Adsorption of 2-amino-6-methylbenzothiazole on colloidal silver particles: Quantum chemical calculations and surface enhanced Raman scattering study

The adsorption of biologically important 2-amino-6-methylbenzothiazole (2A-6MBT) molecule on silver colloids has been investigated by Surface Enhanced Raman Scattering (SERS) study. The SERS spectra of 2A-6MBT at different adsorbate concentrations are compared with its Fourier transform infrared spectrum and normal Raman spectrum in varied environments. Concentration-dependent SERS spectra of the molecule reveal the existence of two types of adsorbed species on colloidal silver particles, whose relative population varies with adsorbate concentrations. The experimentally observed SERS spectra are compared with the theoretically modeled surface complexes using density functional theory calculations. The appearance of Ag-N stretching mode at around 212 cm-1 in the SERS spectra along with theoretically calculated atomic charge density, force us to believe that the molecules are adsorbed through the lone pair electrons of the nitrogen (N9 and N10) atoms with the molecular plane tilted or remain pendant on the colloidal silver surface. The direction of charge transfer contribution to SERS has been discussed from the frontier orbital theory