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

An anthraquinonesulfonyl derivative of beta-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-beta-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 x 10(5) mol(-1) dm(3) and 5.7 x 10(4) mol(-1) dm(3) for the formation of host: guest complexes of the beta-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 beta-CD in the anthraquinonesulfonyl-beta-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 beta-CD. The encapsulation of berberine leads to a fluorescence enhancement on binding to ctDNA, telo24, and myc22 with binding constants of 5.6 x 10(5), 3.3 x 10(5) mol(-1) dm(3), and 1.5 x 10(5) mol(-1) dm(3) respectively. In contrast, kit22 leads to fluorescence quenching on berberine encapsulated-anthraquinonesulfonyl-beta-cyclodextrin conjugate with a Stern-Volmer constant of 3.3 x 10(5) mol(-1) dm(3). Communicated by Ramaswamy H. Sarma

Automated summary

A novel anthraquinonesulfonyl derivative of beta-cyclodextrin was prepared and characterized, showing enhanced fluorescence of ethidium bromide and berberine when encapsulated in the cyclodextrin's cavity. The conjugate displayed selective fluorescence quenching on quadruplex DNAs kit22 and telo24. Binding constants were determined for different molecules encapsulated by the beta-cyclodextrin conjugate, showing varying fluorescence behaviors.