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31.
Myeloperoxidase released from activated phagocytes reacts with H(2)O(2) in the presence of chloride ions to give hypochlorous acid. This oxidant has been implicated in the fragmentation of glycosaminoglycans, such as hyaluronan and chondroitin sulfates. In this study it is shown that reaction of HOCl with glycosaminoglycans and model compounds yields chloramides derived from the N-acetyl function of the glycosamine rings. The results of EPR spin trapping and product studies are consistent with the formation of amidyl radicals from these chloramides via both metal ion-dependent and -independent processes. In the case of glycosaminoglycan-derived amidyl radicals, evidence has been obtained in studies with model glycosides that these radicals undergo rapid intramolecular abstraction reactions to give carbon-centered radicals at C-2 on the N-acetyl glycosamine rings (via a 1,2-hydrogen atom shift) and at C-4 on the neighboring uronic acid residues (via 1,5-hydrogen atom shifts). The C-4 carbon-centered radicals, and analogous species derived from model glycosides, undergo pH-independent beta-scission reactions that result in glycosidic bond cleavage. With N-acetyl glucosamine C-1 alkyl glycosides, product formation via this mechanism is near quantitative with respect to chloramide loss. Analogous reactions with the glycosaminoglycans result in selective fragmentation at disaccharide intervals, as evidenced by the formation of "ladders" on gels; this selectivity is less marked under atmospheric oxygen concentrations than under anoxic conditions, due to competing peroxyl radical reactions. As the extracellular matrix plays a key role in mediating cell adhesion, growth, activation, and signaling, such HOCl-mediated glycosaminoglycan fragmentation may play a key role in disease progression and resolution, with the resulting fragments modulating the magnitude and quality of the immune response in inflammatory conditions. 相似文献
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Carl R. Kemnitz Prof. Joel L. Mackey Mark J. Loewen Julie L. Hargrove Joshua L. Lewis Whitney E. Hawkins Adam F. Nielsen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(23):6942-6949
The potential origins of stability in branched alkanes are investigated, paying close attention to two recent hypotheses: geminal steric repulsion and protobranching. All alkane isomers through C6H14 along with heptane and octane were investigated at the MPW1B95/6‐311++G(d,p) level. Their geminal steric repulsion, total steric repulsion, and orbital interactions were evaluated by using natural bond orbital analysis. All measures of steric repulsion fail to explain the stability of branched alkanes. The extra stability of branched alkanes and protobranching, in general, is tied to stabilizing geminal σ→σ* delocalization, particularly of the type that involves adjacent C? C bonds and, thus, preferentially stabilizes branched alkanes. This picture is corroborated by valence bond calculations that attribute the effect to additional ionic structures (e.g., CH3+ :CH2 :CH3? and CH3:? CH2: CH3+ for propane) that are not possible without protobranching. 相似文献
34.
A new isomorphism invariant of certain measure preserving flows, using sequences of integers, is introduced. Using this invariant, we are able to construct large families of type III0 systems which are not orbit equivalent. In particular we construct an uncountable family of nonsingular ergodic transformations, each having an associated flow that is approximately transitive (and therefore of zero entropy), with the property that the transformations are pairwise not orbit equivalent. 相似文献
35.
An experimental study has been carried out of the low speed Coanda wall jet with both streamwise and axisymmetric curvature. A single component laser Doppler technique was used, and by taking several orientations at a given point, values of the three mean velocities and five of the six Reynolds stresses were obtained. The lateral divergence and convex streamwise curvature both enhanced the turbulence in the outer part of the jet compared with a plane two-dimensional wall jet. The inner layer exhibited a large separation of the positions of maximum velocity and zero shear stress. It was found that the streamwise mean velocity profile became established very rapidly downstream of the slot exit. The profile appeared fairly similar at later downstream positions, but the mean radial velocity and turbulence parameters showed the expected nonself preservation of the flow. Removal of the streamwise curvature resulted in a general return of the jet conditions toward those expected of a plane wall jet. The range and accuracy of the data may be used for developing turbulence models and computational techniques for this type of flow. 相似文献
36.
Xuan J Hamblin MN Stout JM Tolley HD Maynes RD Woolley AT Hawkins AR Lee ML 《Journal of chromatography. A》2011,1218(50):9102-9110
An array of parallel planar nanochannels containing two or three segments with varying inner heights was fabricated and used for size fractionation of inorganic and biological nanoparticles. A liquid suspension of the particles was simply drawn through the nanochannels via capillary action. Using fluorescently labeled 30 nm polyacrylonitrile beads, different trapping behaviors were compared using nanochannels with 200-45 nm and 208-54-30 nm height segments. Addition of sodium dodecyl sulfate (SDS) surfactant to the liquid suspension and application of an AC electric field were shown to aid in the prevention of channel clogging. After initial particle trapping at the segment interfaces, significant particle redistribution occurred when applying a sinusoidal 8V peak-to-peak oscillating voltage with a frequency of 150 Hz and DC offset of 4V. Using the 208-54-30 nm channels, 30 nm hepatitis B virus (HBV) capsids were divided into three fractions. When the AC electric field was applied to this trapped sample, all of the virus particles passed through the interfaces and accumulated at the channel ends. 相似文献
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Count data, most often modeled by a Poisson distribution, are common in statistical process control. They are traditionally monitored by frequentist c or u charts, by cumulative sum and by exponentially weighted moving average charts. These charts all assume that the in‐control true mean is known, a common fiction that is addressed by gathering a large Phase I sample and using it to estimate the mean. “Self‐starting” proposals that ameliorate the need for a large Phase I sample have also appeared. All these methods are frequentist, ie, they allow only retrospective inference during Phase I, and they have no coherent way to incorporate less‐than‐perfect prior information about the in‐control mean. In this paper, we introduce a Bayesian procedure that can incorporate prior information, allow online inference, and should be particularly attractive for short‐run settings where large Phase I calibration exercises are impossible or unreasonable. 相似文献
39.
The inelastic neutron scattering cross section for dense nitrogen gas at several pressures near 240 atmospheres and room temperature has been measured in the region of the first diffraction peak. The Van Hove self-correlation function is calculated from models and subtracted from these cross sections to yield ?S d(Q, ω)/?p. This derivative is related to an integral over the time-dependent triplet correlation function and models for the triplet function are tested. A simple model, based on pair functions, gives moderate agreement. 相似文献
40.
We discuss properties of the Julia and Fatou sets of Weierstrass elliptic ℘ functions arising from real lattices. We give sufficient conditions for the Julia sets to be the whole sphere and for the maps to be ergodic, exact, and conservative. We also give examples for which the Julia set is not the whole sphere. 相似文献