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71.
Badoud F Grata E Boccard J Guillarme D Veuthey JL Rudaz S Saugy M 《Analytical and bioanalytical chemistry》2011,400(2):503-516
The urinary steroid profile is constituted by anabolic androgenic steroids, including testosterone and its relatives, that
are extensively metabolized into phase II sulfated or glucuronidated steroids. The use of liquid chromatography coupled to
mass spectrometry (LC-MS) is an issue for the direct analysis of conjugated steroids, which can be used as urinary markers
of exogenous steroid administration in doping analysis, without hydrolysis of the conjugated moiety. In this study, a sensitive
and selective ultra high-pressure liquid chromatography coupled to quadrupole time-of-flight mass spectrometer (UHPLC-QTOF-MS)
method was developed to quantify major urinary metabolites simultaneously after testosterone intake. The sample preparation
of the urine (1 mL) was performed by solid-phase extraction on Oasis HLB sorbent using a 96-well plate format. The conjugated
steroids were analyzed by UHPLC-QTOF-MSE with a single-gradient elution of 36 min (including re-equilibration time) in the negative electrospray ionization mode.
MSE analysis involved parallel alternating acquisitions of both low- and high-collision energy functions. The method was validated
and applied to samples collected from a clinical study performed with a group of healthy human volunteers who had taken testosterone,
which were compared with samples from a placebo group. Quantitative results were also compared to GC-MS and LC-MS/MS measurements,
and the correlations between data were found appropriate. The acquisition of full mass spectra over the entire mass range
with QTOF mass analyzers gives promise of the opportunity to extend the steroid profile to a higher number of conjugated steroids. 相似文献
72.
Groenhof G Schäfer LV Boggio-Pasqua M Goette M Grubmüller H Robb MA 《Journal of the American Chemical Society》2007,129(21):6812-6819
Multiconfigurational ab initio calculations and QM/MM molecular dynamics simulations of a photoexcited cytosine-guanine base pair in both gas phase and embedded in the DNA provide detailed structural and dynamical insights into the ultrafast radiationless deactivation mechanism. Photon absorption promotes transfer of a proton from the guanine to the cytosine. This proton transfer is followed by an efficient radiationless decay of the excited state via an extended conical intersection seam. The optimization of the conical intersection revealed that it has an unusual topology, in that there is only one degeneracy-lifting coordinate. This is the central mechanistic feature for the decay both in vacuo and in the DNA. Radiationless decay occurs along an extended hyperline nearly parallel to the proton-transfer coordinate, indicating the proton transfer itself is not directly responsible for the deactivation. The seam is displaced from the minimum energy proton-transfer path along a skeletal deformation of the bases. Decay can thus occur anywhere along the single proton-transfer coordinate, accounting for the remarkably short excited-state lifetime of the Watson-Crick base pair. In vacuo, decay occurs after a complete proton transfer, whereas in DNA, decay can also occur much earlier. The origin of this effect lies in the temporal electrostatic stabilization of dipole in the charge-transfer state in DNA. 相似文献
73.
74.
Faure E Halusiak E Farina F Giamblanco N Motte C Poelman M Archambeau C Van de Weerdt C Martial J Jérôme C Duwez AS Detrembleur C 《Langmuir : the ACS journal of surfaces and colloids》2012,28(5):2971-2978
A facile and green approach is developed to impart remarkable protection against corrosion to galvanized steel. A protecting multilayer film is formed by alternating the deposition of a polycation bearing catechol groups, used as corrosion inhibitors, with clay that induces barrier properties. This coating does not affect the esthetical aspect of the surface and does not release any toxic molecules in the environment. 相似文献
75.
Guy Martial Nkiet 《Journal of multivariate analysis》2012,105(1):151-163
We propose a criterion for variable selection in discriminant analysis. This criterion permits to arrange the variables in decreasing order of adequacy for discrimination, so that the variable selection problem reduces to that of the estimation of suitable permutation and dimensionality. Then, estimators for these parameters are proposed and the resulting method for selecting variables is shown to be consistent. In a simulation study, we compute proportions of correct classification after variable selection in order to gain understanding of the performance of our proposal and to compare it to existing methods. 相似文献
76.
The development of atherosclerosis has been shown to correlate with regions of low wall shear stress and seemingly reduced mass transport. The local tortuosity of the arteries and local secondary flow oscillation also seem to be negatively correlated with the local occurrence of the disease. However there is currently no tool or physiological parameter that can be measured non-invasively to assess the local oscillation of the flow. Standard Colour Doppler imaging of secondary flow patterns during the blood pulse is studied and illustrated, and the local oscillation of the secondary flow pattern is proposed as an index, which could be an indicator of the likelihood of future disease development. Preliminary results are presented using a basic estimator developed for the proof of concept in the case of swirling flow, and based on colour-coded video signals collected in different configurations. In vitro results show that there is a correspondence between the Doppler patterns and the secondary flow patterns, the repeatability of the measures, and that the proposed index and its estimator reflect a joint influence of the local oscillation of the secondary flow pattern and of the flow rate. On another hand, while in vivo results still suffer from instabilities, noise and from scanners and processing limitations, they demonstrate that it is possible to use Colour Doppler imaging to image and characterize in vivo the secondary flow patterns and their oscillations non-invasively, and that it is possible for a trained clinician to perform manually such Doppler measurements for processing. 相似文献
77.
Reaction of the dilithium salt of the Schiff-base N,N′-o-phenylene-bis(3,5-di-tert-butyl-salicylidene-imine) (tBu4salophenH2) with 1 equiv. of ZrCl4(THF)2 in toluene at −78 °C affords the dichloro complex ZrCl2[C6H4-1,2-{NCH-(3,5-tBu2C6H2-2-O)}2], isolated as a mixture of the C2v-(3a) and C2-(3b) symmetry isomers. Thermodynamic and kinetic parameters for the equilibrium between 3a and 3b have been determined and studied by 1H NMR spectroscopy. Reactions of ZrCl2[C6H4-1,2-{NCH-(3,5-tBu2C6H2-2-O)}2] with alkylating reagents gave an intractable, unidentified mixture of products from which the NMR spectra in C6D6 solution are unusable. 相似文献
78.
Lucie Nováková Vincent Desfontaine Federico Ponzetto Raul Nicoli Martial Saugy Jean-Luc Veuthey Davy Guillarme 《Analytica chimica acta》2016
This study shows the possibility offered by modern ultra-high performance supercritical fluid chromatography combined with tandem mass spectrometry in doping control analysis. A high throughput screening method was developed for 100 substances belonging to the challenging classes of anabolic agents, hormones and metabolic modulators, synthetic cannabinoids and glucocorticoids, which should be detected at low concentrations in urine. To selectively extract these doping agents from urine, a supported liquid extraction procedure was implemented in a 48-well plate format. At the tested concentration levels ranging from 0.5 to 5 ng/mL, the recoveries were better than 70% for 48–68% of the compounds and higher than 50% for 83–87% of the tested substances. Due to the numerous interferences related to isomers of steroids and ions produced by the loss of water in the electrospray source, the choice of SFC separation conditions was very challenging. After careful optimization, a Diol stationary phase was employed. The total analysis time for the screening assay was only 8 min, and interferences as well as susceptibility to matrix effect (ME) were minimized. With the developed method, about 70% of the compounds had relative ME within the range ±20%, at a concentration of 1 and 5 ng/mL. Finally, limits of detection achieved with the above-described strategy including 5-fold preconcentration were below 0.1 ng/mL for the majority of the tested compounds. Therefore, LODs were systematically better than the minimum required performance levels established by the World anti-doping agency, except for very few metabolites. 相似文献
79.
Balogoun Armando Sosthène Kali Nkiet Guy Martial Ogouyandjou Carlos 《Lithuanian Mathematical Journal》2022,62(3):289-303
Lithuanian Mathematical Journal - In this paper, we deal with the problem of testing the equality of k probability distributions. We introduce a generalization of the maximum mean discrepancy that... 相似文献
80.
Elie B.?Megam Ngouonkadi Martial Kabong?Nono Victor Kamdoum?Tamba Hilaire B.?FotsinEmail author 《The European Physical Journal B - Condensed Matter and Complex Systems》2015,88(11):299
Diffusive electrical connections in neuronal networks are instantaneous, while excitatoryor inhibitory couplings through chemical synapses contain a transmission time-delay.Moreover, chemical synapses are nonlinear dynamical systems whose behavior can bedescribed by nonlinear differential equations. In this work, neuronal networks withdiffusive electrical couplings and time-delayed dynamic chemical couplings are considered.We investigate the effects of distributed time delays on phase synchronization of burstingneurons. We observe that in both excitatory and Inhibitory chemical connections, the phasesynchronization might be enhanced when time-delay is taken into account. This distributedtime delay can induce a variety of phase-coherent dynamical behaviors. We also study thecollective dynamics of network of bursting neurons. The network model presents theso-called Small-World property, encompassing neurons whose dynamics have two time scales(fast and slow time scales). The neuron parameters in such Small-World network, aresupposed to be slightly different such that, there may be synchronization of the bursting(slow) activity if the coupling strengths are large enough. Bounds for the criticalcoupling strengths to obtain burst synchronization in terms of the network structure aregiven. Our studies show that the network synchronizability is improved, as itsheterogeneity is reduced. The roles of synaptic parameters, more precisely those of thecoupling strengths and the network size are also investigated. 相似文献