Selective adsorption of L-tartaric acid on gemini-type self-assembled monolayers

Synchrotron photoelectron spectroscopy and X-ray absorption spectroscopy studies of cationic self-assembled monolayers (SAMs) of quaternary ammonium (QA) sulfur derivates prepared on gold substrates were performed to investigate the adsorption mechanism of L-tartaric acid on a gemini-structured didodecyl dithiol (HS-gQA-SH). Using soft X-rays from a synchrotron light source, the carboxylate (deprotonated carboxylic acid) of L-tartaric acid was found to undergo an exchange reaction with the native bromide counterion of HS-gQA-SH-SAM. We also report the first soft XPS spectra of the bromide counterion of the QA. These results indicate the necessary chemical architecture via distance matching for exchange reactions to occur between complex molecules and point the way to more effective molecular recognition systems.