ADSORPTION OF 2-MERCAPTOPYRIDINE AND 2-MERCAPTOPYRIMIDINE ON A SILVERCOLLOIDAL SURFACE INVESTIGATED BY RAMAN-SPECTROSCOPY

Adsorption of 2-mercaptopyridine (2MP) and 2-mercaptopyrimidine (2MPM) on a silver colloidal surface has been investigated over a wide range of solution pH by surface-enhanced Raman scattering. Even though thes e molecules take various forms in aqueous solution, depending on the b ulk pH, 2MP and 2MPM adsorb on the silver surface mostly as their thio late forms through the Ag-S interaction. Spectacular lowering of the p K(2) values of 2MP and 2MPM on the surface suggests that the nitrogen- silver interaction also plays a secondary role in the adsorption proce ss. 2MP was found to take a more or less perpendicular or tilted stanc e with respect to the surface, whereas the N-protonation changed the o rientation to the flat one. In the case of 2MPM, a Bat orientation see ms to be favored regardless of the N-protonation. (C) 1998 Elsevier Sc ience B.V.