New Route to N‐Alkylated trans‐Pyrrolidine Diols from 2,2,3,3‐Tetramethoxybutane‐Protected Dimethyl Tartrate

A short synthesis of some trans‐pyrrolidine diols is described starting from (2R,3R,5R,6R)‐5,6‐dimethoxy‐5,6‐dimethyl[1,4]dioxane‐2,3‐dicarboxylic acid dimethyl ester 3. The key step was the occurrence of a tandem azide reduction/cyclization sequence on mono‐azide intermediate 6 upon catalytic hydrogenation. This method afforded both (3R,4R)‐(+)‐1‐benzyl‐3,4‐pyrrolidinediol 9a and (3R,4R)‐(+)‐1‐allyl‐3,4‐pyrrolidinediol 9b starting from 3. Cytotoxicity tests were performed on compounds 9a and 9b using the brine shrimp bioassay, but each showed no activity, as were anti‐oxidant tests using the stable free radical diphenylpicrylhydrazyl (DPPH).     

Titanium(IV) complexes as direct TiO2 photosensitizers

Titanium dioxide photosensitization may be achieved in various ways, involving surface modification with appropriate species. The photosensitization process requires a visible light-induced electron or hole injection into conduction or valence band, respectively. Efficiency of this process depends on electronic interaction between the photosensitizer moiety (surface complex) and TiO₂ particle. At least two types of the charge injection mechanisms may be distinguished—in the first, charge is transferred from the excited state of the sensitizer molecule to the conduction or valence band while the second mechanism involves a direct molecule-to-band charge transfer (MBCT). The MBCT process can be realized by surface titanium(IV) complexes with various organic and sometimes inorganic ligands. Catechol, phthalic acid or salicylic acid derivatives, as well as cyanometallate anions, upon chemisorption at TiO₂ surface constitute an especially interesting group of ligands to yield various titanium(IV) surface complexes. Geometry of these complexes, electronic structures and possibility of their use as photosensitizers of TiO₂ are discussed on the basis of experimental data and quantum-chemical modeling. Also prospective applications of photoinduced electron transfer and photocatalytic activity of such systems are presented.     

Influence of silver nano‐additive amount on the supramolecular structure,porosity, and properties of polyacrylonitrile precursor fibers

This work examines the influence of the amount of silver nanoparticles added to polyacrylonitrile spinning solutions on their rheological properties as well as the structure and properties of the fibers produced. The influence of the amount of silver nanoparticles on the supramolecular structure of nanocomposite polyacrylonitrile precursor fibers, their porosity, as well as thermal and tensile strength properties was determined. The distribution of the nano‐ additive in fiber cross‐sections and on the surface was estimated. It was found that the addition of silver nanoparticles to polyacrylonitrile precursor fibers in an amount of up to 1.5% does not cause a decrease in the susceptibility of the fiber matter to deformation at the drawing stage. The produced fibers were characterized by an increased total volume of pores of 0.35 cm³/g and tenacity of more than 34 cN/tex. Copyright © 2009 John Wiley & Sons, Ltd.     

NaNbO3 crystals dispersed in a B2O3 glass matrix – Structural characteristics versus electrical and dielectrical properties

Sodium niobate (NaNbO₃) is a crystal with a perovskite structure that exhibits, at room temperature, an antiferroelectric behaviour. It is a very interesting material due to the several phase transitions that it presents as a function of the temperature (ferroelectric–antiferroelectric–paraelectric). Thus, the preparation of glass-ceramics containing NaNbO₃ crystals is scientifically and technologically important. Besides, there is actually few works available about the preparation of NaNbO₃ crystals embedded in a glass matrix. The present work reports the preparation process and the study of glass and glass-ceramics in the B₂O₃–NaNbO₃ system.The glass with the molar composition 60B₂O₃–30Na₂O–10Nb₂O₅ (mol%) was prepared by the melt-quenching method. Sodium niobate (NaNbO₃) crystallites were precipitated through a controlled heat-treatment (HT) process. NaNbO₃ crystallites were detected by X-ray diffraction (XRD) in the samples treated above 500 °C. The treatments above 600 °C favour also the formation of Na₂B₄O₇ and Nb₂O₅ crystalline phases.Scanning electron microscopy (SEM) reveals that the crystallization occurs in volume and that the number of particles increases with the rise in HT temperature.The number of network modifier ions (Na⁺ and Nb⁵⁺) in the glass network is the main factor in the dc and ac conductivity behaviours. The dielectric constant (?′) value increases with the increase of the volume ratio between the particles and the glass matrix. The sample heat-treated at 550 °C shows two thermally stimulated depolarization current (TSDC) peaks. The high temperature peak can be related to the presence of NaNbO₃ particles.     

Star-Shaped Poly((9-carbazolyl)methylthiirane): A New Polymer for Optoelectronic Applications

Summary: The polymerization of (9-carbazolyl)methylthiirane in the presence of cyclic oligo(potassium glycidoxide) as the macroinitiator activated 18-crown-6 leads to polythioether with the molecular masses relatively near to the calculated ones. This polythioether dispersed in a commercially available transparent polymer gives a new blue photoluminescent material.     

Separation and preconcentration procedures for the determination of lead using spectrometric techniques: a review

Lead is recognized worldwide as a poisonous metal. Thus, the determination of this element is often required in environmental, biological, food and geological samples. However, these analyses are difficult because such samples contain relatively low concentrations of lead, which fall below the detection limit of conventional analytical techniques such as flame atomic absorption spectrometry and inductively coupled plasma optical emission spectrometry. Several preconcentration procedures to determine lead have therefore been devised, involving separation techniques such as liquid-liquid extraction, solid phase extraction, coprecipitation and cloud point extraction. Citing 160 references, this paper offers a critical review of preconcentration procedures for determining lead using spectroanalytical techniques.     

Benzoporphyrins via an olefin ring-closure metathesis methodology

A new route to benzoporphyrins is reported in which readily available vicinal dibromoporphyrins are bis-allylated using the Suzuki reaction, cyclized by way of olefin metathesis and finally oxidized to give mono-, di-, or tri-benzoporphyrins.     

Synthesis and electrochemistry of undeca-substituted metallo-benzoylbiliverdins

The high-yield preparation of metallo-benzoylbiliverdins 9, 10, and 11 from either oxidation of dodeca-substituted porphyrin 6 in the presence of NaNO2/TFA and air followed by metalation or by reaction of the Ni(II) or Cu(II) complexes of 6 with m-chloroperoxybenzoic acid in pyridine under air is reported. The X-ray structures of complexes 9 and 10 and the electrochemistry and spectroelectrochemistry of metallo-benzoylbiliverdins 9-11 are presented and discussed.     

Dearomatization-bis-alkylation of aromatic and heteroaromatic diesters promoted by Me3SnLi via a stanna-Brook rearrangement

[STRUCTURE: SEE TEXT] Reaction of Me3SnLi with aromatic and heteroaromatic diesters proceeds through a fast stanna-Brook rearrangement that generates an stable bis-enolate which can be regioselectively alkylated and cyclized, in one step, to bicyclic compounds containing 6,5-, 6,6-, and 6,7-fused ring systems.