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311.
Analytical solutions for diffuse interface propagation are found for two recently developed Landau potentials that account for the phenomenology of stress-induced martensitic phase transformations. The solutions include the interface profile and velocity as a function of temperature and stress tensor. An instability in the interface propagation near lattice instability conditions is studied numerically. The effect of material inertia is approximately included. Two methods for introducing an athermal interface friction in phase field models are discussed. In the first method an analytic expression defines the location of the diffuse interface, and the rate of change of the order parameters is required to vanish if the driving force is below a threshold. As an alternative and more physical approach, we demonstrate that the introduction of spatially oscillatory stress fields due to crystal defects and the Peierls barrier, or to a jump in chemical energy, reproduces the effect of an athermal threshold. Finite element simulations of microstructure evolution with and without an athermal threshold are performed. In the presence of spatially oscillatory fields the evolution self-arrests in realistic stationary microstructures, thus the system does not converge to an unphysical single-phase final state, and rate-independent temperature- and stress-induced phase transformation hysteresis are exhibited. 相似文献
312.
Joseph P. Tassone Emma V. England Preston M. MacQueen Michael J. Ferguson Mark Stradiotto 《Angewandte Chemie (International ed. in English)》2019,58(8):2485-2489
The base metal‐catalyzed C?N cross‐coupling of bulky α,α,α‐trisubstituted primary alkylamines with (hetero)aryl electrophiles represents a challenging and under‐developed class of transformations that is of significant potential utility, including in the synthesis of lipophilic active pharmaceutical ingredients. Herein, we report that a new, air‐stable Ni(II) pre‐catalyst incorporating the optimized ancillary ligand PhPAd‐DalPhos enables such transformations of (hetero)aryl chloride, bromide, and tosylate electrophiles to be carried out for the first time with substrate scope rivalling that achieved using state‐of‐the‐art Pd catalysts, including room temperature cross‐couplings of (hetero)aryl chlorides that are unprecedented for any catalyst (Pd, Ni, or other). 相似文献
313.
Molecular recognition continues to be an area of keen interest for supramolecular chemists. The investigated [M( L )2]2+ metallo‐ligands (M=PdII, PtII, L =2‐(1‐(pyridine‐4‐methyl)‐1 H‐1,2,3‐triazol‐4‐yl)pyridine) form a planar cationic panel with vacant pyridyl binding sites. They interact with planar neutral aromatic guests through π–π and/or metallophilic interactions. In some cases, the metallo‐ligands also interacted in the solid state with AgI either through coordination to the pendant pyridyl arms, or through metal–metal interactions, forming coordination polymers. We have therefore developed a system that reliably recognises a planar electron‐rich guest in solution and in the solid state, and shows the potential to link the resultant host–guest adducts into extended solid‐state structures. The facile synthesis and ready functionalisation of 2‐pyridyl‐1,2,3‐triazole ligands through copper(I)‐catalyzed azide–alkyne cycloaddition (CuAAC) “click” chemistry should allow for ready tuning of the electronic properties of adducts formed from these systems. 相似文献
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315.
Dr. Dan Preston Prof. Paul E. Kruger 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(7):1781-1786
Structural changes to metallosupramolecular assemblies resulting in the release or uptake of guests are currently well established, whereas transformations turning on and off specific self-recognition are far less developed. We report a novel ligand (2,6-bis(1-(3-pyridin-4-yl)phenyl-1H-1,2,3-triazol-4-yl)pyridine) possessing a tridentate central metal-binding site flanked by two pendant pyridyl arms. In a 2:1 ratio with PdII metal ions, a spiro-type [PdL2]2+ “Figure-of-eight” complex forms with the central tridentate binding pocket unoccupied. The introduction of an additional one equivalent of PdII metal ion results in the conversion to a dimeric [Pd2L2]4+ molecule with the tridentate pocket occupied. There is site-specific self-recognition between dimers in solution with strong NOE peaks between adjacent molecules. The self-recognition between dimers can be turned off in two ways: firstly, adding another equivalent of PdII metal ion brings about binding to the previously uncoordinated pyridyl arms that are key to the self-recognition event, and; secondly, addition of sufficient ligand to return the stoichiometry to 2:1 regenerates the [PdL2]2+ complex. Hence, the self-recognition event can be turned on or off through simple variation of L:PdII stoichiometry. 相似文献
316.
Sensitive methods to measure protein synthetic rate in vivo are required to assess changes in protein expression, especially when comparing healthy with infirm subjects. We have previously applied a ‘flooding dose’ procedure using 2H5‐phenylalanine (2H5‐phe) and 2H8‐phe isotopomers as tracers, which has proven successful in measuring albumin and fibrinogen synthesis in response to feeding in cancer patients. Using tert‐butyldimethylsilyl derivatives, we have observed that 2H7‐phe is formed with time in vivo from 2H8‐phe, probably during transamination. This increases errors when estimating the fractional synthetic rate (FSR) using the 2H8‐phe isotopomer compared with the 2H5‐phe isotopomer. We sought to improve this situation by use of an alternative derivative that overcomes this problem whilst also streamlining sample preparation. When using N‐ethoxycarbonyltrifluoroethyl (ECTFE) amino acid esters, 2H8‐phe is effectively converted into 2H7‐phe through fragmentation under electron ionisation (EI), allowing both 2H8‐phe and 2H7‐phe isotopomers to be measured as a single intense CH fragment at 98 Th. To illustrate the improved situation, the mean RMS residual was calculated for all albumin data, for each isotopomer and for each derivative. Albumin‐bound Phe was analysed as ECTFE‐phe with improved precision, independent of the isotopomer used, confirming that the new derivative is superior. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
317.
D. Keogh Z. Chen R. A. Hughes A. Dabkowski O. Marinov C. Maunders L. Gunawan M. J. Deen J. S. Preston G. A. Botton 《Applied Physics A: Materials Science & Processing》2010,98(1):187-194
The (100) surface of MgAl2O4 is evaluated as a substrate for the thin film deposition of the relaxor ferroelectric PbMg1/3Nb2/3O3(65%)–PbTiO3(35%). With a lattice mismatch of less than 0.5%, this film-substrate combination presents a geometrical template for growth
that is far superior to that formed with other commercially available oxide substrates. Films were deposited using the pulsed
laser deposition technique and were characterized in terms of their crystallographic, microstructural, and dielectric properties.
From a crystallographic perspective the films show excellent cube-on-cube epitaxy, are highly oriented, and show no evidence
of the frequently observed parasitic pyrochlore phase. With the exception of a few faceted surface structures, the film’s
microstructure is single-crystal-like, exhibiting a sharp film-substrate interface, a smooth top surface, and no discernable
granularity. The dielectric response shows the frequency-dependent diffuse phase transition characteristic of a relaxor material,
but with less frequency dispersion and a smaller maximum in the dielectric constant. Taken together, the results suggest that
the (100) MgAl2O4 substrate could prove to be an effective substrate material, not only for the PbMg1/3Nb2/3O3(65%)–PbTiO3(35%) system, but also for a number of other important lattice-matched ferroelectric, relaxor, and ferroelectric superlattice
systems. 相似文献
318.
Simerjeet K. Gill Preston Brown Louisa J. Hope-Weeks 《Journal of Sol-Gel Science and Technology》2011,57(1):68-75
Monolithic aerogels composed of cadmium sulfide nanoparticles partially modified with metallic gold (CdS-Au) are reported.
The semiconductor–metal nanoparticles are synthesized using an inverse micelle media of Bis-(2-ethylhexyl)sulfosuccinate sodium
salt (AOT) in heptane, followed by capping with 4-fluorothiophenol and precipitation with triethylamine. The nanoparticles
are then dispersed in acetone and gel formation is achieved using nanoparticle condensation strategy. The resultant CdS-Au
aerogel materials are mesoporous, with an interconnected network of semiconductor–metal nanoparticles. A detailed microstructure
analysis of the semiconductor–metal aerogels via transmission electron microscopy indicates that the final gold concentration
significantly impacts the semiconductor–metal aerogel morphology and porosity. 相似文献
319.
320.