Synthesis of cholate-based pyridinium receptor and its recognition toward l-tryptophan

Four cholate-based pyridinium compounds were synthesized and their binding abilities toward unmodified amino acids were investigated by UV spectroscopy and fluorescence emission spectroscopy. Studies revealed that the recognition process involved hydrogen bonding, electrostatic force, and π–π interaction. The receptor 4a was found to recognize l-tryptophan specifically, and the complex was studied by 1H NMR spectroscopy. The receptors 4b and 4c showed very little recognition ability toward l-tryptophan, indicating the important role of the benzyl group at pyridinium ring.