt of MES and at the wavenumber characteristic for its aqueous solution. The ratio of both components depends on the concentration of metal cations in the surrounding electrolyte. We suggest that the component at the wavenumber typical for the crystalline salt of MES is due to -SO3- groups strongly interacting with metal cations that have lost some hydration water molecules. The structure of MES monolayers is significantly more stable (especially in neutral solutions of metal salts) than that of layers formed from 3-mercaptopropionic acid, which at present seem to be the most widely used linkage layers of similar type.