Adsorption of mercaptoacetic acid on a colloidal silver surface as investigated by Raman spectroscopy

The vibration v(SH) has never been observed in the surface-enhanced Raman scattering of mercaptoacetic acid recorded in a vide range of pH. This behavior enables as to deduce that the -SH group is deprotonated and links to the metal forming an Ag-S bond as 1-alkanethiols do. Oil the contrary, the carboxylic or carboxylate groups do not link to the metal and the carboxylic group is preserved even at pH values under which it should be deprotonated. This fact enables the stabilization of the adsorbed monolayer by removing the electrostatic repulsions between -COO- groups and by the fomation instead of hydrogen bonds between carboxylic groups. Only Under rather basic conditions (pH > 8) does the carboxylic groups dissociate, but the v(s)(OCO) hand is neither enhanced nor shifted toward low frequencies. (C) 2004 Wiley Periodicals, Inc.