Presence or absence of counterion specificity in the interaction of alkylammonium surfactants with alkylacrylamide gels

Patterns in the interaction of cationic surfactants with nonionic polymer gels, which were inferred from a recent study from our laboratory, are confirmed by measurements of a series of alkylammonium surfactants with different counterions with a series of alkyl acrylamide gels of increasing hydrophobicity. Two swelling patterns were observed: Either the swelling continued above the surfactant critical micelle concentration (cmc) and the maximum swelling differed for different counterions and increased in the order of Br-相似文献   

Complex polyion-surfactant ion salts in equilibrium with water: changing aggregate shape and size by adding oil

The phase behavior of ternary mixtures containing an alkyltrimethylammonium polyacrylate complex salt, water, and a nonpolar "oil" (n-decanol, p-xylene or cyclohexane) is investigated. The complex salts were prepared with short or long polyacrylates (30 or 6000 repeating units) and with hexadecyltrimethylammonium or dodecyltrimethylammonium surfactant ions. Phase diagrams and structures were determined by visual inspection and small-angle X-ray scattering analyses. Systems containing decanol display a predominance of lamellar phases, while hexagonal phases prevail in systems containing p-xylene or cyclohexane. The difference is interpreted as a result of the different locations of the oils within the surfactant aggregates. Decanol is incorporated at the aggregate interface, leading to a decrease in its curvature, which favors the appearance of lamellar structures. p-Xylene and cyclohexane, on the other hand, are mostly incorporated in the interior of the cylindrical aggregate, as reflected by its swelling as the oil content increases. The comparison of these results with those reported for similar systems with monovalent (bromide) counterions indicates a much more limited swelling of the lamellar phases with polymeric counterions by water. This limited swelling behavior is predominantly ascribed to bridging due to the polyions.     

Optimisation of pressurised liquid extraction for the determination of p,p′-DDT and p,p′-DDE in aged contaminated Ethiopian soils

The effectiveness of extracting p,p′-DDT and p,p′-DDE from aged contaminated soil samples by means of pressurized liquid extraction (PLE) was evaluated. Two soil samples, which were contaminated more than 10 years ago, were used in the investigation. The static extraction time was optimised and then validated against the total sum of target analytes obtained from multiple sequential extractions. The PLE results were also compared with Soxhlet extraction (SOX). PLE for 3×10 min at 100 °C was proven to be more exhaustive than SOX in the determination of p,p′-DDE from both soil samples. In the case of p,p′-DDT, PLE was found to be equally as exhaustive as SOX. Additionally, most of the previous PLE investigations used hazardous organic solvents such as n-hexane, toluene and dichloromethane mixed with acetone, whereas in this investigation the less toxic solvent combination n-heptane/acetone has been employed.     

Fast force field-based optimization of protein–ligand complexes with graphics processor

Usually based on molecular mechanics force fields, the post-optimization of ligand poses is typically the most time-consuming step in protein–ligand docking procedures. In return, it bears the potential to overcome the limitations of discretized conformation models. Because of the parallel nature of the problem, recent graphics processing units (GPUs) can be applied to address this dilemma. We present a novel algorithmic approach for parallelizing and thus massively speeding up protein–ligand complex optimizations with GPUs. The method, customized to pose-optimization, performs at least 100 times faster than widely used CPU-based optimization tools. An improvement in Root-Mean-Square Distance (RMSD) compared to the original docking pose of up to 42% can be achieved. © 2012 Wiley Periodicals, Inc.     

Formal Total Synthesis of the Algal Toxin (−)‐Polycavernoside A

A concise and largely catalysis‐based approach to the potent algal toxin polycavernoside A ( 1 ) is described that intercepts a late‐stage intermediate of a previous total synthesis; from there on, this challenging target can be reached in a small number of steps. Key to success was a sequence of a molybdenum‐catalyzed ring‐closing alkyne metathesis (RCAM) reaction to forge the macrocyclic frame, followed by a gold‐catalyzed and strictly regioselective transannular hydroalkoxylation of the resulting cycloalkyne that allows the intricate oxygenation pattern of the macrolactone ring of 1 to be properly set. The required cyclization precursor 5 was assembled by the arguably most advanced fragment coupling process based on an Evans–Tishchenko redox esterification known to date, which was optimized to the extent that the precious coupling partners could be used in an almost equimolar ratio ( 6 / 7 1:1.3). The preparation of these building blocks features, inter alia, the power of the Sc(OTf)₃‐catalyzed Leighton crotylation as well as the superb selectivities of alkene cross metathesis, asymmetric keto‐ester hydrogenation, and the Jacobsen epoxidation/epoxide resolution technologies.     

The Use of Automated Headspace Gas Chromatography for Determination of 1,1,1-Trichloroethane in Rat Blood and Brain Tissue

Abstract

1,1,1-trichloroethane in blood and brain tissue from rats which had been artificially ventilated with solvent (8000 ppm) was analysed by automated headspace gas chromatography using a fused silica capillary column. A given concentration of 1,1,1-trichloroethane in the brain could be correlated with a corresponding concentration in the blood; both the uptake and release of the solvent were quicker in blood than in brain. No volatile metabolites of the solvent were found. Automated headspace gas chromatographic analysis is a rapid and sensitive technique for the quantitative registration of volatile organic solvents, e.g. of industrial importance, in body fluids and tissues.     

Isomerspecific determination of sorption/desorption,transformation and bioaccumulation of hexachlorocyclohexanes at the case site Bitterfeld with special regard to ageing effects

ABSTRACT

The production of hexachlorocyclohexanes (HCHs) at Bitterfeld, Germany, caused heavy contamination of sediments in the receiving waters and soils of riverbanks and floodplains of the Spittelwasser creek with adverse effects on the rivers Mulde and Elbe. This study was launched to investigate the isomer specific behaviour of aged and non-aged hexachlorocyclohexanes focusing on their transformation, sorption and bioaccumulation. Spiked residues of α- and γ-HCH were transformed in aerobic water/sediment systems, while no elimination was observed for β-, δ- and ε-HCH. In contrast, aged residues of all HCH isomers were entirely stable under these aerobic conditions, while under anaerobic conditions a significant transformation was found for all spiked HCH isomers. Desorption hysteresis was identified for all isomers. Ageing led to an increase in the binding strength of HCH isomers to sediment, indicated by elevated logK_OC-values and increased the persistence of HCH isomers in aerobic water/sediment systems. HCH bioaccumulated in benthic organisms of Spittelwasser creek and Schachtgraben canal. After their confluence the lipid normalised HCH concentrations in benthic organisms of Spittelwasser creek increased by a factor of 10, indicating the central role of HCH residues from the Schachtgraben canal for the HCH exposure of benthic biota in the aquatic system of the Spittelwasser creek.     

Hamaker constants of iron oxide nanoparticles

The Hamaker constants for iron oxide nanoparticles in various media have been calculated using Lifshitz theory. Expressions for the dielectric responses of three iron oxide phases (magnetite, maghemite, and hematite) were derived from recently published optical data. The nonretarded Hamaker constants for the iron oxide nanoparticles interacting across water, A(1w1) = 33 - 39 zJ, correlate relatively well with previous reports, whereas the calculated values in nonpolar solvents (hexane and toluene), A(131) = 9 - 29 zJ, are much lower than the previous estimates, particularly for magnetite. The magnitude of van der Waals interactions varies significantly between the studied phases (magnetite < maghemite < hematite), which highlights the importance of a thorough characterization of the particles. The contribution of magnetic dispersion interactions for particle sizes in the superparamagnetic regime was found to be negligible. Previous conjectures related to colloidal stability and self-assembly have been revisited on the basis of the new Lifshitz values of the Hamaker constants.