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

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 ¹H NMR spectrum indicative of a D₅-symmetry. Variable temperature fluorescence spectroscopy titrations performed at very low concentrations ([thionin] = 1.5 µM) allowed determination of the K_a (2.99 × 10⁷ 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 10¹² 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.