Guest-Induced Excimer Formation of β-Cyclodextrin Modified with a Branched Arm Possessing Two Naphthyl Moieties

Abstract

The β-cyclodextrin derivative (DN-β-CyD) having a branched arm derived from L-ornitine and two molecules of 2-naphthoic acid was synthesized for exploring the conformational change associated with guest binding. When DN-β-CyD was alone in a 10% ethylene glycol aqueous solution, one of the naphthoyl residues in the branched arm was accommodated in the DN-β-CyD cavity. This intramolecular self complex was stabilized by the other naphthoyl moiety located ouside of the cavity on the basis of a hydrophobic capping effect. Upon guest binding, the naphthoyl residue residing in the cavity was expelled from the cavity, forming an excimer with the other naphthoyl residue outside of the cavity. DN-β-CyD was not able to bind the guests strongly, owing to the stability of the intramolecular complexation form. Although DN-β-CyD was proven to be a poor host in guest binding, the guest recognition ability of DN-β-CyD could be estimated by the use of guest-induced fluorescence variations. DN-β-CyD could bind both monoterpenes and cholic acid derivatives to nearly the same extent. However, variations in fluorescence intensity induced by guest binding indicated, as a fluproscent sensing system, that DN-β-CyD was able to detect cholic acid derivatives with higher sensitivity than terpenoids.