Molecular encapsulation by eosin yellow-β-cyclodextrin conjugate: Differential binding to quadruplex and duplex DNA

Abstract

G-Quadruplexes exist in cells and are involved in several cancer-related processes. Thus, G-quadruplex binding is an effective way of aiming at cancer cells. In this paper, the binding of a new β-cyclodextrin conjugate, eosin yellow-CD, with quadruplex DNAs viz., kit22, myc22, telo24 and duplex calf-thymus DNA, is studied by UV–vis and fluorescence spectroscopic methods. Berberine, a known G-quadruplex binder, is loaded in the modified cyclodextrin. The binding constant of the host: guest complex is 1.9 × 106 mol−1 dm3. The proximity of the protons of the conjugate and Berberine with those of the internal cavity of β-cyclodextrin in the conjugate is confirmed by two-dimensional rotating-frame Overhauser effect spectroscopy. The conjugate displays a quenching of fluorescence selectively to the quadruplex kit22 and telo24 that contrasts the spectral characteristics of the ligand-bound complexes of myc22 and ctDNA. The Stern-Volmer quenching constants are 1.08 × 106 mol−1 dm3 and 1.6 × 106 mol−1 dm3, respectively for binding to kit22 and telo24. The duplex ctDNA exhibits an enhanced fluorescence in the absence and the presence of Berberine complex, whereas the quadrulex DNAs exhibit dissimilar emission profiles when the eosin yellow-CD encapsulates Berberine. We report the differences in the binding constants and the mode of binding of free- and Berberine-loaded eosin yellow-CD to the duplex and quadruplex DNAs.