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91.
Johnson RL Villa EM Ohlin CA Rustad JR Casey WH 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(34):9359-9367
Rates of oxygen-isotope exchange were measured in the tetrasiliconiobate ion [H(2+x)Si(4)Nb(16)O(56)]((14-x)-) to better understand how large oxide ions interact with water. The molecule has 19 nonequivalent oxygen sites and is sufficiently complex to evaluate hypotheses derived from our previous work on smaller clusters. We want to examine the extent to which individual oxygen atoms react independently with particular attention given to the order of protonation of the various oxygen sites as the pH decreases from 13 to 6. As in our previous work, we find that the set of oxygen sites reacts at rates that vary over approximately 10(4) across the molecule at 6相似文献
92.
Demesa Balderrama G Meneses EP Hernández Orihuela L Villa Hernández O Castro Franco R Pando Robles V Ferreira Batista CV 《Rapid communications in mass spectrometry : RCM》2011,25(8):1017-1027
Immobilized metal ion affinity chromatography (IMAC) has been widely used for the enrichment of phosphopeptides, whereas no report exists describing the use of IMAC columns for the enrichment of sulfopeptides. In this study, we used IMAC-Ga microcolumns for the enrichment of sulfopeptides from a complex mixture of peptides, extracted from skin secretions of the Pachymedusa dacnicolor frog. The enriched fraction obtained by IMAC-Ga was analyzed by liquid chromatograpy/electrospray ionization mass spectrometry (LC/ESI-MS) in an Orbitrap XL and by matrix-assisted laser desorption/ionization time-of-flight time-of-flight (MALDI-TOF/TOF) in an ABI 4800 instrument. From this fraction, different sulfated and non-sulfated peptides belonging to the caerulin and bradykinin families were structurally characterized. Other interesting negatively charged groups, such as phosphate adducts of dermaseptins and pyridoxal phosphate attached to a protease inhibitor, were also characterized. Unexpectedly, some dermaseptin antimicrobial peptides were also enriched by IMAC-Ga and a Sauvatine-like peptide was also fully sequenced. Furthermore, neutral loss of sulfated peptides and their fragmentation patterns in the gas phase were also compared using collision-induced dissociation (CID) and high-energy collision dissociation (HCD). Our present study provides evidence that IMAC-Ga enrichment is a fast, useful and promising method for high-throughput analysis of sulfated-peptides, since high-resolution mass spectrometers can be used for this purpose. 相似文献
93.
Buonsanti R Carlino E Giannini C Altamura D De Marco L Giannuzzi R Manca M Gigli G Cozzoli PD 《Journal of the American Chemical Society》2011,133(47):19216-19239
A colloidal crystal-splitting growth regime has been accessed, in which TiO(2) nanocrystals, selectively trapped in the metastable anatase phase, can evolve to anisotropic shapes with tunable hyperbranched topologies over a broad size interval. The synthetic strategy relies on a nonaqueous sol-gel route involving programmed activation of aminolysis and pyrolysis of titanium carboxylate complexes in hot surfactant media via a simple multi-injection reactant delivery technique. Detailed investigations indicate that the branched objects initially formed upon the aminolysis reaction possess a strained monocrystalline skeleton, while their corresponding larger derivatives grown in the subsequent pyrolysis stage accommodate additional arms crystallographically decoupled from the lattice underneath. The complex evolution of the nanoarchitectures is rationalized within the frame of complementary mechanistic arguments. Thermodynamic pathways, determined by the shape-directing effect of the anatase structure and free-energy changes accompanying branching and anisotropic development, are considered to interplay with kinetic processes, related to diffusion-limited, spatially inhomogeneous monomer fluxes, lattice symmetry breaking at transient Ti(5)O(5) domains, and surfactant-induced stabilization. Finally, as a proof of functionality, the fabrication of dye-sensitized solar cells based on thin-film photoelectrodes that incorporate networked branched nanocrystals with intact crystal structure and geometric features is demonstrated. An energy conversion efficiency of 6.2% has been achieved with standard device configuration, which significantly overcomes the best performance ever approached with previously documented prototypes of split TiO(2) nanostructures. Analysis of the relevant photovoltaic parameters reveals that the utilized branched building blocks indeed offer light-harvesting and charge-collecting properties that can overwhelm detrimental electron losses due to recombination and trapping events. 相似文献
94.
Protein kinases control virtually every aspect of normal and pathological cell physiology and are considered ideal targets for drug discovery. Most kinase inhibitors target the ATP binding site and interact with residue of a hinge loop connecting the small and large lobes of the kinase scaffold. Resistance to kinase inhibitors emerges during clinical treatment or as a result of in vitro selection approaches. Mutations conferring resistance to ATP site inhibitors often affect residues that line the ATP binding site and therefore contribute to selective inhibitor binding. Here, we show that mutations at two specific positions in the hinge loop, distinct from the previously characterized "gatekeeper," have general adverse effects on inhibitor sensitivity in six distantly related kinases, usually without consequences on kinase activity. Our results uncover a unifying mechanism of inhibitor resistance of protein kinases that might have widespread significance for drug target validation and clinical practice. 相似文献
95.
Raffaella Servadei 《Journal of Mathematical Analysis and Applications》2011,383(1):190-199
In this paper we consider a semilinear equation driven by an operator not in divergence form. Precisely, the principal part of the operator is in divergence form, but it has also a lower order term depending on Du. While the right-hand side of the equation satisfies superlinear and subcritical growth conditions at zero and at infinity. The problem has not a variational structure, but, despite that, we use variational techniques in order to prove an existence and regularity result for the equation. 相似文献
96.
Piercarlo Mustarelli Corrado Tomasi Marco Villa Gian Battista Appetecchi Fausto Croce 《Ionics》1995,1(2):147-152
Two composite gel electrolytes prepared from mixtures of poly(acrylonitrile) (PAN), propylene carbonate (PC), ethylene carbonate
(EC) and LiClO4 have been studied with differential scanning calorimetry (DSC) and7Li-6Li NMR. The data allow estimation of ionic conductivities, local (short range) diffusivities, and lattice dynamics. Furthermore,
they point to an unexpected behavior of the Li-rich sample that hints to a complex LiClO4-PAN phase diagram.
Paper presented at the 1st Euroconference on Solid State Ionics, Zakynthos, Greece, September 11–18,1994 相似文献
97.
A two-dimensional electrophoretic analysis of the total proteins was carried out in Vitis rupestris as model system in order to characterize the different developmental stages--from callus to plantlets--of somatic embryogenesis events in the grapevine. The patterns of callus, embryogenetic callus, somatic embryos and plantlets derived from leaf and petiole explants were compared. Each differentiation step was characterized by specific peptide spots. 相似文献
98.
In [3] Dynkin defined the local time of a continuous superprocess as a stochastic integral and gave a criterion for existence of local time. Here we prove that the conditions in Dynkin's existence criterion are satisfied by the multitype Dawson–Watanabe superprocess, and give a Tanaka formula‐like representation of the local time which is used to show that the occupation measure of the multitype superprocess is absolutely continuous with respect to an appropriate reference measure, and that the corresponding density coincides a.s. with the local time. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
99.
G. Gomez-Rosas H. Wang J. Hurtado-Ramos D. Malacara F. Villa O. Pompa 《Optical and Quantum Electronics》1998,30(3):181-186
In this letter we report a new method for measuring light scattered from optically rough surfaces. By collecting scattered light in a given solid angle, the measurement system does not require a detection unit with an extremely large dynamic range. This in turn significantly simplifies the system configuration. Measurements of scattering close to specular reflection (the so-called small angle or near-specular scattering) also can be completed without any difficulty. Unlike in the common angle resolved scattering (ARS) measurement system, in this system a linear movement instead of rotation is adopted to scan scattered light. In this way, the angular resolution of scattering measurements is independent of the resolution of the translation stages and may be adjusted. 相似文献
100.
Giuseppe Cremonesi Piero Dalla Croce Alessandra Forni Maddalena Gallanti Raffaella Gandolfi Concetta La Rosa 《Tetrahedron: Asymmetry》2009,20(16):1940-1947
Enantiomerically pure (5R)-(?)-5-phenyl-4,5-dihydroisoxazole-3-carboxylic acid ethyl ester was obtained via enzymatic resolution of the corresponding racemic mixture using a lipase from hog pancreas (PPL). The following reduction of the ester group to the corresponding alcohol and the oxidation of the latter led to (5R)-(?)-5-phenyl-4,5-dihydroisoxazole-3-carbaldehyde, and the reaction between this and Schöllkopf’s reagent, (2R)-(+)-2,5-dihydro-3,6-dimethoxy-2-isopropylpyrazine, gave mixtures of adducts with a good syn/anti ratio. The steric configurations of the major diastereoisomer were assigned on the basis of spectroscopic data and X-ray analysis. The subsequent controlled hydrolysis of the pyrazine ring led to β-(5-phenyl-4,5-dihydroisoxazol-3-yl)-serine methyl esters and the corresponding dipeptides with (R)-valine. Finally, reductive cleavage of the 4,5-dihydroisoxazole ring under hydrolytic conditions made it possible to obtain the corresponding polyfunctionalised dipeptides. 相似文献