Effect of nanotube functionalization on the properties of single‐walled carbon nanotube/polyurethane composites

A commercially available aliphatic thermoplastic polyurethane formulated with a methylene bis(cyclohexyl) diisocyanate hard segment and a poly(tetramethylene oxide) soft segment and chain‐extended with 1,4‐butanediol was dissolved in dimethylformamide and mixed with dispersed single‐walled carbon nanotubes. The properties of composites made with unfunctionalized nanotubes were compared with the properties of composites made with nanotubes functionalized to contain hydroxyl groups. Functionalization almost eliminated the conductivity of the tubes according to the conductivity of the composites above the percolation threshold. In most cases, functionalized and unfunctionalized tubes yielded composites with statistically identical mechanical properties. However, composites made with functionalized tubes did have a slightly higher modulus in the rubbery plateau region at higher nanotube fractions. Small‐angle X‐ray scattering patterns indicated that the dispersion reached a plateau in the unfunctionalized composites that was consistent with the plateau in the rubbery plateau region. The room‐temperature modulus and tensile strength increase was proportionally higher than almost all increases seen previously in thermoplastic polyurethanes; however, the increase was still an order of magnitude below what has been reported for the best nanotube–polymer systems. Nanotube addition increased the hard‐segment glass transition temperature slightly, whereas the soft‐segment glass transition was so diffuse that no conclusions could be drawn. Unfunctionalized tubes suppressed the crystallization of the hard segment; whereas functionalized tubes had no effect. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 490–501, 2007     

An unusual syn conformation of 5‐formyluracil stabilized by supramolecular interactions

The asymmetric unit of the amino–oxo tautomer of 5‐formyluracil (systematic name: 2,4‐dioxo‐1,2,3,4‐tetrahydropyrimidine‐5‐carbaldehyde), C₅H₄N₂O₃, comprises one planar amino–oxo tautomer, as every atom in the structure lies on a crystallographic mirror plane. At variance with all the previously reported small‐molecule crystal structures containing the 5‐formyluracil residue, the formyl substituent in the title compound exhibits an unusual syn conformation. The molecules are linked into planar sheets parallel to the bc plane by a combination of six N—H...O and C—H...O hydrogen bonds. Four of the hydrogen bonds are utilized to stabilize the formyl group in the syn conformation.     

2-Dimension from the Topological Viewpoint

In this paper we study the 2-dimension of a finite poset from the topological point of view. We use homotopy theory of finite topological spaces and the concept of a beat point to improve the classical results on 2-dimension, giving a more complete answer to the problem of all possible 2-dimensions of an n-point poset.      

Losartan potassium,a non‐peptide agent for the treatment of arterial hypertension

In the title compound, potassium 2‐butyl‐4‐chloro‐1‐{[2′‐(5‐tetrazolido)­bi­phenyl‐4‐yl]­methyl}‐1H‐imidazol‐5‐yl­methanol, K⁺·C₂₂H₂₂ClN₆O^?, the imidazole and tetrazole rings are at angles of 85.0 (2) and 51.8 (1)°, respectively, to the phenyl rings to which they are attached, while the dihedral angle between the latter two rings is 46.7 (1)°. The coordination sphere of the metal cation consists of six tetrazoyl N atoms, the methanol O atom and the π cloud of one of the phenyl rings. These interactions determine the formation of columns of molecular anions that lie parallel to the b axis, while hydrogen bonding contributes to intercolumnar cohesion. Far from the centre of the columns, the hydro­carbon chain is immersed in a hydro­phobic environment.     

A propos de conjectures de Serre et Sullivan

Summary We first give a new proof of a conjecture of J.-P. Serre on the homotopy of finite complexes, which was recently proved by C. McGibbon and J. Neisendorfer. The emphasis is on a property of the mod. 2 homology of certain spaces: their quasi-boundedness as right modules over the Steenrod algebra. This property is preserved when one goes from a simply connected space to its loop space and also when one takes a covering of anH-space. Then we show that this notion of quasi-boundedness simplifies H. Miller's proof of D. Sullivan's conjecture on the contractibility of the space of pointed maps from the classifying space of the groupe /2 into a finite complex.     

A sensitive solid-phase fluoroimmunoassay for detection of opiates in urine

An automated flow fluorometer designed for kinetic binding analysis was adapted to develop a solid-phase competitive fluoroimmunoassay for urinalysis of opiates. The solid phase consisted of polymer beads coated with commercial monoclonal antibodies (MAbs) raised against morphine. Fluorescein-conjugated morphine (FL-MOR) was used as the fluorescein-labeled hapten. The dissociation equilibrium constant (K _D ) for the binding of FL-MOR to the anti-MOR MAb was 0.23 nM. The binding of FL-MOR to the anti-MOR MAb reached steady state within minutes and was displaced effectively by morphine and other opiates. Morphine-3-glucuronide (M3G), the major urinary metabolite of heroin and morphine, competed effectively with FL-MOR in a concentration-dependent manner for binding to the antimorphine MAb and was therefore used to construct the calibration curve. The sensitivity of the assay was 0.2 ng/mL for M3G. The assay was effective at concentrations of M3G from 0.2 to 50 ng/mL, with an IC₅₀ of 2 ng/mL. Other opiates and heroin metabolites that showed >50% crossreactivity when present at 1 μg/mL included codeine, morphine-6-glucuronide, and oxycodone. Methadone showed very low crossreactivity (<5%), which is a benefit for testing in patients being treated for opiate addictions. The high sensitivity of the assay and the relatively high cutoff value for positive opiate tests allows very small sample volumes (e.g., in saliva or sweat) to be analyzed. A double-blind comparison using 205 clinical urine samples showed good agreement between this single-step competitive assay and a commercially performed enzyme multiplied immunoassay technique for the detection of opiates and benzoylecgonine (a metabolite of cocaine).     

HPLC determination of 2-furaldehyde and 5-hydroxymethyl-2-furaldehyde in alcoholic beverages

A method for the determination of 2-furaldehyde (F) and 5-hydroxymethyl-2-furaldehyde (HMF) in alcoholic beverages by high performance liquid chromatography (HPLC) is described. A C-18 column and an acetonitrile-water mobile phase with isocratic elution were used. UV detection at 280 nm was carried out. The method was validated according to the EURACHEM guidelines. The procedure offers a high specificity and detection limits of the order of 0.005 μg mL^− 1. Recoveries of 94-103% were obtained from spiked samples at different levels with both analytes. Intermediate precision calculated for a period of 2 months was + 0.8% for HMF and + 0.4% for F. The method was applied to the analysis of alcoholic beverages like bourbon, rum, brandy, liquors and aperitif wines.     

Photochemistry of perfluoroacyl halides in the presence of O2 and CO

Photolyses of CF₃C(O)X and C₂F₅C(O)X (X=Cl, F) at 254 nm in the presence of O₂ yield the perfluorinated radicals C₂F₅O (C₂) and CF₃O (C₁), respectively. The C₂ radicals decompose to give CF₃ radicals:

C₂F₅O→CF₃+CF₂O

which, in turn, react with O₂ leading to the formation of C₁ radicals. When in addition to O₂, CO is present, the C₁ radicals react with it leading to its catalytic oxidation to CO₂. The trioxide CF₃OC(O)O₃C(O)OCF₃ was observed following the photolysis of all four halides in the presence of O₂ and CO.

The other radical partners coming from the initial step in the photolysis (XC(O)) as well as the products of their reaction with O₂ (XC(O)O_y, y=1, 2) do not react with CO but when X=F they lead to the formation of a new stable peroxy molecule with the formula CF₃OC(O)O₂C(O)F. Some of the properties of this new molecule, its stability and its IR features are presented in this work.