A highly enantioselective catalytic intramolecular Stetter reaction

A family of chiral triazolium salts has been developed for inducing the asymmetric intramolecular Stetter reaction. The use of an aminoindanol-derived catalyst affords optimal results, with the product keto esters formed in 82-97% ee and very good chemical yield. Aromatic and aliphatic aldehydes are equally competent substrates for this reaction. The reaction conditions are reasonably mild and allow the isolation of the newly formed stereocenter without epimerization, although the presumed carbenic intermediates are strong bases.     

Mixed Norm Inequalities for Directional Operators Associated to Potentials

We study mixed norm inequalities for directional operators which appear applying the method of rotations to homogeneous operators with variable kernel and with the homogeneity of Riesz potentials. The results are sharp for a range of values of the parameter and for all its values when the inequalities are restricted to radial functions.     

Novel Cobalt (II) Phthalocyanine‐Containing Polyimides: Synthesis,Characterization, Thermal and Optical Properties

Summary: A novel class of polymer has been prepared by reaction of a copolyimide containing carboxylic acid groups, and a cobalt phthalocyanine peripherally substituted with a reactive hydroxyl group. The incorporation of the phthalocyanine ring was achieved by esterification of the carboxylic acid groups of the polyimide with the free hydroxyl group of the phthalocyanine. In this work, a limited number of phthalocyanine rings have been introduced in order to avoid extensive modification of the copolyimide properties. The extent of modification (percentage of esterified carboxylic groups) was estimated to be about 18%. The resulting material showed good thermal stability and a high glass transition temperature (above 300 °C). The incorporation of the bulky phthalocyanine ring brought about a light decrease of thermal properties, relative to those of the initial polyimide. The presence of phthalocyanine was confirmed by the absorption band at 670 nm showing in the visible region for the modified polyimide. The novel copolyimide also exhibited a remarkable emission peak at 430 nm, when excited at 350 nm, corresponding to the emission of the cobalt phthalocyanine moiety.

Schematic representation of the PI‐CoPc molecule and the chemical structure of the repeat unit.     

Phase Diagram for a System of Polydisperse Components Consisting of the Precursor of an Epoxy/Diamine Thermoset and a Thermoplastic: Analysis Based on a Lattice Theory Model

Summary: The miscibility of a thermoplastic modifier with the precursors of an epoxy/diamine thermoset without chemical reaction was studied thermodynamically. The experimental cloud point curve showed a UCST behavior. A model based on the Flory‐Huggins lattice theory and on the Koningsveld approach was used for the thermodynamic analysis, in which the polydispersity of components was taken into account and the interaction parameter was considered depending on the temperature and composition. A phase diagram for the unreacted system was obtained. Calculations of species distributions in both separated phases were realized for different compositions of the modifier. Finally, the miscibility of our system was compared with that of the same system without diamine, obtaining a greater miscibility in the system with diamine.

Phase diagram for the system formed by the precursors of an epoxy thermoset without chemical reaction modified with different amounts of polystyrene.     

An application of some high order operator splitting methods to systems of stiff differential equations

In this work we compare operator splitting methods of high order that are applied to problems with stiff matrices. In order to efficiently solve the resultant subproblems is possible to use implicit Runge-Kutta methods. We apply an alternative extrapolation technique that works well for the tested problems. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Flow patterns and interfacial velocities near a moving contact line

Experimental data on velocity fields and flow patterns near a moving contact line is shown to be at variance with existing hydrodynamic theories. The discrepancy points to a new hydrodynamic paradox and suggests that the hydrodynamic approach may be incomplete and further parameters or forces affecting the surfaces may have to be included. A contact line is the line of intersection of three phases: (1) a solid, (2) a liquid, and (3) a fluid (liquid or gas) phase. A moving contact line develops when the contact line moves along the solid surface. A flat plate moved up and down, inside and out of a liquid pool defines a simple, reliable experimental model to characterize dynamic contact lines. Highlighted are three important conclusions from the experimental results that should be prominent in the development of new theoretical models for this flow. First, the velocity along the streamline configuring the liquid–fluid interface is remarkably constant within a distance of a couple of millimeters from the contact line. Second, the relative velocity of the liquid–fluid interface, defined as the ratio of the velocity along the interface to the velocity of the solid surface, is independent of the solid surface velocity. Third, the relative interface velocity is a function of the dynamic contact angle.     

On dimers and complexes of tetracene and the Kasha's molecular excitonic model

Aggregation processes that occur in a solution of 3.4 × 10^?5 M tetracene in decalin at 213 K and in a 1.3 × 10^?4 M solution of anthracene in methylcyclohexane at 135 K show that they are second‐order kinetic processes responsible for generating the corresponding dimeric structures of these acenes. The UV–Vis absorption spectra of these dimeric structures show the presence of isosbestic points. We also show that the rate constants of these processes appear to depend on the viscosity of the solvent employed. Excitonic interactions involved in these dimers are described in the light of Kasha's model. We also show that a solution of 6.7 × 10^?5 of tetracene in toluene at 173 K exhibits aggregation but following a first order kinetics and that the corresponding absorption spectra describing the process at 173 K show no isosbestic points. Consequently, it is concluded that in this solvent, the tetracene does not dimerize, but it forms a complex with toluene. The strong similarity between the first band of the tetracene dimer and the tetracene/toluene complex may give rise to a strong controversy over the excitonic model to be considered. Copyright © 2014 John Wiley & Sons, Ltd.