An Electrochemical Strategy to Synthesize Disilanes and Oligosilanes from Chlorosilanes**

Silanes are important compounds in industrial and synthetic chemistry. Here, we develop a general approach for the synthesis of disilanes as well as linear and cyclic oligosilanes via the reductive activation of readily available chlorosilanes. The efficient and selective generation of silyl anion intermediates, which are arduous to achieve by other means, allows for the synthesis of various novel oligosilanes by heterocoupling. In particular, this work presents a modular synthesis for a variety of functionalized cyclosilanes, which may give rise to materials with distinct properties from linear silanes but remain challenging synthetic targets. In comparison to the traditional Wurtz coupling, our method features milder conditions and improved chemoselectivity, broadening the functional groups that are compatible in oligosilane preparation. Computational studies support a mechanism whereby differential activation of sterically and electronically distinct chlorosilanes are achieved in an electrochemically driven radical-polar crossover mechanism.     

Hemisynthesis and structural characterization of flavanol‐(4,8)‐vitisins by mass spectrometry

Vitisins constitute the major group of pyranoanthocyanins naturally occurring in red wines. Regarding their chemical structure, only carboxypyranoanthocyanins have been detected and quantified in red wines, but no vitisin with substitutions in the carbons of the A ring has been identified. However, considering the chemical reactions that take place in red wine, the existence of flavan‐3‐ol‐(4,6/8)‐vitisins is expected. This paper reports for the first time the structural identification of catechin‐vitisin A and catechin‐vitisin B based on their mass data and fragmentation patterns. This work also provides some chromatographic and visible spectroscopic features of these pigments and documents the existence of both in red table wines. Moreover, it is also proposed that Cat‐Vit A pigments arise from the cycloaddition of pyruvic acid to an anthocyanin moiety of a flavanol‐anthocyanin adduct rather than by direct nucleophilic attack of a vitisin A on the carbocation C₄ of catechin. Copyright © 2010 John Wiley & Sons, Ltd.     

High-pressure phase diagram of the drug mitotane in compressed and/or supercritical CO2

This work provides experimental phase diagram of mitotane, a drug used in the chemotherapy treatment of adrenocortical carcinoma, in compressed and/or supercritical CO₂. The synthetic-static method in a high-pressure variable-volume view cell coupled with a transmitted-light intensity probe was used to measure the solid-fluid (SF) equilibrium data. The phase equilibrium experiments were determined in temperature ranging from (298.2 to 333.1) K and pressure up to 22 MPa. Peng–Robinson equation of state (PR-EoS) with classical mixing rule was used to correlate the experimental data. Excellent agreement was found between experimental and calculated values.     

Determination of trace impurities in aluminum nitride by direct solid sampling graphite furnace atomic absorption spectrometry

The trace impurities Cr, Cu, Fe, K, Mn, Sb and Zn were determined in powdered aluminum nitride by direct solid sampling graphite furnace atomic absorption spectrometry using a ZEEnit 60 atomic absorption spectrometer. This spectrometer features inverse Zeeman-effect background correction and a variable magnetic field enabling measurements in two sensitivity modes over a concentration range of three orders of magnitude. The measurement sensitivity can be adjusted to the analyte concentration in the sample. The use of chemical modifiers was not necessary. Calibration was carried out by means of calibration curves obtained with aqueous standard solutions. Accuracy was checked mainly by comparison of the results with those obtained by instrumental and radiochemical neutron activation analysis whereby, excluding the results for potassium, no significant differences were found by carrying out the t-test at the significance level 0.05. The limits of detection were between 0.05 ng g⁻¹ (Zn) and 80 ng g⁻¹ (Fe) and the relative standard deviations below 11 %. With the proposed method, up to ten measurement cycles can be carried out in one hour.     

Correlations in Hot and Dense Quark Matter

 We present a relativistic three-body equation to investigate three-quark clusters in hot and dense quark matter. To derive such an equation we use the Dyson equation approach. The equation systematically includes the Pauli blocking factors as well as the self-energy corrections of quarks. Special relativity is realized through the light front form. Presently we use a zero-range force and investigate the Mott transition. Received October 29, 2001; accepted for publication November 12, 2001     

Combined classical and generalized integral transform approaches for the analysis of the dynamic behavior of a damaged structure

The classical integral transform technique (CITT) is employed to derive an exact analytical solution for the transverse vibrations of a damaged Euler–Bernoulli beam simply supported at both ends. The exact analytical solution derived with the CITT approach requires knowledge of the eigenvalues and eigenfunctions of a related eigenvalue problem, whose hybrid solution is further obtained with the generalized integral transform technique (GITT). Expressions derived for the natural frequencies, mode shapes and frequency response function are valid for any prescribed damage field. Numerical results obtained for a damaged beam with single and multiple damages demonstrate the accuracy, convergence and robustness of the two approaches when combined.     

Asymptotics of Selberg-like integrals by lattice path counting

We obtain explicit expressions for positive integer moments of the probability density of eigenvalues of the Jacobi and Laguerre random matrix ensembles, in the asymptotic regime of large dimension. These densities are closely related to the Selberg and Selberg-like multidimensional integrals. Our method of solution is combinatorial: it consists in the enumeration of certain classes of lattice paths associated to the solution of recurrence relations.