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.