New publication in The Journal of Organic Chemistry

We report here on the development of a fluorescent cone homooxacalix[3]arene-based receptor with a pyrene unit on the wide rim of the macrocycle (Ox3F) for the selective detection of primary ammonium ions, including ones of biological importance. Ox3F was synthesized efficiently via an innovative strategy that enables the regio- and iteroselective wide rim functionalization of the readily available p-tBu-substitued homooxacalix[3]arene precursor. NMR studies and in silico methods highlighted the endo-complexation of primary ammonium ions, including the protonated form of biogenic dopamine, tryptamine, serotonin, mexamine, and 3-iodothyronamine. The binding mode is similar for all guests with the ion deeply inserted into the polyaromatic cavity, enabling the NH3+ head to establish three H-bonds with the ethereal oxygens of the macrocycle. Fluorescence quenching of the pyrene unit was observed following the π-π interaction between the pyrene moiety and the aromatic groups of serotonin, mexamine, and 3-iodothyronamine. No quenching was observed upon complexation of the smaller aromatic neurotransmitter dopamine, as well as aliphatic amines and polyamines. This study presents a novel approach for biologically relevant ammonium ion chemosensing with ongoing efforts focused on translating these systems for aqueous environment applications.