Supramolecular modulation in photophysical features of berberine and its application towards ATP sensing

Abstract

In this study we report supramolecular interaction of the cationic dye berberine (BBR) with the highly substituted polyanionic cyclodextrin derivative, sulfobutylether beta cyclodextrin (SBE10βCD). Though interaction of BBR with parent β-cyclodextrin (βCD) host is very weak, its interaction with SBE10βCD host is significantly strong with an association constant Ka as large as ∼2.67 × 105 M−1. Strong binding of BBR with SBE10βCD is governed by cooperative effect of electrostatic attraction and enhanced hydrophobic interaction caused by extended SBE10βCD cavity for bound BBR dye. In the BBR-SBE10βCD complex, lower micropolarity and rigid microenvironment of host cavity cause a large decrease both in structural agility and intramolecular charge transfer (ICT) state formation of bound BBR. Accordingly, the non-radiative de-excitation of excited BBR in the dye-host complex is reduced significantly, causing its emission intensity to increase quite largely. The BBR-SBE10βCD complex is found to be highly sensitive towards ionic strength of the medium. This property is further explored to form a ternary complex, BBR-SBE10βCD-Cd2+, with largely reduced fluorescence intensity. Interestingly, this ternary complex exhibits selective fluorescence turn-on in response to an important bio-analyte, adenosine triphosphate (ATP). Present study, thus, demonstrates a very strong supramolecular complex, BBR-SBE10βCD, which is found to be very useful in the ATP detection in the presence of Cd2+, involving the ATP responsive fluorescence.