A ‘one-pot’ synthesis of α-1,2,4-oxadiazolo esters from malonic diesters and amidoximes under solvent-free conditions

A ‘one-pot’ procedure for synthesis of α-1,2,4-oxadiazolo esters from malonic diesters and amidoximes under solvent-free conditions is described. It is likely that this reaction goes through a ketene intermediate generated from the malonic diester by elimination of a molecule of alcohol.     

Temperature dependence of homogeneous nucleation rates for water: near equivalence of the empirical fit of Wölk and Strey, and the scaled nucleation model

It is pointed out that the temperature fitting function of W?lk and Strey [J. Phys. Chem. 105, 11683 (2001)], recently shown to convert the Becker-D?ring [Ann. Phys. (Leipzig) 24, 719 (1935)] nucleation rate into an expression in agreement with much of the experimental water nucleation rate data, also converts the Becker-D?ring rate into a form nearly equivalent with the scaled nucleation rate model, J(scaled)=J(oc) exp[-16piOmega(3)(T(c)T-1)(3)3(ln S)(2)]. In the latter expression J(oc) is the inverse thermal wavelength cubed/sec, evaluated at T(c).     

Quinone-modified polymers as electron transfer relay systems in amperometric glucose sensors

A polysiloxane and an acrylonitrile–ethylene copolymer with covalently attached p-hydroquinone/benzoquinone moieties were prepared and tested as electron transfer relay systems in amperometric glucose biosensors. Using experiments involving cyclic voltammetry and stationary potential measurements, it was shown that the polysiloxane relay system can efficiently mediate electron transfer from reduced glucose oxidase to a conventional carbon-paste electrode. Sensors containing this polymeric relay system and glucose oxidase respond rapidly to low (<0.1 mm) glucose concentrations, with steady state current responses achieved in less than 1 min. The acrylonitrile–ethylene copolymer was found to be less efficient than the polysiloxane system at mediating the electron transfer from reduced glucose oxidase to the electrode. The dependence of the sensor response on the nature of the polymer backbone is discussed.     

The influence of bond flexibility and molecular size on the chemically selective bonding of In2O and Ga2O on GaAs(001)-c(2 x 8)/(2 x 4)

The surface structures formed upon deposition of In2O and Ga2O by molecular beam epitaxy onto the arsenic-rich GaAs(001)-c(2 x 8)/(2 x 4) surface have been studied using scanning tunneling microscopy and density functional theory. In2O initially bonds, with indium atoms bonding to second layer gallium atoms within the trough, and proceeds to insert into or between first layer arsenic dimer pairs. In contrast, Ga2O only inserts into or between arsenic dimer pairs due to chemical site constraints. The calculated energy needed to bend a Ga2O molecule approximately 70 degrees, so that it can fit into an arsenic dimer pair, is 0.6 eV less than that required for In2O. The greater flexibility of the Ga2O molecule causes its insertion site to be 0.77 eV more exothermic than the In2O insertion site. This result shows that although trends in the periodic table can be used to predict some surface reactions, small changes in atomic size can play a significant role in the chemistry of gas/surface reactions through the indirect effects of bond angle flexibility and bond length stiffness.     

Method for the determination of the solubility of gases in liquids

A rapid and experimentally simple method for the determination of the solubilities of oxygen or hydrogen in liquids is presented The method employs a membrane-enclosed amperometric detector of the well known Clark type to measure the partial pressure of the gas when distributed at equilibrium between the liquid and a gas space for a series of internal volumes of the system. The amounts of all substances and the temperature are maintained constant throughout the series although the internal pressure changes as a result of the volume changes. The glass apparatus is water jacketed for temperature control, has inlet and outlet ports for gas, and the amperometric sensor is mounted in a gas-tight sliding fitting for effecting the volume changes. The liquid content is vigorously stirred by a magnetic bar during measurements. Equations for the interpretation of results at different internal volumes take into account the conservation of the solvent and of the gas, the dependence of the volume of the liquid on the concentration of dissolved gas and Henry's law describing the distribution of the gas between gas and liquid phases at equilibrium. The solution of these equations yields an equation for the dependence of the measured partial pressure on volume, which includes the Henry's law constant H as a parameter. Conditions can usually be arranged to give a straight line dependence of volume on the reciprocal of partial pressure. The method has been applied to several common liquids, and has been shown to produce results which agree with literature solubilities to within about ±5%. Examples which have been studied include oxygen in water (H=4.039 × 10⁶ kPa at 20°C), in acetone (1.25 × 10⁵ kPa at 20°C), in ethanol (1.758 × 10⁵ kPa at 20°C) and in toluene (1.05 × 10⁵ kPa at 20°C) as well as hydrogen in water (6.89 × 10⁶ kPa at 20°C).     

Splitting tendency of cellulosic fibers – Part 1. The effect of shear force on mechanical stability of swollen lyocell fibers

A procedure for splitting of a lyocell fiber into a multitude of finer fibrils was developed. Crockmeter, usually used for rub-fastness of colored textiles, was modified and used for obtaining required shear force on swollen lyocell fiber. The shear force applied on fibers, and the concentration of NaOH, which affects swelling degree of fiber, were shown to be the leading parameters determining split number of lyocell fiber. While number of shear cycles was found to be of minor relevance for fiber splitting, the applied pressure directly influences the number of splitted fibrils. For example, at a pressure of 34.8 kPa, the average split number of lyocell fiber in 2.5 M NaOH solution was observed as 15, whereas it was observed as 30 for 47 kPa and 41 for 59.3 kPa. Splitting was not observed above 5 M of NaOH solution. Analyses of fiber splitting permit new aspects to study inner structure of lyocell.     

Poly(aryl ethers) by nucleophilic aromatic substitution. I. Synthesis and properties

A series of new aromatic polyethers have been prepared by solution condensation polymerization. The synthesis involves the condensation of a dialkali metal salt of a dihydric phenol with an “activated” or negatively substituted aromatic dihalide in an anhydrous dipolar aprotic solvent at elevated temperatures. The reaction is rapid, free of side reactions, and yields polymers of excellent color. Bakelite polysulfone can be prepared in this manner by reaction of the disodium salt of bisphenol A with 4,4′-dichlorodiphenyl sulfone in dimethyl sulfoxide (DMSO). Only dipolar aprotic solvents are useful for conducting the polymerization. Of these, DMSO and Sulfolane (tetrahydrothiophene 1,1-dioxide) are the most effective. Water or other competing nucleophiles must be absent if high molecular weight is to be obtained. Besides providing the necessary solubility, this highly polar solvent is believed to be essential in providing the rapid polymerization rates observed. The rates are further found to depend on the basicity of the bisphenol salt and upon the electron-withdrawing power of the activating group in the dihalide. As is usual for this type of reaction, the difluorides are found to be more reactive than the corresponding dichlorides. Most of the polyethers are amorphous, rigid, tough thermoplastics with high second-order transitions (T_g). Thermal stability and electrical properties are noteworthy. These and other properties are described for polysulfone, and glass transitions are given for a selected list of the other polyethers.     

Proteomic analysis of detergent-resistant membrane rafts

A combined, detergent- and organic solvent-based proteomic method for the analysis of detergent-resistant membrane rafts (DRMR) is described. These specialized domains of the plasma membrane contain a distinctive and dynamic protein and/or lipid complement, which can be isolated from most mammalian cells. Lipid rafts are predominantly involved in signal transduction and adapted to mediate and produce different cellular responses. To facilitate a better understanding of their biology and role, DRMR were isolated from Vero cells as a Triton X-100 insoluble fraction. After detergent removal, sonication in 60% buffered methanol was used to extract, solubilize and tryptically digest the resulting protein complement. The peptide digestate was analyzed by microcapillary reversed-phase liquid chromatography-tandem mass spectrometry. Gas-phase fractionation in the mass-to-charge range was employed to broaden the selection of precursor ions and increase the number of identifications in an effort to detect less abundant proteins. A total of 380 proteins were identified including all known lipid raft markers. A total of 91 (24%) proteins were classified as integral alpha-helical membrane proteins, of which 51 (56%) were predicted to have multiple transmembrane domains.     

NQR and magnetic characteristics of the solid solution of NaClO3-KClO3

We measured the nuclear quadrupole resonance (NQR) of the solid solutions of NaClO₃-KClO₃ in the range of concentrations from 0 to 100% molar of KClO₃ in (NaClO₃ + + KClO₃). The thermal diagram of the measured samples showed, that the solubility of the components in each other is limited. It is shown that up to 88·6% molar of KlCO₃ it is possible to identify signals at a frequency which almost exactly corresponds to the NQR frequency of NaClO₃, from this concentration the signals belong to the NQR frequency of KClO₃. At the same time the width of the line shows anomalies in samples containing up to 10% KClO₃ or up to 10% NaClO₃. Broadening of the NQR line to the value 35 kHz in this region was interpreted as a result of prevalence of the size-effect, when the solid solution consists of a mixed crystal of one of the components with such a number of cations of the other component, which is sufficient to produce a chaotic order around the resonanting Cl³⁵ nucleus and such alterations of the electrical field gradient, that they will widen the line.We have also interpreted the deviations of the resonance frequency and linewidth corresponding to the monocrystalline, polycrystalline and melted modifications of the pure NaClO₃ and KClO₃ components.The dependence of the molar magnetic susceptibility of the solid solutions on the concentration of KClO₃ in NaClO₃ + KClO₃ is not linear, it has a peak at the concentration that belongs to the eutectic state, when the chaotic order of the ions Na¹⁺, K¹⁺, (ClO₃ ^1– around any of them is most perfect. At this concentration Van Vleck's polarization paramagnetism is minimum and because it is positive, the total negative value of susceptibility of the material is maximum.