Prism[5]MaxQ: A Sulfated Prism[5]Arene and Its Molecular Recognition Properties Toward a Panel of Quaternary Ammonium Guests

We report the synthesis of a sulfated prism[5]arene macrocyclic host. The uncomplexed sulfated prism[5]arene exhibits broadened resonances at NMR concentrations (100 µM), but addition of acetone (0.6%) results in a diagnostic 1 H NMR spectrum indicative of a D 5 ‐symmetry. Variable temperature fluorescence spectroscopy titrations performed at very low concentrations ([ thionin ] = 1.5 µM) allowed determination of the K a (2.99 × 10 7 M −1 ) and ΔH (‐2.60 kcal mol −1 ) values for the sulfated prism[5]arene• thionin complex. Subsequent competitive ITC experiments allowed determination of the thermodynamic parameters for complexation of sulfated prism[5]arene toward a 17‐membered panel of hydrophobic (di)cationic guests. The sulfated prism[5]arene•methylated bipiperidine complex exhibits ultrahigh binding affinity with K a exceeding 10 12 M −1 in phosphate‐buffered saline (PBS). We find that sulfated prism[5]arene preferentially complexes quaternary diammonium over the corresponding primary diammonium ions by factors up to 5136‐fold, leading us to name it Prism[5]MaxQ. The sulfated prism[5]arene host binds more tightly than the carboxylated prism[5]arene host by factors up to 4300‐fold, but is a less potent host than the sulfated pillar[6]arene by factors up to 88000‐fold. Sulfated prism[5]arene is the newest member of the family of ultrahigh binding affinity hosts that is poised for application as a sequestrant for various compounds.