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The biosynthesis of many sulfur-containing molecules depends on cysteine as a sulfur source. Both the cysteine desulfurase (CD) and rhodanese (Rhd) domain-containing protein families participate in the trafficking of sulfur for various metabolic pathways in bacteria and human, but their connection is not yet described in plants. The existence of natural chimeric proteins containing both CD and Rhd domains in specific bacterial genera, however, suggests a general interaction between these proteins. We report here the biochemical relationships between two cytosolic proteins from Arabidopsis thaliana, a Rhd domain-containing protein, the sulfur-transferase 18 (STR18), and a CD isoform referred to as ABA3, and compare these biochemical features to those of a natural CD-Rhd fusion protein from the bacterium Pseudorhodoferax sp. We observed that the bacterial enzyme is bifunctional exhibiting both CD and STR activities using L-cysteine and thiosulfate as sulfur donors but preferentially using L-cysteine to catalyze transpersulfidation reactions. In vitro activity assays and mass spectrometry analyses revealed that STR18 stimulates the CD activity of ABA3 by reducing the intermediate persulfide on its catalytic cysteine, thereby accelerating the overall transfer reaction. We also show that both proteins interact in planta and form an efficient sulfur relay system, whereby STR18 catalyzes transpersulfidation reactions from ABA3 to the model acceptor protein roGFP2. In conclusion, the ABA3-STR18 couple likely represents an uncharacterized pathway of sulfur trafficking in the cytosol of plant cells, independent of ABA3 function in molybdenum cofactor maturation. [ABSTRACT FROM AUTHOR]

The formation of a persulfide group (-SSH) on cysteine residues has gained attention as a reversible posttranslational modification contributing to protein regulation or protection. The widely distributed 3-mercaptopyruvate sulfurtransferases (MSTs) are implicated in the generation of persulfidated molecules and H2S biogenesis through transfer of a sulfane sulfur atom from a suitable donor to an acceptor. Arabidopsis has two MSTs, named STR1 and STR2, but they are poorly characterized. To learn more about these enzymes, we conducted a series of biochemical experiments including a variety of possible reducing systems. Our kinetic studies, which used a combination of sulfur donors and acceptors revealed that both MSTs use 3-mercaptopyruvate efficiently as a sulfur donor while thioredoxins, glutathione, and glutaredoxins all served as high-affinity sulfane sulfur acceptors. Using the redox-sensitive GFP (roGFP2) as a model acceptor protein, we showed that the persulfide-forming MSTs catalyze roGFP2 oxidation and more generally trans-persulfidation reactions. However, a preferential interaction with the thioredoxin system and glutathione was observed in case of competition between these sulfur acceptors. Moreover, we observed that MSTs are sensitive to overoxidation but are protected from an irreversible inactivation by their persulfide intermediate and subsequent reactivation by thioredoxins or glutathione. This work provides significant insights into Arabidopsis STR1 and STR2 catalytic properties and more specifically emphasizes the interaction with cellular reducing systems for the generation of H2S and glutathione persulfide and reactivation of an oxidatively modified form. [ABSTRACT FROM AUTHOR]

Abstract Background Glutaredoxins (GRXs) are oxidoreductases involved in diverse cellular processes through their capacity to reduce glutathionylated proteins and/or to coordinate iron‑sulfur (Fe-S) clusters. Among class II GRXs, the plant-specific GRXS16 is a bimodular protein formed by an N-terminal endonuclease domain fused to a GRX domain containing a 158CGFS signature. Methods The biochemical properties (redox activity, sensitivity to oxidation, p K a of cysteine residues, midpoint redox potential) of Arabidopsis thaliana GRXS16 were investigated by coupling oxidative treatments to alkylation shift assays, activity measurements and mass spectrometry analyses. Results Activity measurements using redox-sensitive GFP2 (roGFP2) as target protein did not reveal any significant glutathione-dependent reductase activity of A. thaliana GRXS16 whereas it was able to catalyze the oxidation of roGFP2 in the presence of glutathione disulfide. Accordingly, Arabidopsis GRXS16 reacted efficiently with oxidized forms of glutathione, leading to the formation of an intramolecular disulfide between Cys158 and the semi-conserved Cys215, which has a midpoint redox potential of - 298 mV at pH 7.0 and is reduced by plastidial thioredoxins (TRXs) but not GSH. By promoting the formation of this disulfide, Cys215 modulates GRXS16 oxidoreductase activity. Conclusion The reduction of AtGRXS16, which is mandatory for its oxidoreductase activity and the binding of Fe-S clusters, depends on light through the plastidial FTR/TRX system. Hence, disulfide formation may constitute a redox switch mechanism controlling GRXS16 function in response to day/night transition or oxidizing conditions. General significance From the in vitro data obtained with roGFP2, one can postulate that GRXS16 would mediate protein glutathionylation/oxidation in plastids but not their deglutathionylation. Highlights • Glutaredoxin S16 catalyzes the oxidation but not the reduction of roGFP2 • Glutaredoxin S16 reacts efficiently with oxidized forms of glutathione • Protein oxidation leads to the formation of an intramolecular disulfide • Glutaredoxin S16 is reduced by plastidial thioredoxins but not reduced glutathione • The conserved C-terminal cysteine modulates the oxidoreductase activity of GRXS16 [ABSTRACT FROM AUTHOR]

Photoelectrochemical (PEC) properties of nanostructured hematite (Fe 2 O 3 ) thin films prepared using plasma-enhanced chemical vapor deposition (PE-CVD) were investigated against the influence of processing parameters and post-synthesis heat-treatment procedures. Annealing at high temperatures (>500 °C) was found to substantially affect the micro-structure (grain growth and densification) and electronic (interdiffusion at the film/substrate interface) concomitantly manifested in an enhancement in the PEC behavior. The Sn impurity level in hematite films was found to increase with the annealing temperature with highest values achieved in samples heat-treated at 750 °C, due to the interdiffusion and substitution of Sn(IV) species at Fe(III) sites. Sn:Fe 2 O 3 films exhibited significantly high photocurrent density of 1.33 mA cm −2 at the water oxidation level of 1.23 V vs . RHE. The diffusion of Sn ions into iron oxide lattice altered the electronic properties of hematite films due to electron–donor behavior of the dopants that was verified by X-ray photoelectron spectroscopy and secondary ion mass spectroscopy (SIMS) analyses. Deposition of a thin overlayer of TiO 2 (10 nm) on hematite films by atomic layer deposition (ALD) was found to further improve the photocurrent density to 1.8 mA cm −2 at 1.23 V vs. RHE. Ab-initio calculations on the effect of substitutional Sn(IV) dopants in the Fe 2 O 3 lattice on the electronic structure and the band alignment between hematite and the TiO 2 over layer revealed that Sn-dopants led to the generation of localized Fe(II) centers augmenting the n-type behavior of hematite. No effect of the Sn-doping on the electrostatic potential was found on a macroscopic scale. However, the charge transfer from the Sn-doping to the Fe(II) centers would cause high electric fields on the nanometer scale and might hence play an important role in the efficient separation of electron and holes. The simulations showed that the hematite band edges are enclosed by the TiO 2 band edges and therefore electron depletion at the surface–liquid interface is enhanced. This might lead to reduced recombination rates near the surface and consequently to increased photocurrents, since the Fe 2 O 3 /TiO 2 interface constitutes a barrier for hole transport. [ABSTRACT FROM AUTHOR]

The prevailing design approaches of semiconductor gas sensors struggle to overcome most of their current limitations such as poor selectivity, and high power consumption. Herein, a new sensing concept based on devices that are capable of detecting gases without the need of any external power sources required to activate interaction of gases with sensor or to generate the sensor read out signal. Based on the integration of complementary functionalities (namely; powering and sensing) in a singular nanostructure, self-sustained gas sensors will be demonstrated. Moreover, a rational methodology to design organic surface functionalization that provide high selectivity towards single gas species will also be discussed. Specifically, theoretical results, confirmed experimentally, indicate that precisely tuning of the sterical and electronic structure of sensor material/organic interfaces can lead to unprecedented selectivity values, comparable to those typical of bioselective processes. Finally, an integrated gas sensor that combine both the self-powering and selective detection strategies in one single device will also be presented. [ABSTRACT FROM AUTHOR]

Abstract: The latest development of Pettifor’s bond-order approach – the analytic bond-order potentials (ABOPs) – represents a significant improvement over the empirical potentials of the Abell–Tersoff–Brenner type. This article aims at a critical evaluation of this promising novel scheme for the hydrocarbon system and assesses its applicability to realistic large-scale atomistic simulations. It is shown that ABOP reproduces the underlying orthogonal tight-binding model accurately for both hydrocarbon molecules and carbon crystalline phases in their ground-state configurations. However, in order to reproduce also non-equilibrium configurations it is necessary to extend the σ bond-order expression to account for the non-negligible sp atomic energy level separation of carbon. While the Brenner hydrocarbon potential exhibits several deficiencies in the description of amorphous hydrocarbon films, the extended ABOP model comes closer to results of accurate non-orthogonal tight-binding calculations. Remaining discrepancies of ABOP can be traced back to the limitations of the underlying orthogonal tight-binding model and its parameterization. [Copyright &y& Elsevier]

This work discusses the use of slipping domains to improve load support in water-lubricated microsystems through a multi-scale approach. A semi-analytical continuum formulation is developed to calculate changes in pressure distribution for a line contact with added slip. It is found that the slipping region maximizing hydrodynamic lift should favor inlet flow, but not be located at the contact outlet. Estimations for its positioning are provided. Slip on flat surfaces gives the largest gains in load support and friction reduction, but moderate improvements are also possible on circular geometries featuring high convergence ratios. Finally, Molecular Dynamics simulations are employed to quantify slip on hydrophobic surfaces. Among the considered topologies, graphene is an excellent candidate to generate slip in water-lubricated microsystems. [ABSTRACT FROM AUTHOR]

Abstract: We use density functional calculations to determine the binding sites and binding energies of Li+ at graphene edges and prismatic graphite surfaces. Binding is favorable at bare and carbonyl terminated surfaces, but not favorable at hydrogen terminated surfaces. These findings have implications for the exfoliation of graphitic anodes in lithium-ion batteries that happens if solute and solvent co-intercalate. First, specific adsorption facilitates desolvation of Li+. Second, chemisorption lowers the surface energy by about 1 J m−2 prismatic surface area, and gives graphite additional stability against exfoliation. The results offer an explanation for experiments that consistently show exfoliation for hydrogenated graphite, but show no exfoliation for oxygenated graphite. [Copyright &y& Elsevier]

The nanoscale lubrication properties of graphene depend on chemical functionalization, adsorbants, and bonding to the substrate. The dependence of friction on the rotational orientation of graphene on a Pt(111) surface was studied by high-resolution friction force microscopy in ultra-high vacuum and interpreted through complementary simulations. Lateral forces reveal an atomic-scale stick-slip motion with the periodicity of the graphene structure. Additionally, the lateral forces were modulated by a Moiré pattern, which depends on the rotation of the respective domain. Comparing the experimental results to simulations of the friction process based on the Prandtl-Tomlinson model and to atomistic simulations of the tip-sample interactions, it was found that the modulation of lateral forces originated from a structural mismatch between Pt(111) and graphene domains that were locally pinned to the substrate. Domains with preferred orientations, such as the R1° and the R24°, appeared to exhibit lower average friction than those with orientations less frequently observed, such as the R10° domain. [ABSTRACT FROM AUTHOR]

Diamond surfaces wear when sliding against silica – a much softer material. Although this plays a major role in chemical mechanical planarization of diamond or machining of rocks, the underlying microscopic mechanisms are hardly understood. Here, the stability of diamond (110) surfaces in sliding contact with amorphous silica and with amorphous silicon (a mechanically similar reference system) is studied by quantum-chemical simulations. Interfacial C–Si bonds with amorphous silicon are too weak to harm diamond (110) surfaces. Conversely, strong C–O and C–Si bonds form between silica and diamond. However, this alone is insufficient to challenge interfacial diamond-like C–C bonds during sliding. Analysis of local forces and electronic structure shows that bonding to silica can chemically activate C–C bonds between terminating carbon zigzag chains and bulk diamond when the zigzag chains stay aromatic. Mechanochemical breaking of these weak bonds and subsequent lifting of C–C–C zigzag units mark the onset of wear on diamond (110) surfaces. This is in contrast to the silicon case, where the higher interfacial bond density renders the diamond surface non-aromatic and diamond-like. [ABSTRACT FROM AUTHOR]

The tribofilm formed on nanocrystalline diamond coating during ultralow friction in presence of water and glycerol lubrication has been studied experimentally by energy filtering transmission electron microscopy (EF-TEM) and electron energy loss spectroscopy (EELS) on focus ion beam (FIB) cross sections. Surprisingly, even under mild tribological conditions, a tribo-induced hybridization change (sp 3 towards sp 2 ) can be clearly detected at the top of the coating resulting in the formation of a 40 nm thick amorphous sp 2 rich carbon layer with embedded diamond nanoparticles less than 5 nm diameter. Classical molecular dynamics simulations of diamond single crystal asperity collisions can explain this finding. Tribochemical amorphization of the contact zone between the colliding diamond grains followed by fracture events at the asperity shoulders produces ultra-nanodiamonds that remain attached to the amorphous carbon phase. An additional atomistic sliding simulation of two ultra-nanocrystalline diamond coatings yields an amorphous sp 2 rich carbon layer that grows at a rate that is comparable to corresponding layers on the softest diamond single crystal surfaces. [ABSTRACT FROM AUTHOR]

Abstract: Macroscopic tribometry is linked to classical atomistic simulations in order to improve understanding of the nanoscale interfacial processes during sliding of hydrogenated DLC (a-C:H) against a metal (W) in dry and lubricated conditions. Experimentally, using an online tribometer, wear and roughness measurements are performed after each sliding cycle, which are then correlated with the frictional resistance. Ex situ analysis is also performed on the worn surfaces (i.e. plates and counterfaces) using X-ray photoelectron spectroscopy, Auger electron spectroscopy and cross-sectional transmission electron microscopy imaging of the near-surface region. Then, in order to elucidate the atomistic level processes that contribute to the observed microstructural evolution in the experiments, classical molecular dynamics are performed, employing a bond order potential for the tungsten–carbon–hydrogen system. Macroscopic tribometry shows that dry sliding of a-C:H against W results in higher frictional resistance and significantly more material transfer compared with lubricated conditions. Similarly, the molecular dynamic simulations exhibit higher average shear stresses and clear material transfer for dry conditions compared with simulations with hexadecane as a lubricant. In the lubricated simulations, the lower shear stress and the absence of a material transfer are attributed to hexadecane monolayers that are partially tethered to the a-C:H surface and significantly reduce adhesion and mechanical mixing between the sliding partners. [Copyright &y& Elsevier]

Abstract: We demonstrate the effect of hydrogen plasma treatment on hematite films as a simple and effective strategy for modifying the existing substrate to improve significantly the band edge positions and photoelectrochemical (PEC) performance. Plasma treated hematite films were consist of mixed phases (Fe3O4:α-Fe2O3) which was confirmed by XPS and Raman analysis, treated films also showed higher absorption cross-section and were found to be a promising photoelectrode material. The treated samples showed enhance photocurrent densities with maximum of 3.5 mA/cm2 at 1.8 V/RHE and the photocurrent onset potentials were shifted from 1.68 VRHE (untreated) to 1.28 VRHE (treated). Hydrogen plasma treatment under non-equilibrium conditions induced a valence dynamics among Fe centers in the sub-surface region that was sustained by the incorporation of hydrogen in the hematite lattice as supported by the density functional theory calculations. [Copyright &y& Elsevier]

Abstract: Inhomogeneous density distributions after die filling are a ubiquitous problem in powder technological part production. In this paper, numerical simulations of the die filling process in realistic, three-dimensional (3D) cavities are presented using the discrete element method with both multi-sphere and single sphere grain models. Good agreement was found between calculated and experimentally measured density distributions. The formation of an inhomogeneous distribution is discussed by a time-resolved analysis of the filling process. Grain rearrangement and densification during subsequent feeding shoe passages are characterized. The shoe velocity was tested for its influence on the density homogeneity. Suggestions for density homogenization with the application of cavity oscillations or volumetric filling are given. A density homogeneity index is introduced. The application of a coarse graining scheme circumvents the intrinsic difficulty of non-manageable grain numbers in 3D filling simulations. The validity and limitations of this scheme are discussed. [Copyright &y& Elsevier]

Abstract: Transmission electron microscopy (TEM) is a standard technique to characterize microelectronic device structures. As structures shrink to the nanoscale, surface damage produced by focused ion beam (FIB) sample preparation destroying the region of interest and degrading the resolution of TEM images becomes increasingly a problem. The thickness of the damaged layer at the sidewalls of a prepared cross section is around 20–30nm for silicon at typical beam energies of 30keV. In order to reduce these artifacts to a minimum low beam energies have been proposed for FIB polishing. We use a combination of molecular dynamics simulations and experiments to assess the influence of the focused ion beam on the surface structure of silicon for beam energies ranging from 1–5keV and a grazing angle of 10° typically used in low voltage FIB polishing. Under these conditions, the thickness of the amorphous layer depends linearly on the beam energy. Intrinsic surface stresses introduced by FIB are always tensile and of a magnitude of around 1GPa. [Copyright &y& Elsevier]

Abstract: Simulations based on the discrete element method are employed to investigate the anisotropic sintering of alumina. The results are compared with accompanying experiments. It is shown that during sinter forging an anisotropic microstructure develops, which leads to anisotropic mechanical properties. Several ways to characterize and measure this anisotropy are presented and utilized to identify the causes for anisotropic sintering behaviour. Discrete element modelling can further be employed to determine anisotropic constitutive parameters as a function of density. Also, the influence of grain rearrangement on the development of anisotropy is investigated. [Copyright &y& Elsevier]

Abstract: A three-dimensional application of the discrete element method to free, constrained and pressure-assisted solid-state sintering of powders is presented. Special emphasis is laid on the generation of realistic random initial configuration as well as on the inertia effects. With this method, internal properties such as coordination number and pair correlation function are directly accessible and compare well with theoretical predictions and experimental data. The simulation scheme also enables one to investigate how grain rearrangements on a mesoscopic scale influence macroscopic properties such as densification rate and bulk and shear viscosity. Finally, crack formation during constrained sintering of low-density films is examined. [Copyright &y& Elsevier]