Functionally antagonistic polyelectrolyte for electro-ionic soft actuator.

Electro-active ionic soft actuators have been intensively investigated as an artificial muscle for soft robotics due to their large bending deformations at low voltages, small electric power consumption, superior energy density, high safety and biomimetic self-sensing actuation. However, their slow responses, poor durability and low bandwidth, mainly resulting from improper distribution of ionic conducting phase in polyelectrolyte membranes, hinder practical applications to real fields. We report a procedure to synthesize efficient polyelectrolyte membranes that have continuous conducting network suitable for electro-ionic artificial muscles. This functionally antagonistic solvent procedure makes amphiphilic Nafion molecules to assemble into micelles with ionic surfaces enclosing non-conducting cores. Especially, the ionic surfaces of these micelles combine together during casting process and form a continuous ionic conducting phase needed for high ionic conductivity, which boosts the performance of electro-ionic soft actuators by 10-time faster response and 36-time higher bending displacement. Furthermore, the developed muscle shows exceptional durability over 40 days under continuous actuation and broad bandwidth below 10 Hz, and is successfully applied to demonstrate an inchworm-mimetic soft robot and a kinetic tensegrity system.

Boosting Alkaline Hydrogen Oxidation Activity of Ru Single-Atom Through Promoting Hydroxyl Adsorption on Ru/WC1- x Interfaces.

The sluggish kinetics of the hydrogen oxidation reaction (HOR) in alkaline conditions continue to pose a significant challenge for the practical implementation of anion-exchange membrane fuel cells. Developing single-atom catalysts can accelerate the pace of new HOR catalyst discovery for highly cost-effective and active HOR performance. However, single-atom catalysts (SACs) for the alkaline HOR have rarely been reported, and fundamental studies on the rational design of SACs are still required. Herein, the design of Ru SAC supported on the tungsten carbide (Ru SA/WC1- x ) via in situ high-temperature annealing strategy is reported. The resulting Ru SA/WC1- x catalyst exhibits remarkably enhanced HOR performance in alkaline media, a level of activity that can not be achieved with carbon-supported Ru SAC. Electrochemical results and density functional theory demonstrate that promoting the hydroxyl adsorption on Ru SA/WC1- x interfaces, which is derived from the low potential of zero charge of WC1- x support, has a significant effect on enhancing the HOR performance of SACs. This enhancement leads to 5.8 and 60.1 times higher Ru mass activity of Ru SA/WC1- x than Ru nanoparticles on carbon and Ru single-atom on N-doped carbon, respectively. This work provides new insights into the design of highly active SACs for alkaline HOR.

Insight into Defect Engineering of Atomically Dispersed Iron Electrocatalysts for High-Performance Proton Exchange Membrane Fuel Cell.

Atomically dispersed and nitrogen coordinated iron catalysts (Fe-NCs) demonstrate potential as alternatives to platinum-group metal (PGM) catalysts in oxygen reduction reaction (ORR). However, in the context of practical proton exchange membrane fuel cell (PEMFC) applications, the membrane electrode assembly (MEA) performances of Fe-NCs remain unsatisfactory. Herein, improved MEA performance is achieved by tuning the local environment of the Fe-NC catalysts through defect engineering. Zeolitic imidazolate framework (ZIF)-derived nitrogen-doped carbon with additional CO2 activation is employed to construct atomically dispersed iron sites with a controlled defect number. The Fe-NC species with the optimal number of defect sites exhibit excellent ORR performance with a high half-wave potential of 0.83 V in 0.5 M H2 SO4 . Variation in the number of defects allows for fine-tuning of the reaction intermediate binding energies by changing the contribution of the Fe d-orbitals, thereby optimizing the ORR activity. The MEA based on a defect-engineered Fe-NC catalyst is found to exhibit a remarkable peak power density of 1.1 W cm-2 in an H2 /O2 fuel cell, and 0.67 W cm-2  in an H2 /air fuel cell, rendering it one of the most active atomically dispersed catalyst materials at the MEA level.

Single-molecule fingerprinting of protein-drug interaction using a funneled biological nanopore.

In drug discovery, efficient screening of protein-drug interactions (PDIs) is hampered by the limitations of current biophysical approaches. Here, we develop a biological nanopore sensor for single-molecule detection of proteins and PDIs using the pore-forming toxin YaxAB. Using this YaxAB nanopore, we demonstrate label-free, single-molecule detection of interactions between the anticancer Bcl-xL protein and small-molecule drugs as well as the Bak-BH3 peptide. The long funnel-shaped structure and nanofluidic characteristics of the YaxAB nanopore enable the electro-osmotic trapping of diverse folded proteins and high-resolution monitoring of PDIs. Distinctive nanopore event distributions observed in the two-dimensional (ΔI/Io-versus-IN) plot illustrate the ability of the YaxAB nanopore to discriminate individual small-molecule drugs bound to Bcl-xL from non-binders. Taken together, our results present the YaxAB nanopore as a robust platform for label-free, ultrasensitive, single-molecule detection of PDIs, opening up a possibility for low-cost, highly efficient drug discovery against diverse drug targets.

Recent advances in amorphous electrocatalysts for oxygen evolution reaction.

Oxygen evolution reaction (OER) has attracted great attention as an important half-reaction in the electrochemical splitting of water for green hydrogen production. However, the inadequacy of highly efficient and stable electrocatalysts has impeded the development of this technology. Amorphous materials with long-range disordered structures have exhibited superior electrocatalytic performance compared to their crystalline counterparts due to more active sites and higher structural flexibility. This review summarizes the preparation methods of amorphous materials involving oxides, hydroxide, phosphides, sulfides, and their composites, and introduces the recent progress of amorphous OER electrocatalysts in acidic and alkaline media. Finally, the existing challenges and future perspectives for amorphous electrocatalysts for OER are discussed. Therefore, we believe that this review will guide designing amorphous OER electrocatalysts with high performance for future energy applications.

Perovskite-based electrocatalysts for oxygen evolution reaction in alkaline media: A mini review.

Water electrolysis is one of the attractive technologies for producing clean and sustainable hydrogen fuels with high purity. Among the various kinds of water electrolysis systems, anion exchange membrane water electrolysis has received much attention by combining the advantages of alkaline water electrolysis and proton exchange membrane water electrolysis. However, the sluggish kinetics of the oxygen evolution reaction, which is based on multiple and complex reaction mechanisms, is regarded as a major obstacle for the development of high-efficiency water electrolysis. Therefore, the development of high-performance oxygen evolution reaction electrocatalysts is a prerequisite for the commercialization and wide application of water electrolysis systems. This mini review highlights the current progress of representative oxygen evolution reaction electrocatalysts that are based on a perovskite structure in alkaline media. We first summarize the research status of various kinds of perovskite-based oxygen evolution reaction electrocatalysts, reaction mechanisms and activity descriptors. Finally, the challenges facing the development of perovskite-based oxygen evolution reaction electrocatalysts and a perspective on their future are discussed.

Structural basis for assembly and disassembly of the IGF/IGFBP/ALS ternary complex.

Insulin-like growth factors (IGFs) have pleiotropic roles in embryonic and postnatal growth and differentiation. Most serum IGFs are bound in a ternary complex with IGF-binding protein 3 (IGFBP3) and acid-labile subunit (ALS), extending the serum half-life of IGFs and regulating their availability. Here, we report cryo-EM structure of the human IGF1/IGFBP3/ALS ternary complex, revealing the detailed architecture of a parachute-like ternary complex and crucial determinants for their sequential and specific assembly. In vitro biochemical studies show that proteolysis at the central linker domain of IGFBP3 induces release of its C-terminal domain rather than IGF1 release from the ternary complex, yielding an intermediate complex that enhances IGF1 bioavailability. Our results provide mechanistic insight into IGF/IGFBP3/ALS ternary complex assembly and its disassembly upon proteolysis for IGF bioavailability, suggesting a structural basis for human diseases associated with IGF1 and IGFALS gene mutations such as complete ALS deficiency (ACLSD) and IGF1 deficiency.

A Dynamic Substrate Pool Revealed by cryo-EM of a Lipid-Preserved Respiratory Supercomplex.

Aims: Mitochondrial respiratory supercomplexes mediate redox electron transfer, generating a proton gradient for ATP synthesis. To provide structural information on the function of supercomplexes in physiologically relevant conditions, we conducted cryoelectron microscopy studies with supercomplexes in a lipid-preserving state. Results: Here, we present cryoelectron microscopy structures of bovine respiratory supercomplex I1III2IV1 by using a lipid-preserving sample preparation. The preparation greatly enhances the intercomplex quinone transfer activity. The structures reveal large intercomplex motions that result in different shapes and sizes of the intercomplex space between complexes I and III, forming a dynamic substrate pool. Biochemical and structural analyses indicated that intercomplex phospholipids mediate the intercomplex motions. An analysis of the different classes of focus-refined complex I showed that structural switches due to quinone reduction led to the formation of a novel channel that could transfer reduced quinones to the intercomplex substrate pool. Innovation and Conclusion: Our results indicate potential mechanism for the facilitated electron transfer involving a dynamic substrate pool and intercomplex movement by which supercomplexes play an active role in the regulation of metabolic flux and reactive oxygen species.

In Situ Formation of Ag Nanoparticles for Fiber Strain Sensors: Toward Textile-Based Wearable Applications.

Wearable electronic devices have attracted significant attention as important components in several applications. Among various wearable electronic devices, interest in textile electronic devices is increasing because of their high deformability and portability in daily life. To develop textile electronic devices, fiber-based electronic devices should be fundamentally studied. Here, we report a stretchable and sensitive fiber strain sensor fabricated using only harmless materials during an in situ formation process. Despite using a mild and harmless reducing agent instead of typical strong and hazardous reducing agents, the developed fiber strain sensors feature a low initial electrical resistance of 0.9 Ω/cm, a wide strain sensing range (220%), high sensitivity (∼5.8 × 104), negligible hysteresis, and high stability against repeated stretching-releasing deformation (5000 cycles). By applying the fiber sensors to various textiles, we demonstrate that the smart textile system can monitor various gestures in real-time and help users maintain accurate posture during exercise. These results will provide meaningful insights into the development of next-generation wearable applications.

ClpL is a functionally active tetradecameric AAA+ chaperone, distinct from hexameric/dodecameric ones.

AAA+ (ATPases associated with diverse cellular activities) chaperones are involved in a plethora of cellular activities to ensure protein homeostasis. The function of AAA+ chaperones is mostly modulated by their hexameric/dodecameric quaternary structures. Here we report the structural and biochemical characterizations of a tetradecameric AAA+ chaperone, ClpL from Streptococcus pneumoniae. ClpL exists as a tetradecamer in solution in the presence of ATP. The cryo-EM structure of ClpL at 4.5 Å resolution reveals a striking tetradecameric arrangement. Solution structures of ClpL derived from small-angle X-ray scattering data suggest that the tetradecameric ClpL could assume a spiral conformation found in active hexameric/dodecameric AAA+ chaperone structures. Vertical positioning of the middle domain accounts for the head-to-head arrangement of two heptameric rings. Biochemical activity assays with site-directed mutagenesis confirmed the critical roles of residues both in the integrity of the tetradecameric arrangement and activities of ClpL. Non-conserved Q321 and R670 are crucial in the heptameric ring assembly of ClpL. These results establish that ClpL is a functionally active tetradecamer, clearly distinct from hexameric/dodecameric AAA+ chaperones.

Interaction Mediator Assisted Synthesis of Mesoporous Molybdenum Carbide: Mo-Valence State Adjustment for Optimizing Hydrogen Evolution.

To overcome inherent limitations of molybdenum carbide (MoxC) for hydrogen evolution reaction (HER), i.e., low density of active site and nonideal hydrogen binding strength, we report the synthesis of valence-controlled mesoporous MoxC as a highly efficient HER electrocatalyst. The synthesis procedure uses an interaction mediator (IM), which significantly increases the density of active site by mediating interaction between PEO-b-PS template and Mo source. The valence state of Mo is tuned by systematic control of the environment around Mo by controlled heat treatment under air before thermal treatment at 1100 °C. Theoretical calculations reveal that the hydrogen binding is strongly influenced by Mo valence. Consequently, MoxC achieves a significant increase in HER activity (exceeding that of Pt/C at high current density ∼35 mA/cm2 in alkaline solution). In addition, a volcano-type correlation between HER activity and Mo valence is identified with various experimental indicators. The present strategies can be applied to various carbide and Mo-based catalysts, and the established Mo valence and HER relations can guide development of highly active HER electrocatalysts.

Structural basis of the fanconi anemia-associated mutations within the FANCA and FANCG complex.

Monoubiquitination of the Fanconi anemia complementation group D2 (FANCD2) protein by the FA core ubiquitin ligase complex is the central event in the FA pathway. FANCA and FANCG play major roles in the nuclear localization of the FA core complex. Mutations of these two genes are the most frequently observed genetic alterations in FA patients, and most point mutations in FANCA are clustered in the C-terminal domain (CTD). To understand the basis of the FA-associated FANCA mutations, we determined the cryo-electron microscopy (EM) structures of Xenopus laevis FANCA alone at 3.35 Å and 3.46 Å resolution and two distinct FANCA-FANCG complexes at 4.59 and 4.84 Å resolution, respectively. The FANCA CTD adopts an arc-shaped solenoid structure that forms a pseudo-symmetric dimer through its outer surface. FA- and cancer-associated point mutations are widely distributed over the CTD. The two different complex structures capture independent interactions of FANCG with either FANCA C-terminal HEAT repeats, or the N-terminal region. We show that mutations that disturb either of these two interactions prevent the nuclear localization of FANCA, thereby leading to an FA pathway defect. The structure provides insights into the function of FANCA CTD, and provides a framework for understanding FA- and cancer-associated mutations.

Investigation of the Support Effect in Atomically Dispersed Pt on WO3-x for Utilization of Pt in the Hydrogen Evolution Reaction.

Single-atom catalysts (SACs) have attracted growing attention because they maximize the number of active sites, with unpredictable catalytic activity. Despite numerous studies on SACs, there is little research on the support, which is essential to understanding SAC. Herein, we systematically investigated the influence of the support on the performance of the SAC by comparing with single-atom Pt supported on carbon (Pt SA/C) and Pt nanoparticles supported on WO3-x (Pt NP/WO3-x ). The results revealed that the support effect was maximized for atomically dispersed Pt supported on WO3-x (Pt SA/WO3-x ). The Pt SA/WO3-x exhibited a higher degree of hydrogen spillover from Pt atoms to WO3-x at the interface, compared with Pt NP/WO3-x , which drastically enhanced Pt mass activity for hydrogen evolution (up to 10 times). This strategy provides a new framework for enhancing catalytic activity for HER, by reducing noble metal usage in the field of SACs.

Versatile Strategy for Tuning ORR Activity of a Single Fe-N4 Site by Controlling Electron-Withdrawing/Donating Properties of a Carbon Plane.

Replacement of Pt-based oxygen reduction reaction (ORR) catalysts with non-precious metal catalysts (NPMCs) such as Fe/N/C is one of the most important issues in the commercialization of proton exchange membrane fuel cells (PEMFCs). Despite numerous studies on Fe/N/C catalysts, a fundamental study on the development of a versatile strategy is still required for tuning the kinetic activity of a single Fe-N4 site. Herein, we report a new and intuitive design strategy for tuning and enhancing the kinetic activity of a single Fe-N4 site by controlling electron-withdrawing/donating properties of a carbon plane with the incorporation of sulfur functionalities. The effect of electron-withdrawing/donating functionalities was elucidated by experimentation and theoretical calculations. Finally, the introduction of an oxidized sulfur functionality decreases the d-band center of iron by withdrawing electrons, thereby facilitating ORR at the Fe-N4 site by lowering the intermediate adsorption energy. Furthermore, this strategy can enhance ORR activity without a decrease in the stability of the catalyst. This simple and straightforward approach can be a cornerstone to develop optimum NPMCs for application in the cathodes of PEMFCs.

Spontaneous Generation of H2O2 and Hydroxyl Radical through O2 Reduction on Copper Phosphide under Ambient Aqueous Condition.

Copper phosphide (Cu xP) was synthesized and tested for its reactivity for generating H2O2 through spontaneous reduction of dioxygen under ambient aqueous condition. The in situ generated H2O2 was subsequently decomposed to generate OH radicals, which enabled the degradation of organic compounds in water. The oxygen reduction reaction proceeded along with the concurrent oxidation of phosphide to phosphate, then copper ions and phosphate ions were dissolved out during the reaction. The reactivity of Cu xP was gradually reduced during 10 cycles with consuming 8.7 mg of Cu xP for the successive removal of 17 µmol 4-chlorophenol. CoP which was compared as a control sample under the same experimental condition also produced H2O2 through activating dioxygen but did not degrade organic compounds at all. The electrochemical analysis for the electron transfers on Cu xP and CoP showed that the number of electrons transferred to O2 is 3 and 2, respectively, which explains why OH radical is generated on Cu xP, not on CoP. The Cu+ species generated on the Cu xP surface can participate in Fenton-like reaction with in situ generated H2O2. Cu xP is proposed as a solid reagent that can activate dioxygen to generate reactive oxygen species in ambient aqueous condition, which is more facile to handle and store than liquid/gas reagents (e.g., H2O2, Cl2, O3).

Modified carbon nitride nanozyme as bifunctional glucose oxidase-peroxidase for metal-free bioinspired cascade photocatalysis.

Nanomaterials-based biomimetic catalysts with multiple functions are necessary to address challenges in artificial enzymes mimicking physiological processes. Here we report a metal-free nanozyme of modified graphitic carbon nitride and demonstrate its bifunctional enzyme-mimicking roles. With oxidase mimicking, hydrogen peroxide is generated from the coupled photocatalysis of glucose oxidation and dioxygen reduction under visible-light irradiation with a near 100% apparent quantum efficiency. Then, the in situ generated hydrogen peroxide serves for the subsequent peroxidase-mimicking reaction that oxidises a chromogenic substrate on the same catalysts in dark to complete the bifunctional oxidase-peroxidase for biomimetic detection of glucose. The bifunctional cascade catalysis is successfully demonstrated in microfluidics for the real-time colorimetric detection of glucose with a low detection limit of 0.8 µM within 30 s. The artificial nanozymes with physiological functions provide the feasible strategies for mimicking the natural enzymes and realizing the biomedical diagnostics with a smart and miniature device.

Moth pheromone-selective projection neurons with cell bodies in the antennal lobe lateral cluster exhibit diverse morphological and neurophysiological characteristics.

Olfactory projection neurons convey information from the insect antennal lobe (AL) to higher brain centers. Previous reports have demonstrated that pheromone-responsive projection neurons with cell bodies in the moth medial cell cluster (mcPNs) predominantly have dendritic arborizations in the sexually dimorphic macroglomerular complex (MGC) and send an axon from the AL to the calyces of the mushroom body (CA) as well as the lateral horn (LH) of the protocerebrum via the medial AL tract. These neurons typically exhibit a narrow odor tuning range related to the restriction of their dendritic arbors within a single glomerulus (uniglomerular). In this study, we report on the diverse physiological and morphological properties of a group of pheromone-responsive olfactory projection neurons with cell bodies in the AL lateral cell cluster (MGC lcPNs) of two closely related moth species. All pheromone-responsive lcPNs appeared to exhibit "basket-like" dendritic arborizations in two MGC compartments and made connections with various protocerebral targets including ventrolateral and superior neuropils via projections primarily through the lateral AL tract and to a lesser extent the mediolateral antennal lobe tract. Physiological characterization of MGC lcPNs also revealed a diversity of response profiles including those either enhanced by or reliant upon presentation of a pheromone blend. These responses manifested themselves as higher maximum firing rates and/or improved temporal resolution of pulsatile stimuli. MGC lcPNs therefore participate in conveying diverse olfactory information relating to qualitative and temporal facets of the pheromone stimulus to a more expansive number of protocerebral targets than their mcPN counterparts.

Ostwald Ripening Driven Exfoliation to Ultrathin Layered Double Hydroxides Nanosheets for Enhanced Oxygen Evolution Reaction.

As a key half-reaction in water splitting, the oxygen evolution reaction (OER) process is kinetically sluggish. Layered double hydroxides (LDHs) are regarded as the highly promising electrocatalysts to promote the OER kinetics. However, the closely stacking layered structure of pristine bulk LDHs restricts the exposure of electrocatalytically active sites, and it remains a great challenge to find an efficient strategy to exfoliate the bulk LDHs into ultrathin and stable nanosheets with increased surface area and exposed active sites. Herein, a novel Ostwald ripening driven exfoliation (ORDE) of NiFe LDHs has been achieved in situ on the electrodes by spontaneously self-etching and redepositing via a simple hydrothermal treatment without the assistance of any exfoliating reagent or surfactant. The thermodynamically driven Ostwald ripening has been expanded to the exfoliation of two-dimensional layered materials for the first time. Compared with conventional exfoliation methods, this ORDE is a time-saving and green strategy that avoids the serious adsorption of surfactant molecules. The ORDE of NiFe LDHs is accomplished in situ on a Cu mesh electrode, which not only exhibits excellent electrical contact between LDHs catalyst and electrodes but also prevents the restacking of the exfoliated LDHs. As a result, the exfoliated ultrathin, clean, and vertically aligned NiFe nanosheets with much higher surface area and numerous exposed active edges and sites demonstrated significantly enhanced OER performances with low overpotential of 292 mV at 10 mA cm-2 and long-term stability for more than 60 h, as well as remarkable flexibility. Additionally, bulk Ni(OH)2 nanosheets on Ni foams have also been exfoliated by a similar mechanism, indicating this ORDE strategy can be widely extended to other 2D layered materials for novel applications.

Synergistic Effect of Molecular-Type Electrocatalysts with Ultrahigh Pore Volume Carbon Microspheres for Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries are regarded as potential high-energy storage devices due to their outstanding energy density. However, the low electrical conductivity of sulfur, dissolution of the active material, and sluggish reaction kinetics cause poor cycle stability and rate performance. A variety of approaches have been attempted to resolve the above issues and achieve enhanced electrochemical performance. However, inexpensive multifunctional host materials which can accommodate large quantities of sulfur and exhibit high electrode density are not widely available, which hinders the commercialization of Li-S batteries. Herein, mesoporous carbon microspheres with ultrahigh pore volume are synthesized, followed by the incorporation of Fe-N-C molecular catalysts into the mesopores, which can act as sulfur hosts. The ultrahigh pore volume of the prepared host material can accommodate up to ∼87 wt % sulfur, while the uniformly controlled spherical morphology and particle size of the carbon microspheres enable high areal/volumetric capacity with high electrode density. Furthermore, the uniform distribution of Fe-N-C (only 0.33 wt %) enhances the redox kinetics of the conversion reaction of sulfur and efficiently captures the soluble intermediates. The resulting electrode with 5.2 mg sulfur per cm2 shows excellent cycle stability and 84% retention of the initial capacity even after 500 cycles at a 3 C rate.

Four-fold Channel-Nicked Human Ferritin Nanocages for Active Drug Loading and pH-Responsive Drug Release.

Human ferritins are emerging platforms for non-toxic protein-based drug delivery, owing to their intrinsic or acquirable targeting abilities to cancer cells and hollow cage structures for drug loading. However, reliable strategies for high-level drug encapsulation within ferritin cavities and prompt cellular drug release are still lacking. Ferritin nanocages were developed with partially opened hydrophobic channels, which provide stable routes for spontaneous and highly accumulated loading of FeII -conjugated drugs as well as pH-responsive rapid drug release at endoplasmic pH. Multiple cancer-related compounds, such as doxorubicin, curcumin, and quercetin, were actively and heavily loaded onto the prepared nicked ferritin. Drugs on these minimally modified ferritins were effectively delivered inside cancer cells with high toxicity.