Selective recognition of choline phosphate by tripodal hexa-urea receptors with dual binding sites: crystal and solution evidenceElectronic supplementary information (ESI) available: Synthetic procedures, characterization data and corresponding CIF files. CCDC 1859609-1859611. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c8sc04338h

Two tripodal hexa-urea receptors functionalized with aromatic terminal groups are capable of binding choline phosphate (CP). Crystal structures of the host-guest complexes reveal that the zwitterion CP is efficiently encapsulated in the tripodal hosts in a dual-site binding mode. The phosphate tail of CP is coordinated by the urea groups and the quaternary ammonium head is bound in a 'composite aromatic box' through cation-π and hydrogen-bonding interactions. Such a partial aromatic binding environment for the Me 3 N- + cation mimics that of most enzymes catalyzing the conversion of quaternary ammonium substrates. Moreover, NMR, ESI-MS, and fluorescence studies demonstrate the selective binding and sensing of CP over other competing species such as ADP, ATP, choline and derivatives. The tripodal hexa-urea receptors functionalized with aromatic terminal groups are able to selectively recognize choline phosphate with dual binding sites.