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961.
Litavadee Chuaboon Thanyaporn Wongnate Pangrum Punthong Cholpisit Kiattisewee Narin Lawan Chia‐Yi Hsu Chun‐Hung Lin Uwe T. Bornscheuer Pimchai Chaiyen 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(8):2450-2454
This work reports the one‐pot enzymatic cascade that completely converts l ‐arabinose to l ‐ribulose using four reactions catalyzed by pyranose 2‐oxidase (P2O), xylose reductase, formate dehydrogenase, and catalase. As wild‐type P2O is specific for the oxidation of six‐carbon sugars, a pool of P2O variants was generated based on rational design to change the specificity of the enzyme towards the oxidation of l ‐arabinose at the C2‐position. The variant T169G was identified as the best candidate, and this had an approximately 40‐fold higher rate constant for the flavin reduction (sugar oxidation) step, as compared to the wild‐type enzyme. Computational calculations using quantum mechanics/molecular mechanics (QM/MM) molecular dynamics (MD) showed that this improvement is due to a decrease in the steric effects at the axial C4‐OH of l ‐arabinose, which allows a reduction in the distance between the C2‐H and flavin N5, facilitating hydride transfer and enabling flavin reduction. 相似文献
962.
The unresolved debate on the active reaction interface of electrochemical oxidation of lithium peroxide (Li2O2) prevents rational electrode and catalyst design for lithium‐oxygen (Li‐O2) batteries. The reaction interface is studied by using isotope‐labeling techniques combined with time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) and on‐line electrochemical mass spectroscopy (OEMS) under practical cell operation conditions. Isotopically labelled microsized Li2O2 particles with an Li216O2/electrode interface and an Li218O2/electrolyte interface were fabricated. Upon oxidation, 18O2 was evolved for the first quarter of the charge capacity followed by 16O2. These observations unambiguously demonstrate that oxygen loss starts from the Li2O2/electrolyte interface instead of the Li2O2/electrode interface. The Li2O2 particles are in continuous contact with the catalyst/electrode, explaining why the solid catalyst is effective in oxidizing solid Li2O2 without losing contact. 相似文献
963.
Jian‐Qiang Huang Chun‐Yu Ho 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(17):5758-5762
A cross‐hydroalkenylation/rearrangement cascade (HARC), using a cyclopropene and alkyne as substrate pairs, was achieved for the first time by using new [(NHC)Ni(allyl)]BArF catalysts (NHC=N‐heterocyclic carbenes). By controlling the (NHC)NiIIH relative insertion reactivity with cyclopropene and alkyne, a broad scope of cyclopentadienes was obtained with highly selectively. The structural features of the new (NHC)NiII catalyst were important for the success of the reaction. The mild reaction conditions employed may serve as an entry for exploring (NHC)NiII‐assisted vinylcyclopropane rearrangement reactivity. 相似文献
964.
965.
Guang‐Yao Ran Xing‐Xing Yang Jing‐Fei Yue Wei Du Ying‐Chun Chen 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(27):9308-9312
An atom‐economic and highly efficient vinylogous umpolung strategy is developed for deconjugated carbonyl compounds, which generate electron‐deficient π‐allylpalladium complexes with Pd(OAc)2 under ligand‐free conditions. In cooperation with a chiral‐phosphonium‐based phase‐transfer catalyst, the asymmetric direct oxidative allylic alkylations of 3‐substituted oxindoles are furnished under O2 atmosphere. The γ‐ or even remote ?‐regioselective alkylation products, with substantial substituents, are delivered with excellent enantioselectivity, and can be further used to access diverse chiral spirocyclic architectures effectively. The Mukaiyama dienol silyl ether can be utilized similarly, indicating that the current active π‐allylpalladium species results from tautomerization of the PdII‐dienolate intermediate. 相似文献
966.
Yu‐Min Liu Yu‐Qian Huang Shun‐He Liu Dandan Chen Chun Tang Zhen‐Lin Qiu Jun Zhu Yuan‐Zhi Tan 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(38):13410-13413
Bowl inversion is a unique property of buckybowls. The polarity and assembly configuration of buckybowls are reversed after bowl inversion. So far, this unique phenomenon has been studied in solution and on surface, but not in solid state due to spatial constraint. Now a series of exo‐type supramolecular assemblies of trithiasumanene and nanographene are investigated. Tuning the electron density of the nanogaphene component was found to directly affect the binding constant of the complex. Reversible bowl inversion in the solid state was then successfully achieved by subjecting the trithiasumanene–nanographene assembly with the weakest binding strength to repeated heating–cooling cycles, which was unambiguously observed by single crystal X‐ray diffraction. 相似文献
967.
Wan‐Lei Yu Yong‐Chun Luo Lei Yan Dan Liu Zhu‐Yin Wang Peng‐Fei Xu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(32):11057-11061
A synergistic catalytic method combining photoredox catalysis, hydrogen‐atom transfer, and proton‐reduction catalysis for the dehydrogenative silylation of alkenes was developed. With this approach, a highly concise route to substituted allylsilanes has been achieved under very mild reaction conditions without using oxidants. This transformation features good to excellent yields, operational simplicity, and high atom economy. Based on control experiments, a possible reaction mechanism is proposed. 相似文献
968.
Zhi‐Shuo Wang Mian Li Yun‐Lei Peng Zhenjie Zhang Wei Chen Xiao‐Chun Huang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(45):16217-16222
In the evolution of metal–organic frameworks (MOFs) for carbon capture, a lasting challenge is to strike a balance between high uptake capacity/selectivity and low energy cost for regeneration. Meanwhile, these man‐made materials have to survive from practical demands such as stability under harsh conditions and feasibility of scale‐up synthesis. Reported here is a new MOF, Zn(imPim) (aka. MAF‐stu‐1), with an imidazole derivative ligand, featuring binding pockets that can accommodate CO2 molecules in a fit‐like‐a‐glove manner. Such a high degree of shape complementarity allows direct observation of the loaded CO2 in the pockets, and warrants its optimal carbon capture performances exceeding the best‐performing MOFs nowadays. Coupled with the record thermal (up to 680 °C) and chemical stability, as well as rapid large‐scale production, both encoded in the material design, Zn(imPim) represents a most competitive candidate to tackle the immediate problems of carbon dioxide capture. 相似文献
969.
Lei LI Jia-Sheng ZHOU Peng WANG Chao-Qun MA Zhuo-Wei ZHU Jiao GU Chun ZHU Guo-Qing CHEN San-Jun ZHANG Jian-Hua XU 《分析化学》2019,47(1):e19009-e19013
Circular permutation fluorescent protein is a novel method to construct biosensors. The ratio of two excitation channels is employed to quantitatively calibrate the level of analysts. SoNar is one of them, which can be used to monitor cellular NADH/NAD+ levels. However, the 490 nm excitation channel of these biosensors is sensitive to pH environments, which is negative in real applications. In this work, we demonstrated that the fractional intensity ratio extracted from time-resolved fluorescence spectroscopy could be used to quantify NADH levels with one excitation (420 nm) and one emission channels. The 420-nm excitation channel was pH resistant. Comparing to average lifetime, the fractional intensity ratio had a 3.2-fold dynamic range, which was much wider than average lifetimes. 相似文献
970.
Benzofuran has antifungal activity as the inhibitor of N‐myristoyltransferase. Twenty‐nine novel benzofuran‐semicarbazide hybrids were designed and synthesized by principle of drug combinationatory. On this basis, the benzofuran ring was simplified to a resorcinol structure, and sixteen novel 1,3‐dialkoxybenzene‐semicarbazide hybrids were designed and synthesized. All structures of the target compounds were characterized by HRMS and NMR. The in vitro antifungal activity of target compounds was evaluated using the microdilution broth method against eight strains of pathogenic fungi with fluconazole as positive control. According to the results of the target compounds, structure‐activity relationship (SAR) is summarized. The inhibitory activity against the tested strains of simplified compounds ( K01 — K16 ) has different levels improvement compared with compounds Z01 — Z29 . K01 — K16 showed significant antifungal activities against A. fumigatus, C. kruseii, and sensitive C. albicans 5314. Notably, compounds Z20 , Z22 , K10 , K11 and K16 also displayed different activities against two fluconazole‐resistance strains that were isolated from AIDS patients. The minimal inhibitory concentration (MIC) values against fluconazole‐resistant strains were in the range of 2—8 μg/mL and 4—32μg/mL, respectively. Furthermore, molecular docking was performed to investigate the binding affinities and interaction modes between the target compound and N‐myristoyltransferase. 相似文献