Reducing complexity of algebraic multigrid by aggregation

A typical approach to decrease computational costs and memory requirements of classical algebraic multigrid methods is to replace a conservative coarsening algorithm and short‐distance interpolation on a fixed number of fine levels by an aggressive coarsening with a long‐distance interpolation. Although the quality of the resulting algebraic multigrid grid preconditioner often deteriorates in terms of convergence rates and iteration counts of the preconditioned iterative solver, the overall performance can improve substantially. We investigate here, as an alternative, a possibility to replace the classical aggressive coarsening by aggregation, which is motivated by the fact that the convergence of aggregation methods can be independent of the problem size provided that the number of levels is fixed. The relative simplicity of aggregation can lead to improved solution and setup costs. The numerical experiments show the relevance of the proposed combination on both academic and benchmark problems in reservoir simulation from oil industry. Copyright © 2016 John Wiley & Sons, Ltd.     

Pyrene-Based Covalent Organic Frameworks for Photocatalytic Hydrogen Peroxide Production

Four highly porous covalent organic frameworks (COFs) containing pyrene units were prepared and explored for photocatalytic H₂O₂ production. The experimental studies are complemented by density functional theory calculations, proving that the pyrene unit is more active for H₂O₂ production than the bipyridine and (diarylamino)benzene units reported previously. H₂O₂ decomposition experiments verified that the distribution of pyrene units over a large surface area of COFs plays an important role in catalytic performance. The Py-Py-COF though contains more pyrene units than other COFs which induces a high H₂O₂ decomposition due to a dense concentration of pyrene in close proximity over a limited surface area. Therefore, a two-phase reaction system (water-benzyl alcohol) was employed to inhibit H₂O₂ decomposition. This is the first report on applying pyrene-based COFs in a two-phase system for photocatalytic H₂O₂ generation.     

Visible-Light-Induced Insertion of Sulfur Dioxide Mediated by Electron Donor–Acceptor Complex: Synthesis and Photophysical Properties of 3-Sulfonyl Indolizines

This work investigates a light-driven 3-component sulfonylation reaction of indolizines without needing any external photocatalyst. The mechanistic investigations support the formation of an electron donor–acceptor (EDA) complex in situ. This transformation offers a mild and sustainable approach with high functional group tolerance for the synthesis of 3-sulfonylated indolizines. This compound class has valuable photophysical properties and represents promising candidates in various applications related to fluorescence.     

Immobilization of Iridium Triazolylidene Complexes into Polymer Scaffolds and Their Application in Water Oxidation

A triazolylidene irdium complex was postmodified with simple methods to introduce two alcohol groups in the triazolylidene backbone. The reaction of this difunctionalized iridium triazolylidene unit with terephthalic acid chloride allowed for integrating these iridium complexes into a polymeric assembly. Both the monomeric complexes as well as the polymerized systems showed activity in water oxidation driven by cerium ammonium nitrate as a chemical oxidant with comparable catalytic performance. Post-reaction analysis of the aqueous reaction solution by ICP MS showed a partial loss of iridium from the polymer into the aqueous phase under catalytic conditions, indicating a need for more robust polymer supports for this type of application.     

Transition metal-free addition of ketones or nitriles to 1,3-dienes

The simpler the better (or going green): The first examples of the catalytic addition of 1,3-dienes to simple ketones or nitriles are described. These reactions can be effected on a kilogram scale, representing the shortest access featuring a perfect atom economy to molecules of interest in the perfume industry.     

Surface immobilization of biomolecules by click sulfonamide reaction

Alkyne-modified biomolecules can be immobilized site- and chemoselectively on sulfonylazide slides under very mild conditions by means of the click sulfonamide reaction.     

Highly conductive Ni steam reforming catalysts prepared by electrodeposition

New highly conductive, active and stable Ni steam reforming catalysts were prepared through a method consisting of the calcination of a hydrotalcite-like compound electrodeposited in a single step on FeCrAlloy foams.     

Promotion of sugar-lectin recognition through the multiple sugar presentation offered by regioselectively addressable functionalized templates (RAFT): a QCM-D and SPR study

The investigation of recognition events between carbohydrates and proteins, especially the understanding of how spatial factors and binding avidity are correlated, remains a great interest for glycobiology. In this context we have investigated by nanogravimetry (QCM-D) and surface plasmon resonance (SPR), the kinetics and thermodynamics of the interaction between concanavalin A (Con A) and various neoglycopeptide ligands of low molecular weight. Regioselectively addressable functionalized templates (RAFT) have been used as scaffolds for the design of multivalent neoglycopeptides bearing thiol or biotin functions for their anchoring on transducer surfaces. Although these multivalent neoglycopeptide ligands cannot span multiple binding sites within the same Con A protein, they have increased activities relative to their monovalent counterpart. Our results emphasize that the multivalent RAFT ligands function by clustering several lectins, which leads to enhanced affinities.     

Primary photoprocesses involved in the sensory protein for the photophobic response of Blepharisma japonicum

We present new femtosecond transient-absorption and picosecond fluorescence experiments performed on OBIP, the oxyblepharismin-binding protein believed to trigger the photophobic response of the ciliate Blepharisma japonicum. The formerly identified heterogeneity of the sample is confirmed and rationalized in terms of two independent populations, called rOBIP and nrOBIP. The rOBIP population undergoes a fast photocycle restoring the initial ground state in less than 500 ps. Intermolecular electron transfer followed by electron recombination is identified as the excited-state decay route. The experimental results support the coexistence of the oxyblepharismin (OxyBP) radical cation signature with a stimulated-emission signal at all times of the evolution of the transient-absorption spectra. This observation is interpreted by an equilibrium being reached between the locally excited state and a charge-transfer state on the ground of a theory developed by Mataga and co-workers to explain the fluorescence quenching of aromatic hydrogen-bonded donor-acceptor pairs in nonpolar solvents. OxyBP is supposed to bind to an as yet unknown electron acceptor by a hydrogen-bond (HB) and the coordinate along which forward and backward electron transfer proceed is assumed to be the shift of the HB proton. The observed kinetic isotope effect supports this interpretation. Protein relaxation is finally proposed to accompany the whole process and give rise to the highly multiexponential observed dynamics. As previously reported, the fast photocycle of rOBIP can be interpreted as an efficient sunscreen mechanism that protects Blepharisma japonicum from continuous irradiation. The nrOBIP population, the transient-absorption of which strongly reminds that of free OxyBP in solution, might be proposed to actually trigger the photophobic response of the organism through excited-state deprotonation of the chromophore occurring in the nanosecond regime. Additional femtosecond transient-absorption spectra of OxyBP and peri-deprotonated OxyBP are also reported and used as a comparison basis to interpret the results on OBIP.     

Solid-phase synthesis of 4-methylcarboxy-1,4-benzodiazepine-2,5-diones

A solid-phase synthesis of 1,4-benzodiazepinone-2,5-diones is described. This new route can afford benzodiazepinone bearing a N-urethane-protected amine and a carboxylic acid function. This kind of building block is valuable as a dipeptide mimic or beta-turn mimetic, and it can be introduced in place of any amino acid in peptide synthesis. Using an "analytical probe" strategy, we optimized the synthesis of a model compound on SynPhase Lanterns. Therefore, the efficiency of several linkers was investigated.