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61.
Metabolism of methylstenbolone studied with human liver microsomes and the uPA+/+‐SCID chimeric mouse model 下载免费PDF全文
Lore Geldof Leen Lootens Michael Polet Daniel Eichner Thane Campbell Vinod Nair Francesco Botrè Philip Meuleman Geert Leroux‐Roels Koen Deventer Peter Van Eenoo 《Biomedical chromatography : BMC》2014,28(7):974-985
Anti‐doping laboratories need to be aware of evolutions on the steroid market and elucidate steroid metabolism to identify markers of misuse. Owing to ethical considerations, in vivo and in vitro models are preferred to human excretion for nonpharmaceutical grade substances. In this study the chimeric mouse model and human liver microsomes (HLM) were used to elucidate the phase I metabolism of a new steroid product containing, according to the label, methylstenbolone. Analysis revealed the presence of both methylstenbolone and methasterone, a structurally closely related steroid. Via HPLC fraction collection, methylstenbolone was isolated and studied with both models. Using HLM, 10 mono‐hydroxylated derivatives (U1–U10) and a still unidentified derivative of methylstenbolone (U13) were detected. In chimeric mouse urine only di‐hydroxylated metabolites (U11–U12) were identified. Although closely related, neither methasterone nor its metabolites were detected after administration of isolated methylstenbolone. Administration of the steroid product resulted mainly in the detection of methasterone metabolites, which were similar to those already described in the literature. Methylstenbolone metabolites previously described were not detected. A GC‐MS/MS multiple reaction monitoring method was developed to detect methylstenbolone misuse. In one out of three samples, previously tested positive for methasterone, methylstenbolone and U13 were additionally detected, indicating the applicability of the method. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
62.
Mathias Kersemans Wim Van Paepegem Koen Van Den Abeele Lincy Pyl Filip Zastavnik Hugo Sol Joris Degrieck 《Ultrasonics》2014
The ultrasonic polar scan (UPS), either in transmission, reflection or backscatter mode, is a promising non-destructive testing technique for the characterization of composites, providing information about the mechanical anisotropy, the viscoelastic damping, the surface roughness, and more. At present, the technique is merely being used for qualitative purposes. The limited quantitative exploration and use of the technique can be primarily ascribed to limitations of current theoretical models as well as the difficulty to perform accurate, and more importantly, reproducible UPS experiments. Over the last years, we have identified several potential pitfalls in the experimental implementation of the technique which severely deteriorate the accurateness and reproducibility of a UPS. In this paper, we make an inventory of the most important difficulties, illustrate each of them by a real experiment and present a feasible mediation, either numerical or experimental in nature. Once the experimental set-up is fine-tuned to overcome these pitfalls, it is expected that the recording of high-level UPS experiments, in combination with numerical computations, will facilitate the technique to become a fully quantitative non-destructive characterization method. 相似文献
63.
64.
Imogen Foubert Eveline Fredrick Jeroen Vereecken Maarten Sichien Koen Dewettinck 《Thermochimica Acta》2008,471(1-2):7-13
Differential scanning calorimeters have frequently been used to study the isothermal crystallization kinetics of fats and oils. In some circumstances (e.g. start of crystallization during cooling to the crystallization temperature, crystallization in emulsion) this straightforward approach is not applicable. This paper describes an indirect DSC method for determination of the crystallization kinetics under these ‘difficult’ circumstances. The principle is to stop the crystallization at different moments during the isothermal crystallization and raise the sample temperature. The amount of heat released is then used as a measure for the amount of crystallization and plotted as function of time. Combination of the stop-and-return method with the direct method may sometimes be used to save on measurement time. Stop-and-return experiments can furthermore be used to gain more insight in the crystallization mechanism based on the fact that different polymorphic forms and fractions have different melting temperatures. 相似文献
65.
The generalized Thomas-Kuhn sum rules are used to eliminate the explicit dependence on dipolar terms in the traditional sum-over-states (SOS) expression for the second hyperpolarizability to derive a new, yet equivalent, SOS expression. This new dipole-free expression may be better suited to study the second hyperpolarizability of nondipolar systems such as quadrupolar, octupolar, and dodecapolar structures. The two expressions lead to the same fundamental limits of the off-resonance second hyperpolarizability; and when applied to a particle in a box and a clipped harmonic oscillator, have the same frequency dependence. We propose that the new dipole-free equation, when used in conjunction with the standard SOS expression, can be used to develop a three-state model of the dispersion of the third-order susceptibility that can be applied to molecules in cases where normally many more states would have been required. Furthermore, a comparison between the two expressions can be used as a convergence test of molecular orbital calculations when applied to the second hyperpolarizability. 相似文献
66.
Kristof Van Hecke Vu Thi Ngan Peter Nockemann Ben Thijs Minh Tho Nguyen Koen Binnemans Luc Van Meervelt 《Journal of Molecular Structure》2008,885(1-3):97-103
The structure of one tautomer (amine form) of cyano-carbamimidic acid ethyl ester or (amino-ethoxy-methylidene)aminoformonitrile (CAS: 13947-84-7) was determined by single crystal X-ray diffraction. Ab initio quantum chemical calculations at the B3LYP, MP2 and G3 levels were performed to investigate the stability and the formation of the different tautomers and conformers. The calculations indicate that the amine form is the more stable tautomer, showing a high degree of electron conjugation. The most stable amine conformer located by the calculations corresponds to the crystallized structure. On the contrary, in the less stable imine form, the conjugation is separated by a N2–C2 single bond. 相似文献
67.
Huan Wang Dr. Mahbod Morshedi Dr. Mahesh S. Kodikara Dr. Yovan de Coene Prof. Koen Clays Prof. Chi Zhang Prof. Mark G. Humphrey 《Angewandte Chemie (International ed. in English)》2023,62(27):e202301754
Porphyrins are important macrocycles with applications in several areas including therapy, catalysis, and sensing. Strong nonlinear optical (NLO) responses are the key to fully exploiting the potential of these biocompatible molecules. We herein report that certain metal-alkynyl donor/nitro acceptor-functionalized porphyrins are attractive candidates for NLO applications. We show that specific examples exhibit record quadratic optical nonlinearity, exceptional two-photon absorption, and outstanding three-photon absorption, and we report the first porphyrins that exhibit four-photon absorption. The two-, three-, and four-photon absorption maxima are found at the corresponding multiples of linear absorption bands that time-dependent density functional theory assigns as admixtures of porphyrin-localized π*←π and donor-porphyrin to porphyrin-acceptor charge-transfer transitions. 相似文献
68.
Anna Szabó Rolando Pasquariello Pedro F. Costa Radmila Pavlovic Indi Geurs Koen Dewettinck Chris Vervaet Tiziana A. L. Brevini Fulvio Gandolfi Sandra Van Vlierberghe 《Macromolecular bioscience》2023,23(10):2300016
To provide prominent accessibility of fishmeal to the European population, the currently available, time- and cost-extensive feeding trials, which evaluate fish feed, should be replaced. The current paper reports on the development of a novel 3D culture platform, mimicking the microenvironment of the intestinal mucosa in vitro. The key requirements of the model include sufficient permeability for nutrients and medium-size marker molecules (equilibrium within 24 h), suitable mechanical properties (G' < 10 kPa), and close morphological similarity to the intestinal architecture. To enable processability with light-based 3D printing, a gelatin-methacryloyl-aminoethyl-methacrylate-based biomaterial ink is developed and combined with Tween 20 as porogen to ensure sufficient permeability. To assess the permeability properties of the hydrogels, a static diffusion setup is utilized, indicating that the hydrogel constructs are permeable for a medium size marker molecule (FITC-dextran 4 kg mol−1). Moreover, the mechanical evaluation through rheology evidence a physiologically relevant scaffold stiffness (G' = 4.83 ± 0.78 kPa). Digital light processing-based 3D printing of porogen-containing hydrogels results in the creation of constructs exhibiting a physiologically relevant microarchitecture as evidenced through cryo-scanning electron microscopy. Finally, the combination of the scaffolds with a novel rainbow trout (Oncorhynchus mykiss) intestinal epithelial cell line (RTdi-MI) evidence scaffold biocompatibility. 相似文献
69.
Pozo OJ Van Eenoo P Deventer K Delbeke FT 《Analytical and bioanalytical chemistry》2007,389(4):1209-1224
A screening method for the urinary detection of 34 exogenous anabolic steroids has been developed. The method involves an
enzymatic hydrolysis, liquid-liquid extraction and detection by liquid chromatography-tandem mass spectrometry. The use of
some adducts such as [M+NH4]+, [M+CH3COO]− and [M+H+MeOH]+ was necessary in order to detect some analytes at the required level (lower than 10 ng/ml). Two transitions were selected
for each analyte. Different concentration factors have been studied in order to increase the sensitivity. A concentration
factor of 50 was selected for the screening method although the high ion suppression observed under these conditions can hamper
its application as a quantitative method. The method was validated and limits of detection were obtained by spiking ten different
blank urine samples at five different concentration levels. Up to 29 analytes were detected in all spiked urines at the required
level. Limits of detection between 1 and 10 ng/ml were obtained for most analytes which fulfil current requirements. The applicability
of the method was shown by analysing positive samples. 相似文献
70.
The ionization of 46 anabolic steroids has been studied. The absence of basic or acidic moieties in most of these analytes makes their direct ionization as [M + H]+ by atmospheric pressure interfaces difficult. The formation of adducts with different components of the mobile phase has been found to be an efficient way to ionize anabolic steroids by electrospray. Different mobile phases using methanol (MeOH) or acetonitrile as organic solvent and HCOOH, Na+ or NH4+ as additives have been tested to favor the adduct formation. A direct correlation between the chemical structure of the anabolic steroid and the possibility to ionize it in a particular chromatographic condition has been found. According to their ionization, anabolic steroids can be divided into seven different groups depending on both the nature and the relative position of their functional groups. The formation of different adducts such as [M + Na + MeOH]+ or [M + H + CH3 CN - H2O]+ is required in order to ionize some of these groups and the optimal mobile phase composition for each group of anabolic steroids is proposed. Despite the ionization limitations due to their chemical structure, most of tested anabolic steroids could be ionized using the adduct formation approach. 相似文献