title: Structural investigations of DNA-polycation complexes.
abstract: The internal structure of DNA-polycation complexes is investigated by synchrotron small-angle X-ray scattering (SAXS). Hexagonal packing of DNA is observed for DNA complexed with poly-L-lysine (PL), poly-L-arginine (PA), spermine (Sp), and linear and branched polyethyleneimine (lPEI and bPEI, respectively). Variations in the internal spacings and degree of long-range ordering are dependent on both polycation type and concentration of added salt. With increasing concentration of monovalent salt, a discontinuous phase transition is observed from compact to loose bundles and finally to an isotropic network phase. This salt-induced melting transition was found to be universal for all polyplexes studied and is in quantitative agreement with a simple free energy model based solely on electrostatic and entropic contributions. Using the osmotic stress method, bulk modulus (K) is measured for PL-DNA and PA-DNA polyplexes at various salt concentrations. With increasing osmotic force, we show that the salt-induced melting transition is shifted and compression in the loose bundle regime is in qualitative agreement with our model.
authors.affiliation: Ludwig-Maximilians-Universität, Sektion Physik, Geschwister-Scholl-Platz 1, 80539, Munich, Germany. jason.derouchey@physik.uni-muenchen.de
authors.forename: J
authors.initials: J
authors.lastname: DeRouchey
authors.forename: R R
authors.initials: RR
authors.lastname: Netz
authors.forename: J O
authors.initials: JO
authors.lastname: Rädler
mesh_terms: D003198:Computer Simulation; D004247:DNA / Q000737:chemistry* / Q000648:ultrastructure*; D006863:Hydrogen-Ion Concentration; D046911:Macromolecular Substances / Q000737:chemistry; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D009690:Nucleic Acid Conformation; D011073:Polyamines / Q000737:chemistry*; D000071228:Polyelectrolytes; D014961:X-Ray Diffraction / Q000379:methods
chemical_list: D004247:DNA; D046911:Macromolecular Substances; D011073:Polyamines; D000071228:Polyelectrolytes; C427203:calf thymus DNA