关键词： Nickel compounds  

摘要： The chiral synthons (S-)-1-phenyl-N-(pyridine-2-yl)ethylidine)ethanamine (L1), (R-)-1phenyl-N-(pyridine-2-yl)ethylidine))ethanamine (L2) (S)-1-phenyl-N-(pyridine-2-yl methylene) ethanamine (L3), and (R)-1-phenyl-N-(pyridine-2-yl methylene) ethanamine (L4) were synthesized in good yields. Treatments of L1-L4 with NiBr2(DME) and NiCl2 precursor afforded dinuclear complexes [Ni-2(L1)(4)-mu-Br-2]NiBr4 (Ni1), [Ni-2(L2)(4)-mu-Br-2]NiBr4 (Ni2), [Ni-2(L3)(4)-mu Br-2]Br-2 (Ni3), [Ni-2(L4)(4)-mu-Br-2]NiBr4 (Ni4) and [Ni(L4)(2)Cl-2] (Ni5). The identities of the compounds were established using NMR, FT-IR and EPR spectroscopy, mass spectrometry, magnetic moments, elemental analysis and single crystal X-ray crystallography. The dinuclear dibromide nickel complexes dissociate into mononuclear species in the presence of strongly coordinating solvents. Compounds Ni1-Ni5 displayed moderate catalytic activities in the asymmetric transfer hydrogenation (ATH) of ketones, but with low enantiomeric excess (ee%). Both mercury and substoichiometric poisoning tests pointed to the homogeneous nature of the active species with the partial formation of catalytically active Ni(0) nanoparticles. Low resolution mass spectrometry analyses of the intermediates supported a dihydride mechanistic pathway for the transfer of hydrogenation reactions.

关键词： siRNA   Lipidoids   Lipid-polymer hybrid nanoparticles (LPNs)   Release   Pulmonary administration   Imaging   Nanomedicine   Drug delivery  

摘要： Understanding the release kinetics of siRNA from nanocarriers, their cellular uptake, their in vivo biodistribution and pharmacokinetics is a fundamental prerequisite for efficient optimisation of the design of nanocarriers for siRNA-based therapeutics. Thus, we investigated the influence of composition on the siRNA release from lipid-polymer hybrid nanoparticles (LPNs) consisting of cationic lipidoid 5 (L-5) and poly(DL-lactic-co-glycolic acid) (PLGA) intended for pulmonary administration. An array of siRNA-loaded LPNs was prepared by systematic variation of:(i) the L-5 content (10-20%, w/w), and (ii) the L-5:siRNA ratio (10,1-30:1, w/w). For comparative purposes, L-5-based lipoplexes, L-5-based stable nucleic acid lipid nanoparticles (SNALPs). and dioleoyl-trimethylammoniumpropane (DOTAP)-modified LPNs loaded with siRNA were also prepared. Release studies in buffer and lung surfactant-containing medium showed that siRNA release is dependent on the presence of both surfactant and heparin (a displacing agent) in the release medium, since these interact with the lipid shell structure thereby facilitating decomplexation of L-5 and siRNA, as evident from the retarded siRNA release when the L-5 content and the L-5:siRNA ratio were increased. This confirms the hypothesis that siRNA loaded in LPNs is predominantly present as complexes with the cationic lipid and primarily is located near the particle surface. Cellular uptake and tolerability studies in the human macrophage cell line THP-1 and the type I-like human alveolar epithelial cell line hAELVi, which together represents a monolayer-based barrier model of lung epithelium, indicated that uptake of LPNs was much higher in THP-1 cells in agreement with their primary clearance role. In vivo biodistributions of formulations loaded with Alexa Fluor (R) 750-labelled siRNA after pulmonary administration in mice were compared by using quantitative fluorescence imaging tomography. The L-5-modified LPNs, SNALPs and DOTAP-modif

关键词： Fluoropolymer   Viton A   Molecular dynamics   Force fields   Mechanical properties  

摘要： Copolymers of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) make up the largest volume of fluoroelastomers sales. Within this family, Viton A (VDF/HFP 60/40 wt%, 66% fluorine) is most important commercially. Determination of thermomechanical properties of such fluorinated polymers is still limited to experimentation or empirical models, while computational prediction of their physical properties is still at its infancy. Considerable efforts have been made to develop molecular force fields for the prediction of properties of various crystalline as well as amorphous fluorinated substances. These force fields were parametrized based on small molecules or oligomers, hence their transferability to longer and more complex (i.e. copolymer) chain architectures must be tested. In this work, thermodynamic, structural, and mechanical properties of the Viton A fluoroelastomer are evaluated using atomistic molecular dynamics (MD) simulations for several force fields and compared with available experimental data. Differences in molecular structure of the chains modeled by different force fields are shown to substantially influence thermodynamic and mechanical behavior. OPLS-derived force fields give rise to extended chains that are more mobile and result in softer material that lack in molecular structure. Other force fields rely on strong nonbonded interactions that interfere with chain dynamics and mechanics. PCFF is shown to most satisfactorily predict structural properties and thermal volumetric behavior around T-g, demonstrating relatively successful transferability to long linear polymer chains. (C) 2019 Elsevier Ltd. All rights reserved.

关键词： Numerical geodynamic modeling   Compressible formulation   Finite element method   Large-strain deformation   Visco-elastic rheology  

摘要： We present LaCoDe (Lagrangian Compressible Deformation), a MATLAB solver for the Stokes equations for compressible non-Newtonian visco-elastic flow in two dimensions, based on a Lagrangian formulation of the Finite Element Method. The incompressible Boussinesq approximation is a widespread assumption in numerical models of lithospheric deformation, thus potentially masking a significant contribution of mechanisms linked to volumetric changes that occur in the asthenospheric mantle and the lithosphere. LaCoDe employs a compressible formulation of the Stokes equations designed to address such volume-changing processes. First, we provide a description of the equations governing the deformation of Earth rocks and detailed overview of the algorithm, its numerical implementation, treatment of the non-linearities rising from the compressible formulation and ineleastic deformation, and the remeshing algorithm that tracks and transfers the physical fields from a highly-distorted mesh to a high-quality one. LaCoDe is then benchmarked by comparing numerical results to analytical solutions for the bending of a thin elastic beam under a constant uniform load, flow around a rigid inclusion, Rayleigh-Taylor instability, stress build-up in a visco-elastic Maxwell body, and Couette flow with viscous heating. The Rayleigh-Taylor instability test is further used to demonstrate the accuracy of the remeshing algorithm. The importance of including volumetric strain for geodynamic processes is illustrated by two numerical experiments: i) volumetric-strain inducing phase changes in amagmatic slow-spreading ridges, and ii) subducting slabs.

关键词： Chemical reactions   Energy   Chemical calculations   Computational chemistry   Polymers  

摘要： In the past decade, ring polymer molecular dynamics (RPMD) has emerged as a very efficient method to determine thermal rate coefficients for a great variety of chemical reactions. This work presents the application of this methodology to study the O(P-3) + HCl reaction, which constitutes a stringent test for any dynamical calculation due to rich resonant structure and other dynamical features. The rate coefficients, calculated on the (3)A' and (3)A '' potential energy surfaces (PESs) by Ramachandran and Peterson [J. Chem. Phys. 2003, 119, 9590], using RPMD and quasiclassical trajectories (QCT) are compared with the existing experimental and the quantum mechanical (QM) results by Xie et al. [J. Chem. Phys. 2005 122, 014301]. The agreement is very good at T > 600 K, although RPMD underestimates rate coefficients by a factor between 4 and 2 in the 200-500 K interval. The origin of these discrepancies lies in the large contribution from tunneling on the (3)A '' PES, which is enhanced by resonances due to quasibound states in the van der Waals wells. Although tunneling is fairly well accounted for by RPMD even below the crossover temperature, the effect of resonances, a long-time effect, is not included in the methodology. At the highest temperatures studied in this work, 2000-3300 K, the RPMD rate coefficients are somewhat larger than the QM ones, but this is shown to be due to limitations in the QM calculations and the RPMD are believed to be more reliable.

关键词： Supercritical   Argon   Nitrogen   Neutron scattering   Molecular dynamics   Ar-N-2   Supercritical mixture  

摘要： The microscopic structure of Ar-N-2 supercritical mixtures was obtained using neutron scattering experiments at temperatures between 128.4 and 154.1 K, pressures between 48.7 and 97.8 bar and various mole fractions. Molecular Dynamics simulations (MD) were used to study the thermodynamics, microscopic structure and single molecule dynamics at the same conditions. The agreement between experimental and theoretical results on the intermolecular structure was very good. Furthermore, a new explicitly-correlated coupled cluster potential energy surface was obtained for the Ar-N-2 van der Waals complex. The ab initio potential energy surface (PES) was found to be in agreement with the MD interaction potential. The global minimum of the ab initio PES D-e = 98.66 cm(-1) was located at the T-shaped geometry and at the intermolecular equilibrium distance of R-e = 7.00a(0). The dissociation energy of the complex was determined to be D-0 = 76.86 cm(-1). Quantum mechanical (QM) calculations on the newly obtained PES were used to provide the bound levels of the complex. Finally, integral and differential QM cross sections in Ar + N-2 collisions were calculated at collision energy corresponding to the average temperature of the experiments and at room temperature. (C) 2019 Elsevier B.V. All rights reserved.

关键词： In-operando   Lithium polysulfide catholyte   In-situ stress measurement   Lithium sulfur battery  

摘要： Enhancing the electrochemical performance of lithium-sulfur batteries requires improved fundamental understanding of the reduction and oxidation of the soluble lithium polysulfide species. To this end, we have designed a 'donut-shaped' cell to enable direct optical observation of phase transformations of a liquid polysulfide catholyte to solid lithium sulfide during electrochemical cycling. We use this technique to image the spatio-temporal distribution of the solid lithium sulfide as it deposits on a carbon matrix at different charging rates. These experiments indicate that the reduction and oxidation of polysulfide catholyte occurs as a thin film deposition and growth process during both lithiation and delithiation. We then investigate the ramifications of these morpological changes in terms of mechanical stability by measuring the evolution of stress during discharge of the polysulfide catholyte. The stress measurements indicate that the average stress during discharging decreases with increasing the charging rate, which we attribute to less dense deposition of lithium sulfide at high discharge rates.

关键词： Thickness   Polymer films   Thin films   Organic compounds   Polymers  

摘要： Understanding the mechanical properties of nanoconfined polymers is essential in the design of nanostructured soft materials. Here, we investigate the mechanical properties of free-standing polymer thin films by employing an atomistically based coarse-grained (CG) modeling approach. By examining three representative CG polymer models, i.e., polystyrene (PS), poly(methyl methacrylate) (PMMA), and poly(1-ethylcyclopentyl methacrylate) (PECPMA), our results show that the elastic moduli of nanoscale thin films are substantially reduced with decreasing film thickness compared to their bulk values at their glassy state. Specifically, the PS and PMMA films exhibit similar size-dependent elastic responses, and their film moduli are reduced compared to bulk values at a thickness of < 40 nm, which agrees well with previous experimental measurements. However, in a model methacrylate-based polymer useful in photolithography, PECPMA, the length scale where elastic modulus deviates from the bulk value is much larger (i.e., around 80 nm). The local molecular stiffness within the films assessed by the Debye-Waller factor further reveals a softer interfacial layer having a size of only a few nanometers. Based on our simulations, a bilayer composite model is employed to predict the elastic moduli of free-standing thin films, which uncovers the size scaling relationship that universally holds for all three polymers.

关键词： C-H activation   density functional calculations   iron   Mossbauer spectroscopy   reaction mechanisms  

摘要： An iron-catalyzed C-H/N-H alkyne annulation was realized by using a customizable clickable triazole amide under exceedingly mild reaction conditions. A unifying mechanistic approach combining experiment, spectroscopy, kinetics, and computation provided strong support for facile C-H activation by a ligand-to-ligand hydrogen transfer (LLHT) mechanism. Combined Mossbauer spectroscopic analysis and DFT calculations were indicative of high-spin iron(II) species as the key intermediates in the C-H activation manifold.