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排序方式: 共有198条查询结果,搜索用时 15 毫秒
111.
Photosensitive copolymers have been obtained by chemical modification of natural rubber. The introduction of the photoreactive cinnamoyl group in different conversions has been carried out by the reaction of natural polyisoprene with maleic anhydride, followed by ring opening and condensation with some oxyalkylcinnamate esters. These reactions gave rise to five polymer series. Each series, for which the anhydride content was kept constant, is constituted of five copolymeric products, differing from each other in the size of the aliphatic chain between the chromophore and the main chain. The photosensitive products were submitted to UV irradiation, and their kinetic behavior has been investigated in order to correlate structural dissimilarities with the dimerization rate constants. 相似文献
112.
The gene products of AK121211, AK066327, and AK070534 from Oryza sativa encode cycloartenol, parkeol, and achilleol B synthases, respectively. Parkeol synthase is a unique enzyme that affords parkeol as a single product. Achilleol B synthase is the third seco-type triterpene cyclase identified to date, and triterpenes produced by this synthase include achilleol B (90%), tetracyclic (5.12%) and pentacyclic scaffolds (4.37%), and unidentified triterpenes (0.51%). The pathway for achilleol B biosynthesis is proposed. 相似文献
113.
Yoshinori SaitoMasato Hattori Yuko IwamotoYuriko Takashima Kanako MiharaYoko Sasaki Miho FujiwaraMisato Sakaoku Anna ShimizuXun Chao Chiaki Kuroda Xun Gong Ryo Hanai Motoo Tori 《Tetrahedron》2011,67(12):2220-2231
Root chemicals and DNA sequences were analyzed for Ligularialamarum samples collected in Yunnan and Sichuan Provinces of China and the relationship between the plant and Ligulariasubspicata, its taxonomically closest species, was examined. Both species produce furanoeremophilanes and eremophilan-8-one derivatives as the major components. Eleven new compounds, including a new seco-bakkane compound, were isolated. The two species were found to harbor overlapping intra-specific diversities with respect to the chemicals and the DNA sequences. 相似文献
114.
Tetsuya Yamada Norihiro Suzuki Kazuya Nakata Chiaki Terashima Nobuhiro Matsushita Kiyoshi Okada Akira Fujishima Dr. Ken-ichi Katsumata 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(11):2380-2385
Solar-driven catalysts on semiconductors to produce hydrogen are considered as a means to solve environmental issues. In this study, H2 production coupling with oxygen consumption by noble metal-free α-FeOOH was demonstrated even though the conduction band edge was lower than the reduction potential of H+ to H2. For activation of α-FeOOH, an electron donor, Hg-Xe irradiation, and low pH (ca. 5) were indispensable factors. The H2 production from H2O was confirmed by GC-MS using isotope-labeled water (D2O) and deuterated methanol. The α-FeOOH synthesized by coprecipitation method showed 25 times more active than TiO2. The photocatalytic activity was stable for over 400 h. Our study suggests that α-FeOOH known as rust can produce H2 by light induction. 相似文献
115.
Yoshina-Ishii C Chan YH Johnson JM Kung LA Lenz P Boxer SG 《Langmuir : the ACS journal of surfaces and colloids》2006,22(13):5682-5689
We recently introduced a method to tether intact phospholipid vesicles onto a fluid supported lipid bilayer using DNA hybridization (Yoshina-Ishii, C.; Miller, G. P.; Kraft, M. L; Kool, E. T.; Boxer, S. G. J. Am. Chem. Soc. 2005, 127, 1356-1357). Once tethered, the vesicles can diffuse in two dimensions parallel to the supported membrane surface. The average diffusion coefficient, D, is typically 0.2 microm(2)/s; this is 3-5 times smaller than for individual lipid or DNA-lipid conjugate diffusion in supported bilayers. In this article, we investigate the origin of this difference in the diffusive dynamics of tethered vesicles by single-particle tracking under collision-free conditions. D is insensitive to tethered vesicle size from 30 to 200 nm, as well as a 3-fold change in the viscosity of the bulk medium. The addition of macromolecules such as poly(ethylene glycol) reversibly stops the motion of tethered vesicles without causing the exchange of lipids between the tethered vesicle and supported bilayer. This is explained as a depletion effect at the interface between tethered vesicles and the supported bilayer. Ca ions lead to transient vesicle-vesicle interactions when tethered vesicles contain negatively charged lipids, and vesicle diffusion is greatly reduced upon Ca ion addition when negatively charged lipids are present both in the supported bilayer and tethered vesicles. Both effects are interesting in their own right, and they also suggest that tethered vesicle-supported bilayer interactions are possible; this may be the origin of the reduction in D for tethered vesicles. In addition, the effects of surface defects that reversibly trap diffusing vesicles are modeled by Monte Carlo simulations. This shows that a significant reduction in D can be observed while maintaining normal diffusion behavior on the time scale of our experiments. 相似文献
116.
Melissa A. Ashley Chiaki Yamauchi John C. K. Chu Shinya Otsuka Hideki Yorimitsu Tomislav Rovis 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(12):4042-4046
The synthetic utility of tertiary amines to oxidatively generate α‐amino radicals is well established, however, primary amines remain challenging because of competitive side reactions. This report describes the site‐selective α‐functionalization of primary amine derivatives through the generation of α‐amino radical intermediates. Employing visible‐light photoredox catalysis, primary sulfonamides are coupled with electron‐deficient alkenes to efficiently and mildly construct C?C bonds. Interestingly, a divergence between intermolecular hydrogen‐atom transfer (HAT) catalysis and intramolecular [1,5] HAT was observed through precise manipulation of the protecting group. This dichotomy was leveraged to achieve excellent α/δ site‐selectivity. 相似文献
117.
Morita S Saito N Suzuki K Ohnishi T Imura C Mitsuhashi N 《Magnetic resonance imaging》2008,26(9):1244-1249
Purpose
To compare the degree of visualization of the bile duct and portal vein in terms of the difference in k-space ordering on a three-dimensional (3D) segmented true fast imaging with steady-state precession (trueFISP) sequence.Materials and Methods
A breath-hold coronal 3D segmented trueFISP sequence was prospectively performed on 14 healthy volunteers. Images obtained with centric and linear k-space ordering in the k(x)–k(y) plane were compared by two independent radiologists qualitatively with depiction scores on a five-point scale (1=not seen to 5=excellent depiction) using the Wilcoxon signed-rank test. Images were also compared quantitatively using relative contrast values for the bile duct and portal vein against the hepatic parenchyma using a paired t-test.Results
With centric ordering, both the mean depiction scores and relative contrast values for the portal vein were significantly lower than those with linear ordering (1.5 vs. 3.5, P<.01; and 0.08±0.19 vs. 0.51±0.10, P<.01, respectively). However, in the bile duct, there were no significant differences, only slight differences were found among the results obtained with centric and linear ordering (3.9 vs. 3.8, P=.72; and 0.59±0.06 vs. 0.68±0.06, P<.01, respectively).Conclusion
For visualizing the bile duct, centric k-space ordering on 3D segmented trueFISP sequence is recommended, while linear ordering is recommended for portal vein visualization. 相似文献118.
Shimizu N Ogino C Dadjour MF Ninomiya K Fujihira A Sakiyama K 《Ultrasonics sonochemistry》2008,15(6):988-994
The generation of hydroxyl (OH) radicals was investigated during ultrasonic irradiation and in the presence of TiO(2). The effect of TiO(2) on an ultrasonic system's oxidation power was evaluated by examining the oxidation of salicylic acid. The generation of the salicylic acid derivatives, 2,3-dihydroxybenzoic acid (DHBA) and 2,5-DHBA, was measured by high-performance liquid chromatography coupled with electrochemical detection under different experimental conditions. The presence of TiO(2) enhanced the generation of DHBA during ultrasonic irradiation, thus indicating a higher oxidation power in the ultrasonic system. Al(2)O(3) also increased the generation of DHBA during irradiation; however, the effect of TiO(2) was found to be higher than that of Al(2)O(3). The addition of OH radical scavengers such as dimethylsulfoxide (DMSO), methanol and mannitol significantly suppressed the production of DHBA, and DMSO was found to have the highest suppressive effect among all scavengers. The effects of dissolved gases on the generation of OH radicals were further studied, and their power was found to be in the order Xe > Ar > O(2) > N(2). The degassing of the irradiation solution completely suppressed the generation of OH radicals. These results indicate that the presence of TiO(2) accelerates the generation of OH radicals during ultrasonic irradiation, and that the process may be mediated through the induction of cavitation bubbles in irradiating solutions. 相似文献
119.
Shoichi Ichinose Chiaki Itoh Toshiyuki Minamikawa Kimio Miura Tsunetoshi Watanabe 《Nuclear Physics B》1985,260(1):113-124
On the basis of the background field method, extended one-loop counterterm formulae are derived, and a method to get the two-loop double-pole counter lagrangian is given. As an example, the double-pole divergences of ξ2X3 counterterms are obtained. 相似文献
120.