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排序方式: 共有387条查询结果,搜索用时 15 毫秒
101.
Berry JF Bill E Bothe E George SD Mienert B Neese F Wieghardt K 《Science (New York, N.Y.)》2006,312(5782):1937-1941
The hexavalent state, considered to be the highest oxidation level accessible for iron, has previously been found only in the tetrahedral ferrate dianion, FeO4(2-). We report the photochemical synthesis of another Fe(VI) compound, an octahedrally coordinated dication bearing a terminal nitrido ligand. M?ssbauer and x-ray absorption spectra, supported by density functional theory, are consistent with the octahedral structure having an FeN triple bond of 1.57 angstroms and a singlet d2(xy) ground electronic configuration. The compound is stable at 77 kelvin and yields a high-spin Fe(III) species upon warming. 相似文献
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Lindenberg AM Larsson J Sokolowski-Tinten K Gaffney KJ Blome C Synnergren O Sheppard J Caleman C Macphee AG Weinstein D Lowney DP Allison TK Matthews T Falcone RW Cavalieri AL Fritz DM Lee SH Bucksbaum PH Reis DA Rudati J Fuoss PH Kao CC Siddons DP Pahl R Als-Nielsen J Duesterer S Ischebeck R Schlarb H Schulte-Schrepping H Tschentscher T Schneider J von der Linde D Hignette O Sette F Chapman HN Lee RW Hansen TN Techert S Wark JS Bergh M Huldt G van der Spoel D Timneanu N Hajdu J Akre RA Bong E 《Science (New York, N.Y.)》2005,308(5720):392-395
The motion of atoms on interatomic potential energy surfaces is fundamental to the dynamics of liquids and solids. An accelerator-based source of femtosecond x-ray pulses allowed us to follow directly atomic displacements on an optically modified energy landscape, leading eventually to the transition from crystalline solid to disordered liquid. We show that, to first order in time, the dynamics are inertial, and we place constraints on the shape and curvature of the transition-state potential energy surface. Our measurements point toward analogies between this nonequilibrium phase transition and the short-time dynamics intrinsic to equilibrium liquids. 相似文献
104.
Karsak M Gaffal E Date R Wang-Eckhardt L Rehnelt J Petrosino S Starowicz K Steuder R Schlicker E Cravatt B Mechoulam R Buettner R Werner S Di Marzo V Tüting T Zimmer A 《Science (New York, N.Y.)》2007,316(5830):1494-1497
Allergic contact dermatitis affects about 5% of men and 11% of women in industrialized countries and is one of the leading causes for occupational diseases. In an animal model for cutaneous contact hypersensitivity, we show that mice lacking both known cannabinoid receptors display exacerbated allergic inflammation. In contrast, fatty acid amide hydrolase-deficient mice, which have increased levels of the endocannabinoid anandamide, displayed reduced allergic responses in the skin. Cannabinoid receptor antagonists exacerbated allergic inflammation, whereas receptor agonists attenuated inflammation. These results demonstrate a protective role of the endocannabinoid system in contact allergy in the skin and suggest a target for therapeutic intervention. 相似文献
105.
Isoprenoid pathway optimization for Taxol precursor overproduction in Escherichia coli 总被引:2,自引:0,他引:2
Ajikumar PK Xiao WH Tyo KE Wang Y Simeon F Leonard E Mucha O Phon TH Pfeifer B Stephanopoulos G 《Science (New York, N.Y.)》2010,330(6000):70-74
Taxol (paclitaxel) is a potent anticancer drug first isolated from the Taxus brevifolia Pacific yew tree. Currently, cost-efficient production of Taxol and its analogs remains limited. Here, we report a multivariate-modular approach to metabolic-pathway engineering that succeeded in increasing titers of taxadiene--the first committed Taxol intermediate--approximately 1 gram per liter (~15,000-fold) in an engineered Escherichia coli strain. Our approach partitioned the taxadiene metabolic pathway into two modules: a native upstream methylerythritol-phosphate (MEP) pathway forming isopentenyl pyrophosphate and a heterologous downstream terpenoid-forming pathway. Systematic multivariate search identified conditions that optimally balance the two pathway modules so as to maximize the taxadiene production with minimal accumulation of indole, which is an inhibitory compound found here. We also engineered the next step in Taxol biosynthesis, a P450-mediated 5α-oxidation of taxadiene to taxadien-5α-ol. More broadly, the modular pathway engineering approach helped to unlock the potential of the MEP pathway for the engineered production of terpenoid natural products. 相似文献
106.
Rizzini L Favory JJ Cloix C Faggionato D O'Hara A Kaiserli E Baumeister R Schäfer E Nagy F Jenkins GI Ulm R 《Science (New York, N.Y.)》2011,332(6025):103-106
To optimize their growth and survival, plants perceive and respond to ultraviolet-B (UV-B) radiation. However, neither the molecular identity of the UV-B photoreceptor nor the photoperception mechanism is known. Here we show that dimers of the UVR8 protein perceive UV-B, probably by a tryptophan-based mechanism. Absorption of UV-B induces instant monomerization of the photoreceptor and interaction with COP1, the central regulator of light signaling. Thereby this signaling cascade controlled by UVR8 mediates UV-B photomorphogenic responses securing plant acclimation and thus promotes survival in sunlight. 相似文献
107.
Eberhard WG 《Science (New York, N.Y.)》1977,198(4322):1173-1175
Mature female Mastophora sp. spiders attract prey with a volatile substance which apparently mimics the female sex attractant pheromone of the fall armyworm Spodoptera frugiperda (Lepidoptera). The rate of prey capture is similar to that of a conventional orb weaver of comparable body size. 相似文献
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