Structural basis for different membrane-binding properties of E. coli anaerobic and human mitochondrial β-oxidation trifunctional enzymes

Facultative anaerobic bacteria such as Escherichia coli have two α2β2 heterotetrameric trifunctional enzymes (TFE), catalyzing the last three steps of the β-oxidation cycle: soluble aerobic TFE (EcTFE) and membrane-associated anaerobic TFE (anEcTFE), closely related to the human mitochondrial TFE (HsTFE). The cryo-EM structure of anEcTFE and crystal structures of anEcTFE-α show that the overall assembly of anEcTFE and HsTFE is similar. However, their membrane-binding properties differ considerably. The shorter A5-H7 and H8 regions of anEcTFE-α result in weaker α-β as well as α-membrane interactions, respectively. The protruding H-H region of anEcTFE-β is therefore more critical for membrane-association. Mutational studies also show that this region is important for the stability of the anEcTFE-β dimer and anEcTFE heterotetramer. The fatty acyl tail binding tunnel of the anEcTFE-α hydratase domain, as in HsTFE-α, is wider than in EcTFE-α, accommodating longer fatty acyl tails, in good agreement with their respective substrate specificities.

Near-atomic resolution reconstructions from in situ revitrified cryo samples

A microsecond time-resolved version of cryo-electron microscopy (cryo-EM) has recently been introduced to enable observation of the fast conformational motions of proteins. The technique involves locally melting a cryo sample with a laser beam to allow the proteins to undergo dynamics in the liquid phase. When the laser is switched off, the sample cools within just a few microseconds and revitrifies, trapping particles in their transient configurations, in which they can subsequently be imaged. Two alternative implementations of the technique have previously been described, using either an optical microscope or performing revitrification experiments in situ. Here, it is shown that it is possible to obtain near-atomic resolution reconstructions from in situ revitrified cryo samples. Moreover, the resulting map is indistinguishable from that obtained from a conventional sample within the spatial resolution. Interestingly, it is observed that revitrification leads to a more homogeneous angular distribution of the particles, suggesting that revitrification may potentially be used to overcome issues of preferred particle orientation.

Elucidating the Origins of High Preferential Crystal Orientation in Quasi-2D Perovskite Solar Cells

Incorporating large organic cations to form 2D and mixed 2D/3D structures significantly increases the stability of perovskite solar cells. However, due to their low electron mobility, aligning the organic sheets to ensure unimpeded charge transport is critical to rival the high performances of pure 3D systems. While additives such as methylammonium chloride (MACl) can enable this preferential orientation, so far, no complete description exists explaining how they influence the nucleation process to grow highly aligned crystals. Here, by investigating the initial stages of the crystallization, as well as partially and fully formed perovskites grown using MACl, the origins underlying this favorable alignment are inferred. This mechanism is studied by employing 3-fluorobenzylammonium in quasi-2D perovskite solar cells. Upon assisting the crystallization with MACl, films with a degree of preferential orientation of 94%, capable of withstanding moisture levels of 97% relative humidity for 10 h without significant changes in the crystal structure are achieved. Finally, by combining macroscopic, microscopic, and spectroscopic studies, the nucleation process leading to highly oriented perovskite films is elucidated. Understanding this mechanism will aid in the rational design of future additives to achieve more defect tolerant and stable perovskite optoelectronics.

Better Cryo-EM Specimen Preparation: How to Deal with the Air-Water Interface?

Cryogenic electron microscopy (cryo-EM) is now one of the most powerful and widely used methods to determine high-resolution structures of macromolecules. A major bottleneck of cryo-EM is to prepare high-quality vitrified specimen, which still faces many practical challenges. During the conventional vitrification process, macromolecules tend to adsorb at the air-water interface (AWI), which is known unfriendly to biological samples. In this review, we outline the nature of AWI and the problems caused by it, such as unpredictable or uneven particle distribution, protein denaturation, dissociation of complex and preferential orientation. We review and discuss the approaches and underlying mechanisms to deal with AWI: 1) Additives, exemplified by detergents, forming a protective layer at AWI and thus preserving the native folds of target macromolecules. 2) Fast vitrification devices based on the idea to freeze in-solution macromolecules before their touching of AWI. 3) Thin layer of continuous supporting films to adsorb macromolecules, and when functionalized with affinity ligands, to specifically anchor the target particles away from the AWI. Among these supporting films, graphene, together with its derivatives, with negligible background noise and mechanical robustness, has emerged as a new generation of support. These strategies have been proven successful in various cases and enable us a better handling of the problems caused by the AWI in cryo-EM specimen preparation.

Influence of Plug Rotational Speed on Microstructure and Texture of the Recrystallized Zone of a Friction Plug Weld Joint for AA6082-T6

Experiments of friction plug weld AA6082-T6 aluminum alloy hole defects were carried out by using the method of friction auxiliary heating between the shaft shoulder and base metal. The grain refinement of the joint's re-crystallized zone was significant, and there was obvious preferred orientation. Under the condition of other constant parameters, the rotational speed of the plug increases as the grain size of RZ increases and the component of High Angle Grain Boundaries decreases. The effect of a high deformation rate on dynamic re-crystallization is greater than that of high deformation temperature. The deformation texture component increased from 1600 r/min to 2000 r/min, while the re-crystallization texture component increased first and then decreased.

Extreme mechanical anisotropy in diamond with preferentially oriented nanotwin bundles

Mechanical properties of covalent materials can be greatly enhanced with strategy of nanostructuring. For example, the nanotwinned diamond with an isotropic microstructure of interweaved nanotwins and interlocked nanograins shows unprecedented isotropic mechanical properties. How the anisotropic microstructure would impact on the mechanical properties of diamond has not been fully investigated. Here, we report the synthesis of diamond from superaligned multiwalled carbon nanotube films under high pressure and high temperature. Structural characterization reveals preferentially oriented diamond nanotwin bundles with an average twin thickness of ca. 2.9 nm, inherited from the directional nanotubes. This diamond exhibits extreme mechanical anisotropy correlated with its microstructure (e.g., the average Knoop hardness values measured with the major axis of the indenter perpendicular and parallel to nanotwin bundles are 233 ± 8 and 129 ± 9 GPa, respectively). Molecular dynamics simulation reveals that, in the direction perpendicular to the nanotwin bundles, the dense twin boundaries significantly hinder the motion of dislocations under indentation, while such a resistance is much weaker in the direction along the nanotwin bundles. Current work verifies the hardening effect in diamond via nanostructuring. In addition, the mechanical properties can be further tuned (anisotropy) with microstructure design and modification.

The Effect of Plug Rotation Speed on Micro-Structure of Nugget Zone of Friction Plug Repair Welding Joint for 6082 Aluminum Alloy

This paper carried out the friction plug repair welding of 6082 aluminum alloy keyhole defects by using the method of friction heating between shaft shoulder and base material. In addition, a well-formed friction plug welding joint was obtained at different plug rotation speeds. In order to study the influence mechanism of plug rotation speeds on the microstructure of the weld nugget zone, EBSD technology was used to analyze the grain morphology, grain size and grain boundary characteristics of the weld nugget zone under different rotation speeds of the plug rod. The results show that in the nugget zone, the grain was fine and equated crystals refinement, and there was a preferred orientation. The deformation texture components in the welded nugget zone increased with the plug rotation speed from 1600 to 2000 rpm. However, the grain size first decreased and then increased, while the components in the High-Angle Boundary first increased and then decreased.

Effect of Partial Ba Substitutions on the Crystallization of Sr2TiSi2O8 (STS) Glass-Ceramics and on the Generation of a SAW Signal at High Temperatures

Because of their characteristics, including a d₃₃ of 10–15 pC/N and high stability up to temperatures over 1000 °C, polar glass–ceramics containing fresnoite crystals can be regarded as highly effective materials for applications requiring piezoelectricity at high temperatures. In the present paper we investigate barium substitutions in an Sr-fresnoite (STS) glass–ceramic. Two aspects are studied: first, the effect of the substitution on the preferential orientation of the crystallization, and second, the ability of the glass–ceramics to generate and propagate surface acoustic waves (SAW) at high temperatures. XRD analyses show that a 10 at.% substitution of Ba allows us to keep a strong preferential orientation of the (00l) planes of the fresnoite crystals down to more than 1 mm below the surfaces. Higher substitution levels (25 and 50 at.%), induce a non-oriented volume crystallization mechanism that competes with the surface mechanism. SAW devices were fabricated from glass–ceramic substrates with 0, 10 and 25 at.% Ba substitutions. Temperature testing reveals the high stability of the frequency and delay for all of these devices. The glass–ceramic with a 10 at.% Ba substitution gives the strongest amplitude of the SAW signal. This is attributed to the high (00l) preferential orientation and the absence of disoriented volume crystallization.

Preferential Orientation of Photochromic Gadolinium Oxyhydride Films

We report preferential orientation control in photochromic gadolinium oxyhydride (GdHO) thin films deposited by a two-step process. Gadolinium hydride (GdH_2-x) films were grown by reactive magnetron sputtering, followed by oxidation in air. The preferential orientation, grain size, anion concentrations and photochromic response of the films were strongly dependent on the deposition pressure. The GdHO films showed a preferential orientation along the [100] direction and exhibited photochromism when synthesized at deposition pressures of up to 5.8 Pa. The photochromic contrast was larger than 20% when the films were deposited below 2.8 Pa with a 0.22 H₂/Ar flow ratio. We argue that the relation of preferential orientation and the post deposition oxidation since oxygen concentration is known to be a key parameter for photochromism in rare-earth oxyhydride thin films. The experimental observations described above were explained by the decrease of the grain size as a result of the increase of the deposition pressure of the sputtering gas, followed by a higher oxygen incorporation.

PROTEINS, INTERFACES, AND CRYO-EM GRIDS

It has become clear that the standard cartoon, in which macromolecular particles prepared for electron cryo-microscopy are shown to be surrounded completely by vitreous ice, often is not accurate. In particular, the standard picture does not include the fact that diffusion to the air-water interface, followed by adsorption and possibly denaturation, can occur on the time scale that normally is required to make thin specimens. The extensive literature on interaction of proteins with the air-water interface suggests that many proteins can bind to the interface, either directly or indirectly via a sacrificial layer of already-denatured protein. In the process, the particles of interest can, in some cases, become preferentially oriented, and in other cases they can be damaged and/or aggregated at the surface. Thus, although a number of methods and recipes have evolved for dealing with protein complexes that prove to be difficult, making good cryo-grids can still be a major challenge for each new type of specimen. Recognition that the air-water interface is a very dangerous place to be has inspired work on some novel approaches for preparing cryo-grids. At the moment, two of the most promising ones appear to be: (1) thin and vitrify the specimen much faster than is done currently or (2) immobilize the particles onto a structure-friendly support film so that they cannot diffuse to the air-water interface.

Preferentially Oriented Ag Nanocrystals with Extremely High Activity and Faradaic Efficiency for CO2 Electrochemical Reduction to CO

Selective electrochemical reduction of CO₂ is one of the most important processes to study because of its promise to convert this greenhouse gas to value-added chemicals at low cost. In this work, a simple anodization treatment was devised that first oxidizes Ag to Ag₂CO₃, then uses rapid electrochemical reduction to create preferentially oriented nanoparticles (PONs) of metallic Ag (PON-Ag) with high surface area as well as high activity and very high selectivity for the reduction of CO₂ to CO. The PON-Ag catalyst was dominated by (110) and (100) orientation, which allowed PON-Ag to achieve a CO Faradaic efficiency of 96.7% at an operating potential of -0.69 V vs RHE. This performance is not only significantly higher than that of polycrystalline Ag (60% at -0.87 V vs RHE) but also represents one of the best combinations of activity and selectivity achieved to date - all with a very simple, scalable approach to electrode fabrication.

Preferentially Oriented TiO2 Nanotubes as Anode Material for Li-Ion Batteries: Insight into Li-Ion Storage and Lithiation Kinetics

Self-organized TiO₂ nanotubes (NTs) with a preferential orientation along the [001] direction are anodically grown by controlling the water content in the fluoride-containing electrolyte. The intrinsic kinetic and thermodynamic properties of the Li intercalation process in the preferentially oriented (PO) TiO₂ NTs and in a randomly oriented (RO) TiO₂ NT reference are determined by combining complementary electrochemical methods, including electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and galvanostatic cycling. PO TiO₂ NTs demonstrate an enhanced performance as anode material in Li-ion batteries due to faster interfacial Li insertion/extraction kinetics. It is shown that the thermodynamic properties, which describe the ability of the host material to intercalate Li ions, have a negligible influence on the superior performance of PO NTs. This work presents a straightforward approach for gaining important insight into the influence of the crystallographic orientation on lithiation/delithiation characteristics of nanostructured TiO₂ based anode materials for Li-ion batteries. The introduced methodology has high potential for the evaluation of battery materials in terms of their lithiation/delithiation thermodynamics and kinetics in general.

Controllable Formation of (004)-Orientated Nb:TiO2 for High-Performance Transparent Conductive Oxide Thin Films with Tunable Near-Infrared Transmittance

A niobium-doped titanium dioxide (Nb:TiO₂, NTO) film is a promising candidate material for indium-free transparent conductive oxide (TCO) films. It is challenging and interesting to control (004)-oriented growth to decrease resistivity. In this work, NTO films with different fractions of preferential (004) orientation (η₍₀₀₄₎) were controllably prepared by direct current sputtering. Notably, the direction of local-ordering of ions-packing could be adjusted by slightly changing the angle between the sputtering source and the glass substrate, which is identified as a key factor to determine the growth direction of a columnar crystal as well as the η₍₀₀₄₎ of films. Hall effect measurements indicate that NTO films with the highest η₍₀₀₄₎ present the lowest resistivity (6.4 × 10^-4 Ω cm), which originates from super-high carrier concentration (2.9 × 10²¹ cm^-3) and mobility (3.4 cm² V^-1 s^-1). The corresponding low sheet resistance (10.3 Ω sq^-1) makes it a potential material for commercial TCO films. We also observe that films with higher η₍₀₀₄₎ show lower transmittance in the near-infrared region.

A Rapid Synthesis of Oriented Palladium Nanoparticles by UV Irradiation

Palladium nanoparticles of average size around 8 nm have been synthesized rapidly by UV irradiation of mixture of palladium chloride and potassium oxalate solutions. A rod-shaped palladium oxalate complex has been observed as an intermediate. In the absence of potassium oxalate, no Pd nanoparticles have been observed. The synthesized Pd nanoparticles have been characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), selective area electron diffraction and energy dispersive analysis by X-rays (EDAX) analyses. XRD analysis indicates the preferential orientation of catalytically active {111} planes in Pd nanoparticles. A plausible mechanism has been proposed for the formation of anisotropic Pd nanoparticles.