Anion Binding Inside a Bambus[6]uril Macrocycle in Chloroform.

Bambus[6]urils are a class of neutral anion receptors with outstanding binding properties in various solvents. The host-guest associations of bambusurils in aqueous environments have been investigated in detail, but their behavior in nonpolar solvents has not yet been reported. This paper presents isothermal calorimetry and 1 H NMR data on the binding of dodecabenzylbambus[6]uril (Bn12 BU[6]) to seventeen anions in chloroform. Under these conditions, anion inclusion in the macrocycle appears to be enthalpy-driven, yielding complexes with stability constants of up to 1010  m-1 . Perchlorate was optimally sized for inclusion in Bn12 BU[6], while larger anions exhibited significantly lower affinity for the macrocycle. In addition, complexes of bambusuril and anions can be differentiated by NMR analysis based on the unique chemical shifts of characteristic peaks in their spectra. This finding was used to perform quantitative and qualitative analysis of multiple anion mixtures.