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排序方式: 共有298条查询结果,搜索用时 31 毫秒
71.
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73.
Tae-Young Kim Stephen J. Valentine David E. Clemmer James P. Reilly 《Journal of the American Society for Mass Spectrometry》2010,21(8):1455-1465
Singly-protonated proline-containing peptides with N-terminal arginine are photodissociated with vacuum ultraviolet (VUV)
light in an ESI linear ion trap/orthogonal-TOF (LIT/o-TOF). When proline is the nth residue from the N-terminus, unusual b
n
+ 2 and a
n
+ 2 ions are observed. Their formation is explained by homolytic cleavage of the Cα− C bond in conjunction with a rearrangement of electrons and an amide hydrogen. The latter is facilitated by a proline-stabilized
gas-phase peptide conformation. 相似文献
74.
The aqueous chemistry of Ti(III) and Ti(IV) in two different chemical environments is investigated given its relevance to environmental, materials, and biological chemistry. Complexes of titanium with the carboxylate ligands citrate and oxalate, found ubiquitously in Nature, were synthesized. The redox properties were studied by using cyclic voltammetry. All the titanium citrate redox couples are quasi-reversible. Electrospray mass spectrometry of the Ti(III) citrate solution shows the presence of a 1:2 Ti/cit complex in solution, in contrast to the predominant 1:3 Ti/cit complex with Ti(IV). The change in the coordination of the ligand to the metal on reduction may explain the quasi-reversible behavior of the electrochemistry. The redox potentials for Ti(IV) citrate in water vary with pH. At pH 7, the approximate E(1/2) is less than -800 mV. This stated change in redox properties is considered in light of the previously reported Ti(IV) citrate solution speciation. Analogous speciation behavior is suggested from the EPR spectroscopy of Ti(III) citrate aqueous solutions. The g tensors are deduced for several pH-dependent species from the simulated data. The X-ray crystal structure of a Ti(III)(2) oxalate dimer Ti(2)(mu-C(2)O(4))(C(2)O(4))(2)(H(2)O)(6).2H(2)O (3), which crystallizes from water below pH 2, is reported. Complex 3 crystallizes in a monoclinic P2(1)/c space group with a = 9.5088(19) Angstroms, b = 6.2382(12) Angstroms, c = 13.494(3) Angstroms, V = 797.8(3) Angstroms(3), and Z = 2. The infrared spectroscopy, EPR spectroscopy, and cyclic voltammetry on complex 3 are reported. The cyclic voltammetry shows an irreversible redox couple approximately -196 mV which likely corresponds to the Ti(IV)(2)/Ti(III)Ti(IV) couple. The EPR spectroscopy on solid complex 3 shows a typical S = 1 triplet-state spectrum. The solid follows non-Curie behavior, and the antiferromagnetic coupling between the two metal centers is determined to be -37.2 cm(-1). However, in solution the complex follows Curie behavior and supports a Ti(III)Ti(IV) oxidation state for the dimer. 相似文献
75.
Laccase was earlier wired to yield an O2 electroreduction catalyst greatly outperforming platinum and its alloys. Here we describe the design, synthesis optimization of the composition, and characterization of the +0.55 V (AgAgCl) laccase-wiring redox hydrogel, with an apparent electron diffusion coefficient (D(app)) of 7.6 x 10(-7) cm2 s(-1). The high D(app) results in the tethering of redox centers to the polymer backbone through eight-atom-long spacer arms, which facilitate collisional electron transfer between proximal redox centers. The O2 flux-limited, true-area-based current density was increased from the earlier reported 560 to 860 microA cm(-2). When the O2 diffusion to the 7-microm-diameter carbon fiber cathode was cylindrical, half of the O2 flux-limited current was reached already at 0.62 V and 90% at 0.56 V vs Ag/AgCl, merely -0.08 and -0.14 V versus the 0.7 V (Ag/AgCl) reversible O2/H2O half-cell potential at pH 5. 相似文献
76.
Harvey SD Mong GM Ozanich RM McLean JS Goodwin SM Valentine NB Fredrickson JK 《Analytical and bioanalytical chemistry》2006,386(2):211-219
A novel, affinity-augmented, bacterial spore-imprinted, bead material was synthesized, based on a procedure developed for
vegetative bacteria. The imprinted beads were intended as a front-end spore capture/concentration stage of an integrated biological
detection system. Our approach involved embedding bead surfaces with Bacillus thuringiensis kurstaki (Bt) spores (as a surrogate for Bacillus anthracis) during synthesis. Subsequent steps involved lithographic deactivation using a perfluoroether; spore removal to create imprint
sites; and coating imprints with the lectin, concanavalin A, to provide general affinity. The synthesis of the intended material
with the desired imprints was verified by scanning electron and confocal laser-scanning microscopy. The material was evaluated
using spore-binding assays with either Bt or Bacillus subtilis (Bs) spores. The binding assays indicated strong spore-binding capability and a robust imprinting effect that accounted for 25%
additional binding over non-imprinted controls. The binding assay results also indicated that further refinement of the surface
deactivation procedure would enhance the performance of the imprinted substrate. 相似文献
77.
Park JJ Luo X Yi H Valentine TM Payne GF Bentley WE Ghodssi R Rubloff GW 《Lab on a chip》2006,6(10):1315-1321
We report facile in situ biomolecule assembly at readily addressable sites in microfluidic channels after complete fabrication and packaging of the microfluidic device. Aminopolysaccharide chitosan's pH responsive and chemically reactive properties allow electric signal-guided biomolecule assembly onto conductive inorganic surfaces from the aqueous environment, preserving the activity of the biomolecules. A transparent and nonpermanently packaged device allows consistently leak-free sealing, simple in situ and ex situ examination of the assembly procedures, fluidic input/outputs for transport of aqueous solutions, and electrical ports to guide the assembly onto the patterned gold electrode sites within the channel. Both in situ fluorescence and ex situ profilometer results confirm chitosan-mediated in situ biomolecule assembly, demonstrating a simple approach to direct the assembly of biological components into a completely fabricated device. We believe that this strategy holds significant potential as a simple and generic biomolecule assembly approach for future applications in complex biomolecular or biosensing analyses as well as in sophisticated microfluidic networks as anticipated for future lab-on-a-chip devices. 相似文献
78.
Scanning electron microscopy with energy dispersive microanalysis confirms the rare occurrence of a titanium mineral in the test of an organism. 相似文献
79.
Nikolay E. Shevchenko Valentine G. Nenajdenko Gerd-Volker Rschenthaler 《Journal of fluorine chemistry》2008,129(5):390-396
Addition of pentafluoroethyllithium to cyclic imines leads to pentafluoroethyl substituted pyrrolidines, piperidines and azepanes while reaction of cyclic lactims gives rise to 2-pentafluoroethyl imines. Oxidative cleavage of 2-furyl-2-pentafluoroethyl pyrrolidine has been found to be an effective method for the preparation of a racemic α-pentafluoroethyl proline. 相似文献
80.