Gas Phase Cucurbit[n]uril Chemistry

The chemistry of cucurbit[n]urils is commanding increasing interest because of potential applications of these molecules in supramolecular structures; in drug encapsulation, protection, and delivery; and in sensitive new analytical assays. It is widely recognized that the binding properties of cucurbit[n]urils are sensitively dependent on solvents and counterions. Hence, gas phase studies, where neither solvent nor counterion species are present, are vital to gain fundamental understanding of cucuribituril complexes and to facilitate future applications. We use Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) and ion mobility techniques to investigate the gas phase chemistry of cucurbit[n]urils and related species, addressing problems such as how trapping molecules inside the cucurbit[n]uril cavity affects the binding of cations on the rims, the mechanism of exchange of bound/trapped species, and the origin of the large pK(a) shifts that occur for trapped guests. This paper is a review of our work.