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.     

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.     

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.     

X-ray photoelectron emission microscopy and time-of-flight secondary ion mass spectrometry analysis of ultrathin fluoropolymer coatings for stent applications

Fluoropolymer plasma coatings have been investigated for application as stent coatings due to their chemical stability, conformability, and hydrophobic properties. The challenge resides in the capacity for these coatings to remain adherent, stable, and cohesive after the in vivo stent expansion, which can generate local plastic deformation of up to 25%. Plasma-coated samples have been prepared by a multistep process on 316L stainless steel substrates, and some coated samples were plastically deformed to mimic a stent expansion. Analyses were then performed by X-ray photoelectron spectroscopy (XPS), X-ray photoelectron emission microscopy (X-PEEM), and time-of-flight secondary ion mass spectrometry (TOF-SIMS) to determine the chemical and physical effects of such a deformation on both the coating and the interfacial region. While XPS analyses always showed a continuous coating with no significant effect of the deformation, TOF-SIMS and near-edge X-ray absorption fine structure (derived from X-PEEM) data indicated the presence of a certain density of porosity and pinholes in all coatings as well as sparse fissures and molecular fragmentation in the deformed ones. The smallness of the area fraction affected by the defects and the subtlety of the chemical changes could only be evidenced through the higher chemical sensitivity of these latter techniques.