title: Effects of Complementary DNA and Salt on the Thermoresponsiveness of Poly(N-isopropylacrylamide)-b-DNA.
abstract: The thermoresponsive structural transition of poly(N-isopropylacrylamide) (PNIPAAm)-b-DNA copolymers was explored. Molecular assembly of the block copolymers was facilitated by adding salt, and this assembly was not nucleated by the association between DNA strands but by the coil-globule transition of PNIPAAm blocks. Below the lower critical solution temperature (LCST) of PNIPAAm, the copolymer solution remained transparent even at high salt concentrations, regardless of whether DNA was hybridized with its complementary partner to form a double-strand (or single-strand) structure. At the LCST, the hybridized copolymer assembled in spherical nanoparticles, surrounded by double-stranded DNA; subsequently, the non-cross-linking aggregation occurred, while the nanoparticles were dispersed if the salt concentration was low or DNA blocks were unhybridized. When the DNA duplex was denatured to a single-stranded state by heating, the aggregated nanoparticles redispersed owing to the recovery of the steric repulsion of the DNA strands. The changes in the steric and electrostatic effects by hybridization and the addition of salt did not result in any specific attraction between DNA strands but merely decreased the repulsive interactions. The van der Waals attraction between the nanoparticles overcame such repulsive interactions so that the non-cross-linking aggregation of the micellar particles was mediated.
authors.affiliation: Bioengineering Laboratory, RIKEN, Hirosawa 2-1, Wako-shi, Saitama 351-0198, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Fujita
authors.affiliation: Department of Advanced Materials Science, School of Frontier Science, The University of Tokyo , Kashiwanoha 5-1-5, Kashiwa-shi, Chiba 277-8561, Japan.
authors.forename: Hayato
authors.initials: H
authors.lastname: Hiramine
authors.affiliation: Bioengineering Laboratory, RIKEN, Hirosawa 2-1, Wako-shi, Saitama 351-0198, Japan.
authors.forename: Pengju
authors.initials: P
authors.lastname: Pan
authors.affiliation: RIKEN SPring-8 Center, Advanced Photon Technology Division, Kouto 1-1-1, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan.
authors.forename: Takaaki
authors.initials: T
authors.lastname: Hikima
authors.affiliation: Bioengineering Laboratory, RIKEN, Hirosawa 2-1, Wako-shi, Saitama 351-0198, Japan.|Department of Advanced Materials Science, School of Frontier Science, The University of Tokyo , Kashiwanoha 5-1-5, Kashiwa-shi, Chiba 277-8561, Japan.
authors.forename: Mizuo
authors.initials: M
authors.lastname: Maeda
mesh_terms: D000178:Acrylamides / Q000737:chemistry*; D000180:Acrylic Resins / Q000737:chemistry*; D003102:Colloids; D018076:DNA, Complementary / Q000737:chemistry*; D008823:Micelles; D054118:Nanospheres / Q000737:chemistry; D009566:Nitrates / Q000737:chemistry*; D009691:Nucleic Acid Denaturation; D009693:Nucleic Acid Hybridization; D013696:Temperature
chemical_list: D000178:Acrylamides; D000180:Acrylic Resins; D003102:Colloids; D018076:DNA, Complementary; D008823:Micelles; D009566:Nitrates; C031618:sodium nitrate