六氢茚满催化开环: 氢解和阳离子反应路径(英文)

Perhydroindan(bicyclo[4.3.0]nonane) was converted in a flow-type apparatus under a hydrogen pressure of 5 MPa on six different catalysts,namely on a bifunctional Pd/Na,H-Beta zeolite,on Ir/Na,H-Y and Pt/Na,H-Y zeolites with a low concentration of Br?nsted acid sites,and on three catalysts containing the three noble metals on the non-acidic support silica.On the bifunctional zeolite Pd/Na,H-Beta,skeletal isomerization of perhydroindan was the primary reaction followed by opening of one naphthenic ring,the formation of open-chain nonanes in low yields of ca.6%,and hydrocracked products C8-.The carbon number distribution of the latter was volcano-shaped with no C1,C2,C7,and C8 indicating a carbocationic hydrocracking of C9 precursors with one naphthenic ring.On Ir/Na,H-Y and Pt/Na,H-Y(high-performance ring-opening catalysts),ring opening and hydrocracking to C8-occurred by hydrogenolysis on the respective metal.Opening of the five-membered ring was found to be much faster than opening of the six-membered ring,in agreement with literature reports.The maximal selectivities of open-chain nonanes(OCNs) attained on Ir/Na,H-Y and Pt/Na,H-Y were very high,viz.49% and 54%,respectively,and significantly better than those of the open-chain decanes observed previously with decalin as model hydrocarbon.The OCNs formed on Pt/Na,H-Y were much less branched than those formed on Ir/Na,H-Y which was interpreted in terms of the different hydrogenolysis mechanisms on both metals.Valuable ancillary mechanistic information was obtained from the selectivities of perhydroindan hydroconversion on the three noble metals on silica.In contrast to Pd/silica,Ir/silica and Pt/silica gave appreciable selectivities of OCNs as well,yet the maximum values of these selectivities were lower than those obtained on the two high-performance zeolite catalysts.     

Validation of HPLC‐UV method for determination of minor glycosides contained in Stevia rebaudiana Bertoni leaves

Leaves of Stevia rebaudiana contain glycosides with sweetness and biological activity. However besides the major glycosides, there are other glycosides within extracts that may contribute to its activity, and therefore it is important to quantify them. In this work, an isocratic HPLC method was validated for determination of dulcoside A, steviolbioside, rebaudioside C and rebaudioside B. An HPLC method was performed using a C₁₈ column (250 × 4.6 mm, particle size 5 µm) and a UV detector set at 210 nm. The mobile phase consisted of a 32:68 (v/v) mixture of acetonitrile and sodium phosphate buffer (10 mmol/L, pH 2.6), set to a flow rate of 1.0 mL/min. The calculated parameters were: sensitivity, linearity, limit of detection (LOD), limit of quantification (LOQ), accuracy and precision. The calibration curves were linear over the working range 25–150 µg/mL, with coefficient of correlation of ≥0.99 and coefficient of determination of ≥0.98. The LOD was 5.68–8.81 µg/mL, while the LOQ was 17.21–26.69 µg/mL. The percentage recoveries of fortified samples were 100 ± 10% and precision, relative standard deviation, was <10%. The method validation showed accuracy, linearity and precision; therefore this method can be applied for quantitative analysis of minor steviol glycosides in S. rebaudiana leaves. Copyright © 2014 John Wiley & Sons, Ltd.     

Enhanced mobility in P3HT-based OTFTs upon blending with a phenylene-thiophene-thiophene-phenylene small molecule

An enhancement in charge transport capacity in a poly(3-hexylthiophene) (P3HT) semicrystalline film, up to field-effect mobilities approaching 0.1 cm(2) V(-1) s(-1), has been achieved by co-deposition with a small molecule, i.e. 5,5'-bis(4-n-hexylphenyl)-2,2'-bithiophene (dH-PTTP), forming highly ordered crystals bridging large polymeric domains.     

Spectrophotometric study of the reaction between cobalt(II)-dipeptide complexes and molecular oxygen

Summary The influence of pH and ligand structure on the reaction of cobalt(II) complexes with various dipeptides and molecular oxygen was examined. The minimum pH value required for the formation of dioxygen adducts was found to be about 6.5. This value should be related to amidic deprotonation of dipeptides, which seems to occur in the examined systems at particularly low values. The location and steric hindrance of the side chains of the dipeptides have a strong influence on the reaction rate. The presence of a substituent group on the N-terminal amino acid promotes oxygen coordination, while, when the substituent group is on the C-terminal residual, a decrease of reaction rate is observed.A stabilizing effect of the aromatic ring on the dioxygen adducts is found only when the substituent is in the C-terminal position, and seems to be independent of the presence of additional coordinating groups.Some information regarding the mechanism of the irreversible decomposition of the cobalt(II) complexes has been obtained by studying the effect of pH and ligand structure on the reaction rate.Work supported by National Research Council of Italy.     

Microdrilling of metals using femtosecond laser pulses and high average powers at 515 nm and 1030 nm

We investigate the microdrilling of metals (stainless steel, copper and tungsten) for two different wavelengths, 1030 nm and 515 nm, in the regime of femtosecond laser pulses. An ytterbium-doped fibre CPA system provides high pulse energies (up to 70 μJ) and high repetition rates (up to 800 kHz), corresponding to high average powers of about 50 W, for this experimental study.     

Isotopomeric conformational changes in the anisole-water complex: new insights from HR-UV spectroscopy and theoretical studies

Resonance enhanced multiphoton ionization and rotationally resolved S1<--S0 electronic spectra of the anisole-2H2O complex have been obtained. The experimental results are compared with high level quantum mechanical calculations and with data already available in the literature. Quite surprisingly, the equilibrium structure of the anisole-2H2O complex in the S0 state shows some non-negligible differences from that of the isotopomer anisole-1H2O complex. Actually, the structure of the deuterated complex is more similar to the corresponding structure of the anisole-1H2O complex in the S1 state. In anisole-water, two equivalent H(D) atoms exist as revealed by line splitting in the rotationally resolved spectra. It is possible to suggest a mechanism for the proton/deuteron exchange ruled by a bifurcated transition state for the exchange reaction, with both water hydrogen atoms interacting with the anisole oxygen atom. From the analysis of all of the available experimental data and of computational results, we can demonstrate that in the S1 excited state the hydrogen bond in which the water molecule acts as an acid is weaker than in the electronic ground state but is still the principal interaction between water and the anisole molecules.     

Study of confined 5-aza[5]helicene in ytterbium(III) bis(2-ethylhexyl) sulfosuccinate reversed micelles

Some relevant physicochemical properties of 5-aza[5]helicene (H5) in solutions of ytterbium bis(2-ethylhexyl) sulfosuccinate (Yb(DEHSS)3) reversed micelles have been investigated by UV-vis-NIR, photoluminescence, and FT-IR techniques with the aim of emphasizing the role played by specific Yb(III)/H5 interactions and confinement effects as driving forces of its binding to reversed micelles, preferential solubilization site, and local photophysical properties. It has been found that the binding strength of 5-aza[5]helicene to reversed micelles, triggered by steric and orientational constrains as well as the water content, is mainly regulated by its interaction with the Yb(III) counterion. Moreover, when H5 is entrapped in Yb(DEHSS)3 reversed micelles, the combined action of this interaction and of confinement effects leads to marked changes of its photophysical properties with respect to those of H5 molecularly dispersed in apolar medium. The influence of the entrapment of finite amounts of H5 on the reversed micelle structure was investigated by SAXS. The analysis of experimental results brings to the hypothesis that H5 is preferentially solubilized and opportunely oriented in the micellar palisade layer and that its insertion causes an unidimensional growth of reversed micelles. From an analysis of WAXS spectra of H5/Yb(DEHSS)3 composites, obtained by complete evaporation of the volatile components of the H5/water/Yb(DEHSS)3/n-heptane solutions, it was ascertained that also on these systems H5 is dispersed molecularly or in a quite amorphous state in the surfactant liquid crystals without forming a separate crystalline nanophase.