G-Quadruplex binding of cavity-containing anthraquinonesulfonyl-β-cyclodextrin conjugate. Effect of encapsulation of ethidium bromide and berberine

Abstract

An anthraquinonesulfonyl derivative of β-cyclodextrin is prepared and characterized employing spectroscopic techniques. The binding interactions of the compound with ethidium bromide, berberine, calf-thymus DNA, quadruplex DNAs viz., kit22, telo24, and myc22 are investigated by ultraviolet-visible, and fluorescence spectroscopic methods. Anthraquinonesulfonyl-β-cyclodextrin conjugate acts as a host molecule and enhances ethidium bromide and berberine fluorescence due to their encapsulation in cyclodextrin’s cavity. The binding constant values are 9.0 × 105 mol−1 dm3 and 5.7 × 104 mol−1 dm3 for the formation of host: guest complexes of the β-CD derivative with ethidium bromide and berberine respectively. The proximity of the protons of ethidium bromide and berberine protons with those of the internal cavity of β-CD in the anthraquinonesulfonyl-β-CD conjugate is confirmed by two-dimensional rotating-frame Overhauser effect spectroscopy. The conjugate displays a quenching of fluorescence selectively to the quadruplexes kit22 and telo24 that is contrast to the spectral behavior with duplex DNA. ctDNA and myc22 exhibit different absorption and emission profiles with ethidium bromide on encapsulation by β-CD. The encapsulation of berberine leads to a fluorescence enhancement on binding to ctDNA, telo24, and myc22 with binding constants of 5.6 × 105, 3.3 × 105 mol−1 dm3, and 1.5 × 105 mol−1 dm3 respectively. In contrast, kit22 leads to fluorescence quenching on berberine encapsulated-anthraquinonesulfonyl-β-cyclodextrin conjugate with a Stern-Volmer constant of 3.3 × 105 mol−1 dm3. Communicated by Ramaswamy H. Sarma