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排序方式: 共有128条查询结果,搜索用时 15 毫秒
21.
H. v. Wartenberg B. Lerner-Steinberg J. Geidel W. Rehwinkel T. Gaydo A. Perrier P. E. Verkade J. Coops Jr. E. Cohen S. Miyake J. A. van der Hoeve C. Moureu W. P. White F. Karas A. Mennucci W. Sturm E. Berner J. Peters J. W. Davis E. L. Wallace W. Kohen S. H. Regester G. B. Watkins J. V. Hunn C. A. Myers Jr. W. Groose W. Dinkler A. Herberholz J. S. G. Thomas M. Barash H. Löffler 《Analytical and bioanalytical chemistry》1930,82(11-12):455-456
22.
Bandaria JN Dutta S Hill SE Kohen A Cheatum CM 《Journal of the American Chemical Society》2008,130(1):22-23
The role of femtosecond-picosecond structural dynamics of proteins in enzyme-catalyzed reactions is a hotly debated topic. We report infrared photon echo measurement of the formate dehydrogenase-NAD+-azide ternary complex. In contrast to earlier studies of protein dynamics, the data show complete spectral diffusion on the femtosecond-picosecond time scale with no static heterogeneity. This result indicates that this transition-state analogue complex completely samples the distribution of structures that determine the distribution of azide vibrational frequencies within a few picoseconds and that there are no slower motions that perturb the H-bond network at the active site. 相似文献
23.
Wasserman V Kizelsztein P Garbuzenko O Kohen R Ovadia H Tabakman R Barenholz Y 《Langmuir : the ACS journal of surfaces and colloids》2007,23(4):1937-1947
The piperidine nitroxide tempamine (TMN) is a cell-permeable, stable radical having antioxidant, anticancer, and proapoptotic and/or pronecrotic activities, as was demonstrated by us in cell cultures. We also demonstrated synergism between TMN and doxorubicin in doxorubicin-sensitive and doxorubicin-resistant cell lines. Treatment of the C26 mouse colon carcinoma model in vivo also demonstrated synergism between TMN and doxorubicin in sterically stabilized liposomes (SSLs) containing TMN (SSL-TMN) and those containing doxorubicin. The above effects of TMN and SSL-TMN motivated us to develop and optimize the SSL-TMN formulation so that it will be able to reach the disease site with a sufficiently high TMN level and a release rate needed to achieve a therapeutic effect. Because TMN is an amphipathic weak base, it was remote loaded by an intraliposome high/extraliposome low transmembrane ammonium sulfate gradient. The kinetics and level of TMN loading were monitored by cyclic voltammetry (CV) and electron paramagnetic resonance (EPR); the latter also indicates TMN precipitation in the intraliposomal aqueous phase. The regeneration of the original CV and EPR signals by the ionophore nigericin indicates that TMN remained fully intact during loading and release. The cardinal role of the transmembrane ammonium ion gradient in the loading process was proven by the use of the selective ionophores nonactin (for NH4+) and nigericin (for H+). The anion of the ammonium salts affects loading stability and the rate of TMN release, both mediated through the TMN state of aggregation in the intraliposomal aqueous phase. The greater the TMN salt precipitation, the slower the TMN release rate. This was supported by measurement of osmolality, which is inversely related to TMN salt precipitate. Precipitation is in the order SO4(-2)>Cl-1>glucuronate-1. Liposome lipid composition, magnitude of the transmembrane ammonium ion gradient, and type of anion of the ammonium salt determine the amount of TMN loaded and its release rate. 相似文献
24.
The mechanistic details of hydrogen transfer in biological systems are not fully understood. The traditional approach has been to use semiclassical transition-state theory. This theory cannot explain many experimental findings, however, so different approaches that emphasize the importance of quantum mechanics and dynamic effects should also be considered. 相似文献
25.
Pump−probe experiments at the TEMPO beamline using the low‐α operation mode of Synchrotron SOLEIL
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Mathieu G. Silly Tom Ferté Marie Agnes Tordeux Debora Pierucci Nathan Beaulieu Christian Chauvet Federico Pressacco Fausto Sirotti Horia Popescu Victor Lopez-Flores Marina Tortarolo Maurizio Sacchi Nicolas Jaouen Philippe Hollander Jean Paul Ricaud Nicolas Bergeard Christine Boeglin Bharati Tudu Renaud Delaunay Jan Luning Gregory Malinowski Michel Hehn Cédric Baumier Franck Fortuna Damjan Krizmancic Luigi Stebel Rudi Sergo Giuseppe Cautero 《Journal of synchrotron radiation》2017,24(4):886-897
The SOLEIL synchrotron radiation source is regularly operated in special filling modes dedicated to pump–probe experiments. Among others, the low‐α mode operation is characterized by shorter pulse duration and represents the natural bridge between 50 ps synchrotron pulses and femtosecond experiments. Here, the capabilities in low‐α mode of the experimental set‐ups developed at the TEMPO beamline to perform pump–probe experiments with soft X‐rays based on photoelectron or photon detection are presented. A 282 kHz repetition‐rate femtosecond laser is synchronized with the synchrotron radiation time structure to induce fast electronic and/or magnetic excitations. Detection is performed using a two‐dimensional space resolution plus time resolution detector based on microchannel plates equipped with a delay line. Results of time‐resolved photoelectron spectroscopy, circular dichroism and magnetic scattering experiments are reported, and their respective advantages and limitations in the framework of high‐time‐resolution pump–probe experiments compared and discussed. 相似文献
26.
The implementation of circuits with complex dynamics is a very challenging problem. In this paper we present a new chaotic circuit based on the dynamical equations introduced in IEEE Trans. Circuits Syst., I: Fundam. Theory Appl. 51, 2476-2490 (2004). This circuit has been realized by using programmable analog devices, and, in particular, field programmable analog arrays have been used to implement a two-dimensional 3x3 grid scroll chaotic attractor. The implementation of complex dynamics with low cost circuits is very appealing; moreover, the implementation of the chaotic attractor discussed in this paper is not present in the literature. The experimental results including the synchronization between two chaotic circuits show complete agreement with the simulation results reported in IEEE Trans. Circuits Syst., I: Fundam. Theory Appl. 51, 2476-2490 (2004). 相似文献
27.
28.
Sousa J Alves G Abrantes J Fortuna A Falcão A 《Analytical and bioanalytical chemistry》2012,403(1):93-129
Fluoroquinolones are one of the most promising and intensively studied drugs of contemporary anti-infective chemotherapy.
New fluoroquinolone antibacterials with improved pharmacokinetic properties and a broad spectrum of activity have been developed,
opening new windows of opportunity for clinical use. To our knowledge, no comprehensive and critical review of the analytical
methods for the determination of these agents, which correspond to the third- and fourth-generation quinolones, has yet been
published. This work summarizes for the first time most of the liquid chromatographic methods reported in the literature for
the separation and quantification of the new fluoroquinolones in biological matrices and pharmaceutical formulations. A systematic
and detailed survey of physicochemical properties, sample preparation procedures, and chromatographic and detection conditions
is presented herein. In the course of this review several liquid chromatographic methods are discussed: reversed-phase high-performance
liquid chromatography (RP-HPLC), ion-exchange high-performance liquid chromatography (IEX-HPLC), hydrophilic interaction liquid
chromatography (HILIC), high-performance thin-layer chromatography (HPTLC) and other chiral chromatographic methods. Their
advantages, applicability and limitations are also examined. 相似文献
29.
Mishanina TV Koehn EM Conrad JA Palfey BA Lesley SA Kohen A 《Journal of the American Chemical Society》2012,134(9):4442-4448
Thymidylate is a DNA nucleotide that is essential to all organisms and is synthesized by the enzyme thymidylate synthase (TSase). Several human pathogens rely on an alternative flavin-dependent thymidylate synthase (FDTS), which differs from the human TSase both in structure and molecular mechanism. It has recently been shown that FDTS catalysis does not rely on an enzymatic nucleophile and that the proposed reaction intermediates are not covalently bound to the enzyme during catalysis, an important distinction from the human TSase. Here we report the chemical trapping, isolation, and identification of a derivative of such an intermediate in the FDTS-catalyzed reaction. The chemically modified reaction intermediate is consistent with currently proposed FDTS mechanisms that do not involve an enzymatic nucleophile, and it has never been observed during any other TSase reaction. These findings establish the timing of the methylene transfer during FDTS catalysis. The presented methodology provides an important experimental tool for further studies of FDTS, which may assist efforts directed toward the rational design of inhibitors as leads for future antibiotics. 相似文献
30.
Ribou AC Vigo J Kohen E Salmon JM 《Journal of photochemistry and photobiology. B, Biology》2003,70(2):107-115
The access to oxygen concentration is of importance in various organelles of living cells, especially in mitochondria. A new probe, (1"-pyrene butyl)-2-rhodamine ester, was designed to target this organelle. We present here the properties of the probe in such an environment. Microspectrofluorometry confirms the localization of the probe in the mitochondrial environment at low doses (1 microM). At these doses, the cell toxicity experiments show no effect on the cell growth. The emission spectrum measured at an excitation wavelength of 340 nm (pyrene centered) indicates energy transfer from the pyrene to the rhodamine chromophore, as also observed in an ethanol solution. With excitation at 337 nm, the excited state decays biexponentially with lifetime decays of 6-9 ns and 90 ns. The first corresponds to the intrinsic fluorescence of the cell and the latter corresponds to the pyrene chromophore. In degassed conditions the pyrene lifetime decay increases up to 130 ns. Under an oxygen atmosphere the lifetime decays decrease to 62 ns. The lifetime changes with the oxygen concentration were compared with the range obtained during our previous study in ethanol solution (5-220 ns). The observed differences were interpreted by studying the lifetime of the probe in simplified environments, liposome suspensions and protein solutions. In this paper we show that the new probe can be used to measure the fluctuation of oxygen concentration in the surroundings of mitochondria. 相似文献