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排序方式: 共有920条查询结果,搜索用时 15 毫秒
911.
912.
We prove optimality of the Arf invariant formula for the generating function of even subgraphs, or, equivalently, the Ising partition function, of a graph. 相似文献
913.
Wendt S McCombie G Daniel J Kienhöfer A Hilvert D Zenobi R 《Journal of the American Society for Mass Spectrometry》2003,14(12):1470-1476
Electrospray time-of-flight mass spectrometry was used to quantitatively determine the dissociation constant of chorismate mutase and a transition state analogue inhibitor. This system presents a fairly complex stoichiometry because the native protein is a homotrimer with three equal and independent substrate binding sites. We can detect the chorismate mutase trimer as well as chorismate mutase-inhibitor complexes by choosing appropriate conditions in the ESI source. To verify that the protein-inhibitor complexes are specific, titration experiments with different enzyme variants and different inhibitors were performed. A plot of the number of bound inhibitors versus added inhibitor concentration revealed saturation behavior with 3:1 (inhibitor:functional trimer) stoichiometry for the TSA. The soft ESI conditions, the relatively high protein mass of 43.5 kDa, and the low charge state (high m/z) result in broad peaks, a typical problem in analyzing noncovalent protein complexes. Due to the low molecular weight of the TSA (226 Da) the peaks of the free protein and the protein with one, two or three inhibitors bound cannot be clearly resolved. For data analysis, relative peak areas of the deconvoluted spectra of chorismate mutase-inhibitor complexes were obtained by fitting appropriate peak shapes to the signals corresponding to the free enzyme and its complexes with one, two, or three inhibitor molecules. From the relative peak areas we were able to calculate a dissociation constant that agreed well with known solution-phase data. This method may be generally useful for interpreting mass spectra of noncovalent complexes that exhibit broad peaks in the high m/z range. 相似文献
914.
Electron-impact studies of diazadiphosphetidines,[YF2PNMe]2(Y? F,Me, Ph, MeO,2,5-Me2C6H3, and m-CF3C6H4) are reported, the most abundant fragments corresponding to m/e [M/2–1]+, [M/2]+ and [M/2–1]+. It is concluded from metastable data that formation of the noval rearrangement ion, [M]+→[M/2+1]+is predominantly due to an electron-impact process. Variable temperature spectra of(F3PNMe)2, (i.e. for Y=F), suggest that ions of m/e [M/2-1]+are formed, in part, by a thermal process. For the compound [(m-CF3C6H4)F2PNMe]2 a well resolved negative ion spectrum has been obtained, with the molecular ion present in 100% abundance. 相似文献
915.
Proczek G Gassner AL Busnel JM Girault HH 《Analytical and bioanalytical chemistry》2012,402(8):2645-2653
The present work reports on the quantification of total IgE in human serum using a microanalytical device whose fluidics is driven by gravity and capillary forces only. Thanks to the eight parallel microchannels in each microchip, calibration and sample analysis are performed simultaneously. A mixture of magnetic bead/analyte/second antibody is incubated off-line and then percolated through the channels where magnetic beads are trapped, enabling the separation of the solid phase from the excess reagents. The entire assay is performed in less than 1 h, and thanks to the miniaturized format, only a small volume of serum is required. Non-specific adsorption was first investigated and a blocking agent compatible with this allergy-based test was chosen. Then, the assay was optimized by determining the best magnetic bead and labelled antibody concentrations. After achievement of a calibration curve with a reference material, the protocol was applied to total IgE quantification of a patient serum sample that showed results in good accordance with those obtained by ImmunoCap® and Immunoaffinity capillary electrophoresis measurements. A detection limit of 17.5 ng ml?1 was achieved and good reproducibility (RSD?10%) inter- and intra-chip was observed. 相似文献
916.
We present a novel centrifugal microfluidic platform for the highly efficient manipulation and analysis of particles for applications in bead-based assays. The platform uses an array of geometrical V-cup barriers to trap particles using stopped-flow sedimentation under highly reproducible hydrodynamic conditions. The impact parameters governing the occupancy distribution and capture efficiency of the arrayed traps are investigated. The unique, nearly 100% capture efficiency paired with the capability to establish sharply peaked, single occupancy distributions enables a novel, digital readout mode for color-multiplexed, particle-based assays with low-complexity instrumentation. The presented technology marks an essential step towards a versatile platform for the integration of bead- and cell-based biological assays. 相似文献
917.
Malcolm H. Mac Gregor 《Foundations of Physics Letters》1995,8(2):135-160
From the perspective of physical realism (PR), a photon is a localized entity that carries energy and momentum, and which is surrounded by a wave packet (anempty wave) that is devoid of observable energy or momentum. In creating quantized PR basis states for a photon wave packet, three requirements must be met:(1) The basis states must each carry the frequency of the wave;(2) They must closely resemble the photon, so that e.g. they scatter in the same manner from an optical mirror;(3) They must have infinitesimal energy, linear momentum, and angular momentum. An essentially zero-energy "empty wave" quantum-a "zeron"-is defined which meets these requirements. It is created as an asymmetric single-particle (or single-antiparticle) excitation of the vacuum state, with the "particle" (or "antiparticle") and its associated "hole" (or "antihole") forming a rotational bound state. The photon is reproduced as a symmetric particle-antiparticle excitation of the vacuum state, with the "particle" and "antiparticle" also forming a rotational bound state. The relativistic transformation problem is discussed. A key point in this development is the deduction of the correct equation of motion for a "hole" state in an external electrostatic field. 相似文献
918.
M. R. Blake J. L. Garnett I. K. Gregor S. B. Wild 《Journal of mass spectrometry : JMS》1980,15(7):369-375
Electron attachment reactions of a series of (η6-arene)tricarbonylchromium(O) complexes have been examined in the gas phase. The electron capture process has been shown to be influenced by the structure of the η6-arene ligand and its substituents. Whereas (η6-benzene)- and (η6-mesitylene)tricarbonylchromium(O) undergo dissocative electron capture, or reductive decarbonylation, yielding [M? CO]?˙ ions of highest abundance in their negative ion mass spectra, [η6-(2,2-dimethylindan-1,3-dione)]tricarbonylchromium(O) forms a molecular negative ion which undergoes sequential CO eliminations and finally a demetallation to give the arene radical ion. A localization of charge on the coordinated arene ligand is proposed for the formation of [M]?˙ in this case. (η6-Methylbenzoate)tricarbonylchromium(O) also forms a molecular negative ion by secondary electron attachment which decomposes by simultaneous and consecutive eliminations of up to four CO molecules. The elucidation of a mechanism and sequence for these CO eliminations has been achieved by synthesizing and examining the negative ion mass spectrum of [η6-(C6H5·13CO2Me)]Cr(CO)3. The first CO loss in the principal fragmentation pathway occurs solely from the –Cr(CO)3 group of [M]?˙. The effect of para substituent groups on the stabilities of molecular negative ions and their fragmentations has been ascertained using a series of para-substituted (η6-methylbenzoate)tricarbonylchromium(O) compounds containing the groups NH2, OH, OCH3, CL and COOMe. The stabilities of the [M]?˙ ions have been rationalized in terms of the Hammett and Taft parameters σP, σI, σRP, σPO and σRO. The overall electronic substituent effect transmitted to the carbonyl groups of the –Cr(CO)3 unit involves both resonance and inductive components. In this series of compounds the stability of [M]?˙ decreases as the electron withdrawing capacities of the para substituents increase. 相似文献
919.
920.