Effects of non-uniform heating on a variable viscosity Rayleigh�CB��nard problem

This study presents a natural convection problem with a temperature-dependent viscosity fluid, driven by buoyancy and influenced by horizontal temperature gradients. A numerical linear stability analysis of the stationary solutions is studied. The horizontal temperature gradients tend to localize motion near the warmer zones and favour pattern formation in the direction perpendicular to the gradient. In fact, the problem is almost 2D in the uniform heating case, but becomes totally 3D in the non-uniform heating case.     

The reaction of o-alkynylarene and heteroarene carboxaldehyde derivatives with iodonium ions and nucleophiles: a versatile and regioselective synthesis of 1H-isochromene, naphthalene, indole, benzofuran, and benzothiophene compounds

The reaction of o-alkynylbenzaldehydes 1 with different alcohols, silylated nucleophiles 5, electron-rich arenes 10, and heteroarenes 12 in the presence of the reagent IPy(2)BF(4), at room temperature, gave functionalized 4-iodo-1H-isochromenes 2, 6, 11, and 13 in a regioselective manner. When alkynes 16 and alkenes 19 and 20 were used as nucleophiles, a regioselective benzannulation reaction took place to form 1-iodonaphthalenes 17 and 1-naphthyl ketones 18, respectively. Moreover, the latter process has been adapted to accomplish the synthesis of indole, benzofuran, and benzothiophene derivatives (23, 27, and 28, respectively). The three patterns of reactivity observed for the o-alkynylbenzaldehyde derivatives with IPy(2)BF(4) stem from a common iodinated isobenzopyrylium ion intermediate, A, that evolves in a different way depending on the nucleophile present in the reaction medium. A mechanism is proposed and the different reaction pathways observed as a function of the type of nucleophile are discussed. Furthermore, the reaction of the o-hexynylbenzaldehyde 1 b with styrene was monitored by NMR spectroscopy. Compound III, a resting state for the common intermediate in the absence of acid, has been isolated. Its evolution in acid media has been also tested, thereby providing support to the proposed mechanism.     

The reverse self-dual serial cost-sharing rule

In this study we define a cost-sharing rule for cost-sharing problems. This rule is related to the serial cost-sharing rule defined by Moulin and Shenker (Econometrica 60:1009–1037, 1992). We give some formulas and axiomatic characterizations for the new rule. The axiomatic characterizations are related to some previous ones provided by Moulin and Shenker (J. Econ. Theory 64:178–201, 1994) and Albizuri (Theory Decis. 69:555–567, 2010).     

NMR assignment in regioisomeric hydroquinones

A set of regioisomeric pairs of tricyclic hydroquinones, analogues of antitumor 9,10-dihydroxy-4,4-dimethyl-5,8-dihydroanthracen-1(4H)-one (1) and other derivatives, were synthesized and their regiochemistry and NMR spectra assigned by using (1)H-detected one-bond (C-H) HMQC and long-range C-H HMBC, in good agreement with theoretical O3LYP/Alhrichs-pVTZ calculations. The 5-hydroxymethyl derivatives (11, 15, 19) showed a (3)J(H, H) coupling constant of methylene protons evidencing the presence of a seven-membered intramolecular hydrogen bonded ring, not observed for the 8-hydroxymethyl isomers.     

Regioselective synthesis of substituted naphthalenes: a novel de novo approach based on a metal-free protocol for stepwise cycloaddition of o-alkynylbenzaldehyde derivatives with either alkynes or alkenes

[reaction: see text]. Iodonium ions, o-alkynyl-substituted carbonyl compounds, and alkynes react to give 1-iodonaphthalene derivatives featuring interesting substitution patterns. The reaction with alkenes instead of acetylenes affords related naphthyl ketone derivatives. These two metal-free processes are conducted at room temperature and furnish products in a regioselective manner.     

Stability of fronts separating domains with different symmetries in hydrodynamical instabilities

A generalization of the Swift-Hohenberg (SH) equation is used to study several stationary patterns that appear in hydrodynamical instabilities. The corresponding amplitude equations allow one to find the stability of planforms with different symmetries. These results are compared with numerical simulations of a generalized SH equation (GSHE). The transition between different symmetries, the hysteretic effects, and the characteristics of the defects observed in experiments are well reproduced in these simulations. The existence of steady fronts between domains with different symmetries is also analyzed. Steady domain boundaries between hexagons and rolls, and between hexagons and squares are possible solutions in the amplitude equation framework and are obtained in numerical simulations for a full range of coefficients in the GSHE.     

MoBioTools: A toolkit to setup quantum mechanics/molecular mechanics calculations

We present a toolkit that allows for the preparation of QM/MM input files from a conformational ensemble of molecular geometries. The package is currently compatible with trajectory and topology files in Amber, CHARMM, GROMACS and NAMD formats, and has the possibility to generate QM/MM input files for Gaussian (09 and 16), Orca (≥4.0), NWChem and (Open)Molcas. The toolkit can be used in command line, so that no programming experience is required, although it presents some features that can also be employed as a python application programming interface. We apply the toolkit in four situations in which different electronic-structure properties of organic molecules in the presence of a solvent or a complex biological environment are computed: the reduction potential of the nucleobases in acetonitrile, an energy decomposition analysis of tyrosine interacting with water, the absorption spectrum of an azobenzene derivative integrated into a voltage-gated ion channel, and the absorption and emission spectra of the luciferine/luciferase complex. These examples show that the toolkit can be employed in a manifold of situations for both the electronic ground state and electronically excited states. It also allows for the automatic correction of the active space in the case of CASSCF calculations on an ensemble of geometries, as it is shown for the azobenzene derivative photoswitch case.     

Copper(II) tetrafluoroborate catalyzed ring-opening reaction of epoxides with alcohols at room temperature

[reaction: see text] Efficient ring opening of different epoxides by reaction with representative alcohols is presented. These processes were carried out at room temperature and rely on the usefulness of commercial copper tetrafluoroborate as catalyst.     

Development and validation of a single HPLC method for determination of α‐tocopherol in cell culture and in human or mouse biological samples

A straightforward and common analytical method for α‐tocopherol (αT) determination in various biological samples, including plasma, red blood cells (RBC), tissues and cultured cell lines, was developed and validated, using a reverse phase‐chromatographic method (RP‐HPLC). Even though many chromatographic methods for αT determination have been reported, most of them require readjustment when applied to different types of samples. Thus, an effective and simple method for αT determination in different biological matrices is still necessary, specifically for translational research. This method was applied using a C₁₈ column (250 × 4.6 mm, 5 µm particle size) under isocratic elution with MeOH:ACN:H₂O (90:9:1 v/v/v) at a flow rate of 1 mL/min and detected using photodiode array at 293 nm. Linearity (r >0.9997) was observed for standard calibration with inter‐ and intraday variation of standard <4%. Lower limits of detection and quantification for αT in this assay were 0.091 and 0.305 µg/mL respectively. Validation proved the method to be selective, linear, accurate and precise. The method was successfully applied in great variety of biological samples, that is, human and mouse plasma, RBCs, murine tissues and human/mouse/rat cultured cell lines. More importantly, a single protocol of extraction and detection can be applied, making this method very convenient for standardization of different types of samples. Copyright © 2014 John Wiley & Sons, Ltd.