Molecular recognition of deoxycholic acids by pyrene-appended gamma-cyclodextrin connected with a rigid azacrown spacer

A gamma-cyclodextrin (gamma-CyD) derivative (1) having a pyrene moiety, con nected through a 4,13-diaza-18-crown-6 ether moiety to gamma-CyD, was synth esized and evaluated for guest binding and sensing properties. In aqueous s olution, 1 existed as an association dimer in which the secondary hydroxyl sides faced each other to accommodate two pyrene moieties, Photo-induced el ectron transfer (PET) between the amino group and the excited pyrene moiety regulated the monomer fluorescence intensity of 1. The monomer-dimer equil ibrium and the PET indicated that 1 may be used as a host capable of detect ing guest complexation by changes in fluorescence intensity from the pyrene moiety, Deoxycholic acids were found to be good guests for detection by 1, and deoxycholic acid itself induced different fluorescence changes compare d to the other deoxycholic acids. This indicated that 1 could recognize the position of the hydroxy groups on the steroidal framework. The azacrown pa rt may participate in the guest selectivity for the deoxycholic acids by re gulating the distance between the amino group and the pyrene moiety, modify ing PET efficiency.