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排序方式: 共有434条查询结果,搜索用时 93 毫秒
91.
92.
Tymtsunik AV Bilenko VA Kokhan SO Grygorenko OO Volochnyuk DM Komarov IV 《The Journal of organic chemistry》2012,77(2):1174-1180
An approach to the synthesis of 1-alkyl-5-((di)alkylamino)tetrazoles by nucleophilic substitution in 1-alkyl-5-sulfonyltetrazoles with anions generated from the primary or secondary amines was developed. Tolerance of the method to the presence of some functional groups (i.e., protected amine) in both components of the reaction was demonstrated. Obtained tetrazoles are promising building blocks for the design of peptide surrogates, in particular, for replacement approaches of alkyl urea derivatives. 相似文献
93.
Donald F. Smith Andriy Kharchenko Marco Konijnenburg Ivo Klinkert Ljiljana Pa?a-Toli? Ron M. A. Heeren 《Journal of the American Society for Mass Spectrometry》2012,23(11):1865-1872
Mass spectrometry imaging by Fourier transform ion cyclotron resonance (FT-ICR) yields hundreds of unique peaks, many of which cannot be resolved by lower performance mass spectrometers. The high mass accuracy and high mass resolving power allow confident identification of small molecules and lipids directly from biological tissue sections. Here, calibration strategies for FT-ICR MS imaging were investigated. Sub-parts-per-million mass accuracy is demonstrated over an entire tissue section. Ion abundance fluctuations are corrected by addition of total and relative ion abundances for a root-mean-square error of 0.158?ppm on 16,764 peaks. A new approach for visualization of FT-ICR MS imaging data at high resolution is presented. The ??Mosaic Datacube?? provides a flexible means to visualize the entire mass range at a mass spectral bin width of 0.001?Da. The high resolution Mosaic Datacube resolves spectral features not visible at lower bin widths, while retaining the high mass accuracy from the calibration methods discussed. 相似文献
94.
Serpil Sayın 《Mathematical Programming》2000,87(3):543-560
One way of solving multiple objective mathematical programming problems is finding discrete representations of the efficient
set. A modified goal of finding good discrete representations of the efficient set would contribute to the practicality of
vector maximization algorithms. We define coverage, uniformity and cardinality as the three attributes of quality of discrete
representations and introduce a framework that includes these attributes in which discrete representations can be evaluated,
compared to each other, and judged satisfactory or unsatisfactory by a Decision Maker. We provide simple mathematical programming
formulations that can be used to compute the coverage error of a given discrete representation. Our formulations are practically
implementable when the problem under study is a multiobjective linear programming problem. We believe that the interactive
algorithms along with the vector maximization methods can make use of our framework and its tools.
Received April 7, 1998 / Revised version received March 1999?Published online November 9, 1999 相似文献
95.
Evgen V. Govor Andrey B. Lysenko Alexander N. Chernega Judith A.K. Howard Andriy A. Mokhir Joachim Sieler Konstantin V. Domasevitch 《Polyhedron》2008
Reaction of copper(II) acetate, lanthanium(III) or gadolinium(III) nitrate (1/5 equiv.) with pyrazinohydroxamic acid (H2Pyzha) in DMF led to a series of new heterobimetallic 15-metallacrown-5 complexes. In a MeOH/H2O solution the complexes exist as molecular unassociated metallacrowns. In solid state their structures are more complicated as it has been confirmed by X-ray analysis: discrete molecular metallacrowns [Gd(NO3)2{Cu(pyzha)}5(DMF)4(NO3)] · 0.5C6H6 · H2O (1), [Gd(NO3)2{Cu(pyzha)}5(DMF)5](NO3) · 1.5DMF · 0.5H2O (2), [La(NO3)2{Cu(pyzha)}5(DMF)5]NO3 · 1.5DMF · 2C6H6 (3) are solvates, whereas compound [{La(NO3)2{Cu(pyzha)}5(DMF)5}2(μ2-NO3)](NO3) · 3DMF (4) is a dimer, where μ-bridged nitrate links two copper centres of the adjacent metallamacrocycles. Complex [Gd(NO3)2{Cu(pyzha)}5(DMF)2(H2O)(NO3)] · CH2Cl2 · DMF (5) self-associates into a polymer chain by means of one pyrazine moiety and the copper ring atom. Reaction of the molecular metallacrowns with excess of inorganic salts CdBr2 or Cu(OAc)2 proceeds as anion methathesis process affording heteroanionic metallacrowns: molecular [Gd(NO3)2{Cu(pyzha)}5(DMF)5] [Gd(NO3)2{Cu(pyzha)}5(DMF)4(H2O)][CdBr4] · 1.5DMF (6), and 3D hydrogen bonded polymer [La(μ2-OAc)(H2O)3{Cu(pyzha)}5 (H2O)4(NO3)](NO3) · 4H2O (7). 相似文献
96.
Perquinoline A–C: neuartige bakterielle Tetrahydroisochinoline mit einer bemerkenswerten Biosynthese
97.
98.
The synthesis of thiosemicarbazide of 1-butyl-6-fluoro-7-morpholino-4-oxo-1,4-dihydroquinoline-3-carboxylic acid as well as its heterocyclic derivatives – 1,3,4-thiadiazole and 1,2,4-triazole are described; the modification of proper 1,2,4-triazole derivative by maleimides is also presented. Spectral properties of the prepared compounds and X-ray analysis for the selected compounds were studied. For the compounds antitrypanosomal potential and the toxicity were determined. 相似文献
99.
Andriy Panasyuk 《Annals of Global Analysis and Geometry》1997,15(4):313-324
Given a complex manifold Mi, structures of Poisson algebras on (Mi)=C(Mi,C) which are associated with a nondegenerate -closed (2,0)-form i on Mi are considered. It is shown that every isomorphism of Poisson structures (M1) (M2) is generated by a biholomorphic map :M2 M1 such that 2 = *1 相似文献
100.
Moralez JG Raez J Yamazaki T Motkuri RK Kovalenko A Fenniri H 《Journal of the American Chemical Society》2005,127(23):8307-8309
The design of nanostructured materials with tunable dimensions and properties that maintain their structural integrity under physiological conditions is a major challenge in biomedical engineering and nanomedicine. Helical rosette nanotubes (HRN) are a new class of materials produced through a hierarchical self-assembly process of low molecular weight synthetic organic modules in water. Here, we describe a synthetic strategy to tune their stability and hierarchy by preorganization of the self-assembling units, control of net charge per unit of nanotube surface area, amphiphilicity, and number of H-bonds per self-assembling module, and through peripheral steric (de)compression. Using these criteria, HRNs with tunable stability and hierarchical architecture were produced from self-assembling modules that (a) persist as individual molecules in solution, (b) self-assemble into HRN but denature at high temperature (<85 degrees C), (c) self-assemble into HRN whose structural integrity persists even in boiling water (>95 degrees C), and (d) self-assemble into well-dispersed short nanotubes, long nanotubes, ribbons, or superhelices. Given the biocompatibility, synthetic accessibility, and chemical and physical tunability of these materials, numerous applications in biomedical engineering, materials science, and nanoscience and technology are envisioned. 相似文献