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41.
The electron-transfer oxidation and subsequent cobalt-carbon bond cleavage of vitamin B12 model complexes were investigated using cobaloximes, (DH)2Co(III)(R)(L), where DH- = the anion of dimethylglyoxime, R = Me, Et, Ph, PhCH2, and PhCH(CH3), and L = a substituted pyridine, as coenzyme B12 model complexes and [Fe(bpy)3](PF6)3 or [Ru(bpy)3](PF6)3 (bpy = 2,2'-bipyridine) as a one-electron oxidant. The rapid one-electron oxidation of (DH)2Co(III)(Me)(py) (py = pyridine) with the oxidant gives the corresponding Co(IV) complexes, [(DH)2Co(IV)(Me)(py)]+, which were well identified by the ESR spectra. The reorganization energy (lambda) for the electron-transfer oxidation of (DH)2Co(Me)(py) was determined from the ESR line broadening of [(DH)2Co(Me)(py)]+ caused by the electron exchange with (DH)2Co(Me)(py). The lambda value is applied to evaluate the rate constants of photoinduced electron transfer from (DH)2Co(Me)(py) to photosensitizers in light of the Marcus theory of electron transfer. The Co(IV)-C bond cleavage of [(DH)2Co(Me)(py)]+ is accelerated significantly by the reaction with a base. The overall activation energy for the second-order rate constants of Co(IV)-C bond cleavage of [(DH)2Co(IV)(Me)(py)]+ in the presence of a base is decreased by charge-transfer complex formation with a base, which leads to a negative activation energy for the Co(IV)-C cleavage when either 2-methoxypyridine or 2,6-dimethoxypyridine is used as the base. 相似文献
42.
Kei Yoshida Junko Kusaki Katsunobu Ehara Shiro Saka 《Applied biochemistry and biotechnology》2005,123(1-3):795-806
Japanese beech (Fagus crenata Blume), its cell wall components, and model compounds were treated by supercritical water (380°C, 100 MPa) for 5 s using a batch-type reactor to investigate the production behavior of low molecular weight organic acids. It was found that cellulose and hemicellulose were decomposed to formic acid, pyruvic acid, glycolic acid, acetic acid, and lactic acid, whereas lignin was barely decomposed to such organic acids under the given conditions. However, after prolonged treatment (380°C, 100 MPa, 4 min) of lignin, some organic acids were recovered owing perhaps to the decomposition of the propyl side chain of lignin. It was additionally revealed that the predominant organic acid recovered was acetic acid, which might be derived from the acetyl group of hemicellulose in Japanese beech. 相似文献
43.
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
44.
Nishikimi A Uruno T Duan X Cao Q Okamura Y Saitoh T Saito N Sakaoka S Du Y Suenaga A Kukimoto-Niino M Miyano K Gotoh K Okabe T Sanematsu F Tanaka Y Sumimoto H Honma T Yokoyama S Nagano T Kohda D Kanai M Fukui Y 《Chemistry & biology》2012,19(4):488-497
Highlights? CPYPP binds to DOCK2 DHR-2 domain and inhibits its catalytic activity ? CPYPP inhibits DOCK2-mediated Rac activation in cells ? The structural features of CPYPP required for its inhibitory effect were revealed ? CPYPP inhibits lymphocyte migration and activation in vitro and in vivo 相似文献
45.
Michiko Sasaki Dr. Hidaka Ikemoto Masatoshi Kawahata Dr. Kentaro Yamaguchi Prof. Kei Takeda Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(18):4663-4666
Don't get trapped : The effect of conjugating electron‐withdrawing groups and α‐anion‐stabilizing heteroatom substituents on configurational stability of chiral carbanions through a double bond was examined on the basis of extent of chirality transfer in intramolecular trapping in [2,3]‐Wittig rearrangement of chiral 3‐substituted 1‐propenyloxy‐1‐phenyl‐2‐propen‐1‐yl carbanions (see scheme).
46.
Kotani H Ohkubo K Crossley MJ Fukuzumi S 《Journal of the American Chemical Society》2011,133(29):11092-11095
Addition of potassium superoxide with 18-crown-6 ether (KO(2)(?-)-18-crown-6) to a toluene solution of an acridinium ion-linked porphyrin triad (Acr(+)-H(2)P-Acr(+)) resulted in a remarkable enhancement of the fluorescence intensity. Thus, Acr(+)-H(2)P-Acr(+) acts as an efficient fluorescence sensor for superoxide. Electron transfer from KO(2)(?-)-18-crown-6 to the Acr(+) moiety to produce the two-electron-reduced species (Acr(?)-H(2)P-Acr(?)) results in inhibition of the fluorescence quenching via photoinduced electron transfer, as revealed by laser flash photolysis measurements. 相似文献
47.
Kô Takehara Takao Fujimori Kei Inagi Mari Kajiwara Yoshikazu Harata Kazuhisa Yoshimura 《Electroanalysis》2013,25(2):387-393
A square‐wave voltammetric method for the determination of boric acid in water has been described based on the new understanding of the electrochemical behavior of boric acid‐Azomethine H complexation. Salicylaldehyde and H‐acid were used as the starting materials of boric acid‐Azomethine H complex and their concentrations were optimized for boric acid determination in water. A glassy carbon electrode, instead of a conventional mercury electrode, was used in the measurement. The detection limit of the proposed method was 0.10 mg B dm?3. The proposed method was successfully used for boric acid determination in the water from a seawater desalination RO plant. 相似文献
48.
The development of a new class of hydrazide type organocatalyst, (4R,5R)-1,3-bis(isopropylamino)-4,5-dihenylimidazolidin-2-one 2a, for enantioselective Diels-Alder reactions between cyclopentadiene and α,β-unsaturated aldehydes are presented. The new organocatalyst 2a promoted the reaction, affording Diels-Alder adducts in good yields with good levels of enantioselectivity. 相似文献
49.
Kei Matsuzaki Shuichi Okuzono Taiichi Kanai 《Journal of polymer science. Part A, Polymer chemistry》1979,17(11):3447-3458
α-Methylvinyl methyl ether, ethyl ether, and isobutyl ether were polymerized under various polymerization conditions and the structure of the polymers was determined by 1H- and 13C-NMR spectroscopy. α-Methyl and β-methylene carbon spectra of poly(α-methylvinyl isobutyl ether) showed splitting and were analyzed by triad and tetrad sequences. β-Methylene carbon spectra of poly(α-methylvinyl ethyl ether) also showed splitting. When Eu(fod)3 was added, α-methyl and methoxy proton spectra in benzene of poly(α-methylvinyl methyl ether) showed splitting assigned to triad tacticities. All the polymers obtained in polar solvents exhibited an increase in syndiotacticity. The polymerization mechanism is discussed. 相似文献
50.