Reactions of O‐aryl S‐aryl dithiocarbonates with secondary alicyclic amines in aqueous ethanol. Kinetics and mechanism

The reactions of O‐(4‐methylphenyl) S‐(4‐nitrophenyl), O‐(4‐chlorophenyl) (4‐nitrophenyl), O‐(4‐chlorophenyl) S‐phenyl, and O‐(4‐methylphenyl) S‐phenyl dithiocarbonates ( 1 , 2 , 3 , and 4 , respectively) with a series of secondary alicyclic (SA) amines are subjected to a kinetic investigation in 44 wt% ethanol‐water, at 25.0 °C and an ionic strength of 0.2 M. The reactions are followed spectrophotometrically. Under amine excess, pseudo‐first‐order rate coefficients (k_obs) are found. For some of the reactions, plots of k_obs vs. free amine concentration at constant pH are linear but others are nonlinear upwards. This kinetic behavior is in accordance with a stepwise mechanism with two tetrahedral intermediates, one zwitterionic (T^±) and the other anionic (T^?). In some cases, there is a kinetically significant proton transfer from T^± to an amine to yield T^?. Values of the rate micro constants k₁ (amine attack to form T^±), k_?1 (its back step), k₂ (nucleofuge expulsion from T^±), and k₃ (proton transfer from T^± to the amine) are determined for some reactions. The Brønsted plots for k₁ are linear with slopes β₁ = 0.2–0.4 in accordance with the slope values found when T^± formation is the rate‐determining step. The sensitivity of log k₁ and log k_?1 to the pK_a of the amine, leaving and non‐leaving groups are determined by a multiparametric equation. For the reactions of 1 – 4 with 1‐formylpiperazine and those of 3 and 4 with morpholine the k₂ and k₃ steps are rate determining. Copyright © 2010 John Wiley & Sons, Ltd.     

Structural analysis of electrolyte solutions for rechargeable Mg batteries by stereoscopic means and DFT calculations

We present a rigorous analysis of unique, wide electrochemical window solutions for rechargeable magnesium batteries, based on aromatic ligands containing organometallic complexes. These solutions are comprised of the transmetalation reaction products of Ph(x)MgCl(2-x) and Ph(y)AlCl(3-y) in different proportions, in THF. In principle, these reactions involve the exchange of ligands between the magnesium and the aluminum based compounds, forming ionic species and neutral molecules, such as Mg(2)Cl(3)(+)·6THF, MgCl(2)·4THF, and Ph(y)AlCl(4-y)(-) (y = 0-4). The identification of the equilibrium species in the solutions is carried out by a combination of Raman spectroscopy, multinuclear NMR, and single-crystal XRD analyses. The association of the spectroscopic results with explicit identifiable species is supported by spectral analyses of specially synthesized reference compounds and DFT quantum-mechanical calculations. The correlation between the identified solution equilibrium species and the electrochemical anodic stability window is investigated. This study advances both development of new nonaqueous solution chemistry and possible development of high-energy density rechargeable Mg batteries.     

Oxygen and hydrogen profiles and electrical properties of unintentionally doped gallium nitride grown by hydride vapor phase epitaxy

Commercially available hydride vapor phase epitaxy gallium nitride (GaN) is characterized with the aim to correlate the oxygen and hydrogen secondary ion mass spectrometry profiles of a GaN wafer with the electrical properties of the sample. A GaN layer model, including doping profile and mobility, is derived, utilizing electrical (capacitance–voltage, Hall), structural (high resolution X‐ray diffraction) and optical (polarized infrared spectroscopy) methods. Oxygen and hydrogen are easily incorporated during hydride vapor phase epitaxy growth of GaN. Oxygen is an n‐type dopant in GaN, whereas hydrogen may passivate some of the donors. Electrical and optical properties correlate with a low defect concentration top GaN layer and a high defect concentration GaN interlayer.     

Microwave-assisted synthesis of tin sulfide nanoflakes and their electrochemical performance as Li-inserting materials

A novel and quick method has been developed for the preparation of tin sulfide (SnS and SnS₂) nanoflakes in high yield (≈93%) by a microwave irradiation technique for 10–40 min. The sulfides were synthesized in a simple domestic microwave oven (DMO) using stannic chloride and stanous chloride as the precursors of tin and thiourea as the precursor of sulfur in ethylene glycol under argon atmosphere. Elemental sulfur and sodium thiosulfate were also tried as precursors of sulfur. The structures, morphologies, compositions, and physical properties of the products were characterized by powder X-ray diffraction (XRD), differential scanning calorimetry, energy dispersive X-ray analysis, transmission electron microscopy, selected area electron diffraction, Raman spectroscopy, and standard electrochemical techniques. The XRD patterns indicate that the as-synthesized product, obtained after microwave irradiation, is crystalline orthorhombic in the case of the SnS phase and amorphous in the case of SnS₂. Heat treatment of this SnS₂ produced a crystalline hexagonal phase. A possible mechanism for the formation of the tin sulfide nanoflakes is proposed herein. The electrochemical performance of these materials as Li-insertion materials was investigated in a number of electrolyte solutions and was found to be highly sensitive to the solution composition. A stable reversible capacity higher than 600 mAh/g could be obtained with SnS electrodes.     

Chaotic scattering and transmission fluctuations

We discuss the phenomenon of chaotic scattering and its application in the study of transmission of electrons in mesoscopic devices as well as the transmission of microwaves through junctions. We show that the fact that the ray optics (classical dynamics) is chaotic, implies fluctuations in the observed transmission coefficients, whose statistics is determined by the theory of random matrices. We also show how the classical distribution functions which reflect the chaotic nature of the classical dynamics, determine the dependence of the correlations observed in the fluctuating transmission coefficients on external parameters. The time domain properties of chaotic scattering systems are also examined, and are shown to depend on the chaotic nature of the classical dynamics, together with a wave mechanical enhancement in time reversal invariant systems. Finally, we study the role of absorption and discuss its effects on the transmission fluctuations and their statistics.     

A combinatorial proof of Dyson's conjecture

Dyson's conjecture, already proved by Gunson, Wilson and Good, is given a direct combinatorial proof.     

Modular invariance and the spectrum of two dimensional conformal field theories

Modular invariance has recently emerged as a powerful tool in conformal field theory. In conjunction with the representation theory of infinite dimensional Lie algebras, the study of modular invariance gave the spectrum of several families of theories. These include the minimal conformal models (Cardy and others), WZW theories which describe string propagation on group manifolds (Gepner and Witten) and parafermionic field theories (Gepner and Qiu). The minimal conformal models models were shown to be a product of two SU(2) WZW theories (Gepner). These results represent a step towards a complete classification of conformal field theories, an important goal both for the study of critical phenomena and string theory.     

An approach to remove alpha amylase for proteomic analysis of low abundance biomarkers in human saliva

Proteomic characterization of human whole saliva for the identification of disease-specific biomarkers is guaranteed to be an easy-to-use and powerful diagnostic tool for defining the onset, progression and prognosis of human systemic diseases and, in particular, oral diseases. The high abundance of proteins, mainly alpha amylase, hampers the detection of low abundant proteins appearing in the disease state and therefore should be removed. In the present study a 2-DE was used to analyze human whole saliva following the removal of alpha amylase by affinity adsorption to potato starch. After alpha amylase removal whole saliva was analyzed by SDS-PAGE showing at least sixfold removal efficiency and by an alpha amylase activity assay showing 97% reduced activity. MS identification of the captured alpha amylase after elution demonstrated specific removal; 2-DE analysis showed the selective removal of alpha amylase and consequently increased gel resolution. MS identification of protein spots in the 60 kDa area revealed 15 proteins, which were masked before alpha amylase removal. In conclusion, treatment of human whole saliva with an alpha amylase removal device increases gel resolution and enables a higher protein sample for analysis.     

Contents of Volumes

The role of the Plateau borders in the patterning occurring under the rapid evaporation of polymer solutions is discussed. The capillary gradient formed along the Plateau border results in the intensive migration of bubbles towards the knots of the pattern network. A semi-quantitative model of the bubbles migration in terms of the border curvature and velocity of transport is presented.