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1.
Foundations of Computational Mathematics - We present a finite element variational integrator for compressible flows. The numerical scheme is derived by discretizing, in a structure-preserving way,... 相似文献
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Gregory S. Constable Alan J. Lesser E. Bryan Coughlin 《Journal of Polymer Science.Polymer Physics》2003,41(12):1323-1333
An in situ ultrasonic spectroscopy technique was used to study the ring‐opening metathesis polymerization of dicyclopentadiene catalyzed by bis(tricyclohexylphosphine)benzylidene ruthenium dichloride. A reaction cell employing a flexible poly(ethylene terephthalate) window for pulse echo ultrasonic spectroscopy was used to monitor the polymerization. The changes in the density, wave speed, acoustic modulus, and attenuation were all simultaneously monitored. In comparison with Fourier transform infrared (FTIR) spectroscopy data, the changes in the density, velocity, and modulus only accurately measured the rate constant for the metathesis of the cyclopentyl unsaturation. The ultrasonic values were within 6% of the values determined by FTIR. The activation energy for metathesis of the cyclopentyl unsaturation was 84 kJ mol?1, following first‐order kinetics. Rate constants for the polymerization of the norbornyl unsaturation could not be determined by ultrasound. The gel point, vitrification, and qualitative information about the reaction rate could be determined from the change in the attenuation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1323–1333, 2003 相似文献
5.
Henry DJ Yiapanis G Evans E Yarovsky I 《The journal of physical chemistry. B》2005,109(36):17224-17231
This study examines the adhesion of graphite to functionalized polyester surfaces using a range of qualitative and quantitative measures of theoretical adhesion. Modifications to the polyester surfaces include the addition of hydroxyl, carboxyl, or fluorine substituents with coverages of 0.4 and 0.9 groups per nm(2). In each case, the introduction of substituents to the surface of the polyester was calculated to lead to reduced adhesion to graphite. Effects of surface relaxation on adhesion are studied by employing different simulation protocols. The theoretical results suggest one mechanism to reduce adhesion to carbonaceous solids is to increase atomic roughness using strongly hydrophilic or alternatively strongly hydrophobic substituents. 相似文献
6.
Fabien Fontaine Evan Bolton Yulia Borodina Stephen H Bryant 《Chemistry Central journal》2007,1(1):12-14
Background
Large chemical databases require fast, efficient, and simple ways of looking for similar structures. Although such tasks are now fairly well resolved for graph-based similarity queries, they remain an issue for 3D approaches, particularly for those based on 3D shape overlays. Inspired by a recent technique developed to compare molecular shapes, we designed a hybrid methodology, alignment-recycling, that enables efficient retrieval and alignment of structures with similar 3D shapes. 相似文献7.
Mingjian Wen Samuel M. Blau Evan Walter Clark Spotte-Smith Shyam Dwaraknath Kristin A. Persson 《Chemical science》2021,12(5):1858
A broad collection of technologies, including e.g. drug metabolism, biofuel combustion, photochemical decontamination of water, and interfacial passivation in energy production/storage systems rely on chemical processes that involve bond-breaking molecular reactions. In this context, a fundamental thermodynamic property of interest is the bond dissociation energy (BDE) which measures the strength of a chemical bond. Fast and accurate prediction of BDEs for arbitrary molecules would lay the groundwork for data-driven projections of complex reaction cascades and hence a deeper understanding of these critical chemical processes and, ultimately, how to reverse design them. In this paper, we propose a chemically inspired graph neural network machine learning model, BonDNet, for the rapid and accurate prediction of BDEs. BonDNet maps the difference between the molecular representations of the reactants and products to the reaction BDE. Because of the use of this difference representation and the introduction of global features, including molecular charge, it is the first machine learning model capable of predicting both homolytic and heterolytic BDEs for molecules of any charge. To test the model, we have constructed a dataset of both homolytic and heterolytic BDEs for neutral and charged (−1 and +1) molecules. BonDNet achieves a mean absolute error (MAE) of 0.022 eV for unseen test data, significantly below chemical accuracy (0.043 eV). Besides the ability to handle complex bond dissociation reactions that no previous model could consider, BonDNet distinguishes itself even in only predicting homolytic BDEs for neutral molecules; it achieves an MAE of 0.020 eV on the PubChem BDE dataset, a 20% improvement over the previous best performing model. We gain additional insight into the model''s predictions by analyzing the patterns in the features representing the molecules and the bond dissociation reactions, which are qualitatively consistent with chemical rules and intuition. BonDNet is just one application of our general approach to representing and learning chemical reactivity, and it could be easily extended to the prediction of other reaction properties in the future.Prediction of bond dissociation energies for charged molecules with a graph neural network enabled by global molecular features and reaction difference features between products and reactants. 相似文献
8.
Mulrooney CA Li X DiVirgilio ES Kozlowski MC 《Journal of the American Chemical Society》2003,125(23):6856-6857
By using oxygen as the terminal oxidant, copper complexes derived from chiral 1,5-diaza-cis-decalin catalyze the enantioselective oxidative biaryl coupling of highly functionalized naphthols to provide octa- and decasubstituted binaphthalenes with high selectivity (86-90% ee). Products containing very electron-rich naphthalenes were prone to epimerization under the reaction conditions. This epimerization could be suppressed by employing naphthol starting materials with phenol protecting groups that attenuated the electron-rich nature of the naphthalenes. Direct oxidation of the resultant chiral 1,1'-binaphthol framework completed the first asymmetric synthesis of a perylenequinone containing only an axial chirality element. 相似文献
9.
Constable EC Handel RW Housecroft CE Farràn Morales A Ventura B Flamigni L Barigelletti F 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(13):4024-4034
A new series of V-shaped trinuclear metallorods and X-shaped pentanuclear metallostars has been prepared by the reaction of metal complexes bearing pendant phenolic functionalities with complexes containing electrophilic ligands. Specifically, {M(tpy)2} motifs (M=Ru or Os; tpy=2,2':6',2'-terpyridine) bearing one or two pendant 3,5-dihydroxyphenyl substituents at the 4-position of the central ring of the tpy have been reacted with the complexes [Ru(tpy)(Xtpy)]2+ (X=Cl or Br) to form new ether-linked species. The energy transfer from ruthenium to osmium in these complexes has been investigated in detail and the efficiency of transfer shown to be highly temperature dependent; the energy transfer is highly efficient at low temperature, whereas at room temperature nonradiative and nontransfer deactivation of the excited {Ru(tpy)2}* domains is most significant. 相似文献
10.
Scherer LJ Merz L Constable EC Housecroft CE Neuburger M Hermann BA 《Journal of the American Chemical Society》2005,127(11):4033-4041
We describe the synthesis and a novel approach to the conformational analysis of 2,2'-bipyridines (bpy) bearing aromatic rich Frechet-type dendritic wedges of the first and second generation as substituents. The evaporation of solutions of these new ligands on graphite surfaces under ambient conditions results in the formation of self-organized monolayers. Scanning tunneling microscopy (STM) investigations of the monolayers under ambient conditions (air, 298 K) gave images at submolecular and near-atomic resolution. The analysis of the STM images includes the following processes: (i) identification and reproduction of potential homoconformational domains, (ii) exclusion of improper data using quality criteria for drift and feedback artifacts, (iii) compilation of running averages and checking for averaging artifacts, (iv) analysis of three-dimensional and contour plots, (v) calculation of the HOMO properties of the free molecules, and (vi) final conformational assignment based on all accessible information. Following this procedure, two different conformations could be assigned to domains observed in the monolayers of the first-generation (G1) and second-generation (G2) dendritic compounds. Homoconformational domains are observed side-by-side. The different conformations arise from syn or anti arrangements at the ether substituents. An additional conformational effect is found upon treating the G1 domains with HCl gas, when a partial rearrangement of the bpy from trans to cis occurs, concomitant with protonation. 相似文献