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排序方式: 共有540条查询结果,搜索用时 15 毫秒
531.
K. Masumoto H. Matsumura K. Bessho A. Toyoda 《Journal of Radioanalytical and Nuclear Chemistry》2008,278(2):449-453
Activation is one of the severe problems at the high-energy accelerator facilities. By using gamma-ray spectrometry and activation
detector technique, we could obtain important information on (1) nuclear reactions, (2) energy spectra of secondary particles,
(3) penetration behavior of secondary particles in shield wall, (4) historical record of beam loss occurred in the accelerator
rooms. It was concluded that the technique and knowledge of activation analysis are very useful to solve the radiation protection
problems at the accelerator facilities. 相似文献
532.
Glycosyl boranophosphate triesters were synthesized via a boranophosphorylation of reducing sugars. The usefulness of the resultant glycosyl boranophosphates as versatile chemically stable precursors of various glycosyl phosphate derivatives is demonstrated. 相似文献
533.
The lipase-catalyzed ROP of molecularly pure cyclic oligomers with a definite degree of oligomerization is analyzed with respect to the molecular weights of the resulting polymers and certain kinetic parameters of the enzymatic reaction. Cyclic BA dimers, trimers, and tetramers polymerize faster than the equivalent monomer; however, the latter produces PBA of significantly higher molecular weight. The reason is that the ring opening of the cyclic monomer is slow, leading to a lower initiator concentration than that produced by the cyclic BA dimer and trimer. Similarly, the cyclic BS dimer produces PBS of higher molecular weight than that obtained from the cyclic BS trimer. 相似文献
534.
Ng YH Ikeda S Harada T Morita Y Matsumura M 《Chemical communications (Cambridge, England)》2008,(27):3181-3183
Platinum nanoparticles embedded in a hollow porous carbon shell prepared by a photocatalytic reaction acted as a reusable catalyst for the aerobic oxidation of alcohols under atmospheric pressure of oxygen in water. 相似文献
535.
Matsumura H Ortiz R Ludwig R Igarashi K Samejima M Gorton L 《Langmuir : the ACS journal of surfaces and colloids》2012,28(29):10925-10933
Achieving efficient electrochemical communication between redox enzymes and various electrode materials is one of the main challenges in bioelectrochemistry and is of great importance for developing electronic applications. Cellobiose dehydrogenase (CDH) is an extracellular flavocytochrome composed of a catalytic FAD containing dehydrogenase domain (DH(CDH)), a heme b containing cytochrome domain (CYT(CDH)), and a flexible linker region connecting the two domains. Efficient direct electron transfer (DET) of CDH from the basidiomycete Phanerochaete chrysosporium (PcCDH) covalently attached to mixed self-assembled monolayer (SAM) modified gold nanoparticle (AuNP) electrode is presented. The thiols used were as follows: 4-aminothiophenol (4-ATP), 4-mercaptobenzoic acid (4-MBA), 4-mercaptophenol (4-MP), 11-mercapto-1-undecanamine (MUNH(2)), 11-mercapto-1-undecanoic acid (MUCOOH), and 11-mercapto-1-undecanol (MUOH). A covalent linkage between PcCDH and 4-ATP or MUNH(2) in the mixed SAMs was formed using glutaraldehyde as cross-linker. The covalent immobilization and the surface coverage of PcCDH were confirmed with surface plasmon resonance (SPR). To improve current density, AuNPs were cast on the top of polycrystalline gold electrodes. For all the immobilized PcCDH modified AuNPs electrodes, cyclic voltammetry exhibited clear electrochemical responses of the CYT(CDH) with fast electron transfer (ET) rates in the absence of substrate (lactose), and the formal potential was evaluated to be +162 mV vs NHE at pH 4.50. The standard ET rate constant (k(s)) was estimated for the first time for CDH and was found to be 52.1, 59.8, 112, and 154 s(-1) for 4-ATP/4-MBA, 4-ATP/4-MP, MUNH(2)/MUCOOH, and MUNH(2)/MUOH modified electrodes, respectively. At all the mixed SAM modified AuNP electrodes, PcCDH showed DET only via the CYT(CDH). No DET communication between the DH(CDH) domain and the electrode was found. The current density for lactose oxidation was remarkably increased by introduction of the AuNPs. The 4-ATP/4-MBA modified AuNPs exhibited a current density up to 30 μA cm(-2), which is ~70 times higher than that obtained for a 4-ATP/4-MBA modified polycrystalline gold electrode. The results provide insight into fundamental electrochemical properties of CDH covalently immobilized on gold electrodes and promote further applications of CDHs for biosensors, biofuel cells, and bioelectrocatalysis. 相似文献
536.
Sivaramakrishnan S Ouellet H Matsumura H Guan S Moënne-Loccoz P Burlingame AL Ortiz de Montellano PR 《Journal of the American Chemical Society》2012,134(15):6673-6684
CYP125 from Mycobacterium tuberculosis catalyzes sequential oxidation of the cholesterol side-chain terminal methyl group to the alcohol, aldehyde, and finally acid. Here, we demonstrate that CYP125 simultaneously catalyzes the formation of five other products, all of which result from deformylation of the sterol side chain. The aldehyde intermediate is shown to be the precursor of both the conventional acid metabolite and the five deformylation products. The acid arises by protonation of the ferric-peroxo anion species and formation of the ferryl-oxene species, also known as Compound I, followed by hydrogen abstraction and oxygen transfer. The deformylation products arise by addition of the same ferric-peroxo anion to the aldehyde intermediate to give a peroxyhemiacetal that leads to C-C bond cleavage. This bifurcation of the catalytic sequence has allowed us to examine the effect of electron donation by the proximal ligand on the properties of the ferric-peroxo anion. Replacement of the cysteine thiolate iron ligand by a selenocysteine results in UV-vis, EPR, and resonance Raman spectral changes indicative of an increased electron donation from the proximal selenolate ligand to the iron. Analysis of the product distribution in the reaction of the selenocysteine substituted enzyme reveals a gain in the formation of the acid (Compound I pathway) at the expense of deformylation products. These observations are consistent with an increase in the pK(a) of the ferric-peroxo anion, which favors its protonation and, therefore, Compound I formation. 相似文献
537.
In order to improve the solubility of intensively fluorescent 2,5-bis(benzimidazol-2-yl)pyrazine (BBIP), we synthesized new BBIP derivatives (2, 3a,b, and 5a,b) possessing two alkyl chains at the N-1 and N-1′ positions of the two benzimidazole moieties. Characterization of these compounds demonstrated that they exhibit high fluorescence intensity even in protic solvents, as well as solvatochromic fluorescence, in which their fluorescence maxima in aqueous methanol exhibited bathochromic shift with increasing ?r value of the medium. We utilized 5a as a microenvironment polarity probe to indicate the variation in polarity around the backbone of the temperature-sensitive poly(N-isopropylacrylamide) by measuring the spectral change caused by the thermal phase transition of the polymer. 相似文献
538.
Shuichi Matsumura Satoshi Harai Kazunobu Toshima 《Macromolecular rapid communications》2001,22(3):215-218
The enzymatic degradation and polymerization using an enzyme were carried out with respect to the establishment of a sustainable chemical recycling system for poly(trimethylene carbonate) [P(TMC)] which is a potentially biodegradable synthetic plastic. The enzymatic transformation of P(TMC)s having an Mn of 3000~48000 using Candida antarctica lipase (lipase CA) in acetonitrile at 70 °C afforded the corresponding cyclic monomer, trimethylene carbonate (TMC: 1,3‐dioxan‐2‐one), in a yield of up to 80%. Thus obtained TMC readily polymerized again using both fresh lipase CA and recovered lipase CA. 相似文献
539.
Shuichi Matsumura Hiroki Ebata Reiko Kondo Kazunobu Toshima 《Macromolecular rapid communications》2001,22(16):1325-1329
The enzymatic transformation of poly(ϵ‐caprolactone) (PCL) into repolymerizable oligomers in supercritical carbon dioxide (scCO2) using an enzyme was carried out in order to establish a sustainable chemical recycling system for PCL, which is a typical biodegradable synthetic plastic. The enzymatic conversion of PCL beads having an M̄n of 110 000 using Candida antarctica lipase (lipase CA) in scCO2 containing small amounts of water quantitatively afforded CL oligomers at 40°C. The CL oligomers were readily repolymerized using the same enzyme to produce high‐molecular weight PCL. 相似文献
540.