Acyclic cucurbit[<i>n</i>]uril bearing alkyl sulfate ionic groups

We report the synthesis and characterization of a new acyclic cucurbit[<i>n</i>]uril (CB[<i>n</i>]) host <b>C1</b> that features four alkyl sulfate ionic groups. The X-ray crystal structure of the <b>C1·Me</b> <b>₆</b> <b>CHDA</b> complex is reported. Host <b>C1</b> is significantly less soluble in water (4 mM) compared to the analogous acyclic CB[<i>n</i>] host <b>M1</b> which features sulfonate ionic groups (346 mM). Host <b>C1</b> does not undergo significant self-association according to the results of ¹H NMR dilution experiments. The molecular recognition behavior of the hosts <b>C1</b> and <b>M1</b> toward a panel of seven ammonium ions was explored by ¹H NMR spectroscopy and isothermal titration calorimetry (ITC). We find that <b>C1</b> generally binds slightly more tightly than <b>M1</b> toward a specific guest. <b>C1</b> binds more tightly to quaternary ammonium guests compared to the corresponding primary ammonium ions.