Encapsulation of l-valine, d-leucine and d-methionine by cucurbit[8]uril

The binding interactions of cucurbit[8]uril (Q[8]) with L-valine, D-leucine, and D-methionine, both in aqueous solution and solid state, have been studied by 1H NMR spectroscopy and X-ray crystallography. 1H NMR data indicate that Q[8] can encapsulate these three kinds of amino acids in aqueous solution. X-ray crystallography reveals how the Q[8] binds with the amino acids to form inclusion complexes L-Val2@Q[8], D-Leu2@Q[8], and D-Met2@Q[8] through host-guest interactions. It was also found that the deformation degree of the Q[8] host is related to the molecular size of the encapsulated guests