The Binding Behaviors between Cyclopentanocucurbit[6]uril and Three Amino Acids in the Solid and the Solution Phases

Abstract

Binding behaviors between CyP 6 Q[6] and three have been investigated by means of X-ray crystallography, 1 H NMR spectroscopy,amino acids and isothermal titration calorimetry (ITC). The results showed that CyP 6 Q[6] forms a 1:2 inclusion complex with glycine, but 1:1 complexes with both leucine and lysine. Whereas the carboxyl group of glycine can enter the interior of the cavity of CyP6Q[6], only the alkyl chains of leucine and lysine can enter this cavity. Interestingly, leucine can adopt two different self-assembly modes upon its interaction with cucurbituril, depending on the external conditions, whereas glycine and lysine do not exhibit such behavior.