Optical and holographic properties of Fe+Mn co-doped Bi4Ge3O12 crystals

The effect of iron and manganese co-doping on the light-induced, dark- and photoconductivity and holographic properties of Bi₄Ge₃O₁₂ crystals in comparison with Fe- and Mn-single doping is studied. Fe+Mn co-doped crystals exhibited strong photochromic effect at room temperature, the photochromic effect being fully reversible by thermal annealing. The observed light-induced absorption changes and non-linear dependence of photoconductivity on light intensities indicate deep and shallow photoactive levels contribution to the charge transport mechanism of Fe+Mn co-doped BGO. Holographic gratings are successfully recorded at different wavelengths and a possibility to extend the photorefractive sensitivity into the red spectral range is demonstrated. It is found furthermore that Fe+Mn-doping combination leads to faster response time during holographic recording, especially after a preliminary exposure with ultraviolet light, in comparison with Fe- and Mn-single doping.     

Separation and Determination of Phenolic Antioxidants by HPLC with Surfactant/n‐Propanol Mobile Phases

The influence of cationic and anionic surfactants and short‐chain alcohols in the mobile phase on the retention of five antioxidants has been studied. The solutes chosen were butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), and propyl, octyl, and dodecyl gallates (PG, OG, DG).The surfactants were hexadecyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS), and n‐propanol (PrOH) was the selected alcohol. A simple isocratic reversed‐phase method for the antioxidant determination is proposed. Separation of five primary antioxidants takes 18 min with the mobile phase SDS 0.10 M/H₃PO₄ 0.01 M/PrOH 30%. Variation of the percentage of alcohol in the mobile phase permits optimization of the retention times of the antioxidants. Detection limits in the pg range were obtained for the all solutes. The method was used to determine the antioxidants in olive oil at three different levels, giving mean recoveries close to 100% for all the solutes (BHA 102%, PG 99%, OG 99%, DG 99%) except BHT (84%).     

Spaghetti Enriched with Inulin: Effect of Polymerization Degree on Quality Traits and α-Amylase Inhibition

Inulin is considered a dietary fiber and represents a noteworthy ingredient for food biofortification due to its health effects and its neutral taste. The aim of the work was the evaluation of the quality of pasta produced using whole-meal flours of two ancient Sicilian landraces (Senatore Cappelli-CAP and Timilia—TIM) fortified with two types of inulin (long-chain topinambur inulin IT and low-chain chicory inulin IC), at two different levels of substitution (2 and 4%) to evaluate its possible effect on α-amylase inhibition. The color indices L* and a* were mainly influenced by cultivars, while IT improved the sensory attributes, mainly the elasticity sensation, and influenced less the other sensory attributes: adhesiveness, color, odor, taste, and Over Quality Score for both landraces. The cooking quality was linked mainly to the landrace used, due to the very different gluten matrix of CAP and TIM. IC and IT showed promising α-Amy inhibitory activity with comparable IC₅₀ values of 0.45 ± 0.04 and 0.50 ± 0.06 mg/mL. The enrichment of spaghetti with inulin with an inhibitory effect on α-amylase determined the hypoglycemic properties of pasta, thus lowering the corresponding IC₅₀ value.     

A simple method for the determination of malachite green and leucomalachite green residues in fish by a modified QuEChERS extraction and LC/MS/MS

A simple method using LC/MS/MS was developed and validated to determine residues of malachite green (MG) and leucomalachite green (LMG) in fish fillet. A modified QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) technique was used to perform the sample preparation. The optimal extraction and cleanup conditions were established using an experimental design. The validation parameters obtained to determine both MG and LMG complied with the requirements established by regulatory agencies for the presence of such substances in fish, which establish that the method must attain, at least, a minimum required performance limit of 2 ng/g. The accuracy values ranged between 95 and 107%, and the precision values were lower than 11.2%. The method was used in the analysis of tilapia samples (n = 20) commercialized in Campinas, SP, Brazil. None of the samples presented detectable levels of MG or LMG residues.     

Surface properties of catalytic aluminas modified by alkaline-earth metal cations: A microcalorimetric and IR-spectroscopic study

Lewis acidic properties of transition aluminas whose surfaces have been doped with alkaline-earth metal cations (Ca²⁺ and Ba²⁺) were studied by means of the room temperature adsorption of carbon monoxide. The vibrational features of CO adsorbed at the surface of doped aluminas were investigated by IR spectroscopy in comparison with pure parent aluminas, while the quantitative and energetic features were studied by adsorption microcalorimetry. Various CO adspecies were found to form at the surface of both pure and doped-alumina, owing to the structural heterogeneity of the Al₂O₃ surface and to the presence of alkaline-earth metal cations. The surface heterogeneity was revealed by different v_co stretching frequencies, namely v_co≈2230, 2218 and 2205 cm⁻¹ for coordinatively unsaturated tetrahedral Al³⁺ cations in different crystallographic configurations, and v_co≈2186 and 2172 cm⁻¹ for coordinatively unsaturated Ca²⁺ and Ba²⁺ cations, respectively. Heats of adsorption of ≈80, 70 and 55 kJ/mol were assigned to the formation of Al³⁺/CO complexes, ≈45 kJ/mol for Ca²⁺/CO and ≈30 kJ/mol for Ba²⁺/CO complexes. The latter value was estimated through a correlation curve existing between v_co stretching frequencies and adsorption enthalpies. This correlation, already proposed in the past for CO adsorbed on non-d/d⁰/d¹⁰ metal cations, has been revisited and confirmed here, by including Al₂O₃ data for which an apparent lack of correlation between the two parameters was first observed. With respect to pure alumina, the population of Lewis acidic sites was found to be significantly depressed by the presence of alkaline-earth cus metal cations. These acidic sites are intrinsically weaker than tetrahedral cus Al³⁺ cations, as witnessed by smaller upward shifts of the v_co stretching frequencies with respect to CO gas and lower heats of adsorption, in accordance with expectations from the charge/ionic radius ratios. Ca²⁺ cations were found to compete in adsorbing CO with Al³⁺ cations more efficiently than the larger Ba²⁺ cations. In the case of CaO/Al₂O₃ systems outgassed at 1023 K, a thin surface layer of calcium aluminate, not detected by XRD or HRTEM, was suggested to form.     

{2‐[(3‐Amino­propyl)­amino­propyl­imino­methyl]­imidazol­ato‐N,N′,N′′,N′′′}­(methanol‐O)­copper(II) per­chlorate

In the title compound, [Cu(C₁₀H₁₈N₅)(CH₄O)]ClO₄, four N atoms from the deprotonated ligand derived from bis(3‐amino­propyl)­amine and 2‐imidazole­carbox­aldehyde are coordinated to the Cu atom. The four N atoms occupy equatorial positions with Cu—N bond distances ranging from 1.998 (2) to 2.046 (3) Å. The methanol O atom occupies one axial position with a Cu—O bond distance of 2.295 (2) Å.     

Light-emitting devices based on solid electrolytes and polyelectrolytes

The properties of light-emitting diodes (LEDs) based on organic layers containing mobile ions, so-called light-emitting electrochemical cells (LECs), are reviewed. These devices have some unique properties: their current–voltage characteristics are antisymmetric with respect to the origin and they emit light under both forward and reverse bias. The physical processes involved in the emission from LECs are discussed in terms of a thermodynamic model. Recent work on blends of luminescent and ion-conducting polymers is summarized. In addition, the properties of novel single-component LECs and polyelectrolyte-based devices are presented. The results show that LECs with performances superior to that of conventional LED devices can be fabricated, but questions concerning the transient behavior and degradation mechanisms persist. © 1998 John Wiley & Sons, Ltd.     

The First Delocalized Phosphole Containing a Planar Tricoordinate Phosphorus Atom: 1-[Bis(trimethylsilyl)methyl]-3,5-bis(trimethylsilyl)-1,2,4-triphosphole

The sterically demanding groups on the tricoordinate phosphorus atom, the π-electron acceptors substituted on the ring, and the dicoordinate phosphorus atoms within the ring are the most significant factors contributing to the planarity and aromaticity of the 1,2,4-triphosphole ring in 1 . The Bird aromaticity index for 1 shows that it has the most pronounced aromatic character of all known phospholes.     

Eulerian equilibria of a triaxial gyrostat in the three body problem: rotational Poisson dynamics in Eulerian equilibria

We consider the noncanonical Hamiltonian dynamics of a triaxial gyrostat in the three body problem. By means of geometric-mechanics methods, we will study the approximated dynamics that arises when we develop the potential in series of Legendre and truncate the series to the second harmonics. Working in the reduced problem, we will study the existence of equilibria that we will denominate of Euler in analogy with classic results on the topic. In this way, we generalize the classical results on equilibria of the three-body problem and many of those obtained by other authors using more classic techniques for the case of rigid bodies. The instability of Eulerian equilibria is proven in this approximate dynamics if the gyrostat is close to the sphere. The rotational Poisson dynamics of the gyrostat placed at an Eulerian equilibrium and the study of the nonlinear stability of some equilibria is considered. The analysis is done in vectorial form avoiding the use of canonical variables and the tedious expressions associated with them.