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101.
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Enikö Kádár David M. Lowe Montserrat Solé Andrew S. Fisher Awadhesh N. Jha James W. Readman Thomas H. Hutchinson 《Analytical and bioanalytical chemistry》2010,396(2):657-666
Nano-Fe particle uptake was experimentally examined in vitro using excised gills and blood cells of the edible blue mussel
Mytilus sp. Whole gills were exposed to both Fe2O3 nanoparticles and a solution of the hydrated FeCl3 salt, for up to 12 h, and blood cells for 30 min. Equimolar Fe+3 in the nano- and the soluble form was estimated under the assumption of dense spherical particles accommodating the same
number of Fe+3 as in the dissolved salt solution, namely: 1,000 μg L−1 Fe2O3 equivalent to 100 μg L−1 FeCl3·6H2O. Putative toxic impact of nano-Fe in gill epithelia and blood cells was assessed by an array of techniques including light-
and electron microscopy, biomarkers for oxidative stress (lipid peroxidation levels), neurotoxic effects (acetylcholinesterase
activity) and cytotoxicity (neutral red retention). Total and filtered fractions (20 and 200 nm, respectively) of Fe were
analysed by ICP-OES. Our results provide evidence for the following: (1) much of both the soluble (95%) and the nano-Fe (90%)
were removed from the water column within 12 h; (2) dissolved- and nano-Fe seemed to follow different routes of uptake within
the gill epithelium; (3) both nano-Fe and soluble FeCl3 caused similar impairment of lysosomal stability in circulating blood cells; (4) lipid peroxidation in gills exposed to the
two distinct forms of Fe was increased, while acetylcholinesterase activity was unaffected. In these short-term in vitro studies,
there appears to be little difference in toxic response between exposure to the Fe salt and the nano-Fe indicating that, in
this case, the nanoparticles do not invoke special properties affecting biological function in gills. However, with the use
of nano-Fe as a food additive, clearly longer-term in vivo studies are warranted. 相似文献
104.
Laura Senft Jamonica L. Moore Alicja Franke Katherine R. Fisher Andreas Scheitler Achim Zahl Ralph Puchta Dominik Fehn Sidney Ison Safaa Sader Ivana Ivanovi-Burmazovi Christian R. Goldsmith 《Chemical science》2021,12(31):10483
Reactivity assays previously suggested that two quinol-containing MRI contrast agent sensors for H2O2, [Mn(H2qp1)(MeCN)]2+ and [Mn(H4qp2)Br2], could also catalytically degrade superoxide. Subsequently, [Zn(H2qp1)(OTf)]+ was found to use the redox activity of the H2qp1 ligand to catalyze the conversion of O2˙− to O2 and H2O2, raising the possibility that the organic ligand, rather than the metal, could serve as the redox partner for O2˙− in the manganese chemistry. Here, we use stopped-flow kinetics and cryospray-ionization mass spectrometry (CSI-MS) analysis of the direct reactions between the manganese-containing contrast agents and O2˙− to confirm the activity and elucidate the catalytic mechanism. The obtained data are consistent with the operation of multiple parallel catalytic cycles, with both the quinol groups and manganese cycling through different oxidation states during the reactions with superoxide. The choice of ligand impacts the overall charges of the intermediates and allows us to visualize complementary sets of intermediates within the catalytic cycles using CSI-MS. With the diquinolic H4qp2, we detect Mn(iii)-superoxo intermediates with both reduced and oxidized forms of the ligand, a Mn(iii)-hydroperoxo compound, and what is formally a Mn(iv)-oxo species with the monoquinolate/mono-para-quinone form of H4qp2. With the monoquinolic H2qp1, we observe a Mn(ii)-superoxo ↔ Mn(iii)-peroxo intermediate with the oxidized para-quinone form of the ligand. The observation of these species suggests inner-sphere mechanisms for O2˙− oxidation and reduction that include both the ligand and manganese as redox partners. The higher positive charges of the complexes with the reduced and oxidized forms of H2qp1 compared to those with related forms of H4qp2 result in higher catalytic activity (kcat ∼ 108 M−1 s−1 at pH 7.4) that rivals those of the most active superoxide dismutase (SOD) mimics. The manganese complex with H2qp1 is markedly more stable in water than other highly active non-porphyrin-based and even some Mn(ii) porphyrin-based SOD mimics.Manganese complexes with polydentate quinol-containing ligands are found to catalyze the degradation of superoxide through inner-sphere mechanisms. The redox activity of the ligand stabilizes higher-valent manganese species. 相似文献
105.
Mäki JM Tuomisto F Varpula A Fisher D Khan RU Martineau PM 《Physical review letters》2011,107(21):217403
We have developed a method called optical transient positron spectroscopy and apply it to study the optically induced carrier trapping and charge transfer processes in natural brown type IIa diamond. By measuring the positron lifetime with continuous and pulsed illumination, we present an estimate of the optical absorption cross section of the vacancy clusters causing the brown color. The vacancy clusters accept electrons from the valence band in the absorption process, giving rise to photoconductivity. 相似文献
106.
Dattatray S. Wavhal Ellen R. Fisher 《Journal of Polymer Science.Polymer Physics》2002,40(21):2473-2488
A general method of modifying the entire cross section of porous poly(ether sulfone) membranes with a low‐temperature CO2‐plasma treatment is reported. Both surfaces of the membranes are highly hydrophilic, with a water drop on the surface disappearing in less than 1 s, even 6 months after plasma treatment. This high hydrophilicity of both membrane surfaces results from the incorporation of hydrophilic functionalities, as evidenced by Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy. The incorporation of these hydrophilic functionalities takes place primarily during plasma treatment, with some incorporation of atmospheric oxygen and nitrogen immediately upon exposure to air. Scanning electron microscopy shows that the membrane surface is covered by a thin, white layer that is likely the result of etching and redeposition of sputtered surface fragments. An increase in the water bubble point and glass‐transition temperature is also observed for CO2‐plasma‐treated membranes. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2473–2488, 2002 相似文献
107.
Let E be a compact subset of the open unit disc Δ and let Hq be the Hardy space of analytic functions f on Δ for which stf¦q has a harmonic majorant. We determine the value of the Kolmogorov, Gel'fand, and linear n-widths in Lp(E, μ) of the restriction to E of the unit ball of Hq when p q or when 1 q < p < ∞ and E is “small”. 相似文献
108.
Jerry W MisnerJack W Fisher John P GardnerSteve W Pedersen Kristina L TrinkleBilly G Jackson Tony Y Zhang 《Tetrahedron letters》2003,44(32):5991-5993
The nucleus of the carbacephem antibiotic loracarbef was synthesized in a highly efficient and enantioselective fashion from 2S,3S-2-amino-3-hydroxy-6-heptenoic acid (AHHA), which was derived from enzyme-catalyzed condensation of glycine and 4-pentenaldehyde. The bicyclic framework of this compound was established through sequential Mitsunobu reaction and aldol condensations. 相似文献
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