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991.
This paper explores the reduced form of horse cytochrome c confined in reverse micelles (RM) of sodium bis-(2-ethylhexyl)
sulfosuccinate (AOT) in isooctane by molecular dynamics simulation. RMs of two sizes were constructed at a water content of
W
o = [ H_2O ]/[AOT] = 5.5 and 9.1. Our results show that the protein secondary structure and the heme conformation both depend on micellar hydration.
At low hydration, the protein structure and the heme moiety remain stable, whereas at high water content the protein becomes
unstable and starts to unfold. At W
o = 9.1 , according to the X-ray structure, conformational changes are mainly localized on protein loops and around the heme
moiety, where we observe a partial opening of the heme crevice. These findings suggest that within our time window (10ns),
the structural changes observed at the heme level are the first steps of the protein denaturation process, previously described
experimentally in micellar solutions. In addition, a specific binding of AOT molecules to a few lysine residues of the protein
was found only in the small-sized RM. 相似文献
992.
In this work numerical methods for integration with respect to binomial measures are considered. Binomial measures are examples
of fractal measures and arise when multifractal properties are investigated. Interpolatory quadrature rules are considered.
An automatic integrator with local quadrature rules that generalize the five points Newton Cotes formula and error estimates
based on null rules is then described. Numerical tests are performed to verify the efficiency and accuracy of the method.
These tests confirm that the automatic integrator turns out to be as good as one of the best known quadrature algorithms with
respect to the Lebesgue measure.
AMS subject classification (2000) 28A25, 60G18, 65D30, 65D32, 68M15 相似文献
993.
Irene T. S. Garcia Fabiane G. da S. Porto Queila D. F. do Amaral Neftalí L. V. Carreño Márcio M. Martins Martin Wallau 《Surface and interface analysis : SIA》2008,40(5):899-905
Amino acids and polypeptides thin films, pure or attached to polymers, present large application as sensors and biosensors. The interactions between such films and the supports, their sensorial properties, as well as the development of techniques to produce thin regular films, are still challenges in the area. In this work, we present the preparation of L ‐glutamine thin films on silicon substrates, the factors that determine amino acid/silicon substrate interaction, and the morphology of the films. For this purpose, a 24 factorial design is used, taking into account the effects of the solvent system, the glutamine concentration, the temperature, as well as the pretreatment of the substrate surface. The contact angles between a drop of glutamine solution and the silicon substrate were taken for the preliminary evaluation of the affinity between the amino acid and the substrate. The results have shown six promising experimental combinations with oxidized silicon as substrate to improve the solution/substrate interaction. Three of these promising conditions involved aqueous solution of L ‐glutamine and three alkalis solution. The obtained films were characterized by scanning electron microscopy (SEM), Rutherford backscattering (RBS), and Fourier transform infrared (FTIR) spectroscopy. The selected experimental conditions permitted to prepare a variety of films with L ‐glutamine, like small crystals, lamellas, needles, and smoothed regular films. The systems prepared in presence of alkalis solution yielded regular and smooth films. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
994.
995.
996.
Tayler MC Marco-Rius I Kettunen MI Brindle KM Levitt MH Pileio G 《Journal of the American Chemical Society》2012,134(18):7668-7671
Hyperpolarized singlet order is available immediately after dissolution DNP, avoiding need for additional preparation steps. We demonstrate this procedure on a sample of [1,2-(13)C(2)]pyruvic acid. 相似文献
997.
Bassanetti I Mezzadri F Comotti A Sozzani P Gennari M Calestani G Marchiò L 《Journal of the American Chemical Society》2012,134(22):9142-9145
The complexation of a preorganized thioether-functionalized bis(pyrazolyl)methane ligand (L) with silver precursors produces supramolecular structures organized at two hierarchical levels: [AgL](6)(X)(6) metal-organic cyclic hexamers and their organization in 3D architectures. The cyclic toroidal hexamers of 22-26 ? external diameter are found to be stable already in solution before self-assembly into the crystalline state. In the 3D lattice, the hexameric building block are arranged in different highly symmetric space groups as a function of a variety of anions (cubic Fd3 with PF(6)(-) or BF(4)(-) and rhombohedral R3 with CF(3)SO(3)(-) or NO(3)(-)) and form cavities with the geometrical shapes of Platonic solids (tetrahedron and octahedron) that can be occupied by a variety of solvent molecules. Upon evacuation, cubic crystals can produce stable frameworks with permanent porosity, which can absorb reversibly several vapors, CO(2) and CH(4). 相似文献
998.
M. De Rosso L. Tonidandel R. Larcher G. Nicolini V. Ruggeri A. Dalla Vedova F. De Marchi M. Gardiman R. Flamini 《Analytica chimica acta》2012
The anthocyanins of 21 hybrid red varieties produced by crossing V. vinifera, V. riparia, V. labrusca, V. lincecumii and V. rupestris species, the profiles for which have not yet been reported, were studied. Profiles were determined by LC/DAD, and identification of single anthocyanins was confirmed by LC/MS precursor-ion analysis. Anthocyanidin precursors (pelargonidin at m/z 271, dephinidin at m/z 303, cyanidin at m/z 287, petunidin at m/z 317, peonidin at m/z 301, and malvidin at m/z 331) and precursors of monoglucoside compounds allowed 24 different compounds to be identified. Analysis of precursor ions of monoglucoside anthocyanins at low capillary voltage revealed the signals of diglucosides only, providing a very selective method for analysis of diglucoside anthocyanins in grape. According to anthocyanin profile, the samples were subdivided into two groups: one characterized by the substantial presence of diglucoside compounds (particularly Seyve Villard 23-399 and Seyve Villard 23-369) and one by the scarce presence or practical absence of diglucosides (Seibel 10878, Burdin 4077, and Galibert 238-35). Particularly interesting for producing anthocyanin for the natural colorant industry were the varieties Siebel 8357, Bacò 30-12 and Terzi 100-31. 相似文献
999.
Szilveszter Gáspár Sorin David Cristina Polonschii Irene Marcu Mihaela Gheorghiu Eugen Gheorghiu 《Analytica chimica acta》2012
The complexity of the cellular response, induced even by the simplest experimental stimulus, requires an increased number of cellular parameters to be simultaneously monitored. An all electrochemical system allowing the simultaneous and real-time monitoring of both cell adherence and superoxide release into the extracellular space was developed to address this challenge. Cell adherence (to neighboring cells and to substrate) was monitored using non-faradaic impedance spectroscopy while the superoxide release was monitored using a cytochrome c-based amperometric biosensor. The system was used to observe for the first time how these two cellular parameters are changing in real-time for renal cells exposed to calcium oxalate, a calculus-forming salt. It was discovered that calcium oxalate crystals decrease cell adherence and in the same time induce oxidative stress by an overproduction of superoxide. Subconfluent cells, without fully developed tight junctions, appear to be more vulnerable than confluent cells with tight junctions indicating the important protective role of these junctions. 相似文献
1000.
In the last twenty years DMC has been employed as an efficient methylating and methoxycarbonylating agent with several monodentate and bidentate nucleophiles, showing great selectivity and unexpected results. In this short review we report on yet another application of DMC chemistry i.e. the synthesis of 5‐membered N‐ and O‐heterocycles. In these reactions DMC acts as a sacrificial molecule since it is not present in the final products, but only in the reaction intermediates as an halogen‐free leaving group. This DMC‐based synthesis of heterocycles resulted of general application, as it is effective for aliphatic and aromatic 1,4‐diols, incorporating several functionalities (primary, secondary, tertiary, allylic, phenolic), as well as, for bifunctional compounds i.e. 4‐amino‐1‐butanol. This synthetic procedure was also employed for industrially relevant compounds such as (‐)‐norlabdane oxide and isosorbide showing to maintain the chiral integrity of the substrate. In one case intramolecular cyclisation of isosorbide was also observed to achieve a strained tricyclic derivative. Comparing this reaction methodology with a chlorine based procedure, the DMC‐mediated pathway is quantitative, occurs in one step, does not require any chlorine‐based chemical or strong acid and does not produce any chlorinated waste material. 相似文献