Kinetic Studies of Block Polycondensation. I. Aggregation of Various Carboxylic Acids in Solvents of Low Dielectric Constant

Self-association of benzoic, octanoic, and octadecanoic acids was studied in solvents with a range of dielectric constants between 2.3 and 10. The number-average molecular weights were determined by means of vapor pressure measurements and were carried out at temperatures ranging from 25 to 90° C. It appears that, in these solvents of low dielectric constant, carboxylic acids are present mainly as molecular or ionic aggregates.     

Recombination of hydrogen atoms on fine-grain graphite

The probability of recombination of hydrogen atoms on surfaces of fine-grain graphite EK98 was investigated as a function of surface roughness. The source of hydrogen atoms used in this experiment was weakly ionised plasma created with an inductively coupled radiofrequency generator at pressures from 30 Pa to 175 Pa in hydrogen. Hydrogen atom density was measured by means of fibre optic catalytic probes. The recombination coefficient of the graphite samples was determined by observing their impact on the spatial distribution of the atom density in a closed side-arm of the reactor. Smith's diffusion model was used to calculate the values of the recombination coefficient. The measured recombination coefficient was found to increase much faster than the measured effective surface. This discrepancy is explained by the fact that on a surface which is not perfectly flat, there is a finite probability for multiple collisions. Impinging atoms collide more than once with the surface before they are reflected into the surface, which results in a larger probability of recombination.     

Functionalization of Polyurethane/Urea Copolymers with Amide Groups by Polymer Treatment with Ammonia Plasma

Samples of porous foam from polyurethane/urea copolymers based on polyethylene glycol (PURPEG) were prepared in the form of 1-mm-thick discs of diameter 10 cm and exposed to ammonia plasma created by inductively coupled radiofrequency discharge in either low density (E mode) or high density (H mode). The evolution of surface composition and structure upon plasma treatment was characterized by X-ray photoelectron spectroscopy. Treatment in the H mode caused depletion of oxygen even after 2 s of treatment, whereas treatment in the E mode caused gentle functionalization with amide groups. The concentration of functional groups depended on the discharge power, and the best results were obtained at moderately high power just before the transition from E to H modes.     

MnOx Nanoparticles Supported on a New Mesostructured Silicate with Textural Porosity

A two‐step synthesis of a novel mesostructured silicate, KIL‐2, and its manganese‐containing analogue, Mn/KIL‐2, has been developed. KIL‐2 possesses interparticle mesopores with pore dimensions between 5 and 60 nm and a surface area of 448 m². The mesopores are formed by the aggregation of silica nanoparticles, which creates a network with interparticle voids. The particle size and the pore diameters depend on the temperature of the ageing step (first step) and on the solvothermal treatment in ethanol (second step), respectively. Mn/KIL‐2 contains octahedrally coordinated Mn³⁺ (80 %) and tetrahedrally coordinated Mn²⁺ (20 %) ions. Mn³⁺ ions are present in the extra‐framework MnO_x nanoparticles with typical dimensions of 2 nm, which are homogeneously distributed throughout the material. Mn²⁺ ions occur as isolated manganese framework sites. The material is also able to retain its structure characteristics after the hydrothermal treatment in boiling water. Because of its non‐toxic nature and cost‐effective synthesis, Mn/KIL‐2 thus exhibits properties that are needed for an environment‐friendly catalyst.     

Synthese et etude de celluloses echangeuses d'ions. Leur emploi dans l'epuration des eaux residuaires de l'industrie textile-III: Traitement des eaux residuaires de l'industrie textile par une cellulose greffee par des chaines d'acide polyacrylique et par une cellulose renfermant des fonctions ammonium quaternaire

Modified celluloses previously described have been studied for ability to remove colour from the effluents of textile industry. The lowest dye concentration for which the celluloses are efficient are far below the lowest concentrations in effluents. It appears that the modified celluloses are more efficient than carbon black and are well adapted for the purification of pretreated or rinsing waters. Their abilities to extract surfactants from effluents and so to break emulsions of water with solvents have been examined and appear to be large. The treated waters can be recycled.     

Determination of phenylalanine and tyrosine by liquid chromatography/mass spectrometry

Phenylketonuria is a common metabolic disorder disease. Those affected appear normal at birth, but without treatment they develop severe psychomotor retardation. Throughout life, they must control their blood levels of phenylalanine (Phe) and consume a diet containing adequate amounts of Phe and tyrosine (Tyr). We have developed a liquid chromatographic/mass spectrometric (LC/MS) method for the quantitative evaluation of Phe and Tyr in food samples. This method takes advantage of the good separation of LC and the selective and reliable quantification provided by MS in the electrospray ionization mode. The LC/MS method is very suitable for the determination of selected amino acids in various matrixes. It is sensitive to levels as low as about 0.30 ppm for Tyr and 0.70 ppm for Phe and robust. Nearly 100 nondietary food samples were analyzed by the developed method.     

Quantifying Uncertainty in Quantitative TLC

JPC – Journal of Planar Chromatography – Modern TLC - The Eurachem/Citac Guide on measurement uncertainty establishes general rules for evaluating and expressing measure¬ment...     

Preparation de membranes echangeuses de cations par photogreffage d'ethers allyliques du poly (alcool vinylique). Etude de certaines de leurs proprietes—III: Caracteristiques physicochimiques des membranes poly (alcool vinylique-g-sulfonique)

The membranes of poly(vinyl alcohol-g-vinyl sulphonic acid) have been studied. The swelling can be controlled: the exchange capacity, the conductivity, the flux of diffusion, the critical current density have been determined and analysed with respect to the experimental parameters of the preparation.     

The IR spectra of DCOOH and HCOOD crystals at low temperatures

We show the IR spectra of HCOOD and DCOOH crystals in the region 1000–3000 cm⁻¹ at 7, 77 and 125 K. This article is a complement to previous articles which described spectra of HCOOH and DCOOD crystals recorded in the same conditions. In this article we also compare the results obtained on the four isotopic species and specially focus our attention on a comparison of the moments or order 0, 1 and 2 of the v_O---H…O (O---H…O) and v_O---D…O bands. Furthermore, we precise some experimental aspects, particularly those concerning polarization effects. In the following paper, we shall deduce from the first moments the relative importance of the different anharmonicities governing the stretching motion of the H or D atoms in the H- or D---bonds.     

From α‐carbamoyl‐α‐cyano­oxiranes to 3‐halogenopyruv­amides

The crystal structures of the first stable α‐diol from the α‐halogenopyruv­amide series, 3‐chloro‐2,2‐di­hydroxy‐3‐phenyl­propan­amide, C₉H₁₀­ClNO₃, and three products [3‐(4‐chloro­phenyl)‐2‐cyano‐2,3‐epoxy­propan­amide, C₁₀H₇­ClN₂O₂, 3‐bromo‐2‐cyano‐2‐hydroxy‐3‐p‐tolyl­propan­amide, C₁₁H₁₁Br­N₂O₂, 3‐bromo‐2‐oxo‐3‐p‐tolyl­propan­amide, C₁₀H₁₀­BrNO₂] obtained during the systematic synthesis of α‐halogenopyruv­amides are reported. The crystal structures are dominated by hydrogen bonds involving an amide group. The stability of the geminal diol could be ascribed to hydrogen bonds which involve both hydroxyl groups.