Prediction of liquid–liquid equilibrium for ternary systems containing ionic liquids with the tetrafluoroborate anion using ASOG

Liquid–liquid equilibrium (LLE) data for different systems involving ionic liquids are essential for design, optimization and operation of separation processes, such as recovery of valuable products and remotion of polluting agents in effluents. In this work, the ASOG model for the activity coefficient is used to predict LLE data for 32 ternary systems at 101.3 kPa and several temperatures; all the systems are formed by ionic liquids including the tetrafluoroborate anion plus alkanes, alkenes, cycloalkanes, alkanols, ketones, carboxylic acids, esters and aromatics. New group interaction parameters were determined by using a modified Simplex method, minimizing a composition-based objective function. The results, in terms of mean deviation between the experimental and calculated compositions, are satisfactory, with rms deviations of about 4%.     

Spectroscopic studies of stratum corneum model membrane from Bothrops jararaca treated with cationic surfactant

This research employed FT-Raman and PAS-FTIR spectroscopic techniques to evaluate the interaction of cetyl trimethyl ammonium chloride (CTAC), a cationic surfactant, on the stratum corneum (SC) of shed snake skins from Bothrops jararaca, used as model membranes. Surfactant aqueous solutions (50.0 and 0.78 gl(-1)) with neutral pH were applied on the samples with intervals of 4, 8 (whole SC) and 12h (SC tape-stripped). Samples presented modifications of the topography for all conditions of the assays and the monomers of the surfactant, instead of the micelles, seemed to interact with the keratin. The SC model membranes treated with CTAC have had an augment of water content (except for whole SC treated for 8h) indicated by the expansion of the band 3600-3300 cm(-1), mainly for the tape-stripped samples after 12h treatment. Concentration appeared to be an important factor related to an increase of the tissue hydration.     

Gold Nanopyramids Assembled into High-Order Stacks Exhibit Increased SERS Response

This Letter describes how gold pyramidal nanoshells (nanopyramids) can be assembled into low- and high-order structures by varying the rate of solvent evaporation and surface wettability. Single-particle and individual-cluster dark field scattering spectra on isolated, dimers and trimers of nanopyramids were compared. We found that the short wavelength resonances blue-shifted as the particles assembled; the magnitude of this shift was greater for high-order structures. To test which assembled architecture supported a larger Raman-active volume, we compared their surface enhanced Raman scattering (SERS) response of the resonant Raman molecule methylene blue (λ(ex) = 633 nm). We discovered that high-order structures exhibited more Raman scattering compared to low-order assemblies. Finite-difference time-domain modeling of nanopyramid assemblies revealed that the highest electromagnetic field intensities were localized between adjacent particle faces, a result that was consistent with the SERS observations. Thus, the local spatial arrangement of the same number of nanoparticles in assembled clusters is an important design parameter for optimizing nanoparticle-based SERS sensors.     

Modeling of high-pressure vapor–liquid equilibrium in ionic liquids + gas systems using the PRSV equation of state

Ionic liquids are environmentally friendly solvents composed of large organic cations and relatively small inorganic anions, whose melting point is below T = 373.15 K. This is an arbitrary limit defined in order to organize the dramatically increasing number of possible applications in chemical processes. These compounds are regarded as potentially environmentally benign solvents due to their almost negligible vapor pressure, which essentially eliminates emission to the atmosphere; besides, they present a wide range of liquid existence. Ionic liquids are applicable in separation processes, such as recovery of valuable products and remotion of polluting agents in effluents 1, 2, 3 and 4 and are a new and exciting class of compounds that have the potential to overcome many of the problems associated with current CO₂-capture techniques. In this work, high-pressure vapor–liquid equilibrium (VLE) of 17 binary mixtures ionic liquid + gas has been modeled with the Peng–Robinson/Stryjek–Vera (PRSV) 5 and 6 equation of state (EoS) applying the Wong–Sandler (WS) [7] mixing rules, including the van Laar (VL) model for the excess Gibbs free energy [8] for the gamma–phi approach and the one-fluid van der Waals (VDW) mixing rules for the phi–phi approach. Critical properties and acentric factor of ionic liquids [pmim][Tf₂N] and [hmmim][Tf₂N] were determined using the extended group contribution method by Lydersen–Joback–Reid [9], while, for the other ionic liquids, these properties are available in the literature 10 and 11. Experimental data were obtained from literature 12, 13, 14, 15, 16, 17 and 18 and the adjustable parameters were fitted by minimizing the errors between predicted and experimental bubble pressure. van Laar and binary interaction parameters were regarded as temperature-dependent. The results, in terms of main deviations between experimental and calculated pressures for the 17 binary systems, are reasonably satisfactory (3.62% and 2.59% for the gamma–phi and phi–phi approaches, respectively).     

Efficient and selective synthesis of glycofuranosyl azides and nucleosides from cyclic 1,2-thiocarbonate sugars

[reaction: see text] Cyclic 1,2-thiocarbonate sugars are convenient starting materials for the selective and efficient preparation of glycofuranosyl azides and nucleosides by regio- and stereoselective thiocarbonate ring-opening.     

Nucleus-independent chemical shift (NICS) profiles in a series of monocyclic planar inorganic compounds

A series of monocyclic planar inorganic compounds have been optimized at the B3LYP/6-311+G^∗ level. GIAO-B3LYP nucleus-independent chemical shifts (NICS) profiles calculated in the perpendicular direction of each ring show that the series of analyzed compounds can be classified in three groups according to their aromatic, non-aromatic or antiaromatic character. Our results suggest exercising caution in the use of single-point NICS calculations as a quantitative measure of aromaticity for these species.     

Speciation of selenite and selenate using living bacteria

In this work, a reliable method is described for speciation of soluble inorganic selenium ions, Se(IV) and Se(VI), which combines an uptake process by using living bacterial cells and electrothermal atomic absorption spectrometry (ETAAS). A selective retention of either Se(IV) or Se(IV) plus Se(VI) can be carried out by using the uptake system made up of either Pseudomonas putida or Escherichia coli strains cultivated in a culture medium based on glucose (P. putida) and glucose plus dipotassium phosphate (E. coli) mixed together with the original sample solution containing the selenium species. Discrimination between inorganic selenium species is possible by combining the optimization of the bacterial cell, the growth conditions and the relative rates of their retention from the sample. In the general procedure, an equilibrium between the analyte in the solution and the uptake system is allowed to be established, and then the concentration of selenium is determined directly in the biomass by slurry sampling ETAAS. Nonetheless, a theoretical model is proposed to describe the retention process by the living bacterial cells, which also provides a feasible quantification of the extraction process before the adsorption equilibrium is reached and whenever the agitation conditions and the sampling time are under control. The detection limits for the inorganic selenium species at the best retention conditions are of 5.7 ng Se(IV) ml(-1) for P. putida and 6.1 ng Se(IV) ml(-1) and 6.3 ng Se(VI) ml(-1) for E. coli. The relative standard deviations of the adsorption/determination process are 2.9-6.3%.     

Laser-polarized 129Xe NMR at 1.88 T and 8.5 mT: a signal-to-noise ratio comparison

The signal-to-noise ratio of nuclear magnetic resonance signals from laser-polarized 129Xe gas was investigated at 8.5 mT and compared to that of signals acquired at 1.88 T. A dedicated 8.5 mT resistive magnet was constructed and used to acquire the signals. The SNR for 1 atm of xenon gas with a polarization of 1% was measured to be 1900 at a field of 1.88 T. Under identical acquisition conditions, the SNR at 8.5 mT was about 60 (or 32 times lower). After measuring and including all of the electrical factors of the detection systems at each field strength, theory indicates the SNR value measured at 8.5m T should be about 36 times lower. Considering the widely differing frequencies and completely different detection systems the agreement is quite good and indicates that extrapolating the frequency dependence of the SNR down to very low fields does work as long as the detection system parameters are carefully accounted for. This work suggests that magnetic resonance (MR) imaging is achievable on ideal gas samples at 8.5 mT using laser-polarized 129Xe gas down to the practical resolution limit of about 0.5mm, although the SNR will be very low (approximately 1.4). The feasibility of imaging small animals at 8.5 mT is discussed and it is suggested that a field of about 50 mT is required.