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排序方式: 共有824条查询结果,搜索用时 31 毫秒
1.
Simon Rohrbach Andrew J. Smith Jia Hao Pang Darren L. Poole Tell Tuttle Shunsuke Chiba John A. Murphy 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(46):16518-16540
Jüngste Entwicklungen in der experimentellen und theoretischen Chemie haben zur Identifizierung einer schnell wachsenden Klasse von nukleophilen aromatischen Substitutionsreaktionen geführt, die einem konzertierten Mechanismus (cSNAr) folgen, und nicht dem klassischen, zweistufigen SNAr‐Mechanismus. Während klassische SNAr‐Reaktionen auf die substantielle Aktivierung des aromatischen Ringes durch elektronenziehende Substituenten angewiesen sind, ist eine solche Aktivierung für den konzertierten Reaktionsverlauf nicht zwingend nötig. 相似文献
2.
Derek Yiren Ong Zhihao Yen Asami Yoshii Julia RevilloImbernon Ryo Takita Shunsuke Chiba 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(15):5046-5051
New protocols for controlled reduction of carboxamides to either alcohols or amines were established using a combination of sodium hydride (NaH) and zinc halides (ZnX2). Use of a different halide on ZnX2 dictates the selectivity, wherein the NaH‐ZnI2 system delivers alcohols and NaH‐ZnCl2 gives amines. Extensive mechanistic studies by experimental and theoretical approaches imply that polymeric zinc hydride (ZnH2)∞ is responsible for alcohol formation, whereas dimeric zinc chloride hydride (H?Zn?Cl)2 is the key species for the production of amines. 相似文献
3.
Shuntaro Chiba Yasushi Okuno Teruki Honma Mitsunori Ikeguchi 《Journal of computational chemistry》2019,40(29):2577-2585
We propose a novel force-field-parametrization procedure that fits the parameters of potential functions in a manner that the pair distribution function (DF) of molecules derived from candidate parameters can reproduce the given target DF. Conventionally, approaches to minimize the difference between the candidate and target DFs employ radial DFs (RDF). RDF itself has been reported to be insufficient for uniquely identifying the parameters of a molecule. To overcome the weakness, we introduce energy DF (EDF) as a target DF, which describes the distribution of the pairwise energy of molecules. We found that the EDF responds more sensitively to a small perturbation in the pairwise potential parameters and provides better fitting accuracy compared to that of RDF. These findings provide valuable insights into a wide range of coarse graining methods, which determine parameters using information obtained from a higher-level calculation than that of the developed force field. © 2019 The Authors. Journal of Computational Chemistry published by Wiley Periodicals, Inc. 相似文献
4.
Back Cover: Understanding the Origins of Nucleophilic Hydride Reactivity of a Sodium Hydride–Iodide Composite (Chem. Eur. J. 21/2016) 下载免费PDF全文
5.
Controllable Electronic Structures and Photoinduced Processes of Bay‐Linked Perylenediimide Dimers and a Ferrocene‐Linked Triad 下载免费PDF全文
Haruki Horinouchi Dr. Hayato Sakai Prof. Yasuyuki Araki Prof. Tomo Sakanoue Prof. Taishi Takenobu Prof. Takehiko Wada Prof. Nikolai V. Tkachenko Prof. Taku Hasobe 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(28):9631-9641
A series of perylene‐3,4,9,10‐bis(dicarboximide) (PDI) dimers linked through the bay regions was systematically synthesized to examine the electronic structures and photophysical properties in dependence on the distance and orientation between the two PDI units. The spectroscopic and electrochemical measurements suggested that the coupling value of a directly linked PDI dimer (PDI)2 is much larger than those of para‐ and meta‐phenylene‐bridged PDI dimers p‐(PDI)2 and m‐(PDI)2. The width of Davydov splitting was quantitatively evaluated to compare the coupling values between the two PDI units in these dimers by absorption spectroscopy in frozen 2‐methyl‐THF. Excimer formation of PDI dimers induced the strong fluorescence quenching and large red‐shifts. Femtosecond transient absorption revealed a broad absorption derived from an excimer in the range from about 600 nm to the near‐IR region. The rate constants of formation and decay of the excimer are strongly dependent on the coupling values. Time‐resolved measurements on ferrocene‐linked p‐(PDI)2 revealed a competition between the photoinduced processes of electron transfer and excimer formation in PhCN, which is in sharp contrast with the sole electron‐transfer process in toluene. 相似文献
6.
7.
Kanna Adachi Tomoshi Yamada Hayate Ishizuka Mana Oki Shunsuke Tsunogae Noriko Shimada Osamu Chiba Tatsuya Orihara Prof. Dr. Masafumi Hidaka Prof. Dr. Takatsugu Hirokawa Dr. Minami Odagi Prof. Dr. Keiichi Konoki Prof. Dr. Mari Yotsu-Yamashita Prof. Dr. Kazuo Nagasawa 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(9):2025-2033
A novel series of C12-keto-type saxitoxin (STX) derivatives bearing an unusual nonhydrated form of the ketone at C12 has been synthesized, and their NaV-inhibitory activity has been evaluated in a cell-based assay as well as whole-cell patch-clamp recording. Among these compounds, 11-benzylidene STX ( 3 a ) showed potent inhibitory activity against neuroblastoma Neuro 2A in both cell-based and electrophysiological analyses, with EC50 and IC50 values of 8.5 and 30.7 nm , respectively. Interestingly, the compound showed potent inhibitory activity against tetrodotoxin-resistant subtype of NaV1.5, with an IC50 value of 94.1 nm . Derivatives 3 a – d and 3 f showed low recovery rates from NaV1.2 subtype (ca 45–79 %) compared to natural dcSTX ( 2 ), strongly suggesting an irreversible mode of interaction. We propose an interaction model for the C12-keto derivatives with NaV in which the enone moiety in the STX derivatives 3 works as Michael acceptor for the carboxylate of Asp1717. 相似文献
8.
Taishi Nakanishi Dr. Jun Kikuchi Dr. Atsushi Kaga Prof. Dr. Shunsuke Chiba Prof. Dr. Masahiro Terada 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(37):8230-8234
A catalytic enantioselective synthesis of β-amino secondary amides was achieved using vinyl azides as the enamine-type nucleophile and chiral N-Tf phosphoramide as the chiral Brønsted acid catalyst through a five-step sequential transformation in one pot. The established sequential transformation involves an enantioselective [4+2] cycloaddition reaction of vinyl azides with N-acyl imines as the key stereo-determining step that is efficiently accelerated by a chiral N-Tf phosphoramide catalyst in a highly enantioselective manner in most cases. Further generation of the iminodiazonium ion intermediate through ring opening of the cycloaddition product and subsequent skeletal rearrangement involving Schmidt-type 1,2-aryl group migration followed by recyclization of the resulting nitrilium ion were also initiated by the same acid catalyst. Final acid hydrolysis of the recyclized products in the same pot gave rise to enantioenriched β-amino amides through C−C bond formation at the α-position of the secondary amides. 相似文献
9.
Dr. Yasuyuki Yamada Hayato Iida Shinya Shibano Dr. Nozomi Mihara Prof. Tatsuhisa Kato Prof. Kentaro Tanaka 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(37):e202200819
Spatial distance is an important factor in controlling the functional interactions between molecular units in a conjugate; therefore, the bridging unit has been closely examined. Here, we examined the effect of the flexibility of bridging alkyl chains on the proximity of stacked porphyrin and phthalocyanine conjugated with a fourfold rotaxane linkage. We found that closely stacking two π systems requires bridging alkyl chains above a certain length, and the shorter bridges hinder stacking because of their lower flexibility. The stacking distance between porphyrin and phthalocyanine in the conjugate with decyl (C10) chains was estimated to be 4.03 Å and showed a unique physical character arising from short-distance interactions. The longer alkyl chains minimized steric restriction inside the fourfold rotaxane and allowed efficient communication between the porphyrin and phthalocyanine units. This is due to the flexibility of the side chains. 相似文献
10.
Coronenetetraimide‐Centered Cruciform Pentamers Containing Multiporphyrin Units: Synthesis and Sequential Photoinduced Energy‐ and Electron‐Transfer Dynamics 下载免费PDF全文
Prof. Taku Hasobe Koichi Ida Dr. Hayato Sakai Prof. Kei Ohkubo Prof. Shunichi Fukuzumi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(31):11196-11205
A series of coronenetetraimide (CorTIm)‐centered cruciform pentamers containing multiporphyrin units, in which four porphyrin units are covalently linked to a CorTIm core through benzyl linkages, were designed and synthesized to investigate their structural, spectroscopic, and electrochemical properties as well as photoinduced electron‐ and energy‐transfer dynamics. These systems afforded the first synthetic case of coroneneimide derivatives covalently linked with dye molecules. The steady‐state absorption and electrochemical results indicate that a CorTIm and four porphyrin units were successfully characterized by the corresponding reference monomers. In contrast, the steady‐state fluorescence measurements demonstrated that strong fluorescence quenching relative to the corresponding monomer units was observed in these pentamers. Nanosecond laser flash photolysis measurements revealed the occurrence of intermolecular electron transfer from triplet excited state of zinc porphyrins to CorTIm. Femtosecond laser‐induced transient absorption measurements for excitation of the CorTIm unit clearly demonstrate the sequential photoinduced energy and electron transfer between CorTIm and porphyrins, that is, occurrence of the initial energy transfer from CorTIm (energy donor) to porphyrins (energy acceptor) and subsequent electron transfer from porphyrins (electron donor) to CorTIm (electron acceptor) in these pentamers, whereas only the electron‐transfer process from porphyrins to CorTIm was observed when we mainly excite porphyrin units. Finally, construction of high‐order supramolecular patterning of these pentamers was performed by utilizing self‐assembly and physical dewetting during the evaporation of solvent. 相似文献