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41.
B3LYP/6-31G* and CASMP2 calculations have been employed to study the ene reaction of singlet oxygen with trans-cyclooctene. These methods predict that the reaction involves a perepoxide intermediate, whereas alkenes such as tetramethylethylene are predicted by the same methods to occur by a two-step no-intermediate mechanism, with no perepoxide intermediate. The change in mechanism arises because the trans-cyclooctene imposes a substantial strain in the transition state for hydrogen abstraction. The perepoxide is formed through a polarized diradical intermediate that can lead to the observation of alkene isomerization. The polarized diradical also becomes a minimum because of the barrier to abstraction. 相似文献
42.
Gabellieri C Reynolds S Lavie A Payne GS Leach MO Eykyn TR 《Journal of the American Chemical Society》2008,130(14):4598-4599
Choline is a precursor of cellular phospholipid metabolism that provides Magnetic Resonance (MR) and Positron Emission Tomography (PET) biomarkers for cancer detection and response assessment. Employing Dynamic Nuclear Polarization we show that the MR signal of 15N in choline can be enhanced by at least 4 orders of magnitude with a relaxation time of ca. 4 min, providing a method to observe the action of choline kinase, an important target for novel cancer therapeutics. 相似文献
43.
A.?PaliathanasisEmail authorView authors OrcID profile K.?Krishnakumar P.?G.?L.?Leach 《International Journal of Theoretical Physics》2016,55(4):2286-2289
We discuss the relationship between the Noether point symmetries of the geodesic Lagrangian, in a (pseudo)Riemannian manifold, with the elements of the Homothetic algebra of the space. We observe that the classification problem of the Noether symmetries for the geodesic Lagrangian is equivalent with the classification of the Homothetic algebra of the space, which in the case of a Friedmann-Lemaître-Robertson-Walker spacetime is a well-known result in the literature. 相似文献
44.
J.A. Leach 《Journal of Differential Equations》2009,247(4):1206-1228
In this paper, we consider an initial-boundary value problem for the Korteweg-de Vries equation on the negative quarter-plane. The normalized Korteweg-de Vries equation considered is given by
45.
Here we discuss a sequence of Lagrangians and corresponding Euler–Lagrange equations and point out some interesting properties that this particular sequence holds. This is an extension on recent results obtained on sequences of differential equations to Lagrangians as it leads to differential equations on the application of the Variational Principle. 相似文献
46.
Stevens F Leach RN Langford SC Dickinson JT 《Langmuir : the ACS journal of surfaces and colloids》2006,22(7):3320-3325
We report observations of poly(methyl methacrylate) films modified by the synergistic effect of solvent exposure and mechanical stress applied by the tip of an atomic force microscope (AFM). We show that these modifications are sensitive to polymer molecular weight as well as solvent strength and the force applied by the tip. Small-area scanning often produces localized patches of raised material as well as depressed areas. The volume change associated with the depressed areas generally increases with increasing solvent strength, increasing applied normal force, and decreasing polymer molecular weight. In contrast, the volume change associated with the raised patches is greatest for 25-145K Mw films in 60 and 100% ethanol solutions. In each case, the normal force applied by the AFM tip must exceed a threshold to significantly modify the surface; this threshold is associated with an increase in lateral force applied by the AFM tip during small-area scanning. We attribute the raised patches to mechanically enhanced swelling due to diffusion of solvent into near-surface material. Permanent net volume loss, when observed, is attributed to localized polymer dissolution. 相似文献
47.
A. Chaudhuri C. Andreoiu M. Brodeur T. Brunner U. Chowdhury S. Ettenauer A. T. Gallant A. Grossheim G. Gwinner R. Klawitter A. A. Kwiatkowski K. G. Leach A. Lennarz D. Lunney T. D. Macdonald R. Ringle B. E. Schultz V. V. Simon M. C. Simon J. Dilling 《Applied physics. B, Lasers and optics》2014,114(1-2):99-105
The introduction of Paul traps, in particular linear radio-frequency quadrupoles in the early 2000s, has revolutionized the use of ion traps for probing the properties of radioactive nuclides. It opened the path to trapping all available nuclides, independent of their chemical properties. We present an overview of direct mass measurements of short-lived nuclides using TITAN, a Penning trap mass spectrometer facility particularly suitable for precision measurements of ms-half-life nuclides. 相似文献
48.
Fascione MA Adshead SJ Mandal PK Kilner CA Leach AG Turnbull WB 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(10):2987-2997
Sulfoxides are frequently used in organic synthesis as chiral auxiliaries and reagents to mediate a wide variety of chemical transformations. For example, diphenyl sulfoxide and triflic anhydride can be used to activate a wide range of glycosyl donors including hemiacetals, glycals and thioglycosides. In this way, an alcohol, enol or sulfide is converted into a good leaving group for subsequent reaction with an acceptor alcohol. However, reaction of diphenyl sulfoxide and triflic anhydride with oxathiane-based thioglycosides, and other oxathianes, leads to a different process in which the thioglycoside is oxidised to a sulfoxide. This unexpected oxidation reaction is very stereoselective and proceeds under anhydrous conditions in which the diphenyl sulfoxide acts both as oxidant and as the source of the oxygen atom. Isotopic labelling experiments support a reaction mechanism that involves the formation of oxodisulfonium (S-O-S) dication intermediates. These intermediates undergo oxygen-exchange reactions with other sulfoxides and also allow interconversion of axial and equatorial sulfoxides in oxathiane rings. The reversibility of the oxygen-exchange reaction suggests that the stereochemical outcome of the oxidation reaction may be under thermodynamic control, which potentially presents a novel strategy for the stereoselective synthesis of sulfoxides. 相似文献
49.
50.
Sara H. Elgazzar Nicoleta S. Tipi Nick J. Hubbard David Z. Leach 《European Journal of Operational Research》2012
The main aim of this paper is to develop a performance measurement method which links supply chain (SC) processes’ performance to a company’s financial strategy through demonstrating and utilising the relationship between SC processes’ performance and a company’s financial performance. 相似文献