Cationic Cyanostilbene-Induced B-Z DNA Transition in Calf-Thymus DNA: Modulation of FRET in DNA Co-Assemblies

Cationic cyanostilbenes (CSs) with variable peripheral alkyl chains demonstrated groove binding to calf-thymus DNA (ctDNA). This led to a variation in their luminescence and the emergence of induced chiral features. Most notably, an ethyl CS analogue induced an intriguing structural transformation in ctDNA in which the original right-handed B-DNA, the most commonly observed regular structural form of the DNA found in living cells under physiological conditions, underwent transformation to Z-DNA, an unconventional form of DNA with left-handed helicity, typically observed with certain sequences under specific biological, physical, or chemical environments. In particular, such structural transitions are observed in specific DNA structures with enriched (CG)_n or (GC)_n sequences. However, the ethyl CS derivative, rather unexpectedly, was able to induce such a structural transition in ctDNA. Moreover, the CS-DNA ensembles demonstrated Förster resonance energy transfer (FRET) to intercalated acceptor dyes, and the energy transfer efficiency was dependent on the structural form of the ctDNA.