Experimental determination and prediction of (solid + liquid) phase equilibria for binary mixtures of heavy alkanes and fatty acids methyl esters

Solid–liquid equilibria for three binary mixtures of {n-eicosane (1) + methyl palmitate (2)}, {n-tetracosane (1) + methyl stearate (2)} and {n-octacosane (1) + methyl stearate (2)} were measured using differential scanning calorimeter. Simple eutectic behaviours for these systems were observed. The experimental results were correlated by means of the modified UNIFAC (Larsen and Gmehling versions), UNIQUAC and ideal models. The root-mean-square deviations of the solubility temperatures for all measured data vary from 0.21 K (for UNIQUAC model) to 1.07 K (for Ideal model) and depend on the particular model used. The best solubility correlation was obtained with UNIQUAC model.     

Gene expression noise facilitates adaptation and drug resistance independently of mutation

We show that the effect of stress on the reproductive fitness of noisy cell populations can be modeled as a first-passage time problem, and demonstrate that even relatively short-lived fluctuations in gene expression can ensure the long-term survival of a drug-resistant population. We examine how this effect contributes to the development of drug-resistant cancer cells, and demonstrate that permanent immunity can arise independently of mutations.     

New solid-phase-nanoscavenger for the analytical enrichment of mercury from water

A nanoscavenger of mercaptopropyl-modified silica microparticles has been developed for the determination of trace levels of mercury(II) in water. The synthesis of silica microparticles nanoscavengers is carried out by modification of pre-formed silica particles with mercaptopropyltrimethoxysilane or by incorporating the thiol modification agent during the growth of the silica particles. The silica nanoscavengers were characterized by SEM, TGA, particle analyzer, IR and the parameters influencing the extraction and recovery phases of the preconcentration process were performed by AAS. The results show that careful choice of particle size and surface characteristics produce a new mercapto-silica-nanoscavenger that disperses in water as a quasi-stable sol. This permits the facile recovery of the mercury-loaded nanoscavenger particles. No agitation is required during the mercury extraction as the dispersion is maintained by Brownian motion and slow gravitational sedimentation. The technique overcomes a number of problems, such as cross-contamination and decreases in mercury concentration during sample transportation to the laboratory. Recovery achieved reaches >97 ± 4% over a wide range of preconcentration factors. At a preconcentration factor of 50 the limit of detection (3σ) was 0.19 ng mL(-1). The method is environmentally friendly as only 300 mg of mercapto-nanoscavenger is used, no organic solvent is required for the extraction and the experiment is performed without the need for manual or mechanical agitation.     

Nanoscavenger based dispersion preconcentration; sub-micron particulate extractants for analyte collection and enrichment

A new approach has been developed for the preconcentration of analytes from solution using nanoscavengers; monodisperse functionalised particles of sub-micron dimensions, that can be suspended as a quasi-stable sol in an aqueous solution, and quantitatively recovered with the analyte by conventional filtration. No external agitation of the sample is required as the particles move naturally through the sample by Brownian motion, convection and sedimentation. By careful choice and control of their particle size and surface chemistries, nanoscavengers can be designed to suit a number of different analytical problems. Surface modification of these nanometre-sized particles, through the grafting of complexing or partitioning functional groups, can produce nanoscavengers having affinities for specific analytes and operating through a wide range of mechanisms from covalent bonding to hydrophobic interaction. The approach is illustrated by the development of an extraction-based preconcentration of metals from solution that employs sub-micron St?ber-type silica spheres, the surfaces of which have been modified using chelating diamine and dithiocarbamate groups. The concept has potentially widespread applicability as it is neither limited to metal extractions, nor to the use of silica-based nanoscavengers. Minimal involvement of organic solvents make nanoscavengers a potentially environmentally benign ("green") alternative to many conventional solvent extraction techniques.     

On the Supra-LUMO Interaction: Case Study of a Sudden Change of Electronic Structure as a Functional Emergence

The synergistic functioning of redox-active components that emerges from prototypical 2,2′-di(N-methylpyrid-4-ylium)-1,1′-biphenyl is described. Interestingly, even if a trans conformation of the native assembly is expected, due to electrostatic repulsion between cationic pyridinium units, we demonstrate that cis conformation is equally energy-stabilized on account of a peculiar LUMO (SupLUMO) that develops through space, encompassing the two pyridiniums in a single, made-in-one-piece, electronic entity (superelectrophoric behavior). This SupLUMO emergence, with the cis species as superelectrophore embodiment, originates in a sudden change of electronic structure. This finding is substantiated by insights from solid state (single-crystal X-ray diffraction) and solution (NOE NMR and UV-vis-NIR spectroelectrochemistry) studies, combined with electronic structure computations. Electrochemistry shows that electron transfers are so strongly correlated that two-electron reduction manifests itself as a single-step process with a large potential inversion consistent with inner creation of a carbon-carbon bond (digital simulation). Besides, absence of reductive formation of dimers is a further indication of a preferential intramolecular reactivity determined by the SupLUMO interaction (cis isomer pre-organization). The redox-gated covalent bond, serving as electron reservoir, was studied via atropisomerism of the reduction product (VT NMR study). The overall picture derived from this in-depth study of 2,2′-di(N-methylpyrid-4-ylium)-1,1′-biphenyl proves that trans and cis species are worth considered as intrinsically sharply different, that is, as doubly-electrophoric and singly-superelectrophoric switchable assemblies, beyond conformational isomerism. Most importantly, the through-space-mediated SupLUMO may come in complement of other weak interactions encountered in Supramolecular Chemistry as a tool for the design of electroactive architectures.     

Rapid thermally assisted donor-acceptor catenation

Charged donor-acceptor [2]catenanes containing cyclobis(paraquat-p-phenylene) as the ring component can be synthesised in yields of up to 88% in under one hour by heating two precursors in the presence of macrocyclic polyether templates in N,N-dimethylformamide at 80 °C.     

Controllable fabrication of highly ordered thin AAO template on Si substrate for electrodeposition of nanostructures

In this work, simple fabrication of hexagonally highly ordered porous anodic aluminum oxide (AAO) of Al thin film (1 μm) on Si substrate is described using two-step anodization method for electrochemical synthesis of nanostructures. In this method, the templates were prepared under the controllable conditions of the parameters, which give rise to the possibility of highly ordered nanopore arrays with a well aspect ratio. Pore widening was then fulfilled in 5 wt% phosphoric acid solution at 25 °C. The pore diameter and spacing are proportional to the applied voltage, which is due to the mechanical stress associated with the volume expansion of the aluminum during the anodization according to the mechanical stress model. Pore-widening solution adjusted the pore diameter and thinned the AAO barrier layer at room temperature under the control of etching time. As an application, Cu nanorods arrays embedded in anodic alumina (AAO) template were fabricated by dc electrodeposition. The characterization of the AAO templates and the Cu nanorods produced was made by X-ray diffraction, field emission scanning microscope, energy dispersive X-ray spectroscopy and atomic force microscope (AFM). The images of AFM show that porous AAO template under constant voltage is 40 V which presents the optimum ordering.     

Computational analysis of convective instabilities in a liquid layer subjected to an inclined gradient of temperature

A 3D numerical study of convective instabilities in a horizontal liquid layer (silicone oil with a Prandtl number Pr = 102) with an upper free surface is presented. The liquid layer is subjected to an inclined gradient of temperature. The influence of both gravity and thermocapillary forces on the formation of convective patterns is studied for different values of the liquid layer depth. Numerical results are found to be in good agreement with experimental data of other authors.     

Sequestration of CO2 using Cu nanoparticles supported on spherical and rod-shape mesoporous silica

The CO₂ sequestration is one of the most promising solutions to tackle global warming. In this study, spherical mesoporous silica particles (MPS-S) and rod-shaped mesoporous silica particles (MPS-R) loaded with Cu nanoparticles were selectively prepared and employed for CO₂ adsorption. For the first time uniform Cu nanoparticles were incorporated into the rod-shaped mesoporous silica particles by post-synthesis modification using both N-[3-(trimethoxysilyl)propyl]ethylenediamine (PEDA) and ethylenediamine (EDA) as coupling agents. The physiochemical properties of the mesoporous and copper grifted silica composites were investigated by CHN elemental analysis, FTIR spectroscopy, thermogravimetric analysis, X-ray diffraction, energy dispersive X-ray spectroscopy (EDX), surface area analysis, scanning, transmission electron microscopy and gas analysis system (GSD 320, TERMO). The mesoporous silica shows highly ordered mesoporous structures, with the rod-shaped particles having a higher surface area than the spherical ones. Copper nanoparticles with an average diameter of 6.0 nm were uniformly incorporated into the MPS-S and MPS-R. Moreover, Cu-loaded mesoporous silica exhibits up to 40% higher CO₂ adsorption capacity than the bare MPS. The MPS-R modified with Cu nanoparticles showed a maximum CO₂ adsorption capacity of 0.62 mmol/g and the humidity showed a slight negative effect on CO₂ uptake process. The enhancement of CO₂ adsorption onto transition metal/mesoporous substrates provides basis for imminent CO₂ sequestration.     

Iodine(III)-mediated bicyclic diazenium salt formation

The hypervalent iodine(III) reagent PhI(OTf)₂ has been shown to be an effective oxidant for the conversion of linear aryl-hydrazones bearing a pendant alkene into bicyclic diazenium salts. This oxidative cyclization presumably occurs by the iodine(III) mediated formation of a 1-aza-2-azoniaallene salt intermediate that undergoes a subsequent intramolecular 1,3-dipolar cycloaddition with the pendant alkene.