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Hartmuth C. Kolb M. G. Finn K. Barry Sharpless 《Angewandte Chemie (International ed. in English)》2001,40(11):2004-2021
Examination of nature's favorite molecules reveals a striking preference for making carbon–heteroatom bonds over carbon–carbon bonds—surely no surprise given that carbon dioxide is nature's starting material and that most reactions are performed in water. Nucleic acids, proteins, and polysaccharides are condensation polymers of small subunits stitched together by carbon–heteroatom bonds. Even the 35 or so building blocks from which these crucial molecules are made each contain, at most, six contiguous C−C bonds, except for the three aromatic amino acids. Taking our cue from nature's approach, we address here the development of a set of powerful, highly reliable, and selective reactions for the rapid synthesis of useful new compounds and combinatorial libraries through heteroatom links (C−X−C), an approach we call “click chemistry”. Click chemistry is at once defined, enabled, and constrained by a handful of nearly perfect “spring‐loaded” reactions. The stringent criteria for a process to earn click chemistry status are described along with examples of the molecular frameworks that are easily made using this spartan, but powerful, synthetic strategy. 相似文献
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Explicit expressions for one- and two-N1 isobar configurations in closed shell nuclei have been derived in the impulse approximation and applied to 4He and 16O. Conventional transition potentials with π- and ?-exchange have been used and the influence of potential regularization and short-range correlations have been studied. The dominant isobar configurations are found to be the one- and two-Δ components and originate from two-nucleon pairs in a relative S-state. The probability for finding a nucleon as a Δ-isobar is about 4.5% in 4He and about 3.2% in 16O. These numbers should be considered as upper limits due to uncertainties in off-shell effects of the transition potentials. 相似文献
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Ley SV Abad-Somovilla A Anderson JC Ayats C Bänteli R Beckmann E Boyer A Brasca MG Brice A Broughton HB Burke BJ Cleator E Craig D Denholm AA Denton RM Durand-Reville T Gobbi LB Göbel M Gray BL Grossmann RB Gutteridge CE Hahn N Harding SL Jennens DC Jennens L Lovell PJ Lovell HJ de la Puente ML Kolb HC Koot WJ Maslen SL McCusker CF Mattes A Pape AR Pinto A Santafianos D Scott JS Smith SC Somers AQ Spilling CD Stelzer F Toogood PL Turner RM Veitch GE Wood A Zumbrunn C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(34):10683-10704
We describe in full the first synthesis of the potent insect antifeedant azadirachtin through a highly convergent approach. An O-alkylation reaction is used to unite decalin ketone and propargylic mesylate fragments, after which a Claisen rearrangement constructs the central C8-C14 bond in a stereoselective fashion. The allene which results from this sequence then enables a second critical carbon-carbon bond forming event whereby the [3.2.1] bicyclic system, present in the natural product, is generated via a 5-exo-radical cyclisation process. Finally, using knowledge gained through our early studies into the reactivity of the natural product, a series of carefully designed steps completes the synthesis of this challenging molecule. 相似文献
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The Scanning Electron Microscope (SEM) is an excellent tool for the characterization of surfaces. In order to evaluate the
accuracy of the reconstruction of a 3D dataset, a known depth standard for tactile depth measurement devices with a step height
of 92 μm was investigated by SEM. The reconstruction of surfaces using two tilted images (StereoCreator) or three different
tilted images (TriCreator) is affected by the tilt angle itself, the image resolution and the working distance. We compare
the results of the obtained data from different combinations of tilt angles and working distances in relation with the type
of reconstruction…. To compare the accuracy and reliability of the 3D datasets from the new Infinite Focus Measurement Machine
(IFM) with the datasets reconstructed from the well known SEM technique, we utilized a groove standard with six trapezoidal
grooves with known width and depth certified by the PTB – Braunschweig – Germany (Physikalisch – Technische Bundesanstalt
Braunschweig – calibration mark 035PTB04 – measured with a traceable stylus instrument according to DIN EN ISO 3274). The
great advantage of the SEM/ESEM (Environmental Scanning Electron Microscope) and IFM technique compared to tactile-profile-measurement
instruments is that it is a non-tactile and a non-destructive method. The potential and accuracy of these methods in comparison
to tactile measurement systems is shown and discussed in this paper. 相似文献
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Wolfgang J. Fischer Armin Zankel Christian Ganser Franz J. Schmied Hartmuth Schroettner Ulrich Hirn Christian Teichert Wolfgang Bauer Robert Schennach 《Cellulose (London, England)》2014,21(1):251-260
Besides the determination of the force and the energy needed to break individual fibre to fibre joints, the investigation of the formerly bonded area (FBA) is of essential importance to learn more about the failure mechanisms of fibre–fibre bonds in general. In this study the surfaces of paper fibres and the FBA of fibre–fibre joints after the determination of the breaking force as well as the bonding energy were analysed by means of low voltage scanning electron microscopy and atomic force microscopy. A comparison between the contact zone of fibres broken at different loading rates as well as under cyclic loading showed that there seems to be no significant difference in the appearance of the FBA in these cases. Only minor delamination of the cell wall could be found in the bonding zone, which indicates no mechanical interlocking of fibrils in the bonding zone. Furthermore, it is shown that some glues used for specimen preparation of fibre–fibre bond strength measurement are forming a glue film on the fiber surface and migrate into the bonding region. 相似文献
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Hartmuth Arenhövel 《Acta Physica Hungarica A》2001,14(1-4):21-31
The development of theoretical photonuclear physics over the last 40 years is illustrated by a few selected examples highlighting a number of important issues like collective motion in nuclei, the role of subnuclear degrees of freedom, relativity and meson production. 相似文献
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