Removal of strontium ions by a crosslinked copolymer containing methacrylic acid functional groups</p> </p>

Summary A tail-made polymer matrix is proposed to remove strontium ions from aqueous solutions. The removal behavior of strontium ions on a crosslinked copolymer containing methacrylic acid as functional groups was investigated as a function of sorptive concentration, time, temperature and pH. It was observed that an increase of these parameters enhanced the removal of Sr(II) ions from aqueous solution. It is found that a maximum adsorption of Sr(II) ions can be obtained on the crosslinked copolymer after 30 minutes and at pH 8. The increase of Sr(II) ion concentration in the solution resulted in an increase in the amount of Sr(II) ions adsorbed on the crosslinked copolymer containing methacrylic acid as functional groups. However, after a maximum of Sr(II) concentration in the solution, the percentage of adsorbed Sr(II) ions decreased. The adsorption data are well represented by the Freundlich, Langmuir and Dubinin-Radushkevich (D-R) isotherms. The adsorption capacity of the copolymer and the free energy change were calculated by using the D-R isotherm. For the adsorption of Sr(II) ions on the crosslinked copolymer the thermodynamic parameters (DH°,DS° andDG°) were calculated.</p> </p>     

Performance of an internal-loop airlift bioreactor for treatment of hexane-contaminated air

Hexane is a toxic volatile organic compound that is quite abundant in gas emissions from chemical industries and printing press and painting centers, and it is necessary to treat these airstreams before they discharge into the atmosphere. This article presents a treatment for hexane-contaminated air in steady-state conditions using an internal-loop airlift bioreactor inoculated with a Pseudomonas aeruginosa strain. Bioprocesses were conducted at 20-mL/min, a load of 1.26 g/m³ of C₆H₁₄, and a temperature of 28°C. The results of hexane removal efficiencies were presented as a function of the inoculum size (approx 0.07 and 0.2 g/L) and cell reuse. Bioprocess monitoring comprises quantification of the biomass, the surface tension of the medium, and the hexane concentration in the fermentation medium as well as in the inlet and outlet airstreams. The steady-state results suggest that the variation in inoculum size from 0.07 to 0.2 g/L promotes hexane abatement from the influent from 65 to 85%, respectively. Total hydrocarbon removal from the waste gas was achieved during experiments conducted using reused cells at an initial microbial concentration of 0.2 g/L.     

SANS study of the aging of xTiO2-SiO2 gels

Silica-titania gels, prepared in acidic conditions, with contents of TiO₂ up to 6 mol%, have been studied by small angle neutron scattering (SANS) as wet gel with increasing aging times. In all samples, small primary particles have been found with a diameter of about 3 nm. At the gel point, cylindrical clusters, ca. 10 nm long, were observed as well. These grow with aging time, becoming branched. The cluster-cluster diffusion limited aggregation model is found to be consistent with the SANS results. The growth process is independent of the TiO₂ content. It is mainly influenced by the ratio of the aging time to the gelation time.     

Catalytic Cyclophanes. Part VIII. Cytochrome P-450 activity of a porphyrin-bridged cyclophane

Following a known synthetic procedure, the porphyrin-cyclophane 1 having a porphyrin attached by two straps to an apolar cyclophane binding site was prepared. Upon metallation, the Zn^II and Fe^III derivatives 2 and 3 , respectively, were obtained in good yields. Treatment of 3 with base yielded the μ-oxo dimer 4 in which the two oxo-bridged porphyrins moieties are both capped by cyclophane binding sites. All compounds 1–4 are freely soluble in protic solvents such as MeOH and CF₃CH₂OH, and the Fe^III derivatives 3 and 4 are active cytochrome P-450 mimics in these protic environments. Strong inclusion complexation of polycyclic aromatic hydrocarbons by 1 and 3 in alcoholic solvents was observed and quantified by ¹H-NMR and UV/VIS titrations. Acenaphthylene binds in an ‘equatorial’ orientation which locates its reactive 1,2-double bond near the porphyrin center, whereas phenanthrene binds ‘axially’ with the reactive 9,10-double bond oriented away from the porphyrin. The reduction potential of 3 was not significantly altered by substrate binding. In the unbound form, the Fe^III center in porphyrin 3 was found by ESR and ¹H-NMR to prefer a high-spin state (S = 5.2). In CF₃CH₂OH, using iodosylbenzene as O-transfer agent, the Fe^III derivative 3 catalyzed the oxidation of acenaphthylene to acenaphthen-1-one ( 14 ). Phenanthrene inhibited the reaction, possibly as a result of strong but nonproductive binding. Under similar conditions, isotetralin ( 18 ) was aromatized with high turnover to 1,4-dihydronaphthalene. The μ-oxo dimer 4 also showed high activity in the oxidation of acenaphthylen in MeOH, a result which provides strong evidence for efficent supramolecular catalysis. Due to as yet unknown reaction channels leading to polymeric products, poor mass balances were generally obtained in the oxidations effected in MeOH and CF₃CH₂OH in the presence of PhIO.     

Synthesis, nuclear, and magnetic structures and magnetic properties of [Mn3(OH)2(SO4)2(H2O)2

[Mn(3)(OH)(2)(SO(4))(2)(H(2)O)(2)] and its deuterated analogue were synthesized by a hydrothermal technique and characterized by differential thermal analysis, thermogravimetric analysis, and IR spectroscopy. Its nuclear structure, determined by single-crystal X-ray analysis and Rietveld analysis of neutron powder-diffraction data, consists of a 3D network of chains of edge-sharing Mn(1)O(6), running along the c axis, connected by the apices of Mn(2)O(6) and SO(4) units. It is isostructural to the nickel analogue. Determination of the magnetic structure and measurements of magnetization and heat capacity indicate the coexistence of both magnetic long-range ordering (LRO) and short-range ordering (SRO) below a Néel temperature of 26 K, while the SRO is retained at higher temperatures. The moments of the two independent Mn atoms lie in the bc plane, and that of Mn(1) rotates continuously by 54 degrees towards the c axis on decreasing the temperature from 25 to 1.4 K. While the SRO may be associated with frustration of the moments within a Mn(3) trimer, the LRO is achieved by antiparallel alignment of the four symmetry-related trimers within the magnetic unit cell. A spin-flop field, measured by dc and ac magnetization on a SQUID, is observed at 15 kOe.     

Mise en evidence de la formation de R2MMR2 a partir de disila-1,2 et digerma-1,2 cyclohexenes-4

Intermediates with π-bonded Si or Ge are generated during gas phase pyrolysis of 1,2-disila- or 1,2-digerma-cyclohex-4-enes.Compounds such as R₂MMR₂ are successfully trapped by addition or [2 + 2] and [4 + 2] cycloadditions. These results were proved by mass spectrometry.     

Substrate-reagent complexation ability in enantioselective 1,4 addition reactions

Hydrogen-aarbonyl chelation and magnesium-arene π coordination are proposed to aooount for enhanced enantioselectivïty in 1,4-addition reactions of chiral cuprates.     

Independence versus indetermination: basis of two canonical clustering criteria

Advances in Data Analysis and Classification - This paper aims at comparing two coupling approaches as basic layers for building clustering criteria, suited for modularizing and clustering very...     

Dynamique des lasers à fibre dopée à I’erbium

The dynamics of the erbium doped fiber laser is analysed both experimentally and theoretically. This laser operates spontaneously in self-pulsing, in sinusoidal or in CW regime. Experiments have allowed to determine the control parameters : the cavity losses, the pumping rate and the ion pairs concentration. An antiphase dynamics is observed when the laser operates simultaneously at 1.55 µn and 1.536 µm. The self-pulsing behavior is attributed to a fast energy transfer which occurs between two neighboring ions (pair induced quenching). A simple model considering the active medium as a mixture of isolated ions and ions pairs is developped and leads to a good qualitative agreement with the experimental results.