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

The formation of liquid-crystalline dispersions as a result of interaction of linear, double-stranded DNA molecules with poly(propyleneimine) dendrimers in water-salt solutions was studied. It was shown, that this process does not depend on the ionic strength of solution and molecular structure of dendrimer. By means of the atomic force microscopy, it was established, that in the case of the dendrimer molecules of the 4th generation (G4), the mean size of particles of (DNA-dendrimer G4) liquid-crystalline dispersion is equal to 300-400 nm. The "boundary" conditions (ionic strength of solutionand molecular mass of dendrimer) of formation of optically active (cholesteric) and optically inactive of the (DNA-dendrimer) dispersions were determined using circular dichroism spectroscopy. The interaction of dendrimers of 1st, 2nd, 3rd and 5th generations with DNA molecules results in the obtaining of the optically inactive dispersions. Dendrimer molecules of 4th generation induce the formation of two types dispersions: in solutions of high ionic strength (micro > 0.4) they induce the formation of cholesteric liquid-crystalline dispersions, and in solutions of low or intermediate ionic strength (micro < 0.4) they can form the optically inactive one. The "molecular crowding" affects both the efficiency of binding of dendrimer molecules of 4th generation to DNA, and the mode of spatial packing of (DNA-dendrimer G4) complexes in particles of liquid-crystalline dispersion. The possible reasons capable of explaining the structural polymorphism of (DNA-dendrimer) liquid-crystalline dispersions are discussed.