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991.
992.
Maxence Valla James W. Harris Rajamani Gounder William N. P. van der Graaff Evgeny A. Pidko Emiel J. M. Hensen Paola Ferrini Jan Dijkmans Bert Sels Ive Hermans Christophe Copéret 《Helvetica chimica acta》2016,99(12):916-927
In recent years, various protocols on preparing Lewis acidic Sn‐β zeolite hydrothermally and postsynthetically have been reported. However, very little is known about the effects of different synthesis protocols on the Sn(IV) speciation in the final material. Even the effects of individual synthesis parameters within a certain preparation method have not been studied systematically. Here, we demonstrate that hydrothermally synthesized Sn‐β zeolites prepared via very similar recipes show significantly different 119Sn‐NMR spectra, suggesting different Sn site speciation. Among postsynthetically prepared Sn‐β zeolites, less variation in the resulting 119Sn‐NMR spectra have been observed, indicating a more reproducible synthesis procedure compared to hydrothermal synthesis in fluoride media. This work highlights the importance of 119Sn‐NMR measurements to elucidate the precise local geometry of the Sn heteroatoms in Sn‐β, and the need to quantify the number of reactive Sn sites on each sample that participate in a given catalytic reaction, in order to accurately compare materials prepared by different routes. 相似文献
993.
Computational SN2‐Type Mechanism for the Difluoromethylation of Lithium Enolate with Fluoroform through Bimetallic C−F Bond Dual Activation
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Kazuya Honda Dr. Travis V. Harris Dr. Miho Hatanaka Prof. Dr. Keiji Morokuma Prof. Dr. Koichi Mikami 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(26):8796-8800
The reaction mechanism for difluoromethylation of lithium enolates with fluoroform was analyzed computationally (DFT calculations with the artificial force induced reaction (AFIR) method and solvation model based on density (SMD) solvation model (THF)), showing an SN2‐type carbon–carbon bond formation; the “bimetallic” lithium enolate and lithium trifluoromethyl carbenoid exert the C?F bond “dual” activation, in contrast to the monometallic butterfly‐shaped carbenoid in the Simmons–Smith reaction. Lithium enolates, generated by the reaction of 2 equiv. of lithium hexamethyldisilazide (rather than 1 or 3 equiv.) with the cheap difluoromethylating species fluoroform, are the most useful alkali metal intermediates for the synthesis of pharmaceutically important α‐difluoromethylated carbonyl products. 相似文献
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Nadiia Kovalenko Dr. Jonathan A. Swain Georgina K. Howard Yann O. Hermant Dr. Alan J. Cameron Dr. Louise A. Stubbing Prof. Paul W. R. Harris Prof. Margaret A. Brimble 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(70):e202202554
In the current global crisis of antimicrobial resistance, antimicrobial peptides represent a promising source of alternative antibiotics. Recently discovered cadaside B, a novel calcium-dependent antibiotic, exhibits potent antimicrobial activity towards Gram-positive pathogens including multi-drug resistant strains. These properties, coupled with a novel structure, non-cytotoxicity, and low likelihood of developing resistance render cadaside B an important synthetic target. Herein, a synthetic strategy towards cadaside B is reported with the key steps involving on-resin depsipeptide bond formation and solution-phase macrolactamization. Good agreement of the synthetic cadaside B MS/MS fragmentation pattern was observed with the natural product, but a different 1H NMR spectrum and absence of antimicrobial activity suggest an undetected epimerization event took place during the synthesis. Herein the findings of our synthetic journey and suggestions for future directions are presented. 相似文献
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Thomas Osborne und Isaak F. Harris 《Fresenius' Journal of Analytical Chemistry》1904,43(6-7):378-382
Ohne ZusammenfassungNach einem gefälligst zugesandten Abdruck aus dem Journal of the American Chemical Society25, No. 8, übersetzt und bearbeitet von Dr. Griessmayer. 相似文献
999.
Harris E. Mason Joshua J. Hirner Wenqian Xu John B. Parise Brian L. Phillips 《Magnetic resonance in chemistry : MRC》2009,47(12):1062-1070
Pb‐containing hydroxylapatite phases synthesized under aqueous conditions were investigated by X‐ray diffraction and solid‐state nuclear magnetic resonance (NMR) techniques to determine the Pb, Ca distribution. 31P and 1H magic‐angle spinning (MAS) NMR results indicate slight shifts of the isotropic chemical shift with increased Ca content and complex lineshapes at compositions with near equal amounts of Ca and Pb. 31P{207Pb} and 1H{207Pb} rotational‐echo double resonance (REDOR) results for intermediate compositions show that resolved spectral features cannot be assigned simply in terms of local Ca, Pb configurations or coexisting phases. 207Pb MAS NMR spectra are easily obtained for these materials and contain well‐resolved resonances for crystallographically unique A1 and A2 Pb sites. Splitting of the A1 and A2 207Pb resonances for pure hydroxyl‐pyromorphite (Pb10(PO4)6(OH)2) compared to natural pyromorphite (Pb5(PO4)3Cl) suggests symmetry reduced from hexagonal. We find that 207Pb{1H} CP/MAS NMR is impractical in Pb‐rich hydroxylapatites due to fast 207Pb relaxation. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
1000.
Rob Moss Ed Kazmierczak Michael Kirley Peter Harris 《Physica D: Nonlinear Phenomena》2009,238(22):2166-2176
The kidney is one of the major organs involved in whole-body homeostasis, and exhibits many of the properties of a complex system. The functional unit of the kidney is the nephron, a complex, segmented tube into which blood plasma is filtered and its composition adjusted. Although the behaviour of individual nephrons can fluctuate widely and even chaotically, the behaviour of the kidney remains stable.In this paper, we investigate how the filtration rate of a multi-nephron system is affected by interactions between nephrons. We introduce a discrete-time multi-nephron network model. The tubular mechanisms that have the greatest effect on filtration rate are the transport of sodium and water, consequently our model attempts to capture these mechanisms. Multi-nephron systems also incorporate two competing coupling mechanisms–vascular and hemodynamic–that enforce in-phase and anti-phase synchronisations respectively. Using a two-nephron model, we demonstrate how changing the strength of the hemodynamic coupling mechanism and changing the arterial blood pressure have equivalent effects on the system. The same two-nephron system is then used to demonstrate the interactions that arise between the two coupling mechanisms. We conclude by arguing that our approach is scalable to large numbers of nephrons, based on the performance characteristics of the model. 相似文献