Highly efficient oxidation of alcohols by the system "hydrogen peroxide-[lmn(o)3mnl](pf6)2 (l = 1,4,7-trimethyl-1,4,7-triazacyclononane)-oxalic acid"

Summary The dinuclear manganese(IV) complex [LMn(O)₃MnL](PF₆)₂ (1, L = 1,4,7-trimethyl-1,4,7-triazacyclononane) catalyzes the extremely efficient oxidation of alcohols with hydrogen peroxide at room temperature. Oxalic acid is an obligatory co-catalyst. The oxidation of isopropanol, for example, yields acetone with turnover numbers up to 40000 after 5-10 h in the absence of a solvent. 2-Cyanoethanol was oxidized by this system with somewhat lower efficiency (conversion 70%). The catalytically active cation from salt 1 was obtained in an insoluble form containing a heteropoly anion [Mn₂O₃(TMTACN)₂]₂[SiW₁₂O₄₀]. Oxidation of 2-cyanoethanol using this heterogenized catalyst and oxalic acid gave the oxo-products with the 54% total yield.     

Optimisation of the method for determination of the temperature of saturation in wines

The temperature of saturation of potassium hydrogentartrate (KHT) in wines was studied as an analytical parameter for wine tartaric stability evaluation. Two types of wines were used: “Vinho Verde” and “Port wine”. The temperature of saturation was determined by the intersection of the plots of conductivity versus temperature for a wine sample and the same wine sample with added KHT, by raising the temperature. The heating rate used was optimised in terms of accuracy and time necessary for the determination. An optimal value of 0.5 °C min⁻¹ was found for both types of wine. The saturation temperature was determined for eight untreated wines and after two different tartaric stabilisation treatments, cold stabilisation and electrodialysis. The temperature of saturation values allowed the evaluation of the tartaric stability achieved and the comparison of the two treatments.     

Time-resolved study of the spectral characteristics of supercontinuum pulses propagating in scattering media

The spectral and temporal characteristics of supercontinuum pulses propagating through monodisperse scattering media consisting of sub-lambda-sized particles have been measured with a broad-bandwidth cross-correlated frequency-resolved optical gating (XFROG) technique. The results show that the ballistic component of the supercontinuum preserves a phase relationship among its spectral components, which acquire a temporal shift in relation to propagation in a non-scattering medium.     

A new approach to factorization of a class of almost-periodic triangular symbols and related Riemann-Hilbert problems

The factorization of almost-periodic triangular symbols, G, associated to finite-interval convolution operators is studied for two classes of operators whose Fourier symbols are almost periodic polynomials with spectrum in the group αZ+βZ+Z (α,β∈]0,1[, α+β>1, α/β∉Q). The factorization problem is solved by a method that is based on the calculation of one solution of the Riemann-Hilbert problem GΦ₊=Φ₋ in L_∞(R) and does not require solving the associated corona problems since a second linearly independent solution is obtained by means of an appropriate transformation on the space of solutions to the Riemann-Hilbert problem. Some unexpected, but interesting, results are obtained concerning the Fourier spectrum of the solutions of GΦ₊=Φ₋. In particular it is shown that a solution exists with Fourier spectrum in the additive group αZ+βZ whether this group contains Z or not. Possible application of the method to more general classes of symbols is considered in the last section of the paper.     

Formation of clusters and the magnetooptical Kerr effect in gallium arsenide implanted with manganese ions

The surface morphology and magnetic properties of GaAs irradiated by manganese ions are studied at room temperature using atomic-force microscopy and the magnetooptical Kerr effect. It is shown that ferromagnetism takes place in the surface layer of the irradiated semiconductor subjected to annealing at 715–750°C. The magnetic properties of this layer are related to the evolution of submicron clusters in GaAs doped with Mn.     

Catalyst concentration distribution in fluidized bed by gamma-ray absorption

Summary The axial and radial distribution of the catalyst concentration, in the riser of an EMC - experimental cold model of a fluid catalytic cracking type unit, was measured by gamma-absorption. The solid concentration in the circulating fluidized bed was determined by measurements with a ²⁴¹Am gamma-source and a NaI(Tl) detector. The operation, instrumental measurements and data acquisition system of the cold unit were automated. The catalyst concentration measurements were carried out in static experiments and in the circulating fluidized bed. A calibration of the distribution concentration was made with experimental data from gas velocity and pressure drop along the riser that gave the best multi-regression model. A spatial resolution of 5.0 ^. 10^-3 m by scanning the riser and a catalyst density resolution of 5.0±0.8 kg/m³ were obtained. The axial catalyst concentration distribution, in the 5-13 kg/m ³ interval, showed a predicted pattern according to the literature. The radial distribution was in an annular configuration for this diluted catalyst concentration.     

Silica imprinted materials containing pharmaceuticals as a template: textural aspects

Silica-based materials were prepared by the acid catalyzed sol?Cgel method using different pharmaceuticals as a template. The template molecules investigated were fluoxetine, gentamicin, lidocaine, morphine, nifedipine, paracetamol and tetracycline. The resulting hybrid silicas underwent ultrasound extraction in the presence of several solvents and were characterized by elemental analysis, porosimetry by adsorption/desorption of nitrogen (BET method), small-angle X-ray scattering and X-ray diffraction. Drug extraction was carried out by the combination of solvent and ultra-sound. The textural characteristics of the hybrid xerogels and resulting imprinted materials were shown to be highly dependent on the molecular weight and molecular volume of the drug template. Increasing the molecular weight of the template results in a decrease in the encapsulation content of the resulting material. In the case of paracetamol and fluoxetine, the dimensions of the surface area are not sufficient to guarantee the adsorption of the smaller molecule. Instead, the shape generated through encapsulation and extraction during the production of the imprinted silica dictates the adsorption behavior.     

Grinding process for the production of nanofibrillated cellulose based on unbleached and bleached bamboo organosolv pulp

Nanofibrillated cellulose (NFC) is a type of nanomaterial based on renewable resources and produced by mechanical disintegration without chemicals. NFC is a potential reinforcing material with a high surface area and high aspect ratio, both of which increase reinforcement on the nanoscale. The raw materials used were unbleached and bleached bamboo organosolv pulp. Organosolv pulping is a cleaner process than other industrial methods (i.e. Kraft process), as it uses organic solvents during cooking and provides easy solvent recovery at the end of the process. The NFC was produced by treating unbleached and bleached bamboo organosolv pulps for 5, 10, 15 and 20 nanofibrillation cycles using the grinding method. Chemical, physical and mechanical tests were performed to determine the optimal condition for nanofibrillation. The delamination of the S2 layer of the fibers during nanofibrillation contributed to the partial removal of amorphous components (mainly lignin), which have low polarity and improved the adhesion of the fibers, particularly the unbleached cellulose. The transverse modulus of elasticity of the unbleached NFC was highest after 10 nanofibrillation cycles. Further treatment cycles decreased the modulus due to the mechanical degradation of the fibers. The unbleached NFC produced by 10 cycles have a greater transverse modulus of elasticity, the crystallite size showed increase with the nanofibrillation, and after 5 nanofibrillation cycles, no differences are observed in the morphology of the fibers.     

Determination of prazosin in pharmaceutical samples by flow injection analysis with multiple-pulse amperometric detection using boron-doped diamond electrode

This work describes the development of a simple, fast and low-cost method for determining prazosin (PRA) in pharmaceutical samples by flow injection analysis with multiple-pulse amperometric (FIA-MPA) detection using a boron-doped diamond film electrode. Electrochemical detection of PRA was optimized in phosphate buffer pH 4.0 by cyclic voltammetry, in which PRA presented two oxidation processes around at 0.97 and 1.40 V versus Ag/AgCl (3.0 mol L^?1 KCl). In these conditions, PRA also showed one reduction process at ?0.75 V that is dependent on the oxidation processes. Thus, the determination of PRA by FIA-MPA detection consisted on the application of a two-potential waveform, E ₁ (generator potential)?=?1.6 V/400 ms and E ₂ (collector potential)?=??1.0 V/30 ms, with sample loop of 150 μL and flow rate of 3.0 mL min^?1. The method showed good repeatability (RSD?<?3.0 %) and high analytical frequency (70 injections per h). The working linear range was obtained from 2 to 200 μmol L^?1 with a limit of detection of 0.5 μmol L^?1. The recovery tests in all samples were approximately 100 %, and the results were compared with chromatographic methods.