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641.
Ultraviolet irradiation of a series of 2H-imidazole N-oxides 2 has been shown to effect a clean isomerisation to derivatives of the new ring system, 1,3-diaza-6-oxabicyclo[3.1.0]hex-3-ene, 7 . Epoxidation of a representative 7 has given access to the hitherto inaccessible trans-fused 1,3-diaza-4,7-dioxatricyclo[4.1.0. 1,603,5]-heptane ring system 9 . 相似文献
642.
James J. Crawford Mark McLaughlin Angus J. Morrison Peter L. Pauson Graeme J. Thurston 《Tetrahedron》2006,62(49):11360-11370
The cedrene carbon skeleton was directly and efficiently assembled from a simple monocyclic precursor by the strategic use of a high yielding intramolecular Pauson-Khand cyclisation reaction. A small number of further synthetic manipulations provided a concise formal total synthesis of α- and β-cedrene. The cyclisation precursor was readily prepared, with a stereoselective ketone alkenylation selectively providing the olefin required for efficient access to the natural target. 相似文献
643.
644.
645.
Jimmy Y. H. Liao Cordelia Selomulya Graeme Bushell Gtz Bickert Rose Amal 《Particle & Particle Systems Characterization》2005,22(5):299-309
Several methods to measure the structures of coal aggregates are compared. Loose and compact coal aggregates were generated through flocculation of ultrafine coal particles (mean volume diameter of 12 μm) under specific shearing conditions. Aggregate structure in terms of mass fractal dimension, Df, was determined using various methods; namely 2D and 3D image analysis, interpretation of intensity patterns from small angle light scattering, changes in aggregation state through light obscuration, and settling behavior. In this study, the measured values of Df ranged from 1.84–2.19 for coal aggregates with more open structures, and around 2.27–2.66 for the compact ones. All of these approaches could distinguish structural differences between aggregates, albeit with variation in Df values estimated by the different techniques. The discrepancy in the absolute values for fractal dimension is due to the different physical properties measured by each approach, depending on the assumptions used to infer Df from measurable parameters. In addition, image analysis and settling techniques are based on the examination of individual aggregates, such that a large number of data points are required to yield statistically representative estimations. Light scattering and obscuration measure the aggregates collectively to give average Df values of the particulate systems; consequently ignoring any structural variation between the aggregates, and leaving possible small contaminations undetected (e.g. by dust particles or air bubbles). Appropriate utilization of a particular method is thus largely determined by system properties and required data quality. 相似文献
646.
Christopher Barner‐Kowollik Michael Buback Bernadette Charleux Michelle L. Coote Marco Drache Takeshi Fukuda Atsushi Goto Bert Klumperman Andrew B. Lowe James B. Mcleary Graeme Moad Michael J. Monteiro Ronald D. Sanderson Matthew P. Tonge Philipp Vana 《Journal of polymer science. Part A, Polymer chemistry》2006,44(20):5809-5831
Investigations into the kinetics and mechanism of dithiobenzoate‐mediated Reversible Addition–Fragmentation Chain Transfer (RAFT) polymerizations, which exhibit nonideal kinetic behavior, such as induction periods and rate retardation, are comprehensively reviewed. The appreciable uncertainty in the rate coefficients associated with the RAFT equilibrium is discussed and methods for obtaining RAFT‐specific rate coefficients are detailed. In addition, mechanistic studies are presented, which target the elucidation of the fundamental cause of rate retarding effects. The experimental and theoretical data existing in the literature are critically evaluated and apparent discrepancies between the results of different studies into the kinetics of RAFT polymerizations are discussed. Finally, recommendations for further work are given. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5809–5831, 2006 相似文献
647.
Dominic W. Berry Graeme Ahokas Richard Cleve 《Communications in Mathematical Physics》2007,270(2):359-371
We present an efficient quantum algorithm for simulating the evolution of a quantum state for a sparse Hamiltonian H over a given time t in terms of a procedure for computing the matrix entries of H. In particular, when H acts on n qubits, has at most a constant number of nonzero entries in each row/column, and ||H|| is bounded by a constant, we may select any positive integer k such that the simulation requires O((log*
n)t
1+1/2k
) accesses to matrix entries of H. We also show that the temporal scaling cannot be significantly improved beyond this, because sublinear time scaling is not
possible. 相似文献
648.
Graeme J. Gainsford Richard H. Furneaux Jenny M. Mason Peter C. Tyler 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(10):e477-e478
The title compound, C16H23NO8, was obtained during studies of australine derivatives. The molecular stereochemistry is similar to that reported for other australine derivatives even though there is no intermolecular hydrogen bonding in this case. 相似文献
649.
Sarah F. Jenkinson K. Victoria Booth Amalia M. Estévez Reino Graeme Horne Ramón J. Estévez George W.J. Fleet 《Tetrahedron: Asymmetry》2009,20(20):2357-2367
Two carbon chain extensions using a Wittig reaction on both a 1-deoxy ribulose derivative and a C-2-branched erythrose derivative are reported. Subsequent dihydroxylation resulted in the synthesis of C-3 and C-4 methyl-branched sugar lactones, the useful synthetic building blocks. Control of the stereoselectivity of both the Wittig reaction and the dihydroxylation is investigated, and 3-C-methyl and 4-C-methyl d-altrono-1,4-lactones and d-glucono-1,4-lactone and 4-C-hydroxymethyl-d-altrono-1,4-lactone were synthesised. 相似文献
650.
Bogdan M. Leu Graeme R.A. Wyllie W.Robert Scheidt E.Ercan Alp J.Timothy Sage 《Journal of Physics and Chemistry of Solids》2005,66(12):2250-2256
High-resolution X-ray measurements near a nuclear resonance reveal the complete vibrational spectrum of the probe nucleus. Because of this, nuclear resonance vibrational spectroscopy (NRVS) is a uniquely quantitative probe of the vibrational dynamics of reactive iron sites in proteins and other complex molecules. Our measurements of vibrational fundamentals have revealed both frequencies and amplitudes of 57Fe vibrations in proteins and model compounds. Information on the direction of Fe motion has also been obtained from measurements on oriented single crystals, and provides an essential test of normal mode predictions. Here, we report the observation of weaker two-quantum vibrational excitations (overtones and combinations) for compounds that mimic the active site of heme proteins. The predicted intensities depend strongly on the direction of Fe motion. We compare the observed features with predictions based on the observed fundamentals, using information on the direction of Fe motion obtained either from DFT predictions or from single crystal measurements. Two-quantum excitations may become a useful tool to identify the directions of the Fe oscillations when single crystals are not available. 相似文献