Liquid-crystalline dispersions formed by the complexes of linear double-stranded DNA molecules with dendrimers

The specific features of liquid-crystalline dispersions formed by double-stranded DNA molecules interacting with polypropylenimine dendrimers of five generations (G1—G5) in aqueous saline solutions of various ionic strengths were studied. It was demonstrated that the binding of dendrimer molecules to DNA led to the formation of dispersions independently of solution ionic strength and dendrimer structure. By the example of a generation 4 dendrimer, it was shown that the shape of dispersion particles of the (DNA-dendrimer G4) complex were close to a sphere with a diameter of 300–400 nm. The boundary conditions (ionic strength of solution and molecular mass of dendrimer) for the formation of optically active (cholesteric) and optically inactive (DNA-dendrimer) dispersions were determined by circular dichroism spectroscopy. The dispersions formed by dendrimers G1–G3 and G5 were optically inactive. Dendrimers G4 formed liquid-crystalline dispersions of two types. Cholesteric liquid-crystalline dispersions were formed in high ionic strength solutions (μ > 0.4), whereas the dispersions formed in low and intermediate ionic strength solutions (μ < 0.4) lacked an intense negative band in their circular dichroism spectra. The effect of molecular crowding on both the (DNA-dendrimer G4) binding efficiency and the pattern of spatial packing of the (DNA-dendrimer G4) complexes in the liquid-crystalline dispersion particles was demonstrated. The factors determining the structural polymorphism of the liquid-crystalline dispersions of (DNA-dendrimer) complexes are postulated.