Surface-Enhanced Raman Spectroscopy (SERS) and Molecular Modeling of the Chromate Interaction with 4-(2-Mercaptoethyl)Pyridinium

The interaction of 4-(2-mercaptoethyl)pyridinium (HMEP + ) hydrochloride with chromate was investigated using surface-enhanced Raman spectroscopy (SERS) and molecular modeling. It was shown that HMEP + on the gold surface attracted chromate to the SERS surface and that the adsorption of chromate onto the substrate is described by a Frumkin isotherm. The ion-pair constant for the chromate−HMEP + interaction is more than 3 orders of magnitude larger than that measured for the HMEP + interaction with perchlorate ion. The high selectivity of HMEP + for chromate is attributed to hydrogen bonding between chromate and the HMEP + moieties on the SERS surface.