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91.
Wang ZJ Brown CJ Bergman RG Raymond KN Toste FD 《Journal of the American Chemical Society》2011,133(19):7358-7360
Gold(I)-phosphine complexes are readily encapsulated by a tetrahedral supramolecular host (Ga(4)L(6)). We have investigated the catalytic activity of the resulting complexes for the intramolecular hydroalkoxylation of allenes. The catalytic activity of Me(3)PAuBr was increased 8-fold by encapsulation, as determined by initial rate kinetics, and we observed up to 67 catalytic turnovers by Me(3)PAu(+) encapsulated in Ga(4)L(6). 相似文献
92.
93.
HPLC determination of four active saponins from Panax notoginseng in rat serum and its application to pharmacokinetic studies 总被引:1,自引:0,他引:1
Four main active saponins (ginsenosides Rg1, Rb1, Rd and notoginsenoside R1) in Panax notoginseng in rat serum after oral and intravenous administration of total saponins of P. notoginseng (PNS) to rats were determined using a simple and sensitive high-performance chromatographic method. The serum samples were pretreated with solid-phase extraction before analysis. The calibration curves for the four saponins were linear in the given concentration ranges. The intra-day and inter-day assay coefficients in serum were less than 10.0% and the recoveries of the method were higher than 80.0% in the high, middle and low concentrations. This method was applied to study the pharmacokinetics following oral and intravenous administration of PNS. 相似文献
94.
The preparation of monolithic poly(butyl methacrylate-co-ethylene dimethacrylate) capillary columns using photoinitiated in situ polymerization within 200 microm i.d. capillaries and their application for microHPLC separations of proteins have been studied. The low resistance to flow characteristic of monolithic columns, enabled the use of very high flow rates of up to 100 microL/min representing a flow velocity of 87 mm/s. Very good separations of a model protein mixture consisting of ribonuclease A, cytochrome c, myoglobin, and ovalbumin was achieved in less than 40 s using a very simple single step gradient of the mobile phase. Interestingly, no effect of the pore size on the separations of proteins was observed for these monolithic columns within the size range of 0.66-2.2 microm. The monolithic microHPLC columns are found very robust and no changes in the long term separation performance and back pressure were observed. 相似文献
95.
Peptides represent an extensive class of biologically active molecules. They may be used as leads in the development of novel therapeutic agents provided the pharmacophoric information present within them can be translated into non-peptide analogs that lack the peptide backbone and are stable to proteolysis. This is the rationale for peptidomimetic drug design. Frequently, the -turn has been implicated as a conformation important for biological recognition of peptides. Empirical evidence from known peptidomimetics, coupled with a theoretical model of peptide binding and the observation that glycine and proline residues are common within the -turn, has suggested the design of molecules to mimic placement of between two and four of the side-chains. The moderate number of different -turn conformations, combined with the combinatoric nature of side-chain selection complicates the procedure. In this paper, cluster analysis has been used to classify the arrangement of C_ atoms about the various fragments of the -turn. Recombination of the observed patterns provides a general model for the -turn which may be used as an effective screen for potential peptidomimetic scaffolds in chemical databases. 相似文献
96.
Walter K. Dean Gary L. Simon Paul M. Treichel Lawrence F. Dahl 《Journal of organometallic chemistry》1973,50(1):193-207
The accidental but intriguing synthesis of acetatobis(triphenylphosphine)dicarbonylmanganese(I), (CH3CO2)Mn(CO)2[P(C6H5)3]2, has been accomplished by the reaction of NaMn(CO)5 with (CH3)3SiCl followed by the addition of triphenylphosphine and acetic acid. A three-dimensional single-crystal X-ray diffraction analysis has shown an octahedral-like molecule containing a symmetrically oxygen-chelating acetate group, the first such group to be reported in a metal carbonyl complex. The two triphenylphosphine ligands occupy mutually trans positions with the two carbonyl ligands possessing the remaining cis sites in the octahedral complex. The compound crystallizes with four molecules in a monoclinic unit cell of space group symmetry and of dimensions a = 17.744(2) Å, b = 9.692(1) Å, c = 20.004(2) Å, and β = 106.195(4)°. The relatively long MnO(acetate) bond lengths [2.066(6) and 2.069(7) Å] and the relatively short MnCO bond lengths [1.701(12) and 1.760(13) Å] and the relatively short MnP(C6H5)3 bond lengths [2.260(3) and 2.275(3) Å], compared to the corresponding MnCO and MnP(C6H5)3 bond lengths in other manganese carbonyl triphenylphosphine complexes, are rationalized on the basis that the acetate ligand in this molecule functions primarily as a σ-donor. 相似文献
97.
The gold(I)-catalyzed regioselective cyclizations of silyl ketene amides or carbamates with alkynes were utilized to construct cyclopentanes or dehydro-delta-lactams. 相似文献
98.
Mohammed A. Bari Siddiqui Shakeel Ahmed Musaed S. Al-Gharami Chistopher F. Dean 《Reaction Kinetics and Catalysis Letters》2007,91(1):61-67
Sulfur reduction ability of alumina supported zinc, gallium and zinc-gallium additives for fluid catalytic cracking catalysts
was evaluated in a micro-activity test unit (MAT). Gallium/alumina showed the highest sulfur reduction of 31%, but the cracking
activity of the catalyst was decreased. Zinc-gallium/alumina reduced sulfur in 24 wt.% without decreasing the base catalyst
activity. 相似文献
99.
Jamin Huang Dean F. Bushey Michael D. Graves Brenda F. Johnson Dianne D. Singleton 《Journal of heterocyclic chemistry》1987,24(1):1-7
A series of 3-substituted-5-methoxy-1,3,4-oxadiazol-2-ones were prepared from aldehydes, ketones, phenylacetic acids, and 1,2- and 1,3-diketones. Conditions for the formation of these oxadiazolones from the precursor N-carbamoyl chlorides depended on the structure, and varied from spontaneous ring closure to those requiring bases. Variation in the N-3 substituents sometimes produced mixtures of isomers which were separated and identified. These molecules were prepared in order to study the effect of the N-3 substituent variation on the biological properties of oxadiazolones. 相似文献
100.
John S. Riley Tomas Baer G. Dean Marbury 《Journal of the American Society for Mass Spectrometry》1991,2(1):69-75
High-resolution mass spectrometry (HRMS), hybrid tandem mass spectrometry (MS/MS) (EBqQ), and photoelectron-photoion coincidence (PEPICO) experiments were conducted to examine a possible ortho-ortho effect resulting in a novel [M - 35]+ fragment ion in 2-alkyl-4, 6-dinitrophenols. For compounds having ethyl or larger alkyl substituents, [M35]+ was observed only when [M - 18]+ ions were present, with the ortho nitro group being involved in the reaction to [M- 35]+. For [M - 18]+ and [M - 35]+, HRMS results were consistent with losses of H2O and H2O + OH, respectively, whereas MS/MS results indicated a sequential reaction due to metastable dissociations. The appearance energy determined by PEPICO for [M - 35]+ was found to be greater than the appearance energy for [M - 18]+, thus supporting a sequential reaction. 69–75). 相似文献