Two structurally analogous ruthenium complexes as naked-eye and reversible molecular light switch for G-quadruplex DNA

A pair of symmetrical furyl based ruthenium(II) complexes ([Ru(phen)(2)dpq-df](2+) (1) and [Ru(bpy)(2)dpq-df](2+) (2) (phen = 1,10-phenanthroline, bpy = 2,2'-bipyridine, dpq-df = dipyrido (3,2-a:2',3'-c) quinoxaline-difuran) have been prepared and characterized. The binding properties of both complexes toward G-quadruplex DNA have been investigated by fluorescence spectroscopy, UV-Vis spectroscopy, circular dichroism (CD), fluorescence resonance energy transfer (FRET) melting assays and molecular docking studies. The experimental results indicated that both Ru-complexes exhibited a remarkable light switch effect in the presence of hybrid G-quadruplex DNA Interestingly, the light switch can be repeated off and on through the successive addition of Cu2+ ions and EDTA, and all these behaviors can be observed even by the naked eyes. Moreover, FRET melting assay revealed that both complexes could be potential stabilizers for G-quadruplex architectures. The computational studies not only confirmed that the two complex molecules bound to one G-quadruplex DNA molecule, but also explained the light switch effect. (C) 2014 Elsevier Inc. All rights reserved.