Effect of preparation of sol-gel coatings on the strength of optical fibres

SiO₂, TiO₂, ZrO₂, and TiO₂-ZrO₂ thin coatings were applied by sol-gel method on quartz fibres during the fibre drawing. Durable layers with the thicknesses up to 0.7 m were obtained. The layer smoothness and thickness were determined using electron microprobe analyzer and electron or optical microscopy. In order to investigate a decrease in the strength of sol-gel coated fibres a novel method employing silica capillaries was developed. The fibre strength decrease was explained by the influence of water penetrating as a result of the coating process into the flaws on the fibre surface.     

The fluorous effect in biomolecular applications

From being a niche area only a few decades ago, fluorous chemistry has gained momentum and is, nowadays, a fervent area of research. It has brought forth, in fact, numerous applicative innovations that stretch among different fields: from catalysis to separation science, from supramolecular to materials and analytical chemistry. Recently, the unique features of perfluorinated compounds have reached the attention of the biochemists' audience. This tutorial review introduces the basic concepts of fluorous chemistry and illustrates its main biomolecular applications. Special attention has been given to fluorous microarrays and their combination with Mass-Spectroscopy (MS) techniques, to protein properties modification by the introduction of local fluorous domains, and to the most recent applications of (19)F-Magnetic Resonance Imaging ((19)F-MRI).     

On the Physical Parameters and Relaxation Processes in Nematic Azobenzene Polymers for Optical Nanowriting

The possibility of achieving devices for rewritable optical storage is provided by liquid-crystalline polymers with azobenzene side groups, because they undergo photochemically induced trans-cis reversible isomerization. In this work we overview our investigations into a nematic azobenzene-polymethacrylate (PMA4) as a suitable material for optical nanowriting. Relaxation processes over different time-length scales are discussed with particular reference to understanding the interplay between homogeneity at the molecular level, bit stability and working temperature range.     

Comparison of two different isolation methods of benzimidazoles and their metabolites in the bovine liver by solid-phase extraction and liquid chromatography–diode array detection

A new analytical method that uses high performance liquid chromatography–diode array detector (HPLC–DAD) was developed for the analysis of 14 benzimidazoles residues, including metabolites, in bovine liver. Samples were extracted using two different extraction procedures: with phosphate buffer after enzymatic hydrolysis (method A) or using organic solvent, i.e. acetonitrile (method B). Then, samples were purified on a strong cation exchange (SCX) cartridge and analyzed in HPLC/DAD. The recovery percentages, obtained spiking the matrix (liver) at concentrations of 500 and 100 μg kg^?1 with a standard mixture of benzimidazoles, were in the range 6–101% and 80–102% for methods A and B, respectively. The repeatability of the methods was assessed in all cases by the % of correlation value (CV) that was lower than 19%. The limits of quantification (LOQs) in the matrix for methods A and B were in the range 40–60 and 20–50 μg kg^?1, respectively. The best of the two methods, method B, was used for the analysis of 10 bovine liver samples.     

Sequential one-pot InBr(3)-catalyzed 1,4- then 1,2-nucleophilic addition to enones

Low sensitivity toward traces of moisture and high tolerance of different functional groups make indium tribromide suitable for carrying out multistep synthetic sequences. In particular, we have realized a 1,4-conjugated addition of indoles/thiols to alpha,beta-unsaturated ketones mediated by a catalytic amount (10 mol %) of InBr(3) obtaining the desired beta-substituted ketones in good yields. The Lewis acidity of indium salts was not affected by coordinating and acid nucleophiles; therefore, the subsequent catalytic 1,2-addition of Me(3)SiCN to carbonyl compounds can be performed in one pot. With the optimized atom-efficient protocol, several polyfunctionalized alpha-silyloxy cyanohydrins were synthesized in good to excellent yields (up to 97%) and a notable level of simple 1,3-diastereoselection (up to 84:16) was recorded in the case of 2-cyclohexen-1-one 2c.     

Quenching of tryptophan (1)(pi,pi*) fluorescence induced by intramolecular hydrogen abstraction via an aborted decarboxylation mechanism

CASSCF computations show that the hydrogen-transfer-induced fluorescence quenching of the (1)(pi,pi*) excited state of zwitterionic tryptophan occurs in three steps: (1) formation of an intramolecular excited-state complex, (2) hydrogen transfer from the amino acid side chain to the indole chromophore, and (3) radiationless decay through a conical intersection, where the reaction path bifurcates to a photodecarboxylation and a phototautomerization route. We present a general model for fluorescence quenching by hydrogen donors, where the radiationless decay occurs at a conical intersection (real state crossing). At the intersection, the reaction responsible for the quenching is aborted, because the reaction path bifurcates and can proceed forward to the products or backward to the reactants. The position of the intersection along the quenching coordinate depends on the nature of the states and, in turn, affects the formation of photoproducts during the quenching. For a (1)(n,pi*) model system reported earlier (Sinicropi, A.; Pogni, R.; Basosi, R.; Robb, M. A.; Gramlich, G.; Nau, W. M.; Olivucci, M. Angew. Chem., Int. Ed. 2001, 40, 4185-4189), the ground and the excited state of the chromophore are hydrogen acceptors, and the excited-state hydrogen transfer is nonadiabatic and leads directly to the intersection point. There, the hydrogen transfer is aborted, and the reaction can return to the reactant pair or proceed further to the hydrogen-transfer products. In the tryptophan case, the ground state is not a hydrogen acceptor, and the excited-state hydrogen transfer is an adiabatic, sequential proton and electron transfer. The decay to the ground state occurs along a second reaction coordinate associated with decarboxylation of the amino acid side chain and the corresponding aborted conical intersection. The results show that, for (1)(pi,pi*) states, the hydrogen transfer alone is not sufficient to induce the quenching, and explain why fluorescence quenching induced by hydrogen donors is less general for (1)(pi,pi*) than for (1)(n,pi*) states.     

Detection of relative dimer and rotamer concentrations of diacetamide in different solvents by FT-IR spectroscopy and DFT calculations

The relative rotamer, dimer and tautomer concentrations of diacetamide have been studied by means of infrared spectroscopy, with the recorded spectra being analyzed employing results from density functional theory calculations. It is observed that the cis–trans monomeric form of diacetamide (1) is found to be the most stable isomer in all studied solvents, with trans–trans diacetamide (2) being found to be 20% of total diacetamide in methanol. While the dimer form of diacetamide (3) is present only in carbontetrachloride (about 34% of the total), its tautomeric forms (4, 5) are not favorable in any of the studied solvents.