Surface-enhanced Raman spectroscopy of indole ring-terminated self-assembled monolayer on silver electrode

A new indole ring-terminated thiol, ω-mercaptooctyltryptamide (MOTA), has been synthesized and the structure of self-assembled monolayer (SAM) on Ag electrode was characterized by surface-enhanced Raman spectroscopy (SERS). The frequency of conformational marker W3 band has been found to increase by 3 cm–1 in surface spectrum as compared with the FT-Raman spectrum of solid MOTA compound, indicating an increase in the torsional angle about the Cβ-C3 bond from 95 to 103°. Potential-dependent spectral changes have indicated a blue shift of W3 mode at more positive potentials. Analysis of W17 mode in SERS spectra has shown that the hydrogen bonding interaction strength at N1H indole site increases in slightly alkaline solutions as compared with acidic conditions.