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21.
Koen Vandyck 《Tetrahedron letters》2005,46(1):75-78
2,3,6,7-Tetrahydro-as-indacene-1,8-dione 4 was prepared in 4 steps starting from 2-methyl-furan by modification of a literature procedure. Appliance of Noyori’s asymmetric transfer hydrogenation, resulted in (1S,8S)-1,2,3,6,7,8-hexahydro-as-indacene-1,8-diol 5 in high yield (81%) and excellent enantioselectivity (>99% ee) or (8S)-8-hydroxy-3,6,7,8-tetrahydro-2H-as-indacen-1-one 6 in moderate yield (58%) and equally high enantioselectivity (98.5% ee), depending on the conditions. The asymmetric reduction was expected to yield the (S)-alcohols using the (S,S)-Ts-DPEN ligand, which was confirmed by the appliance of the exciton chirality method on the corresponding bis(p-dimethylamino)benzoate 7. 相似文献
22.
Uyeda HT Zhao Y Wostyn K Asselberghs I Clays K Persoons A Therien MJ 《Journal of the American Chemical Society》2002,124(46):13806-13813
The syntheses and electrooptic properties of a new family of nonlinear optical chromophores are reported. These species feature an ethyne-elaborated, highly polarizable porphyrinic component and metal polypyridyl complexes that serve as integral donor and acceptor elements. Examples of this structural motif include ruthenium(II) [5-(4'-ethynyl-(2,2';6',2' '-terpyridinyl))-10,20-bis(2',6'-bis(3,3-dimethyl-1-butyloxy)phenyl)porphinato]zinc(II)-(2,2';6',2' '-terpyridine)(2+) bis-hexafluorophosphate (Ru-PZn); osmium(II) [5-(4'-ethynyl-(2,2';6',2'-terpyridinyl))-10,20-bis(2',6'-bis(3,3-dimethyl-1-butyloxy)phenyl)porphinato]zinc(II)-(2,2';6',2'-terpyridine)(2+) bis-hexafluorophosphate (Os-PZn); ruthenium(II) [5-(4'-ethynyl-(2,2';6',2'-terpyridinyl))-15-(4'-nitrophenyl)ethynyl-10,20-bis(2',6'-bis(3,3-dimethyl-1-butyloxy)phen-yl)porphinato]zinc(II)-(2,2';6',2' '-terpyridine)(2+) bis-hexafluorophosphate (Ru-PZn-A); osmium(II) [5-(4'-ethynyl-(2,2';6',2' '-terpyridinyl))-15-(4'-nitrophenyl)ethynyl-10,20-bis(2',6'-bis(3,3-dimethyl-1-butyloxy)phenyl)porphinato]zinc(II)-(2,2';6',2' '-terpyridine)(2+) bis-hexafluorophosphate (Os-PZn-A); and ruthenium(II) [5-(4'-ethynyl-(2,2';6',2' '-terpyridinyl))osmium(II)-15-(4'-ethynyl-(2,2';6',2'-terpyridinyl))-10,20-bis (2',6'-bis(3,3-dimethyl-1-butyloxy)phenyl)porphinato]zinc(II)-bis(2,2';6',2'-terpyridine)(4+) tetrakis-hexafluorophosphate (Ru-PZn-Os). The frequency dependence of the dynamic hyperpolarizability of these compounds was determined from hyperRayleigh light scattering (HRS) measurements carried out at fundamental incident irradiation wavelengths (lambda(inc)) of 800, 1064, and 1300 nm. These data show that (i) coupled oscillator photophysics and metal-mediated cross-coupling can be exploited to elaborate high beta(0) supermolecules that exhibit significant excited-state electronic communication between their respective pigment building blocks; (ii) high-stability metal polypyridyl compounds constitute an attractive alternative to electron releasing dialkyl- and diarylamino groups, the most commonly used donor moieties in a wide range of established nonlinear optical dyes; (iii) this design strategy enables ready elaboration of chromophores having extraordinarily large dynamic hyperpolarizabilities (beta(lambda) values) at telecommunication relevant wavelengths; and (iv) porphyrin B- and Q-state-derived static hyperpolarizabilities (beta(0) values) can be designed to have the same or opposite sign in these species, thus providing a new means to regulate the magnitude of lambda(inc)-specific dynamic hyperpolarizabilities. 相似文献
23.
Sandra K Stals I Sandra P Claeyssens M Van Beeumen J Devreese B 《Journal of chromatography. A》2004,1058(1-2):263-272
N-Glycosylation of cellobiohydrolase I from the fungus Trichoderma reesei (strain Rut-C30) is studied using a combination of electrophoretic, chromatographic and mass spectrometric techniques. As four potential N-glycosylation sites and several uncharged and phosphorylated high-mannose glycans are present, a large number of glycoforms and phospho-isoforms can be expected. Isoelectric focusing both in gel and in capillary format was successfully applied for the separation of the phospho-isoforms. They were extracted in their intact form from the gel and subsequently analysed by nanospray-Q-TOF-MS, thereby making use of a powerful two-dimensional technique. Nano-LC/MS/MS on a Q-Trap MS further allowed the determination of the glycosylation sites. As a novel approach, an oxonium ion was used in precursor ion scanning for selective detection of glycopeptides containing phosphorylated high-mannose glycans. 相似文献
24.
Rafael Mayorga-Gonzlez Miguel Rivera-Torrente Nikolaos Nikolopoulos Koen W. Bossers Roozbeh Valadian Joaquín Yus Beatriz Seoane Bert M. Weckhuysen Florian Meirer 《Chemical science》2021,12(24):8458
Metal–Organic Frameworks (MOFs) have the potential to change the landscape of molecular separations in chemical processes owing to their ability of selectively binding molecules. Their molecular sorting properties generally rely on the micro- and meso-pore structure, as well as on the presence of coordinatively unsaturated sites that interact with the different chemical species present in the feed. In this work, we show a first-of-its-kind tomographic imaging of the crystal morphology of a metal–organic framework by means of transmission X-ray microscopy (TXM), including a detailed data reconstruction and processing approach. Corroboration with Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM) images shows the potential of this strategy for further (non-destructively) assessing the inner architecture of MOF crystals. By doing this, we have unraveled the presence of large voids in the internal structure of a MIL-47(V) crystal, which are typically thought of as rather homogeneous lattices. This challenges the established opinion that hydrothermal syntheses yield relatively defect-free material and sheds further light on the internal morphology of crystals.TXM-tomography unraveled large macropore defects within a MIL-47(V) MOF crystal. These pores do not seem to be well connected and they show a preferential orientation. 相似文献
25.
26.
We prove an analog of the base change functor of Λ-trees in the setting of generalized affine buildings. The proof is mainly
based on local and global combinatorics of the associated spherical buildings. As an application we obtain that the class
of generalized affine buildings is closed under taking ultracones and asymptotic cones. Other applications involve a complex
of groups decompositions and fixed point theorems for certain classes of generalized affine buildings. 相似文献
27.
28.
Mario Lamberger Florian Mendel Vincent Rijmen Koen Simoens 《Designs, Codes and Cryptography》2012,62(1):1-18
We investigate generic methods to find near-collisions in cryptographic hash functions. We introduce a new generic approach
based on methods to find cycles in the space of codewords of a code with low covering radius. We give an analysis of our approach
and demonstrate it on the SHA-3 candidate TIB3. 相似文献
29.
Hesam Makki Koen N. S. Adema Elias A. J. F. Peters Jozua Laven Leendert G. J. van der Ven Rolf A. T. M. van Benthem Gijsbertus de With 《Journal of Polymer Science.Polymer Physics》2016,54(6):659-671
In this article we studied the evolution of thermomechanical properties of a polyester‐urethane coating during degradation under different degradation conditions, i.e., aerobic and anaerobic conditions with and without dry/wet cycling during degradation. Dynamic mechanical and thermal analyses show that under aerobic conditions the coatings become stiffer and more brittle in the glassy state. This stiffening is probably due to the increase in the amount of hydrogen bonding and the formation of oxidized groups which increase the polarity of the material and enhance the interactions of the polymer segments. However, oxidation reactions result in a considerable decrease in cross‐link density and stiffness in the rubbery state. Both changes, in the glassy and rubbery states, give rise to development of internal stresses. These stresses increase as the degradation process proceeds. Nevertheless, for samples exposed to anaerobic conditions, the stiffness remains constant in the glassy state and the cross‐link density slightly increases as a result of degradation. This reconfirms the dominance of the effect of oxidation reactions on the mechanical failure of the coatings. Oxygen permeation measurements show a more‐or‐less time‐independent diffusion coefficient and a gradual decrease in solubility of oxygen as a function of exposure time. This results in a slight decrease in oxygen permeation (mainly in the early stage of the degradation) as degradation proceeds. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 659–671 相似文献
30.
W. Koen C. Bollig H. Strauss M. Schellhorn C. Jacobs M. J. D. Esser 《Applied physics. B, Lasers and optics》2010,99(1-2):101-106
We developed a compact Ho:YLF oscillator–amplifier system in a novel setup to utilise the unpolarised pump power from a fibre laser efficiently, and produced 21.3 mJ at 1 kHz, with an M 2 better than 1.1. The amplified energies agreed well with the predicted values from a two dimensional rotational symmetric amplifier model that we developed. The model considers upconversion losses and ground-state depletion, as well as the spatial distribution of the pump beam. 相似文献