We describe for the first time the crystallization in thin films of a DNA copolymer composed of a low molecular weight chitosan backbone to which a sequence of nucleic acids is grafted (chitosan-g-ssDNA). As assessed by atomic force microscopy, optical microscopy and spectroscopy, crystallization occurs due to intermolecular hydrogen bonding in which the nucleic acid strands engage. The morphology of the crystals depends on the affinity for the surface of the polymer segments that compose the DNA copolymer hybrid. The nucleic acids adsorb on mica and silica on which side-branched structures are observed whereas chitosan interacts preferentially with gold, and dendritic crystals are assembled. Attenuated total reflectance infrared spectroscopy supports the high ordering of the structure and the establishment of strong intermolecular interactions by hydrogen bonding.
 
We report herein on the polymer-crystallization-assisted thiol-ene photosynthesis of an amphiphilic comb/graft DNA copolymer, or molecular brush, composed of a hydrophobic poly(2-oxazoline) backbone and hydrophilic short single-stranded nucleic acid grafts. Coupling efficiencies are above 60% and thus higher as compared with the straight solid-phase-supported synthesis of amphiphilic DNA block copolymers. The DNA molecular brushes self-assemble into sub-micron-sized spherical structures in water as evidenced by light scattering as well as atomic force and electron microscopy imaging. The nucleotide sequences remain functional, as assessed by UV and fluorescence spectroscopy subsequent to isoindol synthesis at the surface of the structures. The determination of a vesicular morphology is supported by encapsulation and subsequent spectroscopy monitoring of the release of a water-soluble dye and spectroscopic quantification of the hybridization efficiency (30% in average) of the functional nucleic acid strands engaged in structure formation: about one-half of the nucleotide sequences are available for hybridization, whereas the other half are hindered within the self-assembled structure. Because speciation between complementary and non complementary sequences in the medium could be ascertained by confocal laser scanning microscopy, the stable self-assembled molecular brushes demonstrate the potential for sensing applications.

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Last update Tuesday March 13 2018