Effects of ultrasonic irradiation in flow-injection systems

The effects of ultrasonic irradiation on transport and reactions in several flow-injection manifolds are described. The influences of ultrasound on the physical dispersion of the injected plug is considered. Its effects on systems involving homogeneous (catalytic and non-catalytic) and heterogeneous (liquid/liquid extraction, precipitation) reactions are critically evaluated. In general, greater sensitivity is obtained, especially for heterogeneous systems, slow reactions and low analyte concentrations. Finally, practical considerations and potential uses of the combination of ultrasonic irradiation with flow-injection analysis are discussed.     

Thermochemistry of Surfactant-Templating of USY Zeolite

With the aim of understanding the thermochemistry of the introduction of mesoporosity in zeolites by using surfactants, high temperature oxide melt solution calorimetry was used to determine the change in the enthalpy of formation of USY zeolite before and after the introduction of mesoporosity. Our results confirm that this process only slightly destabilizes the zeolite by the additional surface area. However, this can be overcome by the stabilizing effect of the interactions between the surfactant and the zeolite framework.     

Interprétation de la susceptibilité magnétique de l'oxysulfure de samarium par un modèle de champ cristallin

The paramagnetic susceptibility of polycrystalline samarium oxysulfide has been measured between 3° and 300°K. The data are interpreted with an approximation to the crystal potential of the form

V_c = _JV₂⁰O₂⁰ + β_JV₄⁰O₄⁰ + β_JV₄³O₄³

and correction taking into account exchange is made. The energy levels and crystal fields parameters have been calculated. Fluorescence studies of Gd₂O₂S: Sm³⁺ and Y₂O₂S: Sm³⁺ have confirmed these results.     

Are inconsistent decisions better? An experiment with pairwise comparisons

This paper tries to contribute to the well-known and lengthy discussion on whether we should allow decision makers to be inconsistent, or, to put it in another way, if intransitive decisions better represent their preferences. We will focus specifically on the multiple-criteria decision making problem, since it is one of the most usual stances where this intransitivity appears. Results from an experiment carried out with graduate students shows that, when intransitivities are removed, the preferences of decision makers are not better represented, and therefore that the effort to do so may not be justified.     

A simple differential titrator for automatic potentiometric titration at zero current, with two identical indicator electrodes

A simple differential titrator for automatic potentiometric titration at zero current, with two identical indicator electrodes, is described. The autoburette is a normal microburette connected to one tube of a peristaltic pump, and the differentiating system is a closed-flow circuit in a second tube of the pump, this tube containing two electrodes 5 cm apart. The apparatus has been applied to the determination of halides and sulphide-disulphide mixtures, with electrodes coated with an appropriate silver salt.     

Molecular dynamics effects on luminescence properties of oligothiophene derivatives: a molecular mechanics-response theory study based on the CHARMM force field and density functional theory

CHARMM force field parameter values for a class of oligothiophene derivatives have been derived with reference to density functional theory/B3LYP potential energy surfaces. The force field parametrization of these luminescent conjugated polyelectrolytes includes the electronic ground state as well as the strongly light absorbing first excited state. In conjunction with quantum chemical response theory calculations of transition state properties, a molecular dynamical model of the Stokes shift is obtained. The theoretical model is benchmarked against experimental data recorded at room temperature which refer to sodium salts of p-HTAA and p-FTAA with distilled water as a solvent. For p-HTAA the theoretically predicted Stokes shift of 112 nm is in good agreement with the experimental result of 124 nm, given the approximations about exciton localization that were introduced to obtain a force field for the excited state.     

Trifluoromethanesulfonic Acid Catalyzed Alkylation of Arenes with Methyl (2R)‐Glycidate

Methyl (R)‐glycidate (=methyl (R)‐oxiranecarboxylate; 2 ) in superacidic trifluoromethanesulfonic acid medium reacts with electron‐rich arenes to give α‐hydroxy‐β‐arylpropanoate derivatives 3a – 3f with high stereospecificity. At the same time, the observed high regioselectivity has been attributed to superelectrophilic activation of the glycidate.     

Anti-Helicobacter pylori Activity of Artemisia ludoviciana subsp. mexicana and Two of Its Bioactive Components,Estafiatin and Eupatilin

Artemisia ludoviciana subsp. mexicana has been traditionally used for the treatment of digestive ailments such as gastritis, whose main etiological agent is Helicobacter pylori. In a previous screening study, the aqueous extract exhibited a good in vitro anti-H. pylori activity. With the aim of determining the efficacy of this species as a treatment for H. pylori related diseases and finding bioactive compounds, its aqueous extract was subjected to solvent partitioning and the fractions obtained were tested for their in vitro anti-H. pylori effect, as well as for their in vivo gastroprotective and anti-inflammatory activities. The aqueous extract showed a MIC = 250 µg/mL. No acute toxicity was induced in mice. A gastroprotection of 69.8 ± 3.8%, as well as anti-inflammatory effects of 47.6 ± 12.4% and 38.8 ± 10.2% (by oral and topical administration, respectively), were attained. Estafiatin and eupatilin were isolated and exhibited anti-H. pylori activity with MBCs of 15.6 and 31.2 µg/mL, respectively. The finding that A. ludoviciana aqueous extract has significant anti-H. pylori, gastroprotective and anti-inflammatory activities is a relevant contribution to the ethnopharmacological knowledge of this species. This work is the first report about the in vivo gastroprotective activity of A. ludoviciana and the anti-H. pylori activity of eupatilin and estafiatin.     

Study of the mixed-metal lanthanummagnesium-purpurin complex: spectrophotometric determination of yttrium and lanthanides

Mixtures of La(III) and Mg(II) form with purpurin (P; 1,2,4-trihydroxyanthraquinone) the mixed-metal complex LaMg₂P₅, which is extracted with methyl isobutyl ketone at pH 7.5. The molar absorptivity of the complex is 6.1 × 10⁴ l.mole⁻¹.cm⁻¹ at 570 nm and its conditional extraction constant 5 × 10¹³ l⁴.mole⁻⁴. Similar complexes have been found to be formed with yttrium, cerium, praseodymium, neodymium and samarium. The use of these complexes for the spectrophotometric determination of yttrium and lanthanides up to 15 μg has been investigated.     

Simultaneous-fluorimetric methods for the determination of ammonia and urea by use of flow injection configurations with dual injection valves

Summary Two fluorimetric methods are proposed for the simultaneous determination of ammonia and urea based on the reaction of the former with o-phthalaldehyde/2-mercaptoethanol and on the use of a dual injection system in which the valves are coupled in series or in parallel. An enzymatic reactor converts urea into ammonia which is determined by the same reaction. These configurations provide very similar results with a linear determination range between 0.5 and 10.0 g ml^–1 and a sampling frequency of 60 h^–1. The proposed methods are very tolerant to foreign species commonly found in water, as shown by applying them to samples of different origins.