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排序方式: 共有87条查询结果,搜索用时 31 毫秒
21.
Grogan G Graf J Jones A Parsons S Turner NJ Flitsch SL 《Angewandte Chemie (International ed. in English)》2001,40(6):1111-1114
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Along with the application of the S-benzoxazolyl glycosides to the high-yielding synthesis of disaccharides of the 2-amino-2-deoxy series, chemoselective assembly of oligosaccharides containing multiple residues of 2-amino-2-deoxyglycoses is reported. This modified armed-disarmed approach is relying on the observation that 2-N-trichloroethoxycarbonyl derivatives of S-benzoxazolyl glycosides are significantly more reactive than their 2-N-phthaloyl counterparts in MeOTf-promoted glycosylations. This allowed efficient chemoselective synthesis of 1,2-trans-linked oligosaccharides, the disarmed reducing end of which can be activated for immediate second step glycosidation in the presence of a more powerful activator, AgOTf. As a result of this two-step activation, trans-trans-patterned trisaccharides could be assembled in a highly efficient manner. This result differs from the classic armed-disarmed technique, according to which usually cis-trans-patterned oligosaccharides are generated. 相似文献
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Freideriki Michailidou Nils Klcker Nicolas V. Cornelissen Rohit K. Singh Aileen Peters Anna Ovcharenko Daniel Kümmel Andrea Rentmeister 《Angewandte Chemie (International ed. in English)》2021,60(1):480-485
Methylation and demethylation of DNA, RNA and proteins has emerged as a major regulatory mechanism. Studying the function of these modifications would benefit from tools for their site‐specific inhibition and timed removal. S‐Adenosyl‐L‐methionine (AdoMet) analogs in combination with methyltransferases (MTases) have proven useful to map or block and release MTase target sites, however their enzymatic generation has been limited to aliphatic groups at the sulfur atom. We engineered a SAM synthetase from Cryptosporidium hominis (PC‐ChMAT) for efficient generation of AdoMet analogs with photocaging groups that are not accepted by any WT MAT reported to date. The crystal structure of PC‐ChMAT at 1.87 Å revealed how the photocaged AdoMet analog is accommodated and guided engineering of a thermostable MAT from Methanocaldococcus jannaschii. PC‐MATs were compatible with DNA‐ and RNA‐MTases, enabling sequence‐specific modification (“writing”) of plasmid DNA and light‐triggered removal (“erasing”). 相似文献
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Dr. Claire M. Young Alex Elmi Dr. Dominic J. Pascoe Rylie K. Morris Calum McLaughlin Andrew M. Woods Dr. Aileen B. Frost Dr. Alix de la Houpliere Dr. Kenneth B. Ling Prof. Terry K. Smith Prof. Alexandra M. Z. Slawin Prof. Patrick H. Willoughby Prof. Scott L. Cockroft Prof. Andrew D. Smith 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(9):3734-3739
The importance of 1,5-O⋅⋅⋅chalcogen (Ch) interactions in isochalcogenourea catalysis (Ch=O, S, Se) is investigated. Conformational analyses of N-acyl isochalcogenouronium species and comparison with kinetic data demonstrate the significance of 1,5-O⋅⋅⋅Ch interactions in enantioselective catalysis. Importantly, the selenium analogue demonstrates enhanced rate and selectivity profiles across a range of reaction processes including nitronate conjugate addition and formal [4+2] cycloadditions. A gram-scale synthesis of the most active selenium analogue was developed using a previously unreported seleno-Hugerschoff reaction, allowing the challenging kinetic resolutions of tertiary alcohols to be performed at 500 ppm catalyst loading. Density functional theory (DFT) and natural bond orbital (NBO) calculations support the role of orbital delocalization (occurring by intramolecular chalcogen bonding) in determining the conformation, equilibrium population, and reactivity of N-acylated intermediates. 相似文献
27.
Benz L Park A Corey JR Mezher MP Park VC 《Langmuir : the ACS journal of surfaces and colloids》2012,28(27):10209-10216
The interaction of two sets of structurally related molecules, thiophenol/thioanisole, and thiophene/tetrahydrothiophene, with vacuum-annealed and ion-bombarded TiO(2)(110) surfaces has been studied using a combination of temperature-programmed reaction spectroscopy (TPRS) and X-ray photoelectron spectroscopy (XPS). All thioethers studied were observed to adsorb and desorb from both surfaces without producing reaction products, while thiophenol, the only species studied containing a S-H bond, reacted with both surfaces. Approximately 25% of surface bound thiophenol decomposed over the vacuum-annealed surface. On the bombarded surface, thiophenol both decomposed into surface-bound C(x)H(y)/S fragments, and reacted to form benzene, which desorbed from the surface at 400 K. We propose that phenylthiolate formation on the bombarded surface leads to the observed production of benzene. These results highlight the importance of defects in the reactivity of titania, and lay the foundation for the study of larger, refractory sulfur compounds present in fuel. 相似文献
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Aileen Höhne Lian Yu Linjing Mu Dr. Markus Reiher Prof. Dr. Ulrike Voigtmann Dr. Ulrich Klar Dr. Keith Graham Dr. P. August Schubiger Prof. Dr. Simon M. Ametamey Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(15):3736-3743
Water stable! Radiochemists have recently discovered silicon chemistry as a tool for the introduction of 18F into biomolecules for positron emission tomography (PET) imaging. 18F‐labeled PET tracers must be stable towards defluorination under physiological conditions. Here, a theoretical model of organofluorosilane hydrolysis is developed that correlates with the experimentally determined hydrolytic half‐lives and allows estimation of the stability of newly designed compounds (see scheme).
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Aileen E. Lozsn R. Manuel S. Romero-Cano 《Journal of colloid and interface science》2009,339(1):36-44
We study the swelling behavior of carboxylated core–shell particles. It is well-known that these particles swell with increasing pH due to the electrostatic repulsion between carboxylate groups. Our results reveal that the swelling behavior is affected by the preparation method. We find that the swelling is promoted in those particles which were initially in a highly swollen state (pH 10). However, the swelling is hindered for those particles which were not previously in this trigger pH. In the hindered systems, a compact conformation of the polymer shell is induced by hydrophobic attractions between the non-charged segments which compete against the swelling driving force. In addition, an interesting hysteresis behavior emerges when promoted systems are subjected to a heating–cooling cycle; a new stable system appears with a less extended polymer shell conformation. Furthermore, salt-induced swelling experiments corroborate not only polymer restructuring but also assembly among carboxylate groups which affects their ionization grade. 相似文献
30.
Aileen Eyou Bao Thanh Pham Tony Kirk Benedicta D. Arhatari Chanh Quoc Tran 《X射线光谱测定》2019,48(2):85-93
We present the theoretical formalism and an experimental demonstration of a technique for two-dimensional quantitative imaging of two-component samples using polychromatic X-rays. The technique takes into account the full spectral information of the incident polychromatic beam to quantify the total X-ray attenuation, due to each component presented in the sample, as functions of both energy and thickness. As a result, this technique is able to effectively ameliorate the effects of beam hardening. Here, we demonstrate the application of this technique to a two-component sample. The technique makes it possible for laboratory-based polychromatic X-ray sources to be used for critical quantitative purposes. 相似文献