Influence of electrolytes on the structure of cysteamine monolayer on silver studied by surface-enhanced Raman scattering

Monolayers of cysteamine (2-aminoethanethiol) frequently work in aqueous so lutions of electrolytes as linkage layers for adsorption of other molecules on metal surfaces. We determined the influence of various ions on the stru cture of the cysteamine monolayer with surface-enhanced Raman scattering (S ERS). The surrounding (pH, electrolytes) considerably influences the confor mation of adsorbed cysteamine molecules. Direct spectral evidence of the in teraction of cysteamine with an Ag surface through Ag . . .N bonds in the g auche conformation is given. It was found that chlorides and iodides signif icantly increase the proportion of the gauche conformer. Probably these ani ons additionally stabilize the gauche conformer by the formation of hydroge n bonds with NH2 groups in addition to the direct N . . . Ag bond. Raman me asurements also revealed that cations, which can form strong coordination b onds with amino groups (Cu2+, Ni2+ or Co2+), change the structure of the cy steamine layer by transforming the trans into a gauche conformer. In contra st, an increase in the proportion of trans conformers is observed with incr ease in the concentration of H+ in the ambient electrolyte. Possible explan ations for these experimental findings are discussed. Copyright (C) 2001 Jo hn Wiley & Sons, Ltd.