Conformations of an amino-amido-thiolate self-assembled layer on gold in air and in electrolytes

The amino-amido-thiol AT (HS-(CH2)10-CO-NH-CH2-CH2-NH2)(HS-(CH2)10-CO-NH-CH2-CH2-NH2), adsorbed on Au(111), was studied by sum frequency generation (SFG) and IR reflection absorption spectroscopy in the CH2 stretching vibration region. The SFG and IR spectra are qual. similar; both show the sym. stretching band and an intense and unusually broad antisym. stretching band. The IR spectra show a reversible difference between a sample dried after rinsing in electrolyte and dried after rinsing in ethanol, thus exhibiting a solvent memory' effect. SFG spectra demonstrate that the dried samples have a high d. of conformational defects. The defects are located in the C10 methylene chain. We ascribe them to intermol. hydrogen-bonding. When the layer is studied by SFG spectroscopy in aq. soln., even in the presence of coordinating Pd2+ ions no vibrational bands are obsd. in the CH2 stretching vibration region. This indicates a strongly reduced defect d. with a straightened mol. backbone. We ascribe this to the solvation of the amine group; in this case intermol. bonds play a minor role. [on SciFinder (R)]