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排序方式: 共有653条查询结果,搜索用时 15 毫秒
531.
532.
Yongzhen Zhang Marcos Gómez-Redondo Dr. Gonzalo Jiménez-Osés Dr. Ana Arda Prof. Dr. Herman S. Overkleeft Prof. Dr. Gijsbert A. van der Marel Prof. Dr. Jesús Jiménez-Barbero Dr. Jeroen D. C. Codée 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(31):12846-12850
Galactosaminogalactan (GAG) is a prominent cell wall component of the opportunistic fungal pathogen Aspergillus fumigatus. GAG is a heteropolysaccharide composed of α-1,4-linked galactose, galactosamine and N-acetylgalactosamine residues. To enable biochemical studies, a library of GAG-fragments was constructed featuring specimens containing α-galactose-, α-galactosamine and α-N-acetyl galactosamine linkages. Key features of the synthetic strategy include the use of di-tert-butylsilylidene directed α-galactosylation methodology and regioselective benzoylation reactions using benzoyl-hydroxybenzotriazole (Bz-OBt). Structural analysis of the Gal, GalN and GalNAc oligomers by a combination of NMR and MD approaches revealed that the oligomers adopt an elongated, almost straight, structure, stabilized by inter-residue H-bonds, one of which is a non-conventional C−H⋅⋅⋅O hydrogen bond between H5 of the residue (i+1) and O3 of the residue (i). The structures position the C-2 substituents almost perpendicular to the oligosaccharide main chain axis, pointing to the bulk solvent and available for interactions with antibodies or other binding partners. 相似文献
533.
Vitaly L. Sushkevich Olga V. Safonova Dennis Palagin Mark A. Newton Jeroen A. van Bokhoven 《Chemical science》2020,11(20):5299
Copper-exchanged zeolites are a class of redox-active materials that find application in the selective catalytic reduction of exhaust gases of diesel vehicles and, more recently, the selective oxidation of methane to methanol. However, the structure of the active copper-oxo species present in zeolites under oxidative environments is still a subject of debate. Herein, we make a comprehensive study of copper species in copper-exchanged zeolites with MOR, MFI, BEA, and FAU frameworks and for different Si/Al ratios and copper loadings using X-ray absorption spectroscopy. Only obtaining high quality EXAFS data, collected at large k-values and measured under cryogenic conditions, in combination with wavelet transform analysis enables the discrimination between the copper-oxo species having different structures. The zeolite topology strongly affects the copper speciation, ranging from monomeric copper species to copper-oxo clusters, hosted in zeolites of different topologies. In contrast, the variation of the Si/Al ratio or copper loading in mordenite does not lead to significant differences in XAS spectra, suggesting that a change, if any, in the structure of copper species in these materials is not distinguishable by EXAFS.The structure of copper-oxo species hosted in zeolites of various topology has been examined using wavelet and Fourier transform analysis of Cu K-edge EXAFS spectra. 相似文献
534.
Michael R. Harvey Fabrizio Chiodo Wouter Noest Cornelis H. Hokke Gijsbert A. van der Marel Jeroen D.C. Code 《Molecules (Basel, Switzerland)》2021,26(8)
Schistosomiasis is caused by blood-dwelling parasitic trematodes of the genus Schistosoma and is classified by the WHO as the second most socioeconomically devastating parasitic disease, second only to malaria. Schistosoma expresses a complex array of glycans as part of glycoproteins and glycolipids that can be targeted by both the adaptive and the innate part of the immune system. Some of these glycans can be used for diagnostic purposes. A subgroup of schistosome glycans is decorated with unique α-(1-2)-fucosides and it has been shown that these often multi-fucosylated fragments are prime targets for antibodies generated during infection. Since these α-(1-2)-fucosides cannot be obtained in sufficient purity from biological sources, we set out to develop an effective route of synthesis towards α-(1-2)-oligofucosides of varying length. Here we describe the exploration of two different approaches, starting from either end of the fucose chains. The oligosaccharides have been attached to gold nanoparticles and used in an enzyme-linked immunosorbent assay ELISA and a microarray format to probe antibody binding. We show that binding to the oligofucosides of antibodies in sera of infected people depends on the length of the oligofucose chains, with the largest glycans showing most binding. 相似文献
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536.
Teng Li Dr. Kanak Roy Dr. Frank Krumeich Dr. Luca Artiglia Dr. Thomas Huthwelker Prof. Jeroen A. van Bokhoven 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(69):15879-15886
Hollow ZSM-5 zeolites of size below one micrometer can be produced by desilication of crystals with aluminium zoning. The parent crystals have a core–shell structure: the core part has nearly no aluminium, whereas the aluminium content in the shell increases when extending to exterior surface. Transmission electron microscopy confirmed the preservation of the crystalline shell after base leaching, but could not identify its subtle change. An increase of the Si/Al ratio of the surface was detected upon leaching the parent material to form the hollow zeolite by using ambient pressure X-ray photoelectron spectroscopy and infrared spectroscopy of substituted alkylpyridines. 27Al MAS NMR showed that base leaching results in a reduced percentage of distorted tetrahedrally coordinated aluminium. The reprecipitation of dissolved species occurs and tetrahedrally coordinated tin atoms can thus be introduced to the shell framework. Overall, the formation of hollow ZSM-5 zeolites by desilication involves not only the removal of silicon-rich core, but also a reduced percentage of exterior aluminium-related acid sites, which should be considered while using hollow zeolites in acid-catalyzed reactions. 相似文献
537.
Maarten Rubens Jeroen H. Vrijsen Joachim Laun Tanja Junkers 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(10):3215-3219
A novel continuous flow system for automated high‐throughput screening, autonomous optimization, and enhanced process control of polymerizations was developed. The computer‐controlled platform comprises a flow reactor coupled to size exclusion chromatography (SEC). Molecular weight distributions are measured online and used by a machine‐learning algorithm to self‐optimize reactions towards a programmed molecular weight by dynamically varying reaction parameters (i.e. residence time, monomer concentration, and control agent/initiator concentration). The autonomous platform allows targeting of molecular weights in a reproducible manner with unprecedented accuracy (<2.5 % deviation from pre‐selected goal) for both thermal and light‐induced reactions. For the first time, polymers with predefined molecular weights can be custom made under optimal reaction conditions in an automated, high‐throughput flow synthesis approach with outstanding reproducibility. 相似文献
538.
Dr. Liulin Yang Aijie Liu Shuqin Cao Rindia M. Putri Prof. Pascal Jonkheijm Prof. Jeroen J. L. M. Cornelissen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(44):15570-15582
The study of protein self‐assembly has attracted great interest over the decades, due to the important role that proteins play in life. In contrast to the major achievements that have been made in the fields of DNA origami, RNA, and synthetic peptides, methods for the design of self‐assembling proteins have progressed more slowly. This Concept article provides a brief overview of studies on native protein and artificial scaffold assemblies and highlights advances in designing self‐assembling proteins. The discussions are focused on design strategies for self‐assembling proteins, including protein fusion, chemical conjugation, supramolecular, and computational‐aided de novo design. 相似文献
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540.