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31.
32.
H J Reeuwijk H Lingeman U R Tjaden E A de Bruijn H J Keizer J van der Greef 《Journal of chromatography. A》1988,428(1):93-102
(E)-5-(2-Bromovinyl)-2'-deoxyuridine is an antiviral drug that is experimentally used for modulation of the antitumour effect of fluoropyrimidines, such as ftorafur and 5-fluorouracil. The isolation of the analyte, in the presence of 5-fluorouracil, from the matrix is performed either by means of a simple protein precipitation (plasma) or by means of a liquid-liquid extraction with ethyl acetate (urine). Following pretreatment, the analyte is analysed by reversed-phase chromatography and quantified by absorbance detection at 307 nm. The minimum detectable concentration in plasma and urine samples is ca. 6 ng/ml. The recovery after deproteination of plasma samples is 75%, while after liquid-liquid extraction of urine the recovery amounts 92%. The degree of protein binding of the analyte, measured by ultrafiltration, is found to be 97%. These data allow the bioanalysis of (E)-5-(2-bromovinyl)-2'-deoxyuridine for pharmacokinetic studies. 相似文献
33.
Rob. J. M. Hermans Henk M. Buck 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3-4):255-265
Abstract An 1H NMR study of the conformation of the dioxaphosphorinane ring of a number of diastereoisomeric bicyclic saturated six-membered ring phosphites (3ab-10ab) has been performed. The dioxaphosphorinane ring of these phosphites is transannelated with a tetrahydrofuran, cyclopen-tane, tetrahydropyran or cyclohexane ring. The substituent on the phosphorus atom is a methoxy or phenoxy group. It is shown that the cis isomers 3a-10a prefer a chair conformation of the dioxaphosphorinane ring, independent of the substituent on the phosphorus atom and of the nature of the transannelated ring. In contrast, for the trans isomers 3b-10b a twist rather than a chair conformation of the dioxaphosphorinane ring is preferred. The fraction of the twist conformer in the trans isomers is mainly determined by the substituent on phosphorus. The size and composition of the transannelated ring are relatively unimportant in this respect. For both cis and trans isomers the preferred geometry is solvent-independent. The measured 3JPOCH couplings of the cis isomers 3a-10a are used to formulate an expression for the dependence of such couplings upon dihedral angles in bicyclic phosphites. 相似文献
34.
Daniel Tordera Andreas M. Bünzli Antonio Pertegás Dr. José M. Junquera‐Hernández Prof. Edwin C. Constable Dr. Jennifer A. Zampese Prof. Catherine E. Housecroft Prof. Enrique Ortí Dr. Henk J. Bolink 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(26):8597-8609
A new approach to obtain green‐emitting iridium(III) complexes is described. The synthetic approach consists of introducing a methylsulfone electron‐withdrawing substituent into a 4‐phenylpyrazole cyclometalating ligand in order to stabilize the highest‐occupied molecular orbital (HOMO). Six new complexes have been synthesized incorporating the conjugate base of 1‐(4‐(methylsulfonyl)phenyl)‐1 H‐pyrazole as the cyclometalating ligand. The complexes show green emission and very high photoluminescence quantum yields in both diluted and concentrated films. When used as the main active component in light‐emitting electrochemical cells (LECs), green electroluminance is observed. High efficiencies and luminances are obtained at low driving voltages. This approach for green emitters is an alternative to the widely used fluorine‐based substituents in the cyclometalating ligands and opens new design possibilities for the synthesis of green emitters for LECs. 相似文献
35.
Microbial adhesion to poly(ethylene oxide) brushes: influence of polymer chain length and temperature 总被引:1,自引:0,他引:1
Roosjen A van der Mei HC Busscher HJ Norde W 《Langmuir : the ACS journal of surfaces and colloids》2004,20(25):10949-10955
Glass surfaces were modified by end-grafting poly(ethylene oxide) (PEO) chains having molecular weights of 526, 2000, or 9800 Da. Characterization using water contact angles, ellipsometry, and X-ray photoelectron spectroscopy confirmed the presence of the PEO brushes on the surface with estimated lengths in water of 2.8-, 7.5-, and 23.7-nm, respectively. Adhesion of two bacterial (Staphylococcus epidermidis and Pseudomonas aeruginosa) and two yeast (Candida albicans and Candida tropicalis) strains to these brushes was studied and compared to their adhesion to bare glass. For the bacterium P. aeruginosa and the yeast C. tropicalis, adhesion to the 2.8-nm brush was comparable to their adhesion on bare glass, whereas adhesion to the 7.5- and 23.7-nm brushes was greatly reduced. For S. epidermidis, adhesion was only slightly higher to the 2.8-nm brush than that to the longer brushes. Adhesion of the yeast C. albicans to the PEO brushes was lower than that to glass, but no differences in adhesion were found between the three brush lengths. After passage of an air bubble, nearly all microorganisms adhering to a brush were removed, irrespective of brush length, whereas retention of the adhering organisms on glass was much higher. No significant differences were found in adhesion nor retention between experiments conducted at 20 and those conducted at 37 degrees C. 相似文献
36.
Huub Kooijman Anthony L. Spek Henk Kleijn Hendrik L. van Maanen Johann T. B. H. Jastrzebski Gerard van Koten 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(4):481-483
The configuration of the chiral ring atoms of the title compound, C26H26N2O, obtained in an enantioselective synthesis, has been established relative to the known R configuration of the α‐methylbenzyl moieties. The crystal packing involves a two‐dimensional network of C—H?π interactions between the aromatic rings. 相似文献
37.
Hanna Talacua Serge H. M. Sntjens Shraddha H. Thakkar Aurelie M. A. Brizard Lex A. van Herwerden Aryan Vink Geert C. van Almen Patricia Y. W. Dankers Carlijn V. C. Bouten Ricardo P. J. Budde Henk M. Janssen Jolanda Kluin 《Macromolecular bioscience》2020,20(7)
For in situ tissue engineering (TE) applications it is important that implant degradation proceeds in concord with neo‐tissue formation to avoid graft failure. It will therefore be valuable to have an imaging contrast agent (CA) available that can report on the degrading implant. For this purpose, a biodegradable radiopaque biomaterial is presented, modularly composed of a bisurea chain‐extended polycaprolactone (PCL2000‐U4U) elastomer and a novel iodinated bisurea‐modified CA additive (I‐U4U). Supramolecular hydrogen bonding interactions between the components ensure their intimate mixing. Porous implant TE‐grafts are prepared by simply electrospinning a solution containing PCL2000‐U4U and I‐U4U. Rats receive an aortic interposition graft, either composed of only PCL2000‐U4U (control) or of PCL2000‐U4U and I‐U4U (test). The grafts are explanted for analysis at three time points over a 1‐month period. Computed tomography imaging of the test group implants prior to explantation shows a decrease in iodide volume and density over time. Explant analysis also indicates scaffold degradation. (Immuno)histochemistry shows comparable cellular contents and a similar neo‐tissue formation process for test and control group, demonstrating that the CA does not have apparent adverse effects. A supramolecular approach to create solid radiopaque biomaterials can therefore be used to noninvasively monitor the biodegradation of synthetic implants. 相似文献
38.
Willi A. Brand Tyler B. Coplen Anita T. Aerts‐Bijma J. K. Böhlke Matthias Gehre Heike Geilmann Manfred Gröning Henk G. Jansen Harro A. J. Meijer Stanley J. Mroczkowski Haiping Qi Karin Soergel Hilary Stuart‐Williams Stephan M. Weise Roland A. Werner 《Rapid communications in mass spectrometry : RCM》2009,23(7):999-1019
Internationally distributed organic and inorganic oxygen isotopic reference materials have been calibrated by six laboratories carrying out more than 5300 measurements using a variety of high‐temperature conversion techniques (HTC) a in an evaluation sponsored by the International Union of Pure and Applied Chemistry (IUPAC). To aid in the calibration of these reference materials, which span more than 125‰, an artificially enriched reference water (δ18O of +78.91‰) and two barium sulfates (one depleted and one enriched in 18O) were prepared and calibrated relative to VSMOW2 b and SLAP reference waters. These materials were used to calibrate the other isotopic reference materials in this study, which yielded:
The seemingly large estimated combined uncertainties arise from differences in instrumentation and methodology and difficulty in accounting for all measurement bias. They are composed of the 3‐fold standard errors directly calculated from the measurements and provision for systematic errors discussed in this paper. A primary conclusion of this study is that nitrate samples analyzed for δ18O should be analyzed with internationally distributed isotopic nitrates, and likewise for sulfates and organics. Authors reporting relative differences of oxygen‐isotope ratios (δ18O) of nitrates, sulfates, or organic material should explicitly state in their reports the δ18O values of two or more internationally distributed nitrates (USGS34, IAEA‐NO‐3, and USGS35), sulfates (IAEA‐SO‐5, IAEA‐SO‐6, and NBS 127), or organic material (IAEA‐601 benzoic acid, IAEA‐602 benzoic acid, and IAEA‐600 caffeine), as appropriate to the material being analyzed, had these reference materials been analyzed with unknowns. This procedure ensures that readers will be able to normalize the δ18O values at a later time should it become necessary. The high‐temperature reduction technique for analyzing δ18O and δ2H is not as widely applicable as the well‐established combustion technique for carbon and nitrogen stable isotope determination. To obtain the most reliable stable isotope data, materials should be treated in an identical fashion; within the same sequence of analyses, samples should be compared with working reference materials that are as similar in nature and in isotopic composition as feasible. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
Reference material | δ18O and estimated combined uncertainty c |
---|---|
IAEA‐602 benzoic acid | +71.28 ± 0.36‰ |
USGS35 sodium nitrate | +56.81 ± 0.31‰ |
IAEA‐NO‐3 potassium nitrate | +25.32 ± 0.29‰ |
IAEA‐601 benzoic acid | +23.14 ± 0.19‰ |
IAEA‐SO‐5 barium sulfate | +12.13 ± 0.33‰ |
NBS 127 barium sulfate | +8.59 ± 0.26‰ |
VSMOW2 water | 0‰ |
IAEA‐600 caffeine | ?3.48 ± 0.53‰ |
IAEA‐SO‐6 barium sulfate | ?11.35 ± 0.31‰ |
USGS34 potassium nitrate | ?27.78 ± 0.37‰ |
SLAP water | ?55.5‰ |
39.
We study quasi-periodic tori under a normal-internal resonance, possibly with multiple eigenvalues. Two non-degeneracy conditions play a role. The first of these generalizes invertibility of the Floquet matrix and prevents drift of the lower dimensional torus. The second condition involves a Kolmogorov-like variation of the internal frequencies and simultaneously versality of the Floquet matrix unfolding. We focus on the reversible setting, but our results carry over to the Hamiltonian and dissipative contexts. 相似文献
40.
David Falck Anna J. Oosthoek-de Vries Ard Kolkman Henk Lingeman Maarten Honing Sybren S. Wijmenga Arno P. M. Kentgens Wilfried M. A. Niessen 《Analytical and bioanalytical chemistry》2013,405(21):6711-6720
Flow-through electrochemical conversion (EC) of drug-like molecules was hyphenated to miniaturized nuclear magnetic resonance spectroscopy (NMR) via on-line solid-phase extraction (SPE). After EC of the prominent p38α mitogen-activated protein kinase inhibitor BIRB796 into its reactive products, the SPE step provided preconcentration of the EC products and solvent exchange for NMR analysis. The acquisition of NMR spectra of the mass-limited samples was achieved in a stripline probe with a detection volume of 150 nL offering superior mass sensitivity. This hyphenated EC–SPE–stripline-NMR setup enabled the detection of the reactive products using only minute amounts of substrate. Furthermore, the integration of conversion and detection into one flow setup counteracts incorrect assessments caused by the degradation of reactive products. However, apparent interferences of the NMR magnetic field with the EC, leading to a low product yield, so far demanded relatively long signal averaging. A critical assessment of what is and what is not (yet) possible with this approach is presented, for example in terms of structure elucidation and the estimation of concentrations. Additionally, promising routes for further improvement of EC–SPE–stripline-NMR are discussed. 相似文献