A rapid access to chiral alkylidene cyclopentenone prostaglandins involving ring-closing metathesis reaction

A synthesis of the alkylidene cyclopentenone prostaglandin TEI 9826 has been realized. The synthesis involved the preparation of the chiral 1,5-diene 8 using a stereoselective Claisen rearrangement from the allylic alcohol 6 giving the ester 7 after vinylation. Then a key RCM reaction allowed the preparation of the cyclopentenol 9 which, after oxidation, gave the cyclopentenone 10, precursor of the prostaglandin.     

On the size consistence of a few approximate multireference CI schemes

Using the canonical problem of N separate electron pairs, theN dependence of approximate multireference CI schemes is analyzed. When the DCI is taken as multireference space, the second order Quasi Degenerate Many Body Perturbation Theory (QD(MB)PT) gives twice the expected correction, while the CIPSI algorithm gives 66% of it, and the MRDCI a vanishing part of it. A modified QDPT effective hamiltonian, and a combination of CIPSI and QDPT algorithms seem to give better trends.     

Etude semiempirique de la configuration moléculaire stable des molécules ionisées ou excitées

Résumé Les déformations stabilisatrices des molécules ionisées ou excitées sont étudiées en supposant connues les coordonnées normales et les constantes de force de l'état fondamental et en calculant les variations de l'énergie d'ionisation ou d'excitation dans les déformations. On en déduit les coordonnées des minimas, les énergies de stabilisation, et les intersections des surfaces potentielles. Cette méthode est appliquée aux anions de la pyrazine calculés par les méthodes SCF et UHF dans les approximations de Pariser et Parr: les variations des longueurs de liaison sont de l'ordre de 0.15 å, celle de l'affinité électronique de 1 eV, et celle des densités de spin de 0.05 e. Ce phénomène peut jouer un rÔle dans l'eifet de charge. En méthode de Hückel des formules générales sont déduites, donnant l'énergie de stabilisation par déformation des ions et des états excités des polyènes.

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The stabilizing deformations of ionized or excited molecules are studied using experimental normal modes and force-constants, and calculating the variations of ionization or excitation energies in the deformations. We deduce new minimas, stabilizing deformations, crossing lines of potential surfaces. This method is applied to negative ions of pyrazine by SCF and UHF (Unstricted Hartree-Fock) methods in the Pariser-Parr approximations: the variations of bond lengths could reach 0.15 å, the electroaffinity could increase of 1 eV, and the spin densities change about 0.05 e. This phenomenon may play a role on the so-called charge-effect. In that scheme, general formulas giving the stabilizing deformation energies for ions and excited states of polyens are deduced from Hückel method.

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Zusammenfassung Die stabilisierenden Deformationen ionisierter oder angeregter Moleküle werden bei bekannten Normalkoordinaten und Kraftkonstanten des Grundzustandes studiert und die Änderungen der Ionisations- und Anregungsenergie bei den Deformationen berechnet. Hieraus werden die Minimumskoordinaten, Stabilisierungsenergien und Schnitte der PotentialflÄchen hergeleitet. Diese Methode wird auf die Anionen von Pyrazin mittels der SCF- und UHF-Methode im Rahmen der Pariser-Parr-NÄherung angewandt. Die Änderungen der BindungslÄngen betragen grö\enordnungsmÄ\ig 0,15 å, die der ElektronenaffinitÄten 1 eV und die der Spindichten 0,05 e. Dieses PhÄnomen spieltbeim sogenannten Ladungseffekt eine Rolle. Mit der Hückel-Methode werden allgemeine Formeln abgeleitet, die die Stabilisierungsenergie der Deformation der Ionen und angeregten ZustÄnde von Polyenen angeben.

     

Experimental study of the frequency response of electrochemical split probes to transversal velocity fluctuations

An experimental investigation of the frequency response of electrochemical probes to transversal velocity fluctuation is reported. The study has been focused on wall shear stress for a modulated flow due to an oscillating cylinder along its own axes since the wall shear stress has been first numerically determined for this flow. Results indicate that a frequency response correction to probe outputs is required and that this correction depends on the amplitude of fluctuations.List of symbols A total area of the electrode - A _i area of the part i of the electrode - a amplitude of oscillation - C concentration - c fluctuation of concentration - D cylinder diameter - D diffusion coefficient - h dimensionless velocity normal to the wall - H transfer function modulus - K _i transfer coefficient - l electrode length - n frequency - S wall shear - S fluctuation of the wall shear - U mean value of the fluid velocity far from the wall - u streamwise component of the fluid velocity - spanwise component of the fluid velocity (along the cylinder axis) - w component of the fluid velocity perpendicular to the wall - x direction of the mean flow - y direction parallel to the cylinder axis - z direction perpendicular to the wall - v kinematic viscosity - dimensionless distance perpendicular to the wall (z) - dimensionless distance (x) - phase shift - azimuthal angle - modulation frequency     

Acrylate nanolatex via self‐initiated photopolymerization

The use of UV light to initiate emulsion polymerization processes is generally overlooked, whilst extensive literature exists on photocuring of monomer films. In this study, the unique potential of UV light to produce at ambient temperature polyacrylate latexes without initiator was exploited. Although radical initiators are utilized at low concentration, their cost, toxicity, and odor provide incentives for finding alternatives. Starting with concentrated (30 wt %) and low scattering acrylate miniemulsions (droplet diameter <100 nm), it was demonstrated that acrylate self‐initiation can promote an efficient and fast photopolymerization in micrometer‐scale reactor (spectrophotometric cell) and lab‐scale photoreactor. Herein, all kinetic, colloidal, and mechanistic aspects involved in the self‐initiation of acrylate miniemulsion were extensively examined to provide a complete picture. In particular, the effects of droplet size, initiating wavelength, optical path, and irradiance on the course of the polymerization were thoroughly discussed. A diradical self‐initiation pathway is the most likely mechanism. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1843–1853     

Improvement of the recursive projection method for linear iterative scheme stabilization based on an approximate eigenvalue problem

An algorithm for stabilizing linear iterative schemes is developed in this study. The recursive projection method is applied in order to stabilize divergent numerical algorithms. A criterion for selecting the divergent subspace of the iteration matrix with an approximate eigenvalue problem is introduced. The performance of the present algorithm is investigated in terms of storage requirements and CPU costs and is compared to the original Krylov criterion. Theoretical results on the divergent subspace selection accuracy are established. The method is then applied to the resolution of the linear advection–diffusion equation and to a sensitivity analysis for a turbulent transonic flow in the context of aerodynamic shape optimization. Numerical experiments demonstrate better robustness and faster convergence properties of the stabilization algorithm with the new criterion based on the approximate eigenvalue problem. This criterion requires only slight additional operations and memory which vanish in the limit of large linear systems.     

Chemo- and Regioselective Additions of Nucleophiles to Cyclic Carbonates for the Preparation of Self-Blowing Non-Isocyanate Polyurethane Foams

Polyurethane (PU) foams are indisputably daily essential materials found in many applications, notably for comfort (for example, matrasses) or energy saving (for example, thermal insulation). Today, greener routes for their production are intensively searched for to avoid the use of toxic isocyanates. An easily scalable process for the simple construction of self-blown isocyanate-free PU foams by exploiting the organocatalyzed chemo- and regioselective additions of amines and thiols to easily accessible cyclic carbonates is described. These reactions are first validated on model compounds and rationalized by DFT calculations. Various foams are then prepared and characterized in terms of morphology and mechanical properties, and the scope of the process is illustrated by modulating the composition of the reactive formulation. With impressive diversity and accessibility of the main components of the formulations, this new robust and solvent-free process could open avenues for construction of more sustainable PU foams, and offers the first realistic alternative to the traditional isocyanate route.     

An ab initio molecular dynamics study of ionic conductivity in hexagonal lithium lanthanum titanate oxide La0.5Li0.5TiO3

To date, the fastest lithium ion-conducting solid electrolytes known are the perovskite-type ABO₃ oxide, with A = Li, La and B = Ti, lithium lanthanum titanate (LLTO) Li_3x La_{( 2 \mathord}