title: Highly packed and oriented DNA mesophases identified using in situ microfluidic X-ray microdiffraction.
abstract: DNA condensation in vivo usually requires proteins and/or multivalent salts. Here, we explore the in vitro compaction of DNA by cationic dendrimers having an intermediate size and charge. The dynamic assembly of DNA-dendrimer mesophases is discernible due to the laminar flow in a specially designed X-ray compatible microfluidic device. The setup ensures a nonequilibrium ascent of reactant concentration, and the resulting progression of DNA compaction was detected online using microfocused small-angle X-ray diffraction. The evolution of a DNA-dendrimer columnar square mesophase as a function of increasing dendrimer content is described. Additionally, in regions of maximum shear, an unexpected high-level perpendicular ordering of this phase is recorded. Furthermore, these assemblies are found to be in coexistence with a densely packed DNA-only mesophase in regions of excess DNA. The latter is reminiscent of dense packing found in bacteriophage and chromosomes, although surprisingly, it is not stabilized by direct dendrimer contact.
authors.affiliation: Max Planck Institute for Dynamics and Self-Organization, Bunsenstrasse 10, Göttingen, Germany. thomas.pfohl@ds.mpg.de
authors.forename: Thomas
authors.initials: T
authors.lastname: Pfohl
authors.forename: Alexander
authors.initials: A
authors.lastname: Otten
authors.forename: Sarah
authors.initials: S
authors.lastname: Köster
authors.forename: Rolf
authors.initials: R
authors.lastname: Dootz
authors.forename: Bernd
authors.initials: B
authors.lastname: Struth
authors.forename: Heather M
authors.initials: HM
authors.lastname: Evans
mesh_terms: D004247:DNA / Q000737:chemistry*; D050091:Dendrimers / Q000737:chemistry; D044085:Microfluidics; D012542:Scattering, Radiation; D014961:X-Ray Diffraction / Q000379:methods*
chemical_list: D050091:Dendrimers; D004247:DNA