Sulfidation of metallic nanoparticles such as silver nanoparticles (AgNPs) released to the environment may be an important detoxification mechanism. Two types of AgNPs-an engineered polydisperse and aggregated AgNP powder, and a laboratory-synthesized, relatively monodisperse AgNP aqueous dispersion-were studied. The particles were sulfidized to varying degrees and characterized to determine the effect of initial AgNP polydispersity and aggregation state on AgNP sulfidation, and then exposed to Escherichia coli to determine if the degree of sulfidation of pristine AgNPs affects growth inhibition of bacteria. The extent of sulfidation was found to depend on the HS(-)/Ag ratio. However, for the same reaction times, the more monodisperse particles were fully transformed to Ag(2)S, and the polydisperse, aggregated particles were not fully sulfidized, thus preserving the toxic potential of Ag(0) in the aggregates. A higher Ag(2)S:Ag(0) ratio in the sulfidized nanoparticles resulted in less growth inhibition of E. coli over 6 h of exposure. These results suggest that the initial properties of AgNPs can affect sulfidation products, which in turn affect microbial growth inhibition, and that these properties should be considered in assessing the environmental impact of AgNPs.

SummaryFlagellar type III secretion systems (T3SS) contain an essential cytoplasmic‐ring (C‐ring) largely composed of two proteins FliM and FliN, whereas an analogous substructure for the closely related non‐flagellar (NF) T3SS has not been observed in situ. We show that the spa33 gene encoding the putative NF‐T3SS C‐ring component in S higella flexneri is alternatively translated to produce both full‐length (Spa33‐FL) and a short variant (Spa33‐C), with both required for secretion. They associate in a 1:2 complex (Spa33‐FL/C2) that further oligomerises into elongated arrays in vitro. The structure of Spa33‐C 2 and identification of an unexpected intramolecular pseudodimer in Spa33‐FL reveal a molecular model for their higher order assembly within NF‐T3SS. Spa33‐FL and Spa33‐C are identified as functional counterparts of a FliM–FliN fusion and free FliN respectively. Furthermore, we show that T hermotoga maritima  FliM and FliN form a 1:3 complex structurally equivalent to Spa33‐FL/C2, allowing us to propose a unified model for C‐ring assembly by NF‐T3SS and flagellar‐T3SS.

Using in situ wafer-curvature measurements of thin-film stress, we determine the critical thickness for strain relaxation in AlxGa1−xN∕GaN heterostructures with 0.14⩽x⩽1. The surface morphology of selected films is examined by atomic force microscopy. Comparison of these measurements with critical-thickness models for brittle fracture and dislocation glide suggests that the onset of strain relaxation occurs by surface fracture for all compositions. Misfit-dislocations follow initial fracture, with slip-system selection occurring under the influence of composition-dependent changes in surface morphology.

The effect of intermixed carbon nanotubes and graphite on the electrochemical functionality of NaTi 2 (PO 4 ) 3 was examined. Specifically, the performance of NaTi 2 (PO 4 ) 3 made with "intimate carbons" containing carbon nanotubes (or graphite) introduced at the precursor stage was compared to the performance of similar materials made with the carbons added post synthesis. Specifically, different combinations of carbon nanotubes and graphite were used as carbon sources both in the precursor blend prior to sintering as well as conductive additives in the test electrodes. Graphite-coated NaTi 2 (PO 4 ) 3 with additional carbon nanotubes added (post synthesis) as conductive agent exhibited the best overall performance: the first cycle discharge specific capacity is 130 mAh/g (close to theoretical value 133 mAh/g) at 0.1C rate. The combination also exhibits good cycling stability in aqueous electrolyte: 86% capacity retention under continuous charge/discharge without relaxation at 1C rate for 100 cycles. This suggests that fully coating the precursor material with carbon is critical for performance, and that a graphite additive in the precursor phase is more effective than nanotubes at performing this function.

Residual stress, microstructure, and structure of tungsten thin films deposited by magnetron sputtering Sputter-deposited W films with nominal thicknesses between 5 and 180 nm were prepared by varying the base pressure prior to film deposition and by including or not including sputtered SiO 2 encapsulation layers. X-ray and electron diffraction studies showed that single phase, polycrystalline a-W could be achieved in as-deposited films as thin as 5 nm. The stress state in the as-deposited films was found to be inhomogeneous. Annealing resulted in stress relaxation and reduction of resistivity for all films, except the thinnest, unencapsulated film, which agglomerated. In-plane film grain sizes measured for a subset of the annealed films with thicknesses between 5 and 180 nm surprisingly showed a near constant value (101-116 nm), independent of film thickness. Thick-film (!120 nm) resistivity values as low as 8.6 lX cm at 301 K were obtained after annealing at 850 C for 2 h. Film resistivities were found to increase with decreasing film thicknesses below 120 nm, even for films which are fully A2 a-W with no metastable, A15 b-W evident.