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71.
Studies have been performed assessing the feasibility and characterizing the automation of solid-phase microextraction (SPME) on a multi-well plate format. Four polycyclic aromatic hydrocarbons (PAHs), naphthalene, fluorene, anthracene and fluoranthene, were chosen as test analytes to demonstrate the technique due to their favorable partition coefficients, K(fw), between polydimethylsiloxane (PDMS) extraction phases and water. Four different PDMS configurations were investigated regarding their suitability. These included (i) a PDMS membrane; (ii) a multi-fiber device containing lengths of PDMS-coated flexible wire; (iii) a stainless steel pin covered with silicone hollow fiber membrane and (iv) commercial PDMS-coated flexible metal fiber assemblies. Of these configurations, the stainless steel pin covered with silicone tubing was chosen as a robust alternative. An array of 96 SPME devices that can be placed simultaneously into a 96-well plate was constructed to demonstrate the high-throughput potential when performing multiple microextractions in parallel. Different agitation methods were assessed including magnetic stirring, sonication, and orbital shaking at different speeds. Orbital shaking whilst holding the SPME device in a stationary position provided the optimum agitation conditions for liquid SPME. Once the analytes had been extracted, desorption of the analytes into an appropriate solvent was investigated. Liquid-phase SPME and solvent desorption on the multi-well plate format is shown to be a viable alternative for automated high-throughput SPME analysis compatible with both gas- and liquid-chromatography platforms. 相似文献
72.
Negar Maafi Abdullah Al Mamun Ondej Janourek Jana Maíkov Kateina Breiterov Adla Diepoltov Klra Kone
n Anna Holkov Daniela Hulcov Jií Kune Elika Kohelov Darja Koutov Marcela afratov Lucie Novkov Lucie Cahlíkov 《Molecules (Basel, Switzerland)》2021,26(19)
The search for novel antimycobacterial drugs is a matter of urgency, since tuberculosis is still one of the top ten causes of death from a single infectious agent, killing more than 1.4 million people worldwide each year. Nine Amaryllidaceae alkaloids (AAs) of various structural types have been screened for their antimycobacterial activity. Unfortunately, all were considered inactive, and thus a pilot series of aromatic esters of galanthamine, 3-O-methylpancracine, vittatine and maritidine were synthesized to increase biological activity. The semisynthetic derivatives of AAs were screened for their in vitro antimycobacterial activity against Mycobacterium tuberculosis H37Ra and two other mycobacterial strains (M. aurum, M. smegmatis) using a modified Microplate Alamar Blue Assay. The most active compounds were also studied for their in vitro hepatotoxicity on the hepatocellular carcinoma cell line HepG2. In general, the derivatization of the original AAs was associated with a significant increase in antimycobacterial activity. Several pilot derivatives were identified as compounds with micromolar MICs against M. tuberculosis H37Ra. Two derivatives of galanthamine, 1i and 1r, were selected for further structure optimalization to increase the selectivity index. 相似文献
73.
Yuxin Liu Abdelkrim Talbi Bahram Djafari-Rouhani El Houssaine El Boudouti Lucie Drbohlavová Vincent Mortet Olivier Bou Matar Philippe Pernod 《Physics letters. A》2019,383(13):1502-1505
The interaction of Love waves with square array of pillars deposited on a cavity defined in a 2D holey phononic crystal is numerically investigated using Finite Element Method. First, the existence of SH surface modes is demonstrated separately for phononic crystals that consist of square arrayed holes, or rectangular arrayed Ni pillars, respectively in, or on, a SiO2 film deposited on a ST-cut quartz substrate. The coupling between SH modes and torsional mode in pillars induces a transmission dip that occurs at a frequency located in the range of the band-gap of the holey phononic crystal. Second, a cavity is constructed by removing lines of holes in the holey phononic crystal and results in a transmission peak that matches the dip. The optimal geometrical parameters enable us to create a coupling of the cavity mode and the localized pillar mode by introducing lines of pillars into the cavity, which significantly improved the efficiency of the cavity without increasing the crystal size. The obtained results will pave the way to implement advanced designs of high-performance electroacoustic sensors based on coupling modes in phononic crystals. 相似文献
74.
Michal?Landa Petr?Sedlák Hanu??Seiner Luděk?Heller Lucie?Bicanová Petr??ittner Václav?Novák 《Applied Physics A: Materials Science & Processing》2009,96(3):557-567
Recent experimental and theoretical improvements of resonant ultrasound spectroscopy (RUS) are summarized to investigate elastic
constants of phases in shape memory alloys. The proposed inversion procedure, described in this work, is particularly suitable
to reliable evaluation of the temperature dependence of elastic constants of low-symmetry ferroelastic materials which may
be strongly elastically anisotropic and tend to exist in twinned forms. The method is applicable even for the evaluation of
single-crystal elastic constants from RUS measurements on microtwinned crystals, since it involves a homogenization algorithm
based on the macroscopic deformation response of the layered structure. This potentially allows performing meaningful acoustic
studies on samples with a general submicron-size layered structure. 相似文献
75.
C.R. Hoffman T. Baumann D. Bazin J. Brown G. Christian D.H. Denby P.A. DeYoung J.E. Finck N. Frank J. Hinnefeld S. Mosby W.A. Peters W.F. Rogers A. Schiller A. Spyrou M.J. Scott S.L. Tabor M. Thoennessen P. Voss 《Physics letters. [Part B]》2009
The decay energy spectrum for neutron unbound states in 24O (Z=8, N=16) has been observed for the first time. The resonance energy of the lowest lying state, interpreted as the 2+ level, has been observed at a decay energy above 600 keV. The resulting excitation energy of the 2+ level above 4.7 MeV, supplies strong evidence that 24O is a doubly magic nucleus. The data is also consistent with the presence of a second excited state around 5.33 MeV which can be interpreted as the 1+ level. 相似文献
76.
Phi Minh Do Alexander Angerhofer Ivan Hrdy Lucie Bardonova Lonnie O. Ingram K. T. Shanmugam 《Applied biochemistry and biotechnology》2009,153(1-3):21-33
Trichomonas vaginalis generates reduced ferredoxin within a unique subcellular organelle, hydrogenosome that is used as a reductant for H2 production. Pyruvate ferredoxin oxidoreductase and NADH dehydrogenase (NADH-DH) are the two enzymes catalyzing the production of reduced ferredoxin. The genes encoding the two subunits of NADH-DH were cloned and expressed in Escherichia coli. Kinetic properties of the recombinant heterodimer were similar to that of the native enzyme from the hydrogenosome. The recombinant holoenzyme contained 2.15 non-heme iron and 1.95 acid-labile sulfur atoms per heterodimer. The EPR spectrum of the dithionite-reduced protein revealed a [2Fe–2S] cluster with a rhombic symmetry of g xyz?=?1.917, 1.951, and 2.009 corresponding to cluster N1a of the respiratory complex I. Based on the Fe content, absorption spectrum, and the EPR spectrum of the purified small subunit, the [2Fe–2S] cluster was located in the small subunit of the holoenzyme. This recombinant NADH-DH oxidized NADH and reduced low redox potential electron carriers, such as viologen dyes as well as Clostridium ferredoxin that can couple to hydrogenase for H2 production from NADH. These results show that this unique hydrogenosome NADH dehydrogenase with a critical role in H2 evolution in the hydrogenosome can be produced with near-native properties in E. coli for metabolic engineering of the bacterium towards developing a dark fermentation process for conversion of biomass-derived sugars to H2 as an energy source. 相似文献
77.
Ascorbic acid (AA) and dehydroascorbic acid (DHA) are small polar molecules difficult to be retained in conventional chromatographic RP systems. Hydrophilic interaction liquid chromatography (HILIC) using Obelisk R (100 × 3.2 mm, 5 μm, Sielc) analytical column and isocratic elution by ammonium acetate buffer pH 4.2 was found to be successful at this task, while other tested HILIC columns – Obelisk N (100 × 3.2 mm, 5 μm, Sielc) and Luna HILIC (100 × 3.0 mm, 3 μm, Phenomenex) were unsuccessful for the purposes of analysis. Charged aerosol detection (CAD) has recently become a new alternative universal detection system in HPLC, and was extremely convenient for the simultaneous analysis of AA and DHA without the need of subtraction approach and oxidation/reduction step. CAD response was found linear in defined range in spite of the fact that CAD is designated as non-linear detection method. A simple and fast HILIC-CAD method was applied for the analysis of pharmaceutical preparations containing AA. Method validation was performed including parameters of precision, accuracy, linearity, limit of detection and limit of quantitation (LOQ). The method was fast, accurate and precise for both detectors with LOQAA 5 μg/ml for UV detection and 10 μg/ml for CAD, respectively. DHA was detected only by CAD within tested concentration range with LOQDHA 1 μg/ml. 相似文献
78.
Thomas C. T. Michaels Lucie X. Liu Samo Curk Peter G. Bolhuis 《Molecular physics》2018,116(21-22):3055-3065
ABSTRACTProbing reaction mechanisms of supramolecular processes in soft and biological matter, such as protein aggregation, is inherently challenging. This is because these processes involve multiple molecular mechanisms that are associated with the rearrangement of large numbers of weak bonds, resulting in complex free energy landscapes with many kinetic barriers. Reaction rate measurements at different temperatures can offer unprecedented insights into the underlying molecular mechanisms. However, to be able to interpret such measurements, a key challenge is to establish which properties of the complex free energy landscapes are probed by the reaction rate. Here, we present a reaction rate theory for supramolecular kinetics based on Kramers theory of diffusive reactions over multiple kinetic barriers. We find that reaction rates for protein aggregation are of the Arrhenius–Eyring type and that the associated activation energies probe only one relevant barrier along the respective free energy landscapes. We apply this advancement to interpret, in experiments and in coarse-grained computer simulations, reaction rates of amyloid aggregation in terms of molecular mechanisms and associated thermodynamic signatures. These results suggest a practical extension of the concept of rate-determining steps for complex supramolecular processes and establish a general platform for probing the underlying energy landscape using kinetic measurements. 相似文献
79.
Jessica Dubois Sofya Kulikova Lucie Hertz-Pannier Jean-François Mangin Ghislaine Dehaene-Lambertz Cyril Poupon 《Magnetic resonance imaging》2014
Objective
Diffusion imaging techniques such as DTI and HARDI are difficult to implement in infants because of their sensitivity to subject motion. A short acquisition time is generally preferred, at the expense of spatial resolution and signal-to-noise ratio. Before estimating the local diffusion model, most pre-processing techniques only register diffusion-weighted volumes, without correcting for intra-slice artifacts due to motion or technical problems. Here, we propose a fully automated strategy, which takes advantage of a high orientation number and is based on spherical-harmonics decomposition of the diffusion signal.Material and methods
The correction strategy is based on two successive steps: 1) automated detection and resampling of corrupted slices; 2) correction for eddy current distortions and realignment of misregistered volumes. It was tested on DTI data from adults and non-sedated healthy infants.Results
The methodology was validated through simulated motions applied to an uncorrupted dataset and through comparisons with an unmoved reference. Second, we showed that the correction applied to an infant group enabled to improve DTI maps and to increase the reliability of DTI quantification in the immature cortico-spinal tract.Conclusion
This automated strategy performed reliably on DTI datasets and can be applied to spherical single- and multiple-shell diffusion imaging. 相似文献80.
Malkov AV Barłóg M Miller-Potucká L Kabeshov MA Farrugia LJ Kočovský P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(22):6873-6884
Enantiopure, Boc-protected alkoxyamines 12 and 13, derived from the readily available homoallylic alcohols 4 via a reaction that involves either inversion or retention of configuration, undergo a diastereoselective Pd-catalyzed ring-closing carbonylative amidation to produce isoxazolidines 16/17 (≤50:1 diastereoisomer ratio (d.r.)) that can be readily converted into the N-Boc-protected esters of β-amino-δ-hydroxy acids and their γ-substituted homologues 37. The key carbonylative cyclization proceeds through an unusual syn addition of the palladium and the nitrogen nucleophile across the C=C bond (19→21), as revealed by the reaction of 15, which afforded isoxazolidine 18 with high diastereoselectivity. 相似文献