The Contrasting Recognition Behavior of β‐Cyclodextrin and Its Sulfobutylether Derivative towards 4′,6‐Diamidino‐2‐phenylindole

Abstract

The noncovalent interactions between 4', 6-diamidino-2-phenylindole (DAPI) and sulfobutylether β-cyclodextrin (SBE7β-CD) are evaluated by using photochemical measurements and compared with that of native β-CD. Contrasting recognition behavior and intriguing modulations in the photochemical behavior of DAPI were observed. In particular, a large enhancement in the fluorescence emission and excited-state lifetime were seen upon binding to SBE7β-CD, with the SBE7β-CD inclusion complex being approximately 1000 times stronger than that of β-CD. The ensuing fluorescence "turn on" was demonstrated to be responsive to chemical stimuli, such as metal ions and adamantylanmine (AD). Upon addition of Ca(2+)/AD, nearly quantitative dissociation of the complex was established to regenerate the free dye and result in fluorescence "turn off". The SO3(-) groups are believed to be critical for the strong and selective binding of the chromophore and the stimuli-responsive tuning. This is as an important design criterion for the optimization of host-guest properties through supramolecular association, which is relevant for drug-delivery applications.