Single-stranded DNA induced chirality and helical twist in achiral liquid crystals

A small quantity of single-stranded DNA (Deoxyribonucleic acid$-$cellulose single-stranded from calf thymus DNA in lyophilized powder form) was doped in an achiral liquid crystal (LC), and the mixture was found to exhibit a weak degree of chirality. The induced chirality in the LC was probed by means of the electroclinic effect in the LC's smectic-A phase, which showed significant pretransitional behavior on approaching the smectic-$A$--smectic-$C$ transition temperature from above. The same DNA was doped in an achiral nematic LC and the mixture was found to exhibit an average mechanical twist over macroscopic dimensions. The single-stranded DNA-induced chiral pitch length $P$ was determined by measuring the radius of curvature of reverse twist disclination lines in 90$^{\mathrm{o}}$ nematic twist cells. In the LC$+$DNA mixture, the LC's benzene rings interact with the nucleobases of the DNA through $\pi -\pi $ stacking, which induces a molecular conformational deracemization in the LC.