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991.
992.
993.
Oscar M. Coronado Dhruv Arora Marek Behr Matteo Pasquali 《ournal of non Newtonian Fluid Mechanics》2006,140(1-3):132
A new Galerkin/Least-Squares (GLS) stabilized finite element method is presented for computing viscoelastic flows of complex fluids described by the conformation tensor; it extends the well-established GLS method for computing flows of incompressible Newtonian fluids. GLS methods are attractive for large-scale computations because they yield linear systems that can be solved easily with iterative solvers (e.g., the Generalized Minimum Residual method) and because they allow simple combinations of interpolation functions that can be conveniently and efficiently implemented on modern distributed-memory cache-based clusters.Like other state-of-the-art methods for computing viscoelastic flows (e.g., DEVSS-TG/SUPG), the new GLS method introduces a separate variable to represent the velocity gradient; with the aid of this variable, the conservation equations of mass, momentum, conformation, and the definition of velocity gradient are converted into a set of first-order partial differential equations in four unknown fields—pressure, velocity, conformation, and velocity gradient. The unknown fields are represented by low-order (continuous piecewise linear or bilinear) finite element basis functions.The method is applied to the Oldroyd-B constitutive equation and is tested in two benchmark problems—flow in a planar channel and flow past a cylinder in a channel. Results show that (1) the mesh-convergence rate of GLS is comparable to the DEVSS-TG/SUPG method; (2) the LS stabilization permits using equal-order basis functions for all fields; (3) GLS handles effectively the advective terms in the evolution equation of the conformation tensor; and (4) GLS yields accurate results at lower computational costs than DEVSS-type methods. 相似文献
994.
Prof. Dr. Holger Braunschweig Dr. K. Geetharani Dr. J. Oscar C. Jimenez‐Halla Marius Schäfer 《Angewandte Chemie (International ed. in English)》2014,53(13):3500-3504
A new catalytic synthetic route to functionalized 1,2‐azaborinines has been developed by the [2+2]/[2+4] cycloaddition reactions of di‐tert‐butyliminoboranes and alkynes in presence of a rhodium catalyst. The first examples of ferrocene‐functionalized azaborinines have been synthesized using this strategy. Moreover, the regioselectivity of this reaction can be controlled by the formation of an intermediate rhodium 1,2‐azaborete complex, which results in the isolation of the first azaborinine boronic ester. The isolation of an NH‐containing BN isostere by elimination of isobutene from an N(tBu) group under thermolytic conditions has also been achieved. Theoretical studies give further insight into the formation of 1,2‐azaborinines and the elimination of isobutene from the N(tBu) group. 相似文献
995.
Combined Heterogeneous Metal/Chiral Amine: Multiple Relay Catalysis for Versatile Eco‐Friendly Synthesis 下载免费PDF全文
Dr. Luca Deiana Dr. Yan Jiang Dr. Carlos Palo‐Nieto Samson Afewerki Celia A. Incerti‐Pradillos Dr. Oscar Verho Dr. Cheuk‐Wai Tai Dr. Eric V. Johnston Prof. Armando Córdova 《Angewandte Chemie (International ed. in English)》2014,53(13):3447-3451
Herein is described a versatile and broad synergistic strategy for expansion of chemical space and the synthesis of valuable molecules (e.g. carbocycles and heterocycles), with up to three quaternary stereocenters, in a highly enantioselective fashion from simple alcohols (31 examples, 95:5 to >99.5:0.5 e.r.) using integrated heterogeneous metal/chiral amine multiple relay catalysis and air/O2 as the terminal oxidant. A novel highly 1,4‐selective heterogeneous metal/amine co‐catalyzed hydrogenation of enals was also added to the relay catalysis sequences. 相似文献
996.
Gas‐Phase Structure Determination of Dihydroxycarbene,One of the Smallest Stable Singlet Carbenes 下载免费PDF全文
Dr. Caroline C. Womack Dr. Kyle N. Crabtree Laura McCaslin Dr. Oscar Martinez Jr. Prof. Robert W. Field Prof. John F. Stanton Dr. Michael C. McCarthy 《Angewandte Chemie (International ed. in English)》2014,53(16):4089-4092
Carbenes are reactive molecules of the form R1? C?? R2 that play a role in topics ranging from organic synthesis to gas‐phase oxidation chemistry. We report the first experimental structure determination of dihydroxycarbene (HO? C?? OH), one of the smallest stable singlet carbenes, using a combination of microwave rotational spectroscopy and high‐level coupled‐cluster calculations. The semi‐experimental equilibrium structure derived from five isotopic variants of HO? C?? OH contains two very short CO single bonds (ca. 1.32 Å). Detection of HO? C?? OH in the gas phase firmly establishes that it is stable to isomerization, yet it has been underrepresented in discussions of the CH2O2 chemical system and its atmospherically relevant isomers: formic acid and the Criegee intermediate CH2OO. 相似文献
997.
Frontispiece: Platinum Complexes Containing Pyramidalized Germanium and Tin Dihalide Ligands Bound through σ,σ ME Multiple Bonds 下载免费PDF全文
998.
Assembly of Palladium(II) and Platinum(II) Metallo‐Rectangles with a Guanosine‐Substituted Terpyridine and Study of Their Interactions with Quadruplex DNA 下载免费PDF全文
Dr. Sushobhan Ghosh Dr. Oscar Mendoza Dr. Leticia Cubo Dr. Frédéric Rosu Dr. Valérie Gabelica Dr. Andrew J. P. White Prof. Dr. Ramon Vilar 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(16):4772-4779
Two novel [2+2] metallo‐assemblies based on a guanosine‐substituted terpyridine ligand ( 1 ) coordinated to palladium(II) ( 2 a ) and platinum(II) ( 2 b ) are reported. These supramolecular assemblies have been fully characterized by NMR spectroscopy, ESI mass spectrometry and elemental analyses. The palladium(II) complex ( 2 a ) has also been characterized by single crystal X‐ray diffraction studies confirming that the system is a [2+2] metallo‐rectangle in the solid state. The stabilities of these [2+2] assemblies in solution have been confirmed by DOSY studies as well as by variable temperature 1H NMR spectroscopy. The ability of these dinuclear complexes to interact with quadruplex and duplex DNA was investigated by fluorescent intercalator displacement (FID) assays, fluorescence resonance energy transfer (FRET) melting studies, and electrospray mass spectrometry (ESI‐MS). These studies have shown that both these assemblies interact selectively with quadruplex DNA (human telomeric DNA and the G‐rich promoter region of c‐myc oncogene) over duplex DNA, and are able to induce dimerization of parallel G‐quadruplex structures. 相似文献
999.
Systematic Dissection of an Aminopyrrolic Cage Receptor for β‐Glucopyranosides Reveals the Essentials for Effective Recognition 下载免费PDF全文
Dr. Oscar Francesconi Matteo Gentili Prof. Cristina Nativi Dr. Ana Ardá Prof. F. Javier Cañada Prof. Jesús Jiménez‐Barbero Dr. Stefano Roelens 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(20):6081-6091
A set of structures designed for the recognition of glucosides has been obtained by systematically destructuring a tripodal aminopyrrolic cage receptor that selectively recognizes octyl‐β‐D ‐glucopyranoside (OctβGlc). NMR spectroscopy and isothermal titration calorimetry binding measurements showed that cleavage of one pillar of the cage was beneficial to the binding properties of the receptor, as long as two residual amino groups of the cleaved pillar were present. Removal of these two residual amino groups produced a dramatic loss of affinity for OctβGlc of the resulting monocyclic analogue of the parent cage receptor. A significant improvement in the binding ability was achieved by replacing one pillar with two aminopyrrolic hydrogen‐bonding arms, despite the loss of a preorganized structure. In contrast to the cage receptor, recognition of OctβGlc was observed, even in a competitive medium (30 % DMF in chloroform). Structural studies in solution, carried out through NMR spectroscopy and molecular modeling calculations, led to the elucidation of the 3D binding modes of the side‐armed monocyclic receptors; this highlighted the key role of the amino groups and demonstrated the occurrence of a rotaxane‐like complex, which featured the octyl chain of the glucoside threaded through the macrocyclic ring. 相似文献
1000.
Mass spectrometric characterisation of a condensation product between porphobilinogen and indolyl‐3‐acryloylglycine in urine of patients with acute intermittent porphyria 下载免费PDF全文
Josep Marcos Maria Ibañez Rosa Ventura Jordi Segura Jordi To‐Figueras Oscar J. Pozo 《Journal of mass spectrometry : JMS》2015,50(7):929-937
We document the presence of a previously unknown species in the urine of patients with acute intermittent porphyria (AIP). The compound was fully characterised by liquid chromatography tandem mass spectrometry. Interpretation of both full spectrum acquisition and product ion spectra acquired in positive and negative ionisation modes by quadrupole time of flight MS allowed for the identification of a condensation product arising from porphobilinogen (PBG, increased in the urine of AIP patients) and indolyl‐3‐acryloylglycine (IAG, derived from indolylacrylic acid and present in human urine). The structure was unequivocally confirmed through comparison between the selected reaction monitoring chromatograms obtained from the urinary species and the condensation product qualitatively synthesised in the laboratory. Owing to the large amounts of both PBG and IAG in urine of AIP patients, the possible ex vivo formation of PBG‐IAG in urine samples was evaluated. The product was spontaneously formed at room temperature, at 4 °C and even during storage at ?20 °C when spiking a control sample with PBG. A positive correlation was found between PBG and PBG‐IAG in samples collected from AIP patients. However, no correlation was found between PBG‐IAG and IAG. Purified PBG‐IAG did not form the characteristic chromogen after application of p‐dimethylaminobenzaldehyde in HCl, thus suggesting that the current techniques used to measure PBG in urine of AIP patients based on Ehlrich's reaction do not detect this newly characterised PBG‐IAG fraction. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献