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101.
Peter M.W. Gill Darragh P. O'Neill Nicholas A. Besley 《Theoretical chemistry accounts》2003,109(5):241-250
Two-electron distribution functions and intracules are functions of electronic coordinates and occupy an important, and frequently
overlooked, middle ground between the beguiling simplicity of electron densities and the bewildering complexity of wavefunctions.
We survey the functions that have been considered by earlier workers and introduce two new ones, the Wigner intracule and
the action intracule, that have not previously been discussed. To illustrate their usefulness, we consider the intracules
of jellium, a few small atoms and the dissociating hydrogen molecule.
Received: 26 July 2002 / Accepted: 20 October 2002 /
Published online: 30 January 2003
Correspondence to: P.M.W. Gill e-mail: peter.gill@nott.ac.uk 相似文献
102.
David K O'DellKenneth M Nicholas 《Tetrahedron》2003,59(6):747-754
A representative o-nitroenone (Z=O) was cyclized by reduction with CO and [CpFe(CO)2]2 (Fp2) as the catalyst to give the corresponding 4-quinolone. In contrast, Baylis-Hillman adducts derived from o-nitrobenzaldehydes were cyclized to N-formylindolines and indoles under the same conditions. 相似文献
103.
[structure: see text] The novel alkaloids 1 and 4 were isolated from an Australian non-verongid sponge, Oceanapia sp. Compound 1 contains an unprecedented imidazolyl-quinolinone substructure attached to a bromotyrosine-derived spiro-isoxazoline. Three other known alkaloids were isolated in addition to 1 and 4 and together represent the first examples of inhibitors of a new mycobacterial enzyme mycothiol S-conjugate amidase (MCA). 相似文献
104.
Alan H. Cowley Andreas Decken Claudia A. Olazbal Nicholas C. Norman 《无机化学与普通化学杂志》1995,621(11):1844-1848
Further investigation of the reaction of Ar*GaCl2 (Ar* = 2,4,6-t-Bu3C6H2) with Na[Mn(CO)5] resulted in the new compound, [Ga(Ar*){Mn(CO)5}2] 2 . The new indium compounds, [In(Ar*){Co(CO)4}2] 3 and [In(Ar*){Mn(CO)5}2] 4 , have been prepared by the treatment of Ar*InBr2 with Na[Co(CO)4] and Na[Mn(CO)5], respectively. The structure of 3 was established by single-crystal X-ray diffraction: space group P1 (No. 2), Z = 2, a = 8.625(1) Å, b = 10.557(2) Å, c = 17.55(2) Å, α = 88.43(1)°, β = 83.45(1)°, γ = 71.14(1)°. The X-ray crystal structure of [Ga{Mn(CO)5}3] is also reported: space group Pbca (No. 61), Z = 8, a = 12.83(3) Å, b = 11.753(2) Å, c = 29.662(6) Å, α = β = γ = 90°. 相似文献
105.
Analytical methodology was developed and validated for the determination of spiroxamine residues in grapes, must, and wine by gas chromatography/ion trap-mass spectrometry (GC/IT-MS). Two extraction procedures were used: the first involved grapes, must, and wine extraction with alkaline cyclohexane-dichloromethane (9 + 1, v/v) solution, and the second grape extraction with acetone, dichloromethane, and petroleum ether. In both procedures, the extract was centrifuged, evaporated to dryness, and reconstituted in cyclohexane or 2,2,4-trimethylpentane-toluene (9 + 1, v/v), respectively. Spiroxamine diastereomers A and B were determined by GC/IT-MS, and a matrix effect was observed in the case of grapes but not in must and wine. Recovery of spiroxamine from fortified samples at 0.02 to 5.0 mg/kg ranged from 78-102% for grapes and must, with relative standard deviation (RSD) <13%; for red and white wines, recoveries ranged from 90 to 101% with RSD <9%. The limit of quantification was 0.02 mg/kg for grapes, must, and wine or 0.10 mg/kg for grapes, depending on the extraction procedure used. 相似文献
106.
Cheesman MR Oganesyan VS Watmough NJ Butler CS Thomson AJ 《Journal of the American Chemical Society》2004,126(13):4157-4166
Fully oxidized cytochrome bo3 from Escherichia coli has been studied in its oxidized and several ligand-bound forms using electron paramagnetic resonance (EPR) and magnetic circular dichroism (MCD) spectroscopies. In each form, the spin-coupled high-spin Fe(III) heme o3 and CuB(II) ion at the active site give rise to similar fast-relaxing broad features in the dual-mode X-band EPR spectra. Simulations of dual-mode spectra are presented which show that this EPR can arise only from a dinuclear site in which the metal ions are weakly coupled by an anisotropic exchange interaction of J 1 cm-1. A variable-temperature and magnetic field (VTVF) MCD study is also presented for the cytochrome bo3 fluoride and azide derivatives. New methods are used to extract the contribution to the MCD of the spin-coupled active site in the presence of strong transitions from low-spin Fe(III) heme b. Analysis of the MCD data, independent of the EPR study, also shows that the spin-coupling within the active site is weak with J approximately 1 cm-1. These conclusions overturn a long-held view that such EPR signals in bovine cytochrome c oxidase arise from an S' = 2 ground state resulting from strong exchange coupling (J > 10(2) cm-1) within the active site. 相似文献
107.
We have performed large-scaleab initio calculations using second order Møller-Plesset perturbation theory (MP2) on the three van der Waals dimers formed from acetylene and carbon dioxide. Intermolecular geometrical parameters are reliably computed at this level of theory. Calculations of vibrational frequencies of the van der Waals modes, currently unobtainable by experimental means, give important information about the intermolecular potential and predict significant large-amplitude motion. Zero point energy contributions are shown to be vital in assessing the relative stability of conformations which are close in energy. Our studies suggest that the barrier to interconversion tunnelling in (CO2)2 is significantly smaller than previously inferred and is approximately the same as in (C2H2)2. The reason for the rigidity of (CO2)2 is the difference in monomer centre-of-mass separation between ground state and transition state. We also show that, in addition to the previously observedC
2v
form, the collinear form of C2H2-CO2 is a local minimum on its potential energy surface. 相似文献
108.
109.
Nicholas J. Higham 《Numerische Mathematik》1992,62(1):539-555
Summary The Hölderp-norm of anm×n matrix has no explicit representation unlessp=1,2 or . It is shown here that thep-norm can be estimated reliably inO(mn) operations. A generalization of the power method is used, with a starting vector determined by a technique with a condition estimation flavour. The algorithm nearly always computes ap-norm estimate correct to the specified accuracy, and the estimate is always within a factorn
1–1/p
of A
p
. As a by-product, a new way is obtained to estimate the 2-norm of a rectangular matrix; this method is more general and produces better estimates in practice than a similar technique of Cline, Conn and Van Loan. 相似文献
110.
Richard J CohenDaniel L Fox Jarrod F EubankRalph Nicholas Salvatore 《Tetrahedron letters》2003,44(47):8617-8621
A mild and convenient synthesis for phosphonates using cesium carbonate (Cs2CO3), tetrabutylammonium iodide (TBAI) and DMF was developed at room temperature. Numerous dialkyl phosphites were screened using a diverse array of alkyl halides and these reaction conditions were found to be highly efficient producing various phosphonates exclusively in moderate to high yields. 相似文献