Dichroic properties of bis(benzoxazolyl)stilbene and bis(benzoxazolyl)thiophene dispersed into oriented polyethylene films: a combined experimental and density functional theory approach

In this work, a combination of experimental and quantum mechanical investigations is performed for the study of dichroic absorption properties of melt-processed linear low-density polyethylene (LLDPE) oriented films containing < or =0.5 wt % of either 4,4'-bis(2-benzoxazolyl)stilbene (BBS) or 2,5-bis(5-tert-butyl-2-benzoxazolyl)thiophene (BTBBT). The data acquired reveal that the film optical anisotropy and the performances as linear polarizer are strongly dependent on the molecular structure of the chromophore. In particular, the rodlike structure of BBS favors the alignment of the dye along the drawing direction of the PE film, providing dichroic ratios as high as 100 and optical performances as linear polarizer close to the pseudo-affine deformation scheme. On the contrary BTBBT, although characterized by huge anisotropic potentialities, confers the oriented film very poor dichroism and is unsuitable for linear polarizer applications. This behavior is attributed to the more complex banana-shaped structure of BTBBT dye caused by the thiophene 2,5-functionalization that limits the molecule parallel orientation to the drawing direction.     

The Role ofChirocephalus diaphanusin the Early Recognition of Environmental Pollution by Trace Elements

A study was undertaken to evaluate whether the fairy shrimpChirocephalus diaphanus(Crustacea: Anostraca) could be considered as a species capable of biomonitoring environmental contamination by accumulating trace elements. This preliminary investigation aimed at assessing the levels of As, Cd, Cu, Hg, Pb, Se, and Zn in natural waters as well as in adults and cysts of fairy shrimps sampled from five different sites in central Italy. Trace elements were determined by inductively coupled plasma (ICP)-based spectrometry. In particular, ICP–mass spectrometry (ICP-MS) was resorted to in most cases due to its high detection power. Pretreatment of samples (adults and cysts) consisted basically in the HNO₃-assisted microwave digestion of the material. The highest levels of trace elements were found in the anostracan cysts, with concentration ranges (μg/g) of 0.464–3.11 for As, up to 0.820 for Cd, 2.62–13.0 for Cu, 0.011–0.213 for Hg, 0.966–8.46 for Pb, 0.295–2.45 for Se, and 16.4–50.4 for Zn. On the other hand, the lowest concentrations were found in natural waters, with values close to the ICP-MS detection power for some elements. These data are probative of a bioconcentration process, the extent of which is proportional to the environmental level of each element. This may turn out to be useful in planning biological monitoring and assessing ecotoxicological consequences which might ensue from the diffusion of the exploitation of such organisms in aquaculture.     

Excited states of linear polyenes in the SCF–RPA method

In the framework of the PPP Hamiltonian, we have studied the low-lying spectra of all trans linear polyenes with the dielectirc function method. It is shown that higher order processes, not included in the RPA scheme as local field correction (LFC) and self-energy (SE) effects can be introduced in a effective way by a suitable parametrization of the residual coulomb interaction. This parametrization is fixed along the polyene series both for singlet and triplet states, at variance with previous RPA calculations. Comparison with the most refined CI calculations, as well as with the experimental findings shows very good agreement. Furthermore, chain length and geometry dependence of the electron–electron correlation is briefly discussed.     

Enantioselective determination of the novel antidepressant mirtazapine and its active demethylated metabolite in human plasma by means of capillary electrophoresis

Mirtazapine is a recent noradrenergic and specific serotonergic antidepressant drug. A capillary electrophoretic method has been developed for the enantioseparation and analysis of mirtazapine and its main active metabolite, N-desmethylmirtazapine, in human plasma. For method optimisation several experimental parameters were investigated, such as type and concentration of the chiral selector, buffer pH and capillary temperature. Baseline enantioseparation of the analytes was achieved in 2.5 min in a fused silica capillary (50 microm i.d.; 48.5 cm total length; 8.5 cm effective length) using carboxymethyl-beta-cyclodextrin, dissolved in a background electrolyte consisting of 50 mM phosphate buffer at pH 2.5, as the chiral selector. UV detection was set at 205 nm. A careful pre-treatment of plasma samples was developed, using solid-phase extraction with hydrophilic-lipophilic balance cartridges (60 mg, 3 mL), eluting the sample with methanol, then concentrating it 37.5 times before injection. Extraction yield values are very satisfactory, being the average 89% for mirtazapine and 73% for N-desmethylmirtazapine. Application of the method to some human plasma samples has given satisfactory results.     

Comparison of three analytical methods for quality control of clozapine tablets

Three different analytical methods for the quality control of clozapine in commercial formulations were developed and compared: a liquid chromatographic (LC) method with UV detection, a capillary zone electrophoretic (CZE) method, and a linear scan voltammetric (LSV) method. The isocratic LC procedure used a C18 reversed-phase column; the CZE method used an uncoated fused-silica capillary and phosphate buffer containing polyvinylpyrrolidone as the background electrolyte; the LSV method analyzed clozapine solutions with acidic phosphate buffer as the supporting electrolyte. The 3 methods gave similar and satisfactory results, in terms of precision and accuracy. Repeatability and intermediate precision were good (RSD% < 2.2) and accuracy, resulting from recovery studies, was between 98 and 102%. The rapidity of analysis was high for all 3 methods, especially for the LSV.     

High sensitivity determination of valproic acid in mouse plasma using semi-automated sample preparation and liquid chromatography with tandem mass spectrometric detection

A high-throughput liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) assay using automated sample preparation has been developed for the determination of valproic acid (VPA) in mouse plasma. A liquid-handling system was programmed to prepare calibration standard solutions in plasma, as well as quality controls and clinical samples. Plasma protein precipitation was performed on a 96-well plate, and the collected supernatant was directly injected into a reversed-phase LC/ESI-MS/MS system in the negative ionization mode. The calibration curve for VPA was linear over a dynamic range of 0.15-100 microg/mL. The limit of detection was 75 ng/mL and the lower limit of quantitation was 150 ng/mL. Intra- and inter-day validation assays of the semi-automated plasma analysis showed satisfactory accuracy and precision.     

Dinuclear cyclopalladated azobenzene complexes: a comparative study on model compounds for organometallic liquid‐crystalline materials

The series of dinuclear 4,4′‐bis(hexyloxy)azobenzene, [H(Azo‐6)], cyclopalladated complexes of general formula [Azo‐6)Pd(µ‐X)]₂, (X = Cl, Br, I, N₃, SCN, OAc) and [Azo‐6)₂Pd₂(µ‐Ox)] (Ox = oxalate) have been synthesized and investigated for mesomorphism and spectroscopic properties. Single‐crystal X‐ray analysis of the dinuclear bromo‐ and iodo‐bridged complexes has been performed. The structural data, compared with those of the known homologous chloro compound, show that all the [Azo‐6)Pd(µ‐X)]₂)] (X = Cl, Br, I) molecules crystallize in the monoclinic space group P2₁/c and are isomorphous. They are arranged in slipped pairs with intermolecular non‐bonding Pd–Pd contacts ranging from 3.668(1) Å(X = Cl) to 3.758(3) Å(X = I). The different nature of the bridging group allows variation of the distance between the palladium atoms and the bond environment experienced by the metal centers. Thus, this comparative study reveals that the effectiveness of the bridging group in promoting thermotropic mesophases is greater for chloride, bromide, azide or oxalate than for iodide, thiocyanate or acetate. The greatest range of liquid‐crystal behavior was displayed by [Azo−6)₂Pd₂(µ−Ox)]. Remarkably, this compound is the first example of a metallomesogen containing the bridging oxalate group. The bimetallic complexes exhibit different absorption spectra (i.e. colors) depending, in general terms, on the nature of the bridge connecting the two cyclometalated [H(Azo‐6)] moieties, which can be varied so as to tune the optical properties. Blocking the azo group in the trans position results in several cases in weakly luminescent complexes, with luminescence efficiencies ϕ ≈10⁻⁴ and luminescence lifetimes of the order of nanoseconds. Using the data obtained from the 4,4′‐bis(hexyloxy)azoxybenzene [H(Azoxy‐6)] derivative, [Azoxy‐6)Pd(µ<?tf="ps2b61">‐Cl)]₂, from the mononuclear acetylacetonate (acac) complexes [(Azo‐6)Pd(acac)] and [(Azoxy‐6)Pd(acac)], and from the uncomplexed [H(Azo‐6)] and [H(Azoxy‐6)] ligands, the nature of the excited states relevant to the photophysical behavior are discussed. Copyright © 1999 John Wiley & Sons, Ltd.     

Relation between surface resistance, infrared-, surface enhanced infrared- and surface enhanced Raman-spectroscopy’s of C2H4 and CO on copper

The common basis of the observations made with the four experimental methods is the transient electron transfer from the metal to the lowest unoccupied electronic states of the adsorbed molecules.     

Qualitative properties for solutions of singular elliptic inequalities on complete manifolds

We establish several qualitative properties for solutions of singular quasilinear elliptic differential inequalities on complete Riemannian manifolds, such as the validity of the compact support principle, of the strong maximum principle, existence of solutions to exterior Dirichlet problems, existence of dead core solutions.