SURFACE-ENHANCED RAMAN-SCATTERING OF MERCAPTOPYRIDINES AND PYRAZINAMIDE INCORPORATED IN SILVER COLLOID ADSORBATE FILMS

Pyrazinamide (pza) and 2-mercaptopyridine (2-MPy) are shown to form Ag colloid-adsorbate films at the interface between an aqueous Ag colloi d and a solution of an adsorbate in dichloromethane. By contrast, unde r the same conditions, 4-mercaptopyridine (4-MPy) forms Ag organosol a ggregates by the interface transfer of adsorbate-covered Ag colloidal particles from the aqueous phase to the organic phase, This result con firms that formation of Ag colloid-adsorbate films is an adsorbate spe cific process. Transmission electron and optical microscopy and surfac e plasmon adsorption measurements are used to characterize the morphol ogy of the deposited Ag colloid-adsorbate structures while SERS spectr a of the incorporated adsorbates probe their internal structure. Furth ermore, we demonstrate that, for a particular adsorbate, the process o f Ag colloid-adsorbate film formation, the morphology of the deposited films, and the SERS spectra are substantially influenced by the Ag co ntent of the parent colloid (Ag-pza and Ag-4-MPy films) and/or by the concentration of the adsorbate in the organic phase (Ag-2-MPy films). We propose that the observed differences in the rates of formation of the films, their morphology, and the orientation of the adsorbate with respect to the Ag surface are related to differences in the actual su rface coverage of Ag colloidal particles by adsorbate molecules.