Macromolecular Organization of Poly(L‐lactide)‐block‐Polyoxyethylene into Bio‐Inspired Nano‐Architectures

Block copolymers create various types of nano‐structures, e. g., spheres, rods, cubes, and lamellae. This review discloses the dynamic macromolecular organization of block copolymers comprising poly(L ‐lactide) (PLLA) and poly(oxyethylene) (PEG) that allows to simulate elaborate biological systems. The block copolymers, AB‐ (PLLA‐PEG) and ABA‐type (PLLA‐PEG‐PLLA), are synthesized by ordinary lactide polymerization to have a controlled block length. They are dispersed into an aqueous medium to prepare nano‐scale particles, consisting of hydrophobic PLLA and hydrophilic PEG in the core and shell, respectively. Then, the particles are placed on a flat substrate by the casting method. The particles are detected as discoids by AFM, having shrunk with loss of water. Heat‐treatment of these particles at 60°C (above T_g of PLLA) gives rise to a collapse into small fragments, which then aggregate into bands with nano‐size width and thickness. The PLLA‐PEG bands align parallel to each other, while the PLLA‐PEG‐PLLA bands form a characteristic network resembling the neuron system created in animal tissue. As analyzed by TEM diffraction, each is composed of α‐crystal of PLLA whose c‐axis (molecular axis) is perpendicular to the substrate surface. Based on this fact, a doubly twisted chain structure of PLLA is proposed in addition to a plausible mechanism for the self‐organization of the block copolymers. Derivatives of the PLLA‐PEG block copolymers can form far more interesting nano‐architectures. An equimolar mixture of enantiomeric copolymers, PLLA‐PEG‐PLLA and PDLA‐PEG‐PDLA, forms a hydrogel that is thermo‐responsive. The terminal‐modified poly(L ‐lactide)‐block‐polyoxyethylene monocinnamate (PLLA‐PEG‐C) forms a highly stabilized nanofiber by the photo‐reaction of the cinnamates placed in the outer layer of the nanobands.     

Tetraaryl‐Substituted Benzo[1,2‐b:4,5‐b′]dipyrroles: Synthesis,Properties, and Applications to Hole‐Injection Materials in OLED Devices

Yes, HIMs can! A series of 2,3,6,7‐tetraarylbenzo[1,2‐b:4,5‐b′]dipyrroles (BDPs) were synthesized using zinc‐mediated double cyclization. Organic light‐emitting diodes consisting of BDP:PPB as a hole‐injection layer could be driven at a lower voltage than a PEDOT:PSS‐based device. Correlation of the IP values with the driving voltage shed some light on the mechanism of hole‐injection processes.

     

Multiple-functional capsule catalysts: a tailor-made confined reaction environment for the direct synthesis of middle isoparaffins from syngas

A capsule catalyst for isoparaffin synthesis based on Fischer-Tropsch reaction was designed by coating a H-ZSM-5 membrane onto the surface of the pre-shaped Co/SiO(2) pellet. Morphological and chemical analysis showed that the capsule catalyst had a core-shell structure. A compact, integral shell of H-ZSM-5 crystallized firmly on the Co/SiO(2) substrate without crack. Syngas passed through the zeolite membrane to reach the Co/SiO(2) catalyst to be converted, and all hydrocarbons formed with straight chain structure must enter the zeolite channels to undergo hydrocracking as well as isomerization in this tailor-made confined reaction environment. A narrow, anti-Anderson-Schultz-Flory law product distribution was observed on these capsule catalysts. Contrary to a mechanical mixture of H-ZSM-5 and Co/SiO(2), C(10+) hydrocarbons were suppressed completely on this novel capsule catalyst, and the selectivity of middle isoparaffins was considerably improved. The carbon number distribution of the products depended on the thickness of the zeolite membrane, and it was possible to selectively synthesize specified distillates, such as gasoline-range, or heavier hydrocarbons from syngas directly, by simply adjusting the thickness of the zeolite membrane of the capsule catalyst. This kind of capsule catalysts can be extended to various consecutive reaction systems as the shell and core components are independent catalysts for different reactions. At the same time, shape selectivity and space-confined effects can be expected for the reactant, intermediates and product of the sequential reactions.     

Electrochemical monitoring of intracellular enzyme activity of single living mammalian cells by using a double-mediator system

We evaluated the intracellular NAD(P)H:quinone oxidoreductase (NQO) activity of single HeLa cells by using the menadione–ferrocyanide double-mediator system combined with scanning electrochemical microscopy (SECM). The double-mediator system was used to amplify the current response from the intracellular NQO activity and to reduce menadione-induced cell damage. The electron shuttle between the electrode and menadione was mediated by the ferrocyanide/ferricyanide redox couple. Generation of ferrocyanide was observed immediately after the addition of a lower concentration (10 μM) of menadione. The ferrocyanide generation rate was constant for 120 min. At a higher menadione concentration (100 μM), the ferrocyanide generation rate decreased within 30 min because of the cytotoxic effect of menadione. We also investigated the relationship between intracellular reactive oxygen species or glutathione levels and exposure to different menadione concentrations to determine the optimal condition for SECM with minimal invasiveness. The present study clearly demonstrates that SECM is useful for the analysis of intracellular enzymatic activities in single cells with a double-mediator system.     

Structure analysis of a soluble polysiloxane-block-polyimide and kinetic analysis of the solution imidization of the relevant polyamic acid

A series of polysiloxane-block-polyimides were synthesized by solution imidization of the polyamic acids derived from the combination of 3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride (DSDA), 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), and diamino(polysiloxane) (PSX (M_w = 750)) in N-methyl-2-pyrrolidone (NMP). Their structures were analyzed by ¹H-, ¹³C-, and ²⁹Si-NMR spectra as well as by IR spectroscopy. The solid-state NMR spectrum was also measured to determine the spin–lattice relaxation time of the copolyimides. The observed relaxation times of both aromatic and polysiloxane segments were similar in the copolyimides having 10–30 wt % of PSX, while those in the copolyimide with 50 wt % of PSX was significantly different. This may be attributed to the morphology change due to the increase in PSX composition in the polymer backbone. The reduced viscosity of the copolyimides could be controlled by changing the monomer ratio in the feed or by adding an end-capping reagent such as phthalic anhydride into the polymerization system. The kinetic study of the solution imidization revealed that the imidization reaction obeyed second-order kinetics. The activation energy calculated for this imidization was 99.2 kJ/mol, being similar to that for the imidization of the DSDA-based aromatic polyimides. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2237–2245, 1998     

Surface acetylation of bacterial cellulose

Bacterial cellulose was partially acetylated by the fibrous acetylationmethod to modify its physical properties, while preserving the microfibrillarmorphology. The overall degree of substitution was varied from 0.04 to 2.77 bychanging the amount of acetic anhydride added. X-ray diffraction of thepartially acetylated samples showed the crystalline pattern of unmodified celluloseI up to moderate degrees of acetylation, and the change in peak widthsindicatedthat acetylation proceeded from the surface of microfibrils, leaving the coreportion unreacted. Scanning electron microscopy revealed that even low levelsofacetylation were effective to maintain the original microfibrillar morphologyofbacterial cellulose on direct drying from water.     

Synthesis and properties of highly fluorescent indolizino[3,4,5-ab]isoindoles

We report here the synthesis, X-ray structures, optical and electrochemical properties, fabrication of light-emitting devices, and density functional calculations for indolizino[3,4,5-ab]isoindole (INI) derivatives. Strongly luminescent heterocycles based on the INI unit were synthesized by 1,3-dipolar cycloaddition reactions between pyrido[2,1-a]isoindole (PIS) and acetylene or ethylene derivatives. They are indolizino[3,4,5-ab]isoindoles 2-9 and 14-15, benzo[1',2'-1,2]indolizino[3,4,5-ab]isoindoles 10, pyridazino[4',5':1,2]indolizino[3,4,5-ab]isoindoles 12-13, and 2,3-hydropyridazino[4',5':1,2]indolizino[3,4,5-ab]isoindole-1,4-dione 11. The relative luminescence quantum yield can be as high as 90%. Their reduction and oxidation potentials and high luminescence can make these heterocycles possible alternatives to tris(8-hydroxyquinolinato)aluminum (Alq(3)). The brightness of the light-emitting device reached as high as 10(4) cd/m(2) and indolizino[3,4,5-ab]isoindole 3 emits beautifully blue light. The X-ray crystal structures of INI derivatives were obtained for the first time. The geometries obtained from X-ray data and density functional theory calculations shed more light on an interesting formally antiaromatic 16pi system, which is divided into 10pi and 6pi aromatic systems. We also report a relatively easy protonation of INI, which occurs at a carbon, rather than nitrogen atom.     

An X-ray absorption spectroscopic study on mixed conductive La0.6Sr0.4Co0.8Fe0.2O(3-δ) cathodes. I. Electrical conductivity and electronic structure

The electrical conduction mechanism of mixed conductive perovskite oxides, La(0.6)Sr(0.4)Co(0.8)Fe(0.2)O(3-δ), for cathode materials of solid oxide fuel cells has been investigated from electronic structural changes during oxygen vacancy formation. La(0.6)Sr(0.4)Co(0.8)Fe(0.2)O(3-δ) was annealed under various oxygen partial pressures p(O(2))s at 1073 K and quenched. Iodometric titration indicated that the oxygen nonstoichiometry of La(0.6)Sr(0.4)Co(0.8)Fe(0.2)O(3-δ) depended on the annealing p(O(2)), with more oxygen vacancies introduced at lower than at higher p(O(2))s. X-Ray absorption spectroscopic measurements were performed at the O K-, Co L-, Fe L-, Co K-, and Fe K-edges. The valence states of the Co and Fe ions were investigated by the X-ray absorption near edge structure (XANES) at the Co and Fe L(III)-edges. While the Fe average valence was almost constant, the valence of the Co ions decreased with oxygen vacancy introduction. The O K-edge XANES spectra indicated that electrons were injected into the Co 3d/O 2p hybridization state with oxygen vacancy introduction. Both absorption edges at the Co and Fe K-edge XANES shifted towards lower energies with oxygen vacancy introduction. The shift at the Co K-edge resulted from the decrease in the Co average valence and that at the Fe K-edge appeared to be caused by changes in the coordination environment around the Fe ions. The total conductivity of La(0.6)Sr(0.4)Co(0.8)Fe(0.2)O(3-δ) decreased with decreasing p(O(2)), due to a decreasing hole concentration.     

The novel assay method for nicotine metabolism to cotinine using high performance liquid chromatography

Nicotine is the primary psychoactive component in tobacco. It is taken into the body by tobacco smoking, and mainly metabolized to cotinine in the hepatic cytochrme P450 (CYP) 2A6. The objective of this study was to develop a sensitive method for the determination of nicotine metabolism to cotinine using HPLC. The internal standard, trans-4'-carboxycotinine methyl ester was synthesized with a simple method. The nicotine and cotinine were separated completely and detected by C(18) 5-μm analytical column (L-column Octa decyl silyl (ODS), 150 mm × 4.6 mm i.d.) equipped with a C(18) 5-μm guard column (L-column ODS, 10 mm × 4.6 mm i.d.) and ultraviolet detection at 260 nm. The detection limit of the assay was 0.05 μM for cotinine (n=5, R.S.D) and 0.1 μM for nicotine. Thus the present results provided a sensitive and useful method for the determination of nicotine metabolism catalyzed by CYP2A6.