145 Spectral characteristics of DNA-EtBr and DNA-MB complexes

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

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.

Molecular encapsulation of berberine and ethidium bromide in anthraquinonecarboxamido-β-cyclodextrin conjugate: supramolecular association with DNA duplex and G-quadruplexes

G-quadruplex DNA in recognized as a potential target for anti-cancer drugs. In this work, an anthraquinonecarboxamido derivative of β-cyclodextrin (AQCC) is synthesized as a novel DNA binder that further can deliver an additional molecule at the target, carrying it in the cavity of modified cyclodextrin. The binding of AQCC with ethidium bromide (EtBr), berberine (Ber), duplex calf-thymus DNA (CT-DNA), quadruplexes (G4) viz., kit22, myc22, and telo24 are studied. The compound acts as a host molecule for the encapsulation of DNA binders viz., EtBr, Ber and enhances their fluorescence due to the encapsulation in its AQCC's cyclodextrin cavity. The binding constant of the host: guest complex of EtBr and Ber with AQCC's cavity are 6.4 × 105 and 3.3 × 106 mol-1 dm3, respectively. The proximity of the protons of the guest and host molecules is confirmed by two-dimensional rotating-frame Overhauser effect spectroscopy (2D ROESY). The conjugate displays a quenching of fluorescence selectively on the association with CT-DNA and quadruplex kit22 that is contrast to the spectral behavior with quadruplex myc22 and telo24. CT-DNA exhibits dissimilar fluorescence spectra in free- and EtBr-bound forms. In addition, kit22 exhibit dissimilar emission profile when AQCC encapsulates Ber. Therefore, the Ber-loaded complexes and the AQCC molecule bind to different G-quadruplexes with different binding strengths. In addition, the effect of Ber in binding to the target DNAs is pronounces since the Ber molecule has more affinity to bind to quadruplexes than the duplex.