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151.
This Account reports the synthesis and characterization of dendrimer-encapsulated metal nanoparticles and their applications to catalysis. These materials are prepared by sequestering metal ions within dendrimers followed by chemical reduction to yield the corresponding zerovalent metal nanoparticle. The size of such particles depends on the number of metal ions initially loaded into the dendrimer. Intradendrimer hydrogenation and carbon-carbon coupling reactions in water, organic solvents, biphasic fluorous/organic solvents, and supercritical CO2 are also described. 相似文献
152.
Preliminary results on MS-325 versus ProHance enhanced magnetic resonance angiography (MRA) at low field strength in a rabbit
model are reported. MS-325-enhanced images were acquired in vivo and compared with pre-contrast as well as conventional contrast-enhanced
images. Visual image quality observations correlated with measurements of signal-to-noise ratio (SNR) and contrast-to-noise
ratio (CNR). While published in vitro data show 7-fold greater relaxivity for MS-325 compared with conventional contrast agents,
we observed an even greater effect here due, presumably, to better matching of the longer vascular lifetime with longer scan
time in this study. In addition, overall vessel clarity improved significantly throughout all the phases of the experiment
in MS-325-enhanced images when compared with conventional contrast-enhanced images. 相似文献
153.
André S Pieters RJ Vrasidas I Kaltner H Kuwabara I Liu FT Liskamp RM Gabius HJ 《Chembiochem : a European journal of chemical biology》2001,2(11):822-830
Galectins are mammalian carbohydrate-binding proteins that are involved in cell-cell and cell-matrix adhesion, cell migration, and growth regulation with relevance to inflammation and tumor spread. These important functions account for the interest to design suitable low molecular weight inhibitors that match the distinct modes of presentation of the carbohydrate recognition domains of the different galectin subfamilies. Using 3,5-di-(2-aminoethoxy)benzoic acid as the branching unit, wedgelike glycodendrimers with two, four, and eight lactose moieties (G1-G3) were synthesized. They were tested in solid-phase competition assays with lactose maxiclusters and various N-glycan branching profiles (miniclusters) as the matrix and also in cell assays. Prototype galectins-1 and -7, chimera-type galectin-3, a plant (AB)(2) toxin, and a lactose-binding immunoglobulin G fraction from human serum were the carbohydrate-binding targets. Potent inhibition and remarkable cluster effects were seen for the homodimeric galectin-1, especially in combination with biantennary N-glycans as the matrix. Remarkably, for the tetravalent G2 glycodendrimer, the inhibitory potency of each lactose unit reached a maximum value of 1667 relative to free lactose. In haemagglutination experiments as a model for cell adhesion, galectin-3 was markedly sensitive to increased sugar valency and a relative potency per lactose of 150 was reached. The spatial orientation of the carbohydrate recognition domains of the endogenous lectins and the branching pattern of the carbohydrates of the glycoprotein matrices used are both important factors in the design and synthesis of glycodendrimers with galectin-selective properties. 相似文献
154.
155.
Production of L-erythrose via L-erythrulose from erythritol using microbial and enzymatic reactions 总被引:4,自引:0,他引:4
Mizanur RM Takeshita K Moshino H Takada G Izumori K 《Journal of Bioscience and Bioengineering》2001,92(3):237-241
A rare aldotetrose, L-erythrose, was produced from erythritol via a two-step reaction. In the first step, complete oxidation of erythritol to L-erythrulose was achieved by using Gluconobacter frateurii IFO 3254. Washed cell suspension of the strain grown on tryptic soy broth (TSB) supplemented with 1% d-sorbitol was used to carry out the transformation reaction at 30 degrees C with shaking at 170 rpm. At 10% substrate concentration, 98% erythritol was converted to L-erythrulose within 48 h. The produced L-erythrulose was then used as a substrate for the production of L-erythrose. The isomerization of L-erythrulose to L-erythrose was carried out using constitutively produced L-ribose isomerase (l-RI) from the mutant strain Acinetobacter sp. DL-28 grown on D-lyxose mineral salt medium. At equilibrium, the yield of L-erythrose from L-erythrulose was 18% and finally 1.7 g L-erythrose was obtained from 10 g erythritol. After a number of simple purification steps, the product was isolated from the reaction mixture by ion-exchange column chromatography (Dowex 50W-X2, Ca2+). The structure of the product was determined after NaBH4 reduction from Infrared (IR) and 13C nuclear magnetic resonance (NMR) spectra. 相似文献
156.
Intraovarian actions of oestrogen 总被引:1,自引:0,他引:1
Oestrogen regulates several hypothalamic and pituitary hormones, which in turn control ovarian functions. Oestrogen and its metabolites, such as catecholoestrogens, also have direct effects within the ovary. This review examines the roles of oestrogen in regulating ovarian folliculogenesis, ovulation and corpus luteum formation. Oestrogen promotes follicular development, which culminates in ovulation, by potentiating follicular development, granulosa cell expression of gonadotrophin receptors, steroidogenesis, and gap junction formation by granulosa cells, and by inhibiting granulosa cell apoptosis. In addition, oestrogen may be needed for corpus luteum formation and maintenance. Studies on mutant mice that either lack one or both of the known oestrogen receptors or are unable to synthesize oestrogen support some but not all of these prior inferences of the roles of oestrogen within the ovary. Although these transgenic mice have proved useful in determining some of the intraovarian actions of oestrogen, they present confounding problems, including hormonal imbalances, that hinder interpretation. Transgenic mice with conditional or tissue-directed mutations in their oestrogen receptors are needed to dissect the ovarian actions of oestrogen further. In addition, microarray technologies, combined with specific hormone treatment regimens are likely to provide an attractive, alternative approach to using mutant mice in clarifying the direct actions of oestrogen in the ovaries of other species. 相似文献
157.
Generation of terawatt pulses by use of optical parametric chirped pulse amplification 总被引:9,自引:0,他引:9
Ross IN Collier JL Matousek P Danson CN Neely D Allott RM Pepler DA Hernandez-Gomez C Osvay K 《Applied optics》2000,39(15):2422-2427
Optical parametric chirped pulse amplifiers offer exciting prospects for generating new extremes in power, intensity, and pulse duration. An experiment is described that was used to investigate the operation of this scheme up to energies approaching a joule, as a step toward its implementation at the petawatt level. The results demonstrate an energy gain of 10(10) with an energy extraction efficiency of 20% and close to diffraction-limited performance. Some spectral narrowing during amplification was shown to be compatible with the time-varying profile of the pump beam and consistent with the measured recompressed pulse durations of 260 and 300 fs before and after amplification, respectively. 相似文献
158.
W.RM 《军民两用技术与产品》2007,(1):9
长期以来,由于我国没有自主的高分辨率立体测图卫星.因而很多基础地理信息数据需要购买国外卫星数据。我国自己的数据因不是“全立体”,所以到目前还没有靠我国卫星绘制出一张本国全境立体地图。 相似文献
159.
Gerling GJ Rigsbee S Childress RM Martin ML 《IEEE transactions on systems, man, and cybernetics. Part A, Systems and humans : a publication of the IEEE Systems, Man, and Cybernetics Society》2009,39(2):388-403
160.