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排序方式: 共有555条查询结果,搜索用时 19 毫秒
1.
Asymmetric Total Synthesis of (−)‐Englerin A through Catalytic Diastereo‐ and Enantioselective Carbonyl Ylide Cycloaddition 下载免费PDF全文
Dr. Taiki Hanari Dr. Naoyuki Shimada Dr. Yasunobu Kurosaki Dr. Neetipalli Thrimurtulu Dr. Hisanori Nambu Dr. Masahiro Anada Prof. Dr. Shunichi Hashimoto 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(33):11671-11676
An asymmetric total synthesis of the guaiane sesquiterpene (?)‐englerin A, a potent and selective inhibitor of the growth of renal cancer cell lines, was accomplished. The basis of the approach is a highly diastereo‐ and enantioselective carbonyl ylide cycloaddition with an ethyl vinyl ether dipolarophile under catalysis by dirhodium(II) tetrakis[N‐tetrachlorophthaloyl‐(S)‐tert‐leucinate], [Rh2(S‐TCPTTL)4], to construct the oxabicyclo[3.2.1]octane framework with concomitant introduction of the oxygen substituent at C9 on the exo‐face. Another notable feature of the synthesis is ruthenium tetraoxide‐catalyzed chemoselective oxidative conversion of C9 ethyl ether to C9 acetate. 相似文献
2.
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
3.
Tuning the Redox Properties of a Nonheme Iron(III)–Peroxo Complex Binding Redox‐Inactive Zinc Ions by Water Molecules 下载免费PDF全文
Dr. Yong‐Min Lee Suhee Bang Heejung Yoon Seong Hee Bae Dr. Seungwoo Hong Dr. Kyung‐Bin Cho Dr. Ritimukta Sarangi Prof. Dr. Shunichi Fukuzumi Prof. Dr. Wonwoo Nam 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(30):10676-10680
Redox‐inactive metal ions play important roles in tuning chemical properties of metal–oxygen intermediates. Herein we report the effect of water molecules on the redox properties of a nonheme iron(III)–peroxo complex binding redox‐inactive metal ions. The coordination of two water molecules to a Zn2+ ion in (TMC)FeIII‐(O2)‐Zn(CF3SO3)2 ( 1 ‐Zn2+) decreases the Lewis acidity of the Zn2+ ion, resulting in the decrease of the one‐electron oxidation and reduction potentials of 1 ‐Zn2+. This further changes the reactivities of 1 ‐Zn2+ in oxidation and reduction reactions; no reaction occurred upon addition of an oxidant (e.g., cerium(IV) ammonium nitrate (CAN)) to 1 ‐Zn2+, whereas 1 ‐Zn2+ coordinating two water molecules, (TMC)FeIII‐(O2)‐Zn(CF3SO3)2‐(OH2)2 [ 1 ‐Zn2+‐(OH2)2], releases the O2 unit in the oxidation reaction. In the reduction reactions, 1 ‐Zn2+ was converted to its corresponding iron(IV)–oxo species upon addition of a reductant (e.g., a ferrocene derivative), whereas such a reaction occurred at a much slower rate in the case of 1 ‐Zn2+‐(OH2)2. The present results provide the first biomimetic example showing that water molecules at the active sites of metalloenzymes may participate in tuning the redox properties of metal–oxygen intermediates. 相似文献
4.
Prof. Dr. Shunichi Fukuzumi Dr. Kei Ohkubo Dr. Yong‐Min Lee Prof. Dr. Wonwoo Nam 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(49):17548-17559
Redox‐inactive metal ions and Brønsted acids that function as Lewis acids play pivotal roles in modulating the redox reactivity of metal–oxygen intermediates, such as metal–oxo and metal–peroxo complexes. The mechanisms of the oxidative C?H bond cleavage of toluene derivatives, sulfoxidation of thioanisole derivatives, and epoxidation of styrene derivatives by mononuclear nonheme iron(IV)–oxo complexes in the presence of triflic acid (HOTf) and Sc(OTf)3 have been unified as rate‐determining electron transfer coupled with binding of Lewis acids (HOTf and Sc(OTf)3) by iron(III)–oxo complexes. All logarithms of the observed second‐order rate constants of Lewis acid‐promoted oxidative C?H bond cleavage, sulfoxidation, and epoxidation reactions of iron(IV)–oxo complexes exhibit remarkably unified correlations with the driving forces of proton‐coupled electron transfer (PCET) and metal ion‐coupled electron transfer (MCET) in light of the Marcus theory of electron transfer when the differences in the formation constants of precursor complexes were taken into account. The binding of HOTf and Sc(OTf)3 to the metal–oxo moiety has been confirmed for MnIV–oxo complexes. The enhancement of the electron‐transfer reactivity of metal–oxo complexes by binding of Lewis acids increases with increasing the Lewis acidity of redox‐inactive metal ions. Metal ions can also bind to mononuclear nonheme iron(III)–peroxo complexes, resulting in acceleration of the electron‐transfer reduction but deceleration of the electron‐transfer oxidation. Such a control on the reactivity of metal–oxygen intermediates by binding of Lewis acids provides valuable insight into the role of Ca2+ in the oxidation of water to dioxygen by the oxygen‐evolving complex in photosystem II. 相似文献
5.
过氧化氢既可用作环境友好的绿色氧化剂,也可用作燃料电池中的太阳能燃料,因而受到越来越多的关注.本文综述了太阳能驱动分子氧氧化水制备过氧化氢及其作为绿色氧化剂和燃料的研究进展.利用太阳能将水的e-和4e-氧化与分子氧的e-还原相结合,使光催化生产过氧化氢成为可能;本文讨论了与e-和4e-水氧化选择性及e-和4e-氧还原选择性相关的催化反应控制.由于光催化e-氧化水和e-还原分子氧的过程都产生过氧化氢,因此该组合的催化效率较高.太阳能光驱动水氧化及分子氧还原生产过氧化氢与过氧化氢催化氧化底物相结合,在该过程中分子氧用作最环保的氧化剂. 相似文献
6.
Fukushima Yasumasa Aikawa Shunichi 《Journal of inclusion phenomena and macrocyclic chemistry》2021,100(1-2):143-148
Journal of Inclusion Phenomena and Macrocyclic Chemistry - A colorimetric chemosensor is reported for Cu2+ by a simple mixture of two commercially available reagents, ponceau 6R (P6R) and... 相似文献
7.
Shunichi Sakamoto Toshiyuki Sasaki Ayana Sato‐Tomita Satoshi Takamizawa 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(39):13860-13864
As altering permanent shapes without loss of material function is of practical importance for material molding, especially for elastic materials, shape‐rememorization ability would enhance the utility of elastic crystalline materials. Since diffusionless plastic deformability can preserve the crystallinity of materials, the interconversion of diffusionless mechanical deformability between superelasticity and ferroelasticity could enable shape rememorization of superelastic single crystals. This study demonstrates the shape rememorization of an organosuperelastic single crystal of 1,4‐dicyanobenzene through time‐reversible interconversion of superelasticity–ferroelasticity relaxation by holding the mechanically twinned crystal without heating. The shape‐rememorization ability of the organosuperelastic crystal indicates the compatibility of superelasticity (antiferroelasticity) and ferroelasticity as well as the intrinsic workability of organic crystalline materials capable of recovering their crystal functions under mild conditions. 相似文献
8.
9.
Ikue Homma Hayaka Fukuzumi Tsuguyuki Saito Akira Isogai 《Cellulose (London, England)》2013,20(5):2505-2515
The biodegradation behaviors of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized cellulose fibers (TOCs) and TEMPO-oxidized cellulose nanofibril (TOCN) films containing various carboxyl-group counter-ions were studied. Na+, H+, Ca2+, NH4 +, Cu2+, K+, and Cs+ were introduced into the TOCs or TOCN films, by ion-exchange treatment, as the carboxyl-group counter-ions. TOCs suspended in distilled water were treated with a commercial crude cellulase, and the TOCN films were subjected to soil burial tests. The crude-cellulase-treated products obtained from the TOCs were separated into water/ethanol-insoluble and -soluble fractions, i.e., high- and low-molecular-weight fractions, respectively. The degradation behaviors of the TOCs were evaluated from the weight recovery ratios of the water/ethanol-insoluble fractions and their viscosity-average degrees of polymerization. The results showed that the degradation behaviors of the TOCs were greatly influenced by the counter ion, and the counter-ion order of degradability was Na+ ≈ NH4 + ≈ K+ ≈ Cs+ ? Ca2+ > H+ > Cu2+. These degradability differences were influenced by the swelling behavior of the corresponding TOCs in distilled water; the higher the swelling degree of the TOC, the higher the degradation efficiency of the TOC in the reaction with crude cellulase. Similar biodegradation behaviors were observed in soil burial tests for TOCN films containing various carboxyl-group counter-ions in soil burial test; again the counter ion greatly influenced the resultant biodegradability. The biodegradation behaviors of TOCs and TOCN films can therefore be controlled by selecting an appropriate carboxyl-group counter-ion. 相似文献
10.
Wen‐Jing Shi Dr. Mohamed E. El‐Khouly Dr. Kei Ohkubo Prof. Shunichi Fukuzumi Prof. Dennis K. P. Ng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(34):11332-11341
An efficient functional mimic of the photosynthetic antenna‐reaction center has been designed and synthesized. The model contains a near‐infrared‐absorbing aza‐boron‐dipyrromethene (ADP) that is connected to a monostyryl boron‐dipyrromethene (BDP) by a click reaction and to a fullerene (C60) using the Prato reaction. The intramolecular photoinduced energy and electron‐transfer processes of this triad as well as the corresponding dyads BDP‐ADP and ADP‐C60 have been studied with steady‐state and time‐resolved absorption and fluorescence spectroscopic methods in benzonitrile. Upon excitation, the BDP moiety of the triad is significantly quenched due to energy transfer to the ADP core, which subsequently transfers an electron to the fullerene unit. Cyclic and differential pulse voltammetric studies have revealed the redox states of the components, which allow estimation of the energies of the charge‐separated states. Such calculations show that electron transfer from the singlet excited ADP (1ADP*) to C60 yielding ADP.+‐C60.? is energetically favorable. By using femtosecond laser flash photolysis, concrete evidence has been obtained for the occurrence of energy transfer from 1BDP* to ADP in the dyad BDP‐ADP and electron transfer from 1ADP* to C60 in the dyad ADP‐C60. Sequential energy and electron transfer have also been clearly observed in the triad BDP‐ADP‐C60. By monitoring the rise of ADP emission, it has been found that the rate of energy transfer is fast (≈1011 s?1). The dynamics of electron transfer through 1ADP* has also been studied by monitoring the formation of C60 radical anion at 1000 nm. A fast charge‐separation process from 1ADP* to C60 has been detected, which gives the relatively long‐lived BDP‐ADP.+C60.? with a lifetime of 1.47 ns. As shown by nanosecond transient absorption measurements, the charge‐separated state decays slowly to populate mainly the triplet state of ADP before returning to the ground state. These findings show that the dyads BDP‐ADP and ADP‐C60, and the triad BDP‐ADP‐C60 are interesting artificial analogues that can mimic the antenna and reaction center of the natural photosynthetic systems. 相似文献