Helical aggregates of bis(styryl) dyes formed by DNA templating

• Bisstyryl dyes possessing OMe or/and NMe 2 substituents in phenyl ring were synthesized. • Two steps of binding of dyes with ct-DNA were aggregation and laying in minor groove. • Bis(styryl) dye with OMe substituent forms the helical dye aggregates of right-handed chirality. • Bis(styryl) dye containing NMe 2 group demonstrates formation of left-handed chiral aggregates. • Fluorescence intensity enhancement was observed in 60 times on DNA-dye interaction. In order to further investigate mechanism of the styryl dye – DNA interaction, three different bis(styryl)pyridinium dyes possessing OMe or/and NMe 2 substituents in phenyl ring were selected and interaction of these compounds with the calf thymus DNA (ct-DNA) was monitored by using of UV–vis and fluorescence spectroscopic techniques, circular dichroism (CD), Hoechst 33258 displacement experiments and quantum-chemical calculations. The experimental results indicated a higher fluorescence enhancement for dyes containing NMe 2 group upon binding with DNA. The results proved the interaction of the molecules with ct-DNA occurs through the formation of aggregates in minor groove at high dye concentration. Bis(styryl) dye with OMe substituent forms the helical dye aggregates of right-handed chirality, whereas, dye containing NMe 2 group demonstrates formation of left-handed chiral aggregates in minor groove of DNA. As the DNA concentration increases, the dyes begin to spread out along the minor groove. This research provided a better understanding of mechanism of styryl dye - DNA interaction and effect of dye structure on interacting mode with DNA.