Raman spectroscopic investigation of the adsorption of 4-mercaptopyridine on a silver-sol surface

Adsorption of 4-mercaptopyridine (4MP) on a silver-sol surface has been investigated over a wide range of solution pH by surface-enhanced Raman (SER) scattering. Although various structural forms could be present in the bulk phase, when the sol solution was under medium acidic to basic conditions 4MP was chemisorbed on the silver surface as a thiolate by formation of an Ag-S bond. Furthermore, upon being adsorbed on the silver surface the pK value of N-deprotonation was reduced by as much as S, implying that nitrogen-to-metal interaction was playing a secondary role in the adsorption process. It was thus concluded that the adsorbed 4MP species had a Bat orientation relative to the sol surface. This view was confirmed more firmly by comparing SER spectra taken in silver sols containing chloride ions with those taken in chloride-free sols. (C) 1997 Elsevier Science B.V.