Network Formation of DNA/Polyelectrolyte Fibrous Aggregates Adsorbed at the Water–Air Interface

This is the authors' abstract. We don't add key points for this paper.

It is discovered that complexes of DNA and hydrophobically modified polyelectrolytes form a rigid network of threadlike or fibrous aggregates at the liquid–gas interface whose morphology can dramatically affect the mechanical properties. While mixed solutions of DNA and poly( N, N -diallyl- N, N -dimethylammonium chloride) (PDADMAC) exhibit no notable surface activity, the complexes formed from DNA with poly( N, N -diallyl- N -butyl- N -methylammonium chloride) are surface-active, in contrast to either of the separate components. Further, complexes of DNA and poly( N, N -diallyl- N -hexyl- N -methylammonium chloride) (PDAHMAC) with its longer hydrophobic side chains exhibit pronounced surface activity with values of surface pressures up to 16 mN/m and dynamic surface elasticity up to 58 mN/m. If the PDAHMAC nitrogen to DNA phosphate molar ratio, N/P, is between 0.6 and 3, abrupt compression of the adsorption layer leads unexpectedly to a noticeable decrease of the surface elasticity. The application of imaging techniques reveals that this effect is a consequence of the destruction of a rigid network of threadlike DNA/polyelectrolyte aggregates at the interface. The toroidal aggregates, which are typical for the bulk phase of DNA/PDADMAC solutions in this range of N/P ratios, are not observed in the surface layer. The observed link between the mechanical properties and interfacial morphology of surface-active complexes formed from DNA with hydrophobically modified polyelectrolytes indicates that tuning polyelectrolyte hydrophobicity in these systems may be a means to develop their use in applications ranging from nonviral gene-delivery vehicles to conductive nanowires.