The Fate of ZnO Nanoparticles Administered to Human Bronchial Epithelial Cells

A particular challenge for nanotoxicology is the evaluation of the biological fate and toxicity of nanomaterials that dissolve in aqueous fluids. Zinc oxide nanomaterials are of particular concern because dissolution leads to release of the toxic divalent zinc ion. Although zinc ions have been implicated in ZnO cytotoxicity, direct identification of the chemical form of zinc taken up by cells exposed to ZnO nanoparticles, and its intracellular fate, has not yet been achieved. We combined high resolution X-ray spectromicroscopy and high elemental sensitivity X-ray microprobe analyses to determine the fate of ZnO and less soluble iron-doped ZnO nanoparticles following exposure to cultures of human bronchial epithelial cells, BEAS-2B. We complemented two-dimensional X-ray imaging methods with atomic force microscopy of cell surfaces to distinguish between nanoparticles that were transported inside the cells from those that adhered to the cell exterior. The data suggest cellular uptake of ZnO nanoparticles is a mechanism of zinc accumulation in cells. Following uptake, ZnO nanoparticles dissolved completely generating intracellular Zn²⁺ complexed by molecular ligands. These results corroborate a model for ZnO nanoparticle toxicity that is based on nanoparticle uptake followed by intracellular dissolution

Asymmetric Catalysis at the Mesoscale: Gold Nanoclusters Embedded in Chiral Self-Assembled Monolayer as Heterogeneous Catalyst for Asymmetric Reactions

Research to develop highly versatile, chiral, heterogeneous catalysts for asymmetric organic transformations, without quenching the catalytic reactivity, has met with limited success. While chiral supramolecular structures, connected by weak bonds, are highly active for homogeneous asymmetric catalysis, their application in heterogeneous catalysis is rare. In this work, asymmetric catalyst was prepared by encapsulating metallic nanoclusters in chiral self-assembled monolayer (SAM), immobilized on mesoporous SiO₂ support. Using olefin cyclopropanation as an example, it was demonstrated that by controlling the SAM properties, asymmetric reactions can be catalyzed by Au clusters embedded in chiral SAM. Up to 50% enantioselectivity with high diastereoselectivity were obtained while employing Au nanoclusters coated with SAM peptides as heterogeneous catalyst for the formation of cyclopropane-containing products. Spectroscopic measurements correlated the improved enantioselectivity with the formation of a hydrogen-bonding network in the chiral SAM. These results demonstrate the synergetic effect of the catalytically active metallic sites and the surrounding chiral SAM for the formation of a mesoscale enantioselective catalyst

Supported Au Nanoparticles with <i>N</i>‑Heterocyclic Carbene Ligands as Active and Stable Heterogeneous Catalysts for Lactonization

Attachment of <i>N</i>-heterocyclic carbenes (NHCs) on the surface of metal nanoparticle (NP) catalysts permits fine-tuning of catalytic activity and product selectivity. Yet, NHC-coated Au NPs have been seldom used in catalysis beyond hydrogenation chemistry. One challenge in this field has been to develop a platform that permits arbitrary ligand modification without having to compromise NP stability toward aggregation or leaching. Herein, we exploit the strategy of supported dendrimer-encapsulated metal clusters (DEMCs) to achieve aggregation-stable yet active heterogeneous Au NP catalysts with NHC ligands. Dendrimers function as aggregation-inhibitors during the NP synthesis, and NHCs, well-known for their strong attachment to the gold surface, provide a handle to modify the stereochemistry, stereoelectronics, and chemical functionality of the NP surface. Indeed, compared to “ligandless” Au NPs which are virtually inactive below 80 °C, the NHC-ligated Au NP catalysts enable a model lactonization reaction to proceed at 20 °C on the same time scale (hours). Based on Eyring analysis, proto-deauration is the turnover-limiting step accelerated by the NHC ligands. Furthermore, the use of chiral NHCs led to asymmetric induction (up to 16% enantiomeric excess) in the lactonization transformations, which demonstrates the potential of supported DEMCs with ancillary ligands in enantioselective catalysis

Quantification, Localization, and Speciation of Selenium in Seeds of Canola and Two Mustard Species Compared to Seed-Meals Produced by Hydraulic Press

<i>Brassica</i> plants accumulate selenium (Se) especially in seeds when grown in soils laden with Se. We report a chemical analysis of Se in <i>Brassica</i> seeds (canola, Indian mustard, and white mustard) and in their hydraulically pressed seed meals, which are used as a Se supplement in livestock animal feeds. Complementary techniques were used to measure total Se concentrations, to map the localization of Se, and to quantify different Se forms. Seeds and hydraulically pressed seed meals contained an average of 1.8 and 2.0 μg Se g^–1 DW, respectively. Selenium was primarily located in cotyledons and roots of seed embryos. Microfocused Se K-edge XANES and bulk XANES showed that seeds contained 90% of Se as C–Se–C forms. Hydraulically pressing seeds for oil caused changes in the forms of Se as follows: 40–55% C–Se–C forms, 33–42% selenocystine, 5–12% selenocysteine, and 11–14% trimethylselenonium ion. Aqueous extracts of seed and seed meals were also analyzed by SAX-HPLC/ICPMS and found to contain mainly the C–Se–C form SeMet, but also another C–Se–C form MeSeCys, which is of dietary pharmacological interest for cancer inhibition. In addition, SAX-HPLC/ICPMS also detected selenocystine and selenocysteine, further confirming the results obtained by XANES analyses

Chemical forms of Se found in seeds of <i>S. pinnata</i> and <i>A. bisulcatus</i>.

<p>Results from least-squares linear combination fitting of each samples XANES spectra in comparison to standard selenium compounds.</p><p>The regions where the spectra were collected are indicated in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0050516#pone-0050516-g001" target="_blank">Figure 1</a>.</p><p>SeO₃²⁻: selenite; Se(GSH)₂: seleno-diglutathione, C-Se-C: methyl-selenocysteine, seleno-methionine or seleno-cystathionine.</p><p>Se⁰: red or gray elemental Se. SS: normal sum of squares (quality of fit; 0 = perfect fit); nd: compound not detectable. Additional standard compounds included in the fit but not detected in any location were selenate, seleno-cystine and seleno-cysteine. Note: fractions do not always add up to exactly 100% because the margin of error can be up to10%.</p

Localization of Se, Zn and Ca in two seed herbivores of Se hyperaccumulator <i>A. bisulcatus</i>, a seed herbivorous chalcid wasp and a seed beetle.

<p>(a) Photograph of a chalcid wasp that emerged from <i>A. bisulcatus</i> seed. (b) Tricolor-coded µXRF map of the chalcid wasp showing Se (in red), Zn (in green) and Ca (in blue). (c) Photograph of a seed beetle that emerged from seed of <i>A. bisulcatus</i>. (d) Tricolor-coded µXRF map of the seed beetle showing Se (in red), Zn (in green) and Ca (in blue). The locations where XANES spectra were collected are indicated with numbered circles and results from XANES analyses are displayed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0050516#pone-0050516-t002" target="_blank">Table 2</a>.</p

Chemical Speciation of Vanadium in Particulate Matter Emitted from Diesel Vehicles and Urban Atmospheric Aerosols

We report on the development and application of an integrated set of analytical tools that enable accurate measurement of total, extractable, and, importantly, the oxidation state of vanadium in sub-milligram masses of environmental aerosols and solids. Through rigorous control of blanks, application of magnetic-sector-ICPMS, and miniaturization of the extraction/separation methods we have substantially improved upon published quantification limits. The study focused on the application of these methods to particulate matter (PM) emissions from diesel vehicles, both in baseline configuration without after-treatment and also equipped with advanced PM and NO_<i>x</i> emission controls. Particle size-resolved vanadium speciation data were obtained from dynamometer samples containing total vanadium pools of only 0.2–2 ng and provide some of the first measurements of the oxidation state of vanadium in diesel vehicle PM emissions. The emission rates and the measured fraction of V(V) in PM from diesel engines running without exhaust after-treatment were both low (2–3 ng/mile and 13–16%, respectively). The V(IV) species was measured as the dominant vanadium species in diesel PM emissions. A significantly greater fraction of V(V) (76%) was measured in PM from the engine fitted with a prototype vanadium-based selective catalytic reductors (V-SCR) retrofit. The emission rate of V(V) determined for the V-SCR equipped vehicle (103 ng/mile) was 40-fold greater than that from the baseline vehicle. A clear contrast between the PM size-distributions of V(V) and V(IV) emissions was apparent, with the V(V) distribution characterized by a major single mode in the ultrafine (<0.25 μm) size range and the V(IV) size distribution either flat or with a small maxima in the accumulation mode (0.5–2 μm). The V(V) content of the V-SCR PM (6.6 μg/g) was 400-fold greater than that in PM from baseline (0.016 μg/g) vehicles, and among the highest of all environmental samples examined. Synchrotron based V 1s XANES spectroscopy of vanadium-containing fine-particle PM from the V-SCR identified V₂O₅ as the dominant vanadium species

Scanning Electron Micrographs of seed chalcid wasp, seed chalcid wasp larva (in situ <i>Stanleya pinnata</i> seed) and seed beetle.

<p>Images A–C are views of the chalcid wasp, areas around the mouth, thorax, legs and abdomen were targeted for Se using EDS. On these external surfaces only very low levels of Se were detected from upper leg segment spines (more detail is provided in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0050516#pone.0050516.s002" target="_blank">Material S1</a>). The seed chalcid wasp larva in image D (white arrow head) & H at higher magnification gave low positive Se signals around a spiracle and also on some bristles/spines seen on the external surface (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0050516#pone.0050516.s002" target="_blank">Material S1</a>). Images E – G are views of the seed beetle, which was also targeted for Se around the mouth, legs and abdomen using EDS, with no positive signals detected.</p

Localization of Se, Zn and Ca in seeds of Se hyperaccumulators <i>S. pinnata</i> and <i>A. biculcatus</i>.

<p>(a) Photograph of three seeds of <i>S. pinnata</i> (left) and three of <i>A. bisulcatus</i> (right) taken after synchrotron analysis. Note: at this time one of the <i>A. bisulcatus</i> seeds had shifted slightly toward the bottom left. (b) X-ray fluorescence (XRF) map showing Se distribution (in white) in the <i>S. pinnata</i> and <i>A. bisulcatus</i> seeds. (c) Tricolor-coded µXRF map of <i>S. pinnata</i> and <i>A. bisulcatus</i> seeds showing Se (in red), Zn (in green) and Ca (in blue). (d) Tricolor-coded µXRF map of <i>S. pinnata</i> and <i>A. bisulcatus</i> seeds showing Se (in red), Fe (in green) and K (in blue). The locations where XANES spectra were collected are indicated with numbered circles in panels B and C and results from XANES analyses are tabulated in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0050516#pone-0050516-t001" target="_blank">Table 1</a>.</p

Correlative Cryogenic Spectromicroscopy to Investigate Selenium Bioreduction Products

Accurate mapping of the composition and structure of minerals and associated biological materials is critical in geomicrobiology and environmental research. Here, we have developed an apparatus that allows the correlation of cryogenic transmission electron microscopy (cryo-TEM) and synchrotron hard X-ray microprobe (SHXM) data sets to precisely determine the distribution, valence state, and structure of selenium in biofilms sampled from a contaminated aquifer near Rifle, CO. Results were replicated in the laboratory via anaerobic selenate-reducing enrichment cultures. 16S rRNA analyses of field-derived biofilm indicated the dominance of Betaproteobacteria from the Comamonadaceae family and uncultivated members of the Simplicispira genus. The major product in field and culture-derived biofilms is ∼25–300 nm red amorphous Se⁰ aggregates of colloidal nanoparticles. Correlative analyses of the cultures provided direct evidence for the microbial dissimilatory reduction of Se­(VI) to Se­(IV) to Se⁰. Extended X-ray absorption fine-structure spectroscopy showed red amorphous Se⁰ with a first shell Se–Se interatomic distance of 2.339 ± 0.003 Å. Complementary scanning transmission X-ray microscopy revealed that these aggregates are strongly associated with a protein-rich biofilm matrix. These findings have important implications for predicting the stability and mobility of Se bioremediation products and understanding of Se biogeochemical cycling. The approach, involving the correlation of cryo-SHXM and cryo-TEM data sets from the same specimen area, is broadly applicable to biological and environmental samples