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Regio‐ and Enantioselective Sequential Dehalogenation of rac‐1,3‐Dibromobutane by Haloalkane Dehalogenase LinB 下载免费PDF全文
Johannes Gross Prof. Zbyněk Prokop Prof. Dick Janssen Prof. Kurt Faber Dr. Mélanie Hall 《Chembiochem : a European journal of chemical biology》2016,17(15):1437-1441
The hydrolytic dehalogenation of rac‐1,3‐dibromobutane catalyzed by the haloalkane dehalogenase LinB from Sphingobium japonicum UT26 proceeds in a sequential fashion: initial formation of intermediate haloalcohols followed by a second hydrolytic step to produce the final diol. Detailed investigation of the course of the reaction revealed favored nucleophilic displacement of the sec‐halogen in the first hydrolytic event with pronounced R enantioselectivity. The second hydrolysis step proceeded with a regioselectivity switch at the primary position, with preference for the S enantiomer. Because of complex competition between all eight possible reactions, intermediate haloalcohols formed with moderate to good ee ((S)‐4‐bromobutan‐2‐ol: up to 87 %). Similarly, (S)‐butane‐1,3‐diol was formed at a maximum ee of 35 % before full hydrolysis furnished the racemic diol product. 相似文献
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Wasps of genus Asobara, a larval parasitoid of Drosophila, have become model organisms for the study of host-parasite interactions. However, little is known about the role of pheromones in locating mates and courtship behavior in this genus. In the present study, we aimed to identify the female courtship pheromone in Asobara tabida. The chemical compositions of solvent extracts from male and female wasps were analyzed by GC/MS. These extracts, fractions thereof, and synthetic pheromone candidates were tested for their activity in behavioral bioassays. The results demonstrate that the courtship pheromone of A. tabida is characterized by a remarkable chemical diversity. A multi-component blend of female-specific compounds including methyl 6-methylsalicylate (M6M), fatty alcohol acetates (FAAs), and cuticular hydrocarbons (CHCs) released male courtship behavior. Using a combinatory approach that included both purified natural products and synthetic analogs, it was shown that none of the three chemical classes alone was sufficient to release a full behavioral response in males. However, a blend of M6M and FAAs or combinations of one or both of these with female-derived CHCs resulted in wing-fanning responses by males comparable to those elicited by the crude extract of females. Thus, components from all three chemical classes contribute to the bioactivity of the pheromone, but none of the elements plays a key role or is irreplaceable. The fact that one of the FAAs, vaccenyl acetate, is also used as a kairomone by Asobara females to locate Drosophila hosts suggests that a pre-existing sensory responsiveness to vaccenyl acetate might have been involved in the evolution of the female sex pheromone in Asobara. 相似文献
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Solid‐state NMR study of spin finish of thermally treated PAN and PAN/CNT precursor fibers 下载免费PDF全文
Sushanta Ghoshal Yaodong Liu Prabhakar Gulgunje Kishor Gupta Han Gi Chae Johannes Leisen Satish Kumar 《应用聚合物科学杂志》2014,131(17)
Dry‐jet wet‐spun polyacrylonitrile (PAN) and PAN/carbon nanotubes (CNTs) precursor fibers coated by spin finishes were characterized using the solid‐state 1H nuclear magnetic resonance technique. Series of fiber samples were prepared upon thermal treatment at different temperatures (room temperature to 180°C). Using the Hahn echo sequence, relatively mobile components were identified and the effect of the heat treatment on those components was studied. It was observed that the mobile components are mainly the spin finishes. Heat treatment caused loss of one of the spin finishes (Type B) to a great extent (~80%), whereas the other two spin finishes (Type A and Type C) were more stable. Additional information regarding the change in molecular mobility due to heat treatment was obtained by the spin‐lattice relaxation time ( T1 ) analysis. It was found that the presence of CNT affects the T1 relaxation time of the polymer in the composite fiber, however, that of relatively mobile components remains unaffected. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40734. 相似文献
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Johannes Schilling Christian Horend André Bardow 《American Institute of Chemical Engineers》2020,66(5):e16903
The key to many chemical and energy conversion processes is the choice of the right molecule, for example, used as working fluid. However, the choice of the molecule is inherently coupled to the choice of the right process flowsheet. In this work, we integrate superstructure-based flowsheet design into the design of processes and molecules. The thermodynamic properties of the molecule are modeled by the PC-SAFT equation of state. Computer-aided molecular design enables considering the molecular structure as degree of freedom in the process optimization. To consider the process flowsheet as additional degree of freedom, a superstructure of the process is used. The method results in the optimal molecule, process, and flowsheet. We demonstrate the method for the design of an organic Rankine cycle considering flowsheet options for regeneration, reheating, and turbine bleeding. The presented method provides a user-friendly tool to solve the integrated design problem of processes, molecules, and process flowsheets. 相似文献
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Umberto De Rossi Johannes Moll Monika Spieles Günther Bach Siegfried Dhne Jrg Kriwanek Maria Lisk 《Advanced Synthesis \u0026amp; Catalysis》1995,337(1):203-208
Cyanine dyes ( 1a–d ) with the 5,5′,6,6′-tetrachloro-1,1′-dialkyl-3,3′-di-(3-carboxypropyl)-benzimidocarbocyanine chromophore differing only in the chain length of their alkyl groups in 1,1′-position have been synthesized, spectroscopically characterized, and compared with 5,5′6,6′-tetrachloro-1,1′-diethyl-3,3′-di-(4-sulfobutyl)-benzimidocarbocyanine( TDBC ). In aqueous solution the dyes form J-aggregates which, depending on the alkyl group chain length, exhibit J-bands differing in spectral positions, bandwidth, and in the number of peaks. 相似文献