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排序方式: 共有160条查询结果,搜索用时 15 毫秒
81.
AM Cardoso SM Alexandre CM Barros AJ Correia NM Nibbering 《Rapid communications in mass spectrometry : RCM》1999,13(19):1885-1888
The collision-induced dissociation (CID) of deprotonated arylalkylamines of general formula R(1)C(6)H(4)CHR(2)CH(2)NR(3)(2) (where R(1) = H, OH, F or NO(2); R(2) = H or OH; R(3) = H or CH(3)) generated by negative chemical ionization with H(2)O and D(2)O as ionizing reagents, is discussed. The negative chemical ionization mass spectra show that, in the absence of a hydroxy group in the aromatic ring, deprotonation takes place at the benzylic position whereas the proton is lost from the OH group when present. The nitro compound forms only M(-.) ions. The CID spectra of the deprotonated molecules show that fragmentations are strongly dependent on the structural features of the molecules, namely the presence or absence of substituents in the aromatic ring or aliphatic chain. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
82.
Reinout Meijboom Marco Haumann Andreas Roodt Llewellyn Damoense 《Helvetica chimica acta》2005,88(3):676-693
The dinuclear complex [Co2(CO)6{P(O‐2,4‐t‐Bu2C6H3)3}2] ( 6 ) has been synthesised and fully characterised. X‐Ray crystal‐structure analysis revealed a trans‐diaxial geometry, no bridging carbonyls, and Co? Co and Co? P bond lengths of 2.706(5) and 2.134(4) Å, respectively. The hydroformylation of pent‐1‐ene in the presence of 6 was studied at 120–180° at pressures between 20 and 80 bar Syngas. High‐pressure (HP) spectroscopy (IR, NMR) was used to detect potential hydride intermediates. HP‐IR Studies revealed the formation of [CoH(CO)3{P(O‐2,4‐t‐Bu2C6H3)3}] ( 2 ) at ca. 105°, with no significant amount of [CoH(CO)4] detectable. The intermediate 2 was synthesised and characterised. The formation of the undesired complex [CoH(CO)2{P(O‐2,4‐t‐Bu2C6H3)3}2] was completely suppressed due to the large cone angle of the sterically demanding phosphite. 相似文献
83.
Zlotea C Phanon D Mazaj M Heurtaux D Guillerm V Serre C Horcajada P Devic T Magnier E Cuevas F Férey G Llewellyn PL Latroche M 《Dalton transactions (Cambridge, England : 2003)》2011,40(18):4879-4881
The hydrogen adsorption capacity and heat of adsorption at 77 K have been evaluated for several porous metal terephthalate MOFs (MIL-53(Fe), MIL-125(Ti) and UiO-66(Zr)), as well as in their -NH(2) and -(CF(3))(2) functionalized isoreticular structures. The capacity of hydrogen is basically related to the textural properties of the solids and not to their composition. The heats of adsorption at low coverage are on the whole close to those usually reported for MOFs (6-7 kJ mol(-1)), except for the UiO-66(Zr) and MIL-53(Fe)-(CF(3))(2) analogues, whereas the presence of Lewis acid sites and/or a confinement effect enhances significantly the strength of interaction with hydrogen. 相似文献
84.
Stefan G. Llewellyn Smith 《Physica D: Nonlinear Phenomena》2011,240(20):1644-1651
The equations of motion of point vortices embedded in incompressible flow go back to Kirchhoff. They are a paradigm of reduction of an infinite-dimensional dynamical system, namely the incompressible Euler equation, to a finite-dimensional system, and have been called a “classical applied mathematical playground”. The equation of motion for a point vortex can be viewed as the statement that the translational velocity of the point vortex is obtained by removing the leading-order singularity due to the point vortex when computing its velocity. The approaches used to obtain this result are reviewed, along with their history and limitations. A formulation that can be extended to study the motion of higher singularities (e.g. dipoles) is then presented. Extensions to more complex physical situations are also discussed. 相似文献
85.
Joo Marreiros Lenz Van Dommelen Guillaume Fleury Rodrigo de Oliveira‐Silva Timothe Stassin Paul Iacomi Shuhei Furukawa Dimitrios Sakellariou Philip L. Llewellyn Maarten Roeffaers Rob Ameloot 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(51):18642-18646
Zeolitic imidazolate frameworks (ZIFs) are a sub‐class of metal–organic frameworks (MOFs). Although generally stable, ZIFs can undergo post‐synthetic linker exchange (PSLE) in solution under mild conditions. Herein, we present a novel, solvent‐free approach to post‐synthetic linker exchange through exposure to linker vapor. 相似文献
86.
Salles F Jobic H Maurin G Koza MM Llewellyn PL Devic T Serre C Ferey G 《Physical review letters》2008,100(24):245901
Quasielastic neutron scattering measurements are combined with molecular dynamics simulations to extract the self-diffusion coefficient of hydrogen in the metal organic frameworks MIL-47(V) and MIL-53(Cr). We find that the diffusivity of hydrogen at low loading is about 2 orders of magnitude higher than in zeolites. Such a high mobility has never been experimentally observed before in any nanoporous materials, although it was predicted in carbon nanotubes. Either 1D or 3D diffusion mechanisms are elucidated depending on the chemical features of the MIL framework. 相似文献
87.
Glyn Llewellyn Moore Philip John Humphries-Cuff Alexander Ernest Watson 《Spectrochimica Acta Part B: Atomic Spectroscopy》1984,39(7):915-929
A medium power (5 kW) nitrogen-cooled argon inductively coupled plasma (ICP) system was used in an investigation of the basic and modified simplex methods of optimization. The optimum operating conditions for the ICP system were established for 23 commonly determined elements covering a wavelength range from 180 to 340 nm and including an approximately equal number of atomic and ionic lines.Initially the optimization was carried out for individual elements on the basis of two responses: net signal-to-background ratio (SBR) and ionization interference (II).The simplex technique indicated a need to improve the nebulization system.In achievement of maximum SBR, interesting correlations were found between the optimum power required, on the one hand, and the difficulty of excitation of the elements and the optimum intermediate-gas flowrate, on the other.Finally a method for optimization of the conditions for the plasma in multi-element analysis, based on the sequential use of maximum SBR and minimum ionization interference (MII) responses, was devised and successfully tested against several routine analytical methods. Application of the conditions established during these optimizations result in an analytically useful plasma giving good detection limits as well as minimum ionization interference effects. 相似文献
88.
Precise temperature control in microfluidic devices using Joule heating of ionic liquids 总被引:1,自引:0,他引:1
Microfluidic devices for spatially localised heating of microchannel environments were designed, fabricated and tested. The devices are simple to implement, do not require complex manufacturing steps and enable intra-channel temperature control to within +/-0.2 degrees C. Ionic liquids held in co-running channels are Joule heated with an a.c. current. The nature of the devices means that the internal temperature can be directly assessed in a facile manner. 相似文献
89.
Mumby PJ Edwards AJ Arias-González JE Lindeman KC Blackwell PG Gall A Gorczynska MI Harborne AR Pescod CL Renken H Wabnitz CC Llewellyn G 《Nature》2004,427(6974):533-536
Mangrove forests are one of the world's most threatened tropical ecosystems with global loss exceeding 35% (ref. 1). Juvenile coral reef fish often inhabit mangroves, but the importance of these nurseries to reef fish population dynamics has not been quantified. Indeed, mangroves might be expected to have negligible influence on reef fish communities: juvenile fish can inhabit alternative habitats and fish populations may be regulated by other limiting factors such as larval supply or fishing. Here we show that mangroves are unexpectedly important, serving as an intermediate nursery habitat that may increase the survivorship of young fish. Mangroves in the Caribbean strongly influence the community structure of fish on neighbouring coral reefs. In addition, the biomass of several commercially important species is more than doubled when adult habitat is connected to mangroves. The largest herbivorous fish in the Atlantic, Scarus guacamaia, has a functional dependency on mangroves and has suffered local extinction after mangrove removal. Current rates of mangrove deforestation are likely to have severe deleterious consequences for the ecosystem function, fisheries productivity and resilience of reefs. Conservation efforts should protect connected corridors of mangroves, seagrass beds and coral reefs. 相似文献
90.
Influence of Solvent‐Like Sidechains on the Adsorption of Light Hydrocarbons in Metal–Organic Frameworks 下载免费PDF全文
Andreas Schneemann Dr. Eric D. Bloch Dr. Sebastian Henke Dr. Philip L. Llewellyn Prof. Dr. Jeffrey R. Long Prof. Dr. Roland A. Fischer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(51):18764-18769
A variety of strategies have been developed to adsorb and separate light hydrocarbons in metal–organic frameworks. Here, we present a new approach in which the pores of a framework are lined with four different C3 sidechains that feature various degrees of branching and saturation. These pendant groups, which essentially mimic a low‐density solvent with restricted degrees of freedom, offer tunable control of dispersive host–guest interactions. The performance of a series of frameworks of the type Zn2(fu‐bdc)2(dabco) (fu‐bdc2?=functionalized 1,4‐benzenedicarboxylate; dabco=1,4‐diazabicyclo[2.2.2]octane), which feature a pillared layer structure, were investigated for the adsorption and separation of methane, ethane, ethylene, and acetylene. The four frameworks exhibit low methane uptake, whereas C2 hydrocarbon uptake is substantially higher as a result of the enhanced interaction of these molecules with the ligand sidechains. Most significantly, the adsorption quantities and selectivity were found to depend strongly upon the type of sidechains attached to the framework scaffold. 相似文献