Synthesis of polypyridine-graft-PEG copolymer for protein repellent and stable interface

Polypyridine grafted with poly(ethylene glycol) (Py-g-PEG) have been synthesized. Radical copolymerization of methyl-terminated PEG macromonomer with 4-pyridylmethyl methacrylate homogeneously proceeded and the obtained copolymer spontaneously adsorbs from aqueous solution onto gold surfaces, where the pyridine parts act as the multipoint anchor to the surface and the PEG parts provide the strong steric repulsion between the chains. As a result, the highly protein repellent and stable surface was constructed through multipoint pyridine attachment as compared with singlepoint pyridine attachment. Py-g-PEGs thus synthesized are promising material to functionalize metal and semiconductor material and to self-assemble into micelle in biotechnological and biomedical field.     

Novel temperature-responsive polymer brushes with carbohydrate residues facilitate selective adhesion and collection of hepatocytes

Temperature-responsive glycopolymer brushes were designed to investigate the effects of grafting architectures of the copolymers on the selective adhesion and collection of hypatocytes. Homo, random and block sequences of N-isopropylacrylamide and 2-lactobionamidoethyl methacrylate were grafted on glass substrates via surface-initiated atom transfer radical polymerization. The galactose/lactose-specific lectin RCA₁₂₀ and HepG2 cells were used to test for specific recognition of the polymer brushes containing galactose residues over the lower critical solution temperatures (LCSTs). RCA₁₂₀ showed a specific binding to the brush surfaces at 37 °C. These brush surfaces also facilitated the adhesion of HepG2 cells at 37 °C under nonserum conditions, whereas no adhesion was observed for NIH-3T3 fibroblasts. When the temperature was decreased to 25 °C, almost all the HepG2 cells detached from the block copolymer brush, whereas the random copolymer brush did not release the cells. The difference in releasing kinetics of cells from the surfaces with different grafting architectures can be explained by the correlated effects of significant changes in LCST, mobility, hydrophilicity and mechanical properties of the grafted polymer chains. These findings are important for designing ‘on–off’ cell capture/release substrates for various biomedical applications such as selective cell separation.     

Controlling the microadsorption structure of porphyrin dye assembly on clay surfaces using the "size-matching rule" for constructing an efficient energy transfer system

The microadsorption structure of two kinds of porphyrin molecules on an anionic clay surface was investigated by photochemical energy transfer reaction. Three procedures were examined for the preparation of the clay/porphyrin complexes: (i) coadsorption (CA) method, (ii) sequential adsorption (SA) method, and (iii) independent adsorption (IA) method as described in the text. Efficient and moderate energy transfer reactions were observed in the CA and SA complexes, respectively. On the contrary, the energy transfer did not occur in the IA complex. These results indicate that the microadsorption structure of the two kinds of porphyrin on the clay mineral surface resulting from the sample preparation methods, affects the energy transfer efficiency. As a result, it was revealed that (i) the adsorbed porphyrins can move on the clay mineral surface but cannot move from one clay surface to another clay sheet, and (ii) the integration structure of two kinds of porphyrin is more stable than the segregation structure in the present system. This unusual structure originated from an extremely strong electrostatic interaction between the porphyrin and the clay mineral as a result of a "size-matching rule". These unique strongly fixed dye assemblies on the clay mineral surface, in which the aggregation and segregation of dyes are suppressed, is very promising and attractive for constructing efficient photochemical reaction systems.     

High energy-resolution electron energy-loss spectroscopy study of the electric structure of double-walled carbon nanotubes

Electron energy-loss spectra were obtained from two double-walled carbon nanotubes (DWCNTs) with an energy resolution of 85 meV. The spectra showed multiple peak structures between 2 and 3 eV. However, peak positions are different for these two DWCNTs. The chiral indices of CNT layers of the two DWCNTs were determined to be (29,4)(in) (17,8)(out) and (46,6)(out) (26,21)(in), respectively, by comparing experimental electron diffraction patterns with simulated ones. The spectra were also compared with simulated joint density of states, which were derived from the determined chiral indices. It was confirmed that the peak structures in the spectra are due to interband transitions intrinsic for tubular structures of graphitic sheets.     

Dramatic effect of dispersed carbon nanotubes on the mechanical and electroconductive properties of polymers derived from ionic liquids

Free-radical polymerization of an imidazolium ion-based ionic liquid bearing a methacrylate group, gelling with single-walled carbon nanotubes (SWNTs), allows fabrication of a mechanically reinforced, electroconductive soft material (bucky plastic). A film sample of this material displays an excellent conductivity of 1 S cm(-1) and a 120-fold enhancement of the Young's modulus at a 7 wt % content of SWNTs. The conductivity is temperature-dependent in the range 5-300 K, suggesting that the conductive process involves carrier hopping. Scanning electron and atomic force micrographs of a bucky plastic film display the presence of crosslinked networks consisting of finely dispersed SWNTs. Such nanotube networks, developed in the polymer matrix, likely suppress slipping of entrapped polymer molecules via a strong interfacial interaction and also facilitate intertubular carrier transport. Although a bucky plastic derived from a vinylimidazolium ion-based ionic liquid monomer shows a comparable conductivity to that of the methacrylate version, the film is brittle irrespective of the presence or absence of SWNTs.     

Structural phase transition in the perovskite-type tantalum oxynitrides, Ca1−xEuxTa(O,N)3

Pure Ca_1−xEu_xTa(O,N)₃ were successfully synthesized in the whole range of Ca/Eu compositions by means of ammonia nitridation via a citrate precursor route. As-nitrided products with x < 0.4 were apparently orthorhombic, while those with x ≥ 0.4 crystallized in a cubic structure. The anionic composition was found to be essentially O₂N and independent of Eu content (x). The as-nitrided EuTaO₂N possessed a cubic perovskite-type structure, while high-temperature post-annealing led to a tetragonal EuTaO₂N phase with better crystallinity. The re-nitridation transformed the post-annealed product into the original cubic lattice, which might be an average of the tetragonal micro-domains.     

Design method for a new control system for an autonomous underwater vehicle using linear matrix inequalities

The independent administrative corporation Japan Agency for Marine–Earth Science and Technology (JAMSTEC) has developed a small light autonomous underwater vehicle (AUV) named marine robot experimental 1 (MR-X1).¹ The motion control of MR-X1 is considered in this article. Since the dynamics of MR-X1 mainly depends on its own speed, the motion control is a nonlinear control system. We propose a new controller design method for this system using linear matrix inequalities (LMIs). This algorithm gives a solution as a linear matrix inequality, and can be adapted to solve many LMIs simultaneously. LMIs can be obtained by substituting several speeds into the dynamics of the MR-X1. The proposed controller, which can be derived from the solution of the LMIs, was adapted to MR-X1 and showed good performance in experiments. This work was presented in part at the 11th International Symposium on Artificial Life and Robotics, Oita, Japan, January 23–25, 2006     

Aliphatic Halogenase Enables Late‐Stage C−H Functionalization: Selective Synthesis of a Brominated Fischerindole Alkaloid with Enhanced Antibacterial Activity

The anion promiscuity of a newly discovered standalone aliphatic halogenase WelO5 was probed and enabled the selective synthesis of 13R‐bromo‐12‐epi‐fischerindole U via late‐stage enzymatic functionalization of an unactivated sp³ C?H bond. Pre‐saturating the WelO5 active site with a non‐native bromide anion was found to be critical to the highly selective in vitro transfer of bromine, instead of chlorine, to the target carbon center and also allowed the relative binding affinity of bromide and chloride towards the WelO5 enzyme to be assessed. This study further revealed the critical importance of halogen substitution on modulating the antibiotic activity of fischerindole alkaloids and highlights the promise of WelO5‐type aliphatic halogenases as enzymatic tools to fine‐tune the bioactivity of complex natural products.