Cationic silanes stabilize intermediates in DNA condensation

In vitro condensation of DNA has been widely studied to gain insight into the mechanisms of DNA compaction in biological systems such as chromosomes and phage heads and has been used to produce nanostructured particles with novel material and functional properties. Here we report on the condensation of DNA in aqueous solutions by cationic silanes, which combine the condensing properties of polyamines with the cross-linking chemistry of silanes. DNA can be reversibly condensed into classical toroidal and rod-shaped structures with these agents. At low silane concentrations DNA forms a variety of looped structures with well-defined characteristics, including flower- and sausage-shaped forms. These structures suggest that at low silane concentrations a DNA-DNA contact in which the strands are at very large angles to each other is stabilized. Changes in these structures observed as a function of silane concentration suggest possible pathways for the formation of toroids and rods.