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排序方式: 共有1360条查询结果,搜索用时 31 毫秒
101.
Dr. Takaaki Mitsuhashi Dr. Lena Barra Zachary Powers Volga Kojasoy Andrea Cheng Feng Yang Dr. Yoshimasa Taniguchi Dr. Takashi Kikuchi Prof. Dr. Makoto Fujita Prof. Dr. Dean J. Tantillo Prof. Dr. John A. Porco Jr Prof. Dr. Ikuro Abe 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(52):23980-23989
Fungal meroterpenoids are a diverse group of hybrid natural products with impressive structural complexity and high potential as drug candidates. In this work, we evaluate the promiscuity of the early structure diversity-generating step in fungal meroterpenoid biosynthetic pathways: the multibond-forming polyene cyclizations catalyzed by the yet poorly understood family of fungal meroterpenoid cyclases. In total, 12 unnatural meroterpenoids were accessed chemoenzymatically using synthetic substrates. Their complex structures were determined by 2D NMR studies as well as crystalline-sponge-based X-ray diffraction analyses. The results obtained revealed a high degree of enzyme promiscuity and experimental results which together with quantum chemical calculations provided a deeper insight into the catalytic activity of this new family of non-canonical, terpene cyclases. The knowledge obtained paves the way to design and engineer artificial pathways towards second generation meroterpenoids with valuable bioactivities based on combinatorial biosynthetic strategies. 相似文献
102.
Journal of Computer-Aided Molecular Design - In this study, a new method is proposed for calculating the relative binding free energy between a ligand and a protein, derived from a free energy... 相似文献
103.
Mami Miyairi Tsuyoshi Taniguchi Tatsuya Nishimura Katsuhiro Maeda 《Angewandte Chemie (International ed. in English)》2020,59(35):14772-14780
An alternative reaction mechanism of the polymerization of diphenylacetylelnes using a catalytic system composed of tungsten(VI) chloride and tetraphenyltin has been proposed through the optimization of reaction conditions and investigation of the effect of the electronic nature of diphenylacetylene monomers on the polymerizability. The detailed structures of the polymers have been suggested by mass spectrometric analysis of the obtained polymers and oligomers, which suggested that a phenyl group of tetraphenyltin has been introduced to an initiating end of the polymer chain. Mass spectrometric analysis also provided information about the termination processes of the polymerization. The experimental results strongly suggested that the polymerization of diphenylacetylenes using tungsten(VI) chloride and tetraphenyltin proceeds through a migratory insertion mechanism rather than the long‐accepted metathesis mechanism. 相似文献
104.
Shahi Imam Reja Yuichiro Hori Takuya Kamikawa Kohei Yamasaki Miyako Nishiura Steven D. Bull Kazuya Kikuchi 《Chemical science》2022,13(5):1419
The ability to monitor proteolytic pathways that remove unwanted and damaged proteins from cells is essential for understanding the multiple processes used to maintain cellular homeostasis. In this study, we have developed a new protein-labeling probe that employs an ‘OFF–ON–OFF’ fluorescence switch to enable real-time imaging of the expression (fluorescence ON) and degradation (fluorescence OFF) of PYP-tagged protein constructs in living cells. Fluorescence switching is modulated by intramolecular contact quenching interactions in the unbound probe (fluorescence OFF) being disrupted upon binding to the PYP-tag protein, which turns fluorescence ON. Quenching is then restored when the PYP-tag–probe complex undergoes proteolytic degradation, which results in fluorescence being turned OFF. Optimization of probe structures and PYP-tag mutants has enabled this fast reacting ‘OFF–ON–OFF’ probe to be used to fluorescently image the expression and degradation of short-lived proteins.An “OFF–ON–OFF” fluorescence probe for real-time imaging of the expression (fluorescence ‘OFF’) and degradation (fluorescence ‘ON’) of short lived PYP-tag proteins in cellular systems. 相似文献
105.
106.
Novel gas chromatography-mass spectrometry database for automatic identification and quantification of micropollutants 总被引:1,自引:0,他引:1
A novel gas chromatography-mass spectroscopy (GC-MS) database for identification and quantification of micropollutants in environmental and food samples is reported. GC retention times, calibration curves, and mass spectra of nearly 700 chemicals were registered in the database, and the GC retention times of registered chemicals in actual samples were predicted from the retention times of n-alkanes measured before sample analysis. Differences between predicted and actual retention times were less than 3 s, an accuracy that is nearly identical to that obtained by analysis of standard substances. After the retention times were predicted, a calibration file for the GC-MS instrument was created from the predicted retention times, calibration curves, and mass spectra of the registered chemicals. With the resulting calibration file, automated identification of all the chemicals in actual samples was possible without the use of standards, and the identification method was as reliable as conventional methods. When the GC inlet, column, and tuning conditions were adjusted using GC-MS performance check standards, relative standard deviations of 20% or less for determination values could be obtained. More than 90% of the chemicals in the database could be detected at a sensitivity sufficient for all practical purposes (100 pg or less). Because each chemical in the database, to which new substances can easily be added, can be determined in 1 h, micropollutants in samples can be analyzed efficiently and inexpensively. 相似文献
107.
Preparation and physical properties of flame retardant acrylic resin containing nano-sized aluminum hydroxide 总被引:1,自引:0,他引:1
Kazuki Daimatsu Yasunori Kato Katsuhiro Inomata Kazuki Takemura 《Polymer Degradation and Stability》2007,92(8):1433-1438
Poly(methylmethacrylate) (PMMA) shows high strength and transparency but is a flammable material. In this study, the surface of aluminum hydroxide was modified with methacrylate containing phosphoric acid moieties before dispersion in MMA, and organic-inorganic nano-hybrid materials were obtained by bulk polymerization in the presence of the surface-modified aluminum hydroxide. The resulting hybrid materials retained the high transparency of PMMA, with transparency values similar to that of pure PMMA. Moreover, the flame resistance of the hybrid materials was improved in comparison with that of pure PMMA, with depression of the horizontal burning rate becoming a maximum at an inorganic content of 3 wt%. These results suggest that the use of aluminum hydroxide surface-modified with phosphoric acid groups is an efficient method for obtaining good performance fire-resistant polymer materials. 相似文献
108.
Dr. Yasunori Toda Takayuki Yoshida Kaoru Arisue Prof. Dr. Kazuaki Fukushima Dr. Hiroyoshi Esaki Ayaka Kikuchi Prof. Dr. Hiroyuki Suga 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(41):10578-10582
Chiral Lewis acid-catalyzed asymmetric alcohol addition reactions to cyclic carbonyl ylides generated from N-(α-diazocarbonyl)-2-oxazolidinones featuring a dual catalytic system are reported. Construction of a chiral quaternary heteroatom-substituted carbon center was accomplished in which the unique heterobicycles were obtained in good yields with high stereoselection. The alcohol adducts were successfully converted to optically active oxazolidine-2,4-diones by hydrolysis. Mechanistic studies by DFT calculations revealed that alcohols could be activated by Lewis acids, enabling enantioselective protonation of the carbonyl ylides. 相似文献
109.
110.
Takeyuki Kikuchi Tatsuya Nakamura Makoto Nakanishi Jun Takada 《Journal of magnetism and magnetic materials》2010,322(16):2381-2385
Magnetic properties of La-Co substituted M-type strontium hexaferrites were studied. The samples were prepared by polymerizable complex method. Crystal structure of samples has been investigated by powder X-ray diffraction (XRD). Single-phase M-type strontium hexaferrites with chemical composition of Sr1.05−xLaxFe12−xCoxO19 (x=0-0.4) were formed by heating at 1173 K for 24 h in air. Magnetic properties were discussed by measurements of M-H curves with vibrating sample magnetometer (VSM). La-Co substituted M-type strontium hexaferrites prepared by polymerizable complex method showed typical magnetic hysteresis of hard ferrite. The coercive force increased significantly by La-Co substitution with polymerizable complex method. Maximum coercive force achieved in this study is 8.0 kOe (640 kA/m). Scanning electron microscopy revealed that the prepared ferrite particles have plate-like shape of diameter range between 20 and 500 nm. 相似文献