Speciation of the Vanadium(III) Complexes with 1,10-Phenanthroline, 2,2′-Bipyridine,and 8-Hydroxyquinoline

The complex species formed between vanadium(III) and 1,10-phenanthroline (phen), 2,2′-bipyridine (bipy), and 8-hydroxyquinoline (8hq) were studied in aqueous solution by means of electromotive forces measurements, emf(H), at 25 °C with 3.0 mol⋅dm⁻³ KCl as the ionic medium. The potentiometric data were analyzed using the least-squares computational program LETAGROP, taking into account the hydrolytic vanadium(III) species formed in solution. Analysis of the vanadium(III)–phen system data shows the formation of [VHL]⁴⁺, [V(OH)L]²⁺, [V₂OL₂]⁴⁺ and [V₂OL₄]⁴⁺ complexes. In the vanadium(III)–bipy system the [VHL]⁴⁺, [V(OH)L]²⁺, [V₂OL₂]⁴⁺ and [V₂OL₄]⁴⁺ complexes were observed, and in the vanadium(III)–8hq system the complexes [V(OH)L]⁺, [V(OH)₂L], [VL₂]⁺ and [VL₃] were detected.     

Microwave-assisted extraction and large-volume injection gas chromatography tandem mass spectrometry determination of multiresidue pesticides in edible seaweed

A microwave-assisted extraction method followed by clean-up with solid-phase extraction (SPE) combined with large-volume injection gas chromatography–tandem mass spectrometry (LVI-GC-MS/MS) for the analysis of 17 pesticides in wild and aquaculture edible seaweeds has been developed. An experimental central composite design was employed to evaluate the effects of the main variables potentially affecting the extraction (temperature, time, and solvent volume) and to optimize the process. The most effective microwave extraction conditions were achieved at 125 °C and 12 min with 24 mL of hexane/ethyl acetate (80:20). SPE clean-up of the extracts with graphitized carbon and Florisil, optimized by means of the experimental design, proved to be efficient in the removal of matrix interferences. The analytical recoveries were close to 100% for all the analytes, with relative standard deviations lower than 13%. The limits of detection ranged from 0.3 to 23.1 pg g⁻¹ and the limits of quantification were between 2.3 and 76.9 pg g⁻¹, far below the maximum residue levels established by the European Union for pesticides in seaweed. The results obtained prove the suitability of the microwave-assisted extraction for the routine analysis of pesticides in aquaculture and wild seaweed samples.     

How accurate is the cancelation of the first even zonal harmonic of the geopotential in the present and future LAGEOS-based Lense-Thirring tests?

The strategy followed so far in the performed or proposed tests of the general relativistic Lense-Thirring effect in the gravitational field of the Earth with laser-ranged satellites of LAGEOS type relies upon the cancelation of the disturbing huge precessions induced by the first even zonal harmonic coefficient J ₂ of the multipolar expansion of the Newtonian part of the terrestrial gravitational potential by means of suitably designed linear combinations of the nodes Ω of more than one spacecraft. Actually, such a removal does depend on the accuracy with which the coefficients of the combinations adopted can be realistically known. Uncertainties of the order of 2 cm in the semimajor axes a and 0.5 milliarcseconds in the inclinations I of LAGEOS and LAGEOS II, entering the expression of the coefficient c ₁ of the combination of their nodes used so far, yield an uncertainty δc ₁ = 1.30 × 10⁻⁸. It gives an imperfectly canceled J ₂ signal of 10.8 milliarcseconds per year corresponding to 23% of the Lense-Thirring signature. Uncertainties of the order of 10–30 microarcseconds in the inclinations yield δc ₁ = 7.9 × 10⁻⁹ which corresponds to an uncanceled J ₂ signature of 6.5 milliarcseconds per year, i.e. 14% of the Lense-Thirring signal. Concerning a future LAGEOS-LAGEOS II-LARES combination with coefficients k ₁ and k ₂, the same uncertainties in a and the less accurate uncertainties in I as before yield δk ₁ = 1.1 × 10⁻⁸, δk ₂ = 2 × 10⁻⁹; they imply a residual J ₂ combined precession of 14.7 milliarcseconds per year corresponding to 29% of the Lense-Thirring trend. Uncertainties in the inclinations at ≈ 10 microarcseconds level give δk ₁ = 5 × 10⁻⁹, δk ₂ = 2 × 10⁻⁹; the uncanceled J ₂ effect is 7.9 milliarcseconds per year, i.e. 16% of the relativistic effect.     

Robust vanishing of all Lyapunov exponents for iterated function systems

Given any compact connected manifold $M$ , we describe $C^2$ -open sets of iterated functions systems (IFS’s) admitting fully-supported ergodic measures whose Lyapunov exponents along $M$ are all zero. Moreover, these measures are approximated by measures supported on periodic orbits. We also describe $C^1$ -open sets of IFS’s admitting ergodic measures of positive entropy whose Lyapunov exponents along $M$ are all zero. The proofs involve the construction of non-hyperbolic measures for the induced IFS’s on the flag manifold.     

Phase diagram of Si-doped spin-Peierls compound CuGeO3

We have performed magnetic susceptibility measurements on CuGe_1−xSi_xO₃ single crystals and obtained a detailed (T,x) phase diagram. In order to fully characterize the nature of the SP and AF phases in this diagram, we studied both order parameters by neutron diffraction as a function of temperature and Si concentration.     

Surface study of the building steps of enzymatic sol–gel biosensors at the micro- and nano-scales

We have studied, by scanning electron and atomic force (AFM) microscopies, how each step involved in the building process of massive carbon-based sol–gel enzymatic biosensors changes and determines the resulting surface morphology and nano-mechanical properties. The biosensor, selected as a model, is developed by the entrapment of glucose oxidase (GOx), a redox mediator and a material conferring conductivity (graphite powder, C) into a polymeric tridimensional network generated by sol–gel technology using tetraethoxysilane (TEOS) as precursor. The smooth TEOS morphology is formed by an irregular nanoporous network, which is very adequate for enzyme encapsulation. Upon addition of carbon powder to the system (TEOS/C), the surface morphology changes but it is still rather irregular since carbon powder micro-grains are found scattered on it. This morphology results in a rather rough surface at the micro- scale whereas at the nano- scale both atomically flat graphitic and nanoporous TEOS domains are found. In contrast, the final biosensing device surface is quite homogeneous and composed by flat platelets separated by deep crevices. On top of most of these platelets there is a soft, as assessed by AFM force indentation experiments, layer of globular structures whose dimensions are compatible with GOx molecules. The final device surface architecture results to be open and accessible both at the micro and nano scales, which turns it as adequate to enhance both the accessibility of the analytes to entrapped proteins and the mass-transfer rates. Finally, in order to show the applicability of the studied biosensor, its response was evaluated towards varying glucose concentrations, displaying a clear electrocatalytic activity.     

Iodosobenzene Diacetate and Diphenyl Diselenide: An Electrophilic Selenenylating Agent of Double Bonds

Phenylseleno-acetoxylation, hydroxylation, etherification and lactonization products are obtained in good yields from the reaction of alkenes with diphenyl diselenide and iodosobenzene diacetate, in acetonitrile.

     

Experimental design for optimization of microwave-assisted extraction of benzodiazepines in human plasma

A simple and fast microwave-assisted-extraction (MAE) method has been evaluated as an alternative to solid-phase extraction (SPE) for the determination of six benzodiazepines widely prescribed in European countries (alprazolam, bromazepam, diazepam, lorazepam, lormetazepam and tetrazepam) in human plasma. For MAE optimization a Doehlert experimental design was used with extraction time, temperature and solvent volume as influential parameters. A desirability function was employed in addition to the simultaneous optimization of the MAE conditions. The analysis of variance showed that the solvent volume had a positive influence on the extraction of all the analytes tested, achieving a statistically significant effect. Also, the extraction time had a statistically significant effect on the extraction of four benzodiazepines. The selected MAE conditions—89 °C, 13 min and 8 mL of chloroform/2-propanol (4:1, v/v)—led to recoveries between 89.8 ± 0.3 and 102.1 ± 5.2% for benzodiazepines using a high performance liquid chromatography method coupled with diode-array detection. The comparison of MAE and SPE shows better results for MAE, with a lower number of steps in handling the sample and greater efficiency. The applicability of MAE was successfully tested in 27 plasma samples from benzodiazepine users.