The increasing use of nanotechnology in consumer products and medical applications underlies the importance of understanding its potential toxic effects to people and the environment. Although both fullerene and carbon nanotubes have been demonstrated to accumulate to cytotoxic levels within organs of various animal models and cell types and carbon nanomaterials have been exploited for cancer therapies, the molecular and cellular mechanisms for cytotoxicity of this class of nanomaterial are not yet fully apparent. To address this question, we have performed whole genome expression array analysis and high content image analysis based phenotypic measurements on human skin fibroblast cell populations exposed to multiwall carbon nano-onions (MWCNOs) and multiwall carbon nanotubes (MWCNTs). Here we demonstrate that exposing cells to MWCNOs and MWCNTs at cytotoxic doses induces cell cycle arrest and increases apoptosis/necrosis. Expression array analysis indicates that multiple cellular pathways are perturbed after exposure to these nanomaterials at these doses, with material-specific toxigenomic profiles observed. Moreover, there are also distinct qualitative and quantitative differences in gene expression profiles, with each material at different dosage levels (6 and 0.6 microg/mL for MWCNO and 0.6 and 0.06 microg/mL for MWCNT). MWCNO and MWCNT exposure activates genes involved in cellular transport, metabolism, cell cycle regulation, and stress response. MWCNTs induce genes indicative of a strong immune and inflammatory response within skin fibroblasts, while MWCNO changes are concentrated in genes induced in response to external stimuli. Promoter analysis of the microarray results demonstrate that interferon and p38/ERK-MAPK cascades are critical pathway components in the induced signal transduction contributing to the more adverse effects observed upon exposure to MWCNTs as compared to MWCNOs.
Reduction reactions of molybdate in acidic, aqueous solution lead to colored, mixed-valent Mo V/VI polyoxomolybdate (POM) species. [1][2][3][4][5] The two-century-old mystery of the "molybdenum blues" 6 exemplifies the difficulty in characterizing suspensions of POM particles. Müller, Liu, and co-workers revealed the fundamental compositions of the related "molybdenum browns", including I h symmetrical keplerates. In general, reduced molybdates assemble into nanometric species (Figure 1a). Light-scattering, small-angle X-ray scattering (SAXS), and microscopy show slow aggregation of Na 15 The key methodology of our study is field-flow fractionation (FFF), a flow-based, chromatography-like separation and sizing technique that can monitor changes in the particle-size distribution of a suspension in situ. FFF is conducted in a thin, empty channel, with separation based on relative hydrodynamic behavior. [21][22][23] In flow field-flow fractionation (FlFFF), a cross-flow perpendicular to the direction of laminar channel flow forces dissimilar particles to different levels in the channel, where they are eluted at different flow velocities. FlFFF fractionates particles between 1 and 1000 nm and allows analysis of the eluate. 24 We used FlFFF to monitor the evolution of molybdate nanoparticles in a {Mo 132 } suspension prepared by Müller's procedure. 7,15,16 Under our FlFFF conditions, 25 soluble species and particles smaller than 3 nm are swept to the waste stream by the cross-flow, while larger particles are separated and eluted through a UV-visible detector. FlFFF fractograms monitoring the absorbance of the eluate at 455 nm are shown in Figure 1b.The particle-size distributions calculated 26 from the data in Figure 1b have diameters ranging from 3 to 75 nm, roughly distributed in three populations with maxima about 3.4, 12, and 25 nm. The mean diameter is 31((1) nm (confidence level 95%), averaged over 24 FFF runs from 8 days. The baseline fractogram at 10 min indicates that no particles over ca. 3 nm had yet formed. At 2 h, the 3.4-nm population is largest. The total area under the fractogram increases rapidly from 2 to 8 h, at which time the 12-and 25-nm populations are larger. We suggest that the 3.4-nm particles, decreasing after 2 h but observed consistently throughout the entire period, are the {Mo 132 } with their associated counterions and solvation shell. The overall particle population reaches a maximum at ca. 8 h, decreases rapidly for about 2 days and more slowly thereafter (Figure 1b). The decrease parallels the precipitation of large particles that are not sampled by FlFFF shown in the SEM 27 image in Figure 2a. The precipitate is in dynamic equilibrium with species still in solution or suspension, yielding after several days ca. 0.1-mm octahedral crystals of {Mo 132 }, Fm3 with a ≈ 46 Å, 15 shown in Figure 2b.The particle-size distribution of the molybdate suspension was corroborated by AFM, SEM, and HRTEM. Good agreement between particle-size distributions obtained by FFF and microscopy suggests t...
The anodic oxidation of EDTA was studied in acid sulfate solutions on platinized-Pt at 25~ Polarization relationships were obtained for the EDTA concentration range 3.42 • 10 -5 to 3.42 • 10-3M and pH range 0.35 to 3.80. Numerous reaction products were identified that indicated a sequential removal of acetate groups from the EDTA, each by an initial decarboxylation followed by a reverse Schiff-type reaction, that produced formaldehyde and the corresponding amine. A reaction sequence which correlated the experimental data involved Frumkin-type adsorption of the EDTA species through an unionized acetate group followed by a rate-determining electrochemical decarboxylation.Ethylenediaminetetraacetic acid, commonly abbreviated "EDTA," forms very stable, water-soluble complexes with many metal ions. Because of this, studies * Electrochemical Society Active Member.
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