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Abstract: Mackinawite, a metastable 1:1 compound of iron and sulfur that adopts an anti-PbO-type structure, is of interest because of its relationship to known iron chalcogenide superconductors, as well as its biogeochemical relevance. Colloidal nanosheets of mackinawite-type FeS were synthesized by first generating an amorphous Fe–S precursor via the aqueous room-temperature co-precipitation of Fe2+ and S2−, then solvothermally crystallizing it in ethylene glycol at 200°C in an autoclave. The product is highly crystalline, with lattice constants of a=3.674(3)Å and c=5.0354(3)Å. The nanosheets, with their surface normal oriented along the [001] direction, are irregularly faceted with edge lengths that range from 100nm to over 1μm and average thicknesses of approx. 30nm. The samples showed a ferromagnetic background signal with no evidence of superconductivity. [Copyright &y& Elsevier]

Single-crystal colloidal SnSe nanosheets react with atrioctylphosphine–telluriumcomplex to transform into porous single-crystal SnTe nanosheets withoriented nanocube protrusions. This chemical transformation reaction,which provides chemical and crystallographic guidelines for designingsecondary nanostructural features into single crystal colloidal nanosheetsand also results in two-dimensional nanosheets of a three-dimensionallybonded material, proceeds via a diffusion-mediated anion exchangepathway. Intermediate nanosheets reveal that SnTe nucleates with crystallographicalignment on the surface of the SnSe nanosheet, which ultimately isconsumed to produce the porous SnTe nanosheet product. The anion exchangereaction is general, successfully converting a library of metal selenidesand sulfides to the corresponding tellurides. [ABSTRACT FROM AUTHOR]

Controlling the composition and phase formation of bulk and nanoscale solids underpins efforts to control physical properties. Here, we introduce a powerful new chemical pathway that facilitates composition-tunable synthesis, post-synthesis purification, and precise phase targeting in metal chalcogenide systems. `When metal sele-nides and sulfides react with trioctylphosphine (TOP) at temperatures that range from 65 to 270 °C, selenium and sulfur are selectively extracted to produce the most metal-rich chalcogenide that is stable in a particular binary system. This general approach is demonstrated for SnSe2, FeS2, NiSe2, and CoSe2, which convert to SnSe, FeS, Ni3Se2, and Co9Se8, respectively. In-depth studies of the Fe-Se system highlight the precise phase targeting and purification that is achievable, with PbO-type FeSe (the most metal-rich stable Fe-Se phase) forming exclusively when other Fe-Se phases, including mixtures, react with TOP. This chemistry also represents a new template-based nanoparticle "conversion chemistry" reaction, transforming hollow NiSe2 nano-spheres into hollow NiSe nanospheres with morphological retention. [ABSTRACT FROM AUTHOR]

We examine the kinetics of polymer chain exchange between mixed block copolymer-detergent micelles, a system relevant to the synthesis of protein-containing biomimetic membranes. While chain exchange between block copolymer (BCP) aggregates in water is too slow to observe, and detergent molecules exchange between micelles on a time scale of nanoseconds to microseconds, BCP chains exchange between mixed detergent-polymer micelles on intermediate time scales of many minutes to a few days. We examine a membrane-protein-relevant, vesicle-forming, ultrashort polymer, poly(ethyl ethylene)20-poly(ethylene oxide)18 (PEE20-PEO18). PEE20-PEO18 was solubilized in mixed micelles with the membrane protein compatible nonionic detergent octyl-β-D-glucoside (OG). Using cryo-TEM and small-angle neutron scattering (SANS), we demonstrate complete solubilization of the polymer into micelles. Using time-resolved SANS (TR-SANS), we provide the first direct evidence that detergents activate BCP chain exchange and determine kinetic parameters at two detergent concentrations slightly above the critical micellar concentration (CMC) of OG. We find that chain exchange increases 2 orders of magnitude when temperature increases from 35 to 55 °C and that even a 1 mg/mL increase in OG concentration leads to a noticeable increase in exchange rate. Our kinetic data are consistent with a single rate-limiting process rather than the distribution of exchange rates known to exist for BCPs in the absence of detergent, indicating a different exchange mechanism than the simple chain escape dominant in single-component micelles. Using the Arrhenius equation, we determine that at the detergent concentrations examined the activation energy for polymer chain exchange is only 2-3 times higher for PEE20PEO18 than for short-chained lipids and that the activation barrier decreases with increasing OG concentration. On the basis of these results, we postulate that mixed micelles exchange BCPs through a detergent-mediated process such as the fusion and fragmentation mechanisms also known to occur in micellar systems. These findings explain the need for high detergent concentration and/or temperature to synthesize polymer/protein membranes. Further, we postulate this is a more general phenomenon applicable to mixed micelle systems containing amphiphiles with vastly different solubilities and CMCs differing by many orders of magnitude. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) alignment and crystallization of membrane proteins (MPs) is increasingly important in characterizing their three-dimensional (3D) structure, in designing pharmacological agents, and in leveraging MPs for biomimetic devices. Large, highly ordered MP 2D crystals in block copolymer (BCP) matrices are challenging to fabricate, but a facile and scalable technique for aligning and crystallizing MPs in thin-film geometries would rapidly translate into applications. This work introduces a novel method to grow larger and potentially better ordered 2D crystals by performing the crystallization process in the presence of a strong magnetic field. We demonstrate the efficacy of this approach using a ß-barrel MP, outer membrane protein F (OmpF), in short-chain polybutadiene-poly(ethylene oxide) (PB-PEO) membranes. Crystals grown in a magnetic field were up to 5 times larger than conventionally grown crystals, and a signal-to-noise (SNR) analysis of diffraction peaks in Fourier transforms of specimens imaged by negative-stain electron microscopy (EM) and cryo-EM showed twice as many high-SNR diffraction peaks, indicating that the magnetic field also improves crystal order. [ABSTRACT FROM AUTHOR]

Abstract: Biomimetic approaches to developing membranes for separations have seen a renewed interest in recent years. Biomimetic membranes incorporate biological elements or borrow concepts, ideas or inspiration from biological systems. Such membranes can take advantage of the strategies evolved by nature over billions of years for improving transport efficiency and specificity. This review covers biological paradigms that are relevant to membranes for separations and then presents an overview of strategies that are inspired by these paradigms. It also presents both fundamental and practical challenges to implementation of these strategies at application relevant scales. [Copyright &y& Elsevier]

Transition metal chalcogenides are important materials because of their range of useful properties and applications, including as thermoelectrics, magnetic semiconductors, superconductors, quantum dots, sensors, and photovoltaics. In particular, iron chalcogenides have received renewed attention following the discovery of superconductivity in PbO-type β-FeSe and related solid solutions. This paper reports a low-temperature solution chemistry route to the synthesis of β-FeSe, β-FeTe, FeTe2, and several members of the β-Fe(Se,Te) solid solution. The samples were analyzed by powder XRD, TEM, EDS, SAED, SEM with elemental mapping, AFM, and SQUID magnetometry. Consistent with the layered crystal structures, the FeSe, FeTe, and Fe(Se,Te) products are predominantly two-dimensional single-crystal nanosheets with thicknesses of approximately 2−3 nm and edge lengths ranging from 200 nm to several micrometers. FeTe2forms a mixture of nanosheets and one-dimensional sheet-derived nanostructures. None of the samples are superconducting, which could be due to size effects, nonstoichiometry, or low-level impurities. [ABSTRACT FROM AUTHOR]

The article presents a study which examines the conversion of metal nanoparticles into multimetal nanoparticle products through solution chemistry reactions. It discusses the process of transformation of metal nanoparticles structures into multielement shape-controlled nanostructures. It concludes that the solution chemistry conversion reactions that were developed for metal nanoparticles are directly applicable to on-wire transformations.