A highly oriented cubic phase formed by lipids under shear

We demonstrate the formation of a macroscopically oriented inverse bicontinuous cubic (Q(II)) lipid phase from a sponge (L(3)) phase by controlled hydration during shear flow. The L(3) phase was the monoolein/butanediol/water system; the addition of water reduces the butanediol concentration, inducing the formation of a diamond (Q(II)(D)) cubic phase, which is oriented by the shear flow. The phenomenon was reproduced in both capillary and Couette geometries, indicating that this represents a robust general route for the production of highly aligned bulk Q(II) samples, with applications in nanomaterial templating and protein research.     

The influence of solvation and finite temperatures on theWittig reaction: A theoretical study

The effects of the solvent and finite temperature (entropy) on the Wittig reaction are studied by using density functional theory in combination with molecular dynamics and a continuum solvation model. Standard gas-phase zero-temperature calculations are found to give similar results to previous studies. Gas-phase dynamics simulations allow the free energy profile of the reaction to be calculated through thermodynamic integration. The free energy profile is found to have a significant entropic barrier to the addition step of the reaction where only a small barrier was present in the potential energy curve. The introduction of the solvent dimethyl sulfoxide causes a change in the structure of the intermediate from the oxaphosphetane structure to the dipolar betaine structure. The overall reaction energy is changed only slightly. When the effects of both entropy and the solvent are included a significant entropic barrier to the addition reaction is obtained and the predicted intermediate again has the betaine structure.     

Stochastic simulations of polymer growth and isomerization in the polymerization of propylene catalyzed by Pd-based diimine catalysts

A model is presented that employs a stochastic approach to the simulation of polyolefin chain growth and isomerization. The model is applied to propylene polymerization catalyzed by Pd-based diimine catalysts. The stochastic approach links the microscopic (quantum chemical) approach with modeling of the macroscopic systems. The DFT calculated energies of the elementary reactions and their barriers have been used as input parameters for the simulations. The influence of the catalyst's steric bulk, as well as polymerization temperature and olefin pressure on the polymer branching and its microstructure, is discussed. The results are in good agreement with available experimental data. In the propylene polymerization catalyzed by Pd(II) complexes with methyl backbone- and -Ph-(i)Pr(2) imine substituents a number of branches of 238 branches/1000 C have been obtained. An increase in polymerization temperature leads to a decrease in the number of branches. Change in olefin pressure does not affect the global number of branches, while it strongly affects the polymer microstructure, leading to hyperbranched structures at low pressures. Further, the simulations confirm the experimental interpretation of the mechanistic details for this process: (1) both 1,2- and 2,1-insertion happen with the ratio of ca. 7:3; (2) there are no insertions at the secondary carbons; and (3) most of the 2,1-insertions are followed by a chain straightening isomerization. Thus, for this catalyst the total number of branches is controlled exclusively by the 1,2-/2,1-insertion ratio. For the catalysts with different substituents the branching can be controlled by a 1,2-/2,1-insertion ratio as well as the fraction of the insertions at the secondary carbons. The results of the present studies demonstrate that a stochastic approach can be successfully used to model the polyolefin microstructures and their catalyst, temperature, and pressure dependence. Further, it can also facilitate interpretation of the experimental results, and can be used to draw general conclusions about the influence of the specific elementary reaction barriers on the polymer structures; this can be helpful for a rational design of the catalysts producing a desired microstructure.     

A copper(II)–pyrazole complex cation with imposed symmetry

The reaction of Cu(ClO₄)₂·6H₂O, NaAsF₆ and excess pyrazole yields hexakis­(pyrazole‐κN²)copper(II) bis­(hexa­fluoroarsenate), [Cu(C₃H₄N₂)₆](AsF₆)₂ or [Cu(pzH)₆](AsF₆)₂ (pzH is pyrazole), (I). The analogous hexakis­(pyrazole‐κN²)copper(II) hexafluorophosphate perchlorate complex, [Cu(C₃H₄N₂)₆](PF₆)_1.29(ClO₄)_0.71 or [Cu(pzH)₆](PF₆)_1.29(ClO₄)_0.71, (II), is obtained in a similar fashion, using KPF₆ in place of NaAsF₆. Both compounds contain the hitherto unknown [Cu(pzH)₆]²⁺ complex cation, in which the copper(II) ion lies at the center of a regular octahedron of coordinated N atoms. The cation has crystallographically imposed symmetry. The X‐ray data indicate that the lack of the expected distortion can be accounted for by the presence of either static Jahn–Teller disorder or dynamic Jahn–Teller distortion.     

Photo-Oxidation of phenosafranine and neutral red in the presence of iron(III): Determination of trace amounts of iron and phosphate

Summary Phenosafranine (Ph) and Neutral Red (NR) in the presence of iron(III) are decolorized by illumination with light of wavelength shorter than 360 nm. The decolorization mechanism involves ·OH radicals, formed during the photo-excitation of hydrolysed iron(III) species. In the presence of oxygen, iron(III) acts as a catalyst in the photochemical process. The photo-oxidation of Ph and NR is followed by measuring the decrease in absorbance of the dyes, and linear calibration graphs in the range 1–11 ppm of iron are obtained. The decrease in the fluorescence of phenosafranine has also been used to measure the photo-oxidation of this dye, and is linearly related to iron concentration in the range 0.1–1.1 ppm. Phosphate strongly inhibits the iron(III)-catalysed photodecolorization and this can be made the basis of a method for its determination (concentration limit 1×10^–5 M).

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Photooxydation von Phenosafranin und Neutralrot in Gegenwart von Eisen(III): Bestimmung von Spuren Eisen und Phosphat

Zusammenfassung Phenosafranin (Ph) und Neutralrot (NR) werden in Gegenwart von Fe(III) durch Belichtung unter 360 nm entfärbt. Der Mechanismus dieses Vorgangs erfordert die Gegenwart von OH-Radikalen, die sich bei Belichtung von hydrolysierten Fe(III)-Verbindungen bilden. In Gegenwart von Sauerstoff wirkt Fe(III) als Katalysator der photochemischen Reaktion. Die Photooxydation von Ph und NR läßt sich durch Abnahme der Absorbanz der beiden Farbstoffe verfolgen. Dabei ergeben sich lineare Eichkurven für 1–11 ppm Fe. Die Abnahme der Fluoreszenz von Ph dient ebenfalls zur Messung der Photooxydation dieses Farbstoffes und verläuft für 0,1–1,1 ppm Fe linear. Phosphat hindert die Fe(III)-katalysierte Photoentfärbung, was als Grundlage für die Phosphatbestimmung bis zu 1×10^–5 M dienen kann.

     

Computational Science and Engineering On-line: an integrated web-based environment for multi-scale modelling of complex reaction systems

We present a development of an integrated extendable web-based environment called Computational Science and Engineering On-line (CSEO) to include different fields of computational science. Our initial efforts are focusing on an integrated environment for multi-scale modelling of complex reacting systems from fundamental quantum chemistry with different entry points. CSEO provides an information management system that allows data flow from one application to another in a transparent manner. In addition, it provides a set of web-based graphic-user interfaces (GUIs) to different scientific applications. Current available GUIs are for quantum chemistry, thermodynamics and kinetics. Work is in progress to allow CSEO accessing resources from the computing grids using the Globus technology. CSEO can be accessed at http://cseo.net. It can also be hosted at different mirror sites.