Ute Golla-Schindler

Predictive Toxicology of Cobalt Nanoparticles and Ions: Comparative In Vitro Study of Different Cellular Models Using Methods of Knowledge Discovery from Data

The toxicological effects of cobalt nanoparticles (Co-NPs) aggregates were examined and compared with those of cobalt ions (Co-ions) using six different cell lines representing lung, liver, kidney, intestine, and the immune system. Dose-response curves were studied in the concentration range of 0.05-1.0 mM, employing 3-(4,5-dimethylthiazol-2-Yl)-2,5-diphenyltetrazolium bromide test, neutral red, and Alamar blue as end point assays following exposures for 48 and 72 h. Data analysis and predictive modeling of the obtained data sets were executed by employing a decision tree model (J48), where training and validation were carried out by an iterative process. It was established, as expected, that concentration is the highest rank parameter. This is because concentration parameter provides the highest information gain with respect to toxicity. The second-rank parameter emerged to be either the compound type (Co-ions or Co-NPs) or the cell model, depending on the concentration range. The third and the lowest rank in the model was exposure duration. The hierarchy of cell sensitivity toward cobalt ions was found to obey the following sequence of cell lines: A549 > MDCK > NCIH441 > Caco-2 > HepG2 > dendritic cells (DCs), with A549 being the most sensitive cell line and primary DCs were the least sensitive ones. However, a different hierarchy pattern emerged for Co-NPs: A549 = MDCK = NCIH441 = Caco-2 > DCs > HepG2. The overall findings are in line with the hypothesis that the toxic effects of aggregated cobalt NPs are mainly due to cobalt ion dissolution from the aggregated NPs.

Single step transformation of sulphur to Li2S2/Li2S in Li-S batteries

Lithium-sulphur batteries have generated tremendous research interest due to their high theoretical energy density and potential cost-effectiveness. The commercial realization of Li-S batteries is still hampered by reduced cycle life associated with the formation of electrolyte soluble higher-order polysulphide (Li2Sx, x = 4–8) intermediates, leading to capacity fading, self-discharge, and a multistep voltage profile. Herein, we have realized a practical approach towards a direct transformation of sulphur to Li2S2/Li2S in lithium-sulphur batteries by alteration of the reaction pathway. A coconut shell derived ultramicroporous carbon-sulphur composite cathode has been used as reaction directing template for the sulphur. The lithiation/delithiation and capacity fading mechanism of microporous carbon confined sulphur composite was revealed by analyzing the subsurface using X-ray photoelectron spectroscopy. No higher-order polysulphides were detected in the electrolyte, on the surface, and in the subsurface of the cathode composite. The altered reaction pathway is reflected by a single-step profile in the discharge/charge of a lithium-sulphur cell.

Nanosized IrO(x)-Ir Catalyst with Relevant Activity for Anodes of Proton Exchange Membrane Electrolysis Produced by a Cost-Effective Procedure.

We have developed a highly active nanostructured iridium catalyst for anodes of proton exchange membrane (PEM) electrolysis. Clusters of nanosized crystallites are obtained by reducing surfactant-stabilized IrCl3 in water-free conditions. The catalyst shows a five-fold higher activity towards oxygen evolution reaction (OER) than commercial Ir-black. The improved kinetics of the catalyst are reflected in the high performance of the PEM electrolyzer (1 mg(Ir) cm(-2)), showing an unparalleled low overpotential and negligible degradation. Our results demonstrate that this enhancement cannot be only attributed to increased surface area, but rather to the ligand effect and low coordinate sites resulting in a high turnover frequency (TOF). The catalyst developed herein sets a benchmark and a strategy for the development of ultra-low loading catalyst layers for PEM electrolysis.

Predictive Toxicology of cobalt ferrite nanoparticles: comparative in-vitro study of different cellular models using methods of knowledge discovery from data

BackgroundCobalt-ferrite nanoparticles (Co-Fe NPs) are attractive for nanotechnology-based therapies. Thus, exploring their effect on viability of seven different cell lines representing different organs of the human body is highly important.MethodsThe toxicological effects of Co-Fe NPs were studied by in-vitro exposure of A549 and NCIH441 cell-lines (lung), precision-cut lung slices from rat, HepG2 cell-line (liver), MDCK cell-line (kidney), Caco-2 TC7 cell-line (intestine), TK6 (lymphoblasts) and primary mouse dendritic-cells. Toxicity was examined following exposure to Co-Fe NPs in the concentration range of 0.05 -1.2 mM for 24 and 72 h, using Alamar blue, MTT and neutral red assays. Changes in oxidative stress were determined by a dichlorodihydrofluorescein diacetate based assay. Data analysis and predictive modeling of the obtained data sets were executed by employing methods of Knowledge Discovery from Data with emphasis on a decision tree model (J48).ResultsDifferent dose–response curves of cell viability were obtained for each of the seven cell lines upon exposure to Co-Fe NPs. Increase of oxidative stress was induced by Co-Fe NPs and found to be dependent on the cell type. A high linear correlation (R2=0.97) was found between the toxicity of Co-Fe NPs and the extent of ROS generation following their exposure to Co-Fe NPs. The algorithm we applied to model the observed toxicity belongs to a type of supervised classifier. The decision tree model yielded the following order with decrease of the ranking parameter: NP concentrations (as the most influencing parameter), cell type (possessing the following hierarchy of cell sensitivity towards viability decrease: TK6 > Lung slices > NCIH441 > Caco-2 = MDCK > A549 > HepG2 = Dendritic) and time of exposure, where the highest-ranking parameter (NP concentration) provides the highest information gain with respect to toxicity. The validity of the chosen decision tree model J48 was established by yielding a higher accuracy than that of the well-known “naive bayes” classifier.ConclusionsThe observed correlation between the oxidative stress, caused by the presence of the Co-Fe NPs, with the hierarchy of sensitivity of the different cell types towards toxicity, suggests that oxidative stress is one possible mechanism for the toxicity of Co-Fe NPs.

Laterally resolved EELS for ELNES mapping of the Fe L2,3- and O K-edge

Nowadays fingerprinting techniques are well established for phase analysis. One of the common problems is the accurate calibration of the energy scale to compare the electron energy loss (ELNES) and to determine the energy shift precisely. One solution to this problem is laterally resolved electron energy loss spectroscopy (EELS), which involves orienting the specimen area or structure of interest, parallel to the energy dispersive direction and dispersing the intensity across the interface as a function of energy. This ELNES information can now be used to quantify and map changes in the electronic environment. The most critical instrumental performance for ELNES investigations is the available energy resolution, which for our instrument was estimated using the 0.5eV splitting of the Mn L(3)-edge of the mineral bixbyite. An ideal test sample for the ELNES investigations is a titanohematite, a solid solution between ilmenite (FeTiO(3)), with Fe in a divalent oxidation state, and hematite (Fe(2)O(3)) with Fe in a trivalent oxidation state. Using energy filtered imaging with a slit width of 4eV it is possible to map the Fe(2+)/Fe(3+) ratio as well as the near-edge structure of the O(K) signal and correlate these ELNES maps with a spatial resolution of a few nanometres. Quantitative compositional mapping on a nanometre scale was obtained by electron spectroscopic imaging. Quantitative point analyses also yield the chemical composition and the valence states. The precise knowledge of the energy shift and near edge structure enables us to select the characteristic ELNES structure and calculate jump ratio images. This yields quantitative valence state maps by using the Fe L(2,3)-edge, as well as phase maps by using the O K-edge.

Direct observation of spinodal decomposition in the magnetite-hercynite system by susceptibility measurements and transmission electron microscopy

Abstract The magnetic susceptibility and Curie temperatures Tc have been investigated for a series of synthetic samples with solid-solution compositions ranging from pure magnetite (Fe3O4) to hercynite (FeAl2O4). The determined Tc can be fitted by a straight line, which also fits the theoretical values for these end-members. With increasing hercynite concentration, susceptibility curves for one heating and cooling cycle become irreversible, indicating changes in the structural state of the samples during annealing. These changes occur in specific temperature ranges for each composition. For a sample of composition Mag40Hec60, irreversible changes occurring between about 200 and 300°C are likely due to changes in the cation distribution, whereas above 300°C, compositional Fluctuations due to spinodal decomposition are evident. The exsolution mechanism has been investigated using energy- filtered transmission electron microscopy, which has allowed direct imaging of the compositional Fluctuations consistent with the theoretical predictions of spinodal decomposition

High-resolution and energy-filtered TEM of the interface between hematite and ilmenite exsolution lamellae: Relevance to the origin of lamellar magnetism

Abstract The interfaces between fine-scale exsolution lamellae of hematite and ilmenite from an igneous rock in Rogaland, Norway have been studied by conventional transmission electron microscopy (TEM), high-resolution TEM, and energy-filtered TEM (EFTEM), to investigate the lamellar magnetism hypothesis for the origin of the unusual magnetic properties of this rock. Very fine hematite and ilmenite lamellae, less than 50 nm in length and parallel to (001) of their host, were abundant throughout the hemo-ilmenite sample. Dark-field and EFTEM observations indicated the hematite and ilmenite have very sharp structural and compositional interfaces with their hosts. The interfaces between the coarse hematite and ilmenite lamellae (length >1 μm) and their hosts have some interface dislocations to relieve elastic coherency strain. On the other hand, very fine lamellae (length <50 nm) have no interface dislocations and are perfectly coherent. The interface dislocations for lamellae on the order of 100 nm in length are distributed heterogeneously, and more than 80% of the length of the interfaces seen by TEM is dislocation free. Thus, most of the interfaces in the sample are coherent. These results are in accord with the predictions of Monte Carlo simulations of the exsolution process (Harrison and Becker 2001) and with the hypothesis that coherent and sharp structural and compositional interfaces are the origin of lamellar magnetism (Robinson et al. 2002).

In situ observation of electron beam-induced phase transformation of CaCO3 to CaO via ELNES at low electron beam energies.

It is demonstrated that energy-filtered transmission electron microscope enables following of in situ changes of the Ca-L2,3 edge which can originate from variations in both local symmetry and bond lengths. Low accelerating voltages of 20 and 40 kV slow down radiation damage effects and enable study of the start and finish of phase transformations. We observed electron beam-induced phase transformation of single crystalline calcite (CaCO3) to polycrystalline calcium oxide (CaO) which occurs in different stages. The coordination of Ca in calcite is close to an octahedral one streched along the <111> direction. Changes during phase transformation to an octahedral coordination of Ca in CaO go along with a bond length increase by 5 pm, where oxygen is preserved as a binding partner. Electron loss near-edge structure of the Ca-L2,3 edge show four separated peaks, which all shift toward lower energies during phase transformation at the same time the energy level splitting increases. We suggest that these changes can be mainly addressed to the change of the bond length on the order of picometers. An important pre-condition for such studies is stability of the energy drift in the range of meV over at least 1 h, which is achieved with the sub-Ångström low-voltage transmission electron microscope I prototype microscope.

Insights into the Impact of Impurities and Non‐Stoichiometric Effects on the Electrochemical Performance of Li2MnSiO4

A series of Li2 MnSiO4 samples with various Li, Mn, and/or Si concentrations are reported to study for the first time the effect of impurities and deviation from ideal stoichiometry on electrochemical behavior. Carbon-coated and nanosized powders are obtained at 600 °C and compared with those synthetized at 900 °C. Samples are investigated using XRD, SEM, high-resolution TEM, attenuated total reflection infrared spectroscopy and Brunauer-Emmett-Teller surface area to characterize crystal structure, particle size, impurity amount, morphology, and surface area. Electrochemical performance depends on impurities such as MnO as well as crystallite size, surface area, and non-stoichiometric phases, which lead to the formation of additional polymorphs such as Pmnb and P21 /n of Li2 MnSiO4 at low calcination temperatures. A systematic analysis of the main parameters affecting the electrochemical behavior is performed and trends in synthesis are identified. The findings can be applied to optimize different synthesis routes for attaining stoichiometric and phase-pure Pmn21 Li2 MnSiO4 as cathode material for Li-ion batteries.

The Role of Secondary Electron Emission in the Charging of Thin-Film Phase Plates

In the past few years, physical phase plates (PP) have become a viable tool to enhance the contrast of weak-phase objects in transmission electron microscopy (TEM). Thin-film PPs, such as the Zernike and Hilbert PP, are based on the mean inner potential of microstructured thin films [1,2]. Typically, a thin amorphous carbon (aC)-film is applied, whose thickness is adjusted to induce a well-defined phase shift between unscattered and scattered electrons. However, the illumination with high-energy electrons initiates an irreversible degeneration of the aC-film, which causes electrostatic charging and affects the phase-shifting properties. Taking even advantage of charging, hole-free PPs were recently developed [3,4].