Growth mechanisms and anisotropic softness-dependent conductivity of orientation-controllable metal-organic framework nanofilms.

Conductive metal-organic frameworks (cMOFs) manifest great potential in modern electrical devices due to their porous nature and the ability to conduct charges in a regular network. cMOFs applied in electrical devices normally hybridize with other materials, especially a substrate. Therefore, the precise control of the interface between cMOF and a substrate is particularly crucial. However, the unexplored interface chemistry of cMOFs makes the controlled synthesis and advanced characterization of high-quality thin films, particularly challenging. Herein, we report the development of a simplified synthesis method to grow "face-on" and "edge-on" cMOF nanofilms on substrates, and the establishment of operando characterization methodology using atomic force microscopy and X-ray, thereby demonstrating the relationship between the soft structure of surface-mounted oriented networks and their characteristic conductive functions. As a result, crystallinity of cMOF nanofilms with a thickness down to a few nanometers is obtained, the possible growth mechanisms are proposed, and the interesting anisotropic softness-dependent conducting properties (over 2 orders of magnitude change) of the cMOF are also illustrated.

Colossal barocaloric effects in plastic crystals.

Refrigeration is of vital importance for modern society-for example, for food storage and air conditioning-and 25 to 30 per cent of the world's electricity is consumed for refrigeration1. Current refrigeration technology mostly involves the conventional vapour compression cycle, but the materials used in this technology are of growing environmental concern because of their large global warming potential2. As a promising alternative, refrigeration technologies based on solid-state caloric effects have been attracting attention in recent decades3-5. However, their application is restricted by the limited performance of current caloric materials, owing to small isothermal entropy changes and large driving magnetic fields. Here we report colossal barocaloric effects (CBCEs) (barocaloric effects are cooling effects of pressure-induced phase transitions) in a class of disordered solids called plastic crystals. The obtained entropy changes in a representative plastic crystal, neopentylglycol, are about 389 joules per kilogram per kelvin near room temperature. Pressure-dependent neutron scattering measurements reveal that CBCEs in plastic crystals can be attributed to the combination of extensive molecular orientational disorder, giant compressibility and highly anharmonic lattice dynamics of these materials. Our study establishes the microscopic mechanism of CBCEs in plastic crystals and paves the way to next-generation solid-state refrigeration technologies.

Low-Temperature Chiral Crystal Structure and Superconductivity in (Pt0.2Ir0.8)3Zr5.

We report the observation of superconductivity in (Pt0.2Ir0.8)3Zr5 with a chiral space group (P6122) at low temperatures. The bulk nature of the superconductivity at a transition temperature of 2.2 K was confirmed using specific heat measurements. We revealed that (Pt0.2Ir0.8)3Zr5 obeys the weak-coupling Bardeen-Cooper-Schrieffer model, and the dominant mechanism in the upper critical field is the orbital pair-breaking limit rather than the Pauli-Clogston limit. This indicates that the antisymmetric spin-orbit coupling caused by the chiral crystal structure does not significantly affect the superconductivity of (Pt0.2Ir0.8)3Zr5.

Denary High-Entropy Oxide Nanoparticles Synthesized by a Continuous Supercritical Hydrothermal Flow Process.

High-entropy oxide nanoparticles (HEO NPs) have been intensively studied because of their attractive properties, such as high stability and enhanced catalytic activity. In this work, for the first time, denary HEO NPs were successfully synthesized using a continuous supercritical hydrothermal flow process without calcination. Interestingly, this process allows the formation of HEO NPs on the order of seconds at a relatively lower temperature. The synthesized HEO NPs contained 10 metal elements, La, Ca, Sr, Ba, Fe, Mn, Co, Ru, Pd, and Ir, and had a perovskite-type structure. Atomic-resolution high-angle annular dark-field scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy measurements revealed homogeneous dispersion of the 10 metal elements. The obtained HEO NPs also exhibited a higher catalytic activity for the CO oxidation reaction than that of the LaFeO3 NPs.

Submillisecond in situ X-ray diffraction measurement system with changing temperature and pressure using diamond anvil cells at BL10XU/SPring-8.

Recently, there has been a high demand for elucidating kinetics and visualizing reaction processes under extreme dynamic conditions, such as chemical reactions under meteorite impact conditions, structural changes under nonequilibrium conditions, and in situ observations of dynamic changes. To accelerate material science studies and Earth science fields under dynamic conditions, a submillisecond in situ X-ray diffraction measurement system has been developed using a diamond anvil cell to observe reaction processes under rapidly changing pressure and temperature conditions replicating extreme dynamic conditions. The development and measurements were performed at the high-pressure beamline BL10XU/SPring-8 by synchronizing a high-speed hybrid pixel array detector, laser heating and temperature measurement system, and gas-pressure control system that enables remote and rapid pressure changes using the diamond anvil cell. The synchronized system enabled momentary heating and rapid cooling experiments up to 5000 K via laser heating as well as the visualization of structural changes in high-pressure samples under extreme dynamic conditions during high-speed pressure changes.

High-throughput and high-resolution powder X-ray diffractometer consisting of six sets of 2D CdTe detectors with variable sample-to-detector distance and innovative automation system.

The demand for powder X-ray diffraction analysis continues to increase in a variety of scientific fields, as the excellent beam quality of high-brightness synchrotron light sources enables the acquisition of high-quality measurement data with high intensity and angular resolution. Synchrotron powder diffraction has enabled the rapid measurement of many samples and various in situ/operando experiments in nonambient sample environments. To meet the demands for even higher throughput measurements using high-energy X-rays at SPring-8, a high-throughput and high-resolution powder diffraction system has been developed. This system is combined with six sets of two-dimensional (2D) CdTe detectors for high-energy X-rays, and various automation systems, including a system for automatic switching among large sample environmental equipment, have been developed in the third experimental hutch of the insertion device beamline BL13XU at SPring-8. In this diffractometer system, high-brilliance and high-energy X-rays ranging from 16 to 72 keV are available. The powder diffraction data measured under ambient and various nonambient conditions can be analysed using Rietveld refinement and the pair distribution function. Using the 2D CdTe detectors with variable sample-to-detector distance, three types of scan modes have been established: standard, single-step and high-resolution. A major feature is the ability to measure a whole powder pattern with millisecond resolution. Equally important, this system can measure powder diffraction data with high Q exceeding 30 Å-1 within several tens of seconds. This capability is expected to contribute significantly to new research avenues using machine learning and artificial intelligence by utilizing the large amount of data obtained from high-throughput measurements.

Polymorphism of Two-Dimensional Semiconducting Coordination Polymers: Impact of a Lead-Sulfur Network on Photoconductivity.

Sulfur-coordinated coordination polymers (S-CPs) have unique optoelectrical properties that originate from infinite M-S bond networks. In this study, we synthesized and characterized two polymorphs of a two-dimensional (2D) Pb(II) S-CP with a formula of [Pb(tzdt)(OAc)] (Htzdt=1,3-thiazolidine-2-thione, OAc=acetate). Our findings revealed that the thermodynamic product (KGF-26) possesses quasi-2D (-Pb-S-)n layers with weak nonbonded Pb-S bonds, whereas the kinetic product (KGF-27) has intrinsic 2D (-Pb-S-)n layers with Pb-S bonds. The results of time-resolved microwave conductivity measurements and first-principles calculations confirmed that KGF-27 exhibits higher photoconductivity than KGF-26, which establishes that the inorganic (-Pb-S-)n networks with Pb-S bonds are crucial for achieving high photoconductivity. This is the first experimental demonstration of the impact of the (-M-S-)n networks in S-CPs on photoconductivity through the comparison of crystal polymorphisms.

The double-stranded RNA-dependent protein kinase PKR negatively regulates the protein expression of IFN-ß induced by RIG-I signaling.

Retinoic acid-inducible gene-I (RIG-I) is a cytoplasmic RNA sensor that plays an important role in innate immune responses to viral RNAs. Double-stranded RNA (dsRNA)-dependent protein kinase (PKR) is a eukaryotic initiation factor 2α (eIF2α) kinase that is initially involved in the responses of the translational machinery to dsRNA. PKR is also thought to play an essential role in antiviral innate immunity. However, the coordinated mechanisms of RIG-I and PKR that induce the expression of type I interferons (IFNs), essential cytokines involved in antiviral defense, are not completely understood. In this study, we show that PKR negatively participates in the RIG-I-mediated induction of IFN-ß expression. Stress granule (SG) formation is crucial to sequester mRNA to prevent aberrant protein synthesis by various stresses. SG formation in response to dsRNA was triggered by a PKR-mediated antiviral stress response. However, IFN-ß mRNA was not sequestered in the SGs of dsRNA-treated cells. dsRNA-induced translational silencing was thought to be PKR dependent. However, our results indicated that some proteins, including IFN-ß, were clearly translated despite PKR-mediated translational silencing. This study suggests that RIG-I responds mainly to IFN-ß expression in cells to which non-self dsRNA is introduced. In addition, PKR negatively regulates IFN-ß protein expression induced by RIG-I signaling. This may explain the essential role of PKR in fine-tuning the expression of IFN-ß in RIG-I-mediated antiviral immune responses.

The inhibitory effect of DIF-3 on polyinosinic-polycytidylic acid-induced innate immunity activation in human cerebral microvascular endothelial cells.

For the treatment and prevention of autoinflammatory diseases, it is essential to develop the drug, regulating the innate immune system. Although differentiation-inducing factor (DIF) derivatives, extracted from the cellular slime mold, Dictyostelium discoideum, exhibit immunomodulatory effects, their effects on the regulation of innate immunity in brain are unknown. In this study, we used the human cerebral microvascular endothelial cell line, hCMEC/D3, to investigate the effects of DIF derivatives on the generation of C-X-C motif chemokine (CXCL) 10 and interferon (IFN)-ß induced by polyinosinic-polycytidylic acid (poly IC). DIF-3 (1-10 µM), but not DIF-1 and DIF-2, dose-dependently inhibited the biosynthesis of not only CXCL10 but also CXCL16 and C-C motif chemokine 2 induced by poly IC. DIF-3 also strongly decreased IFN-ß mRNA expression and protein release from the cells induced by poly IC through the prohibition of p65, a subtype of NF-ĸB, not interferon regulatory transcription factor 3 phosphorylation. In the docking simulation study, we confirmed that DIF-3 had a high affinity to p65. These results suggest that DIF-3 regulates the innate immune system by inhibiting TLR3/IFN-ß signaling axis through the NF-ĸB phosphorylation inhibition.

Possible involvement of DExD/H box helicase 60 in synovial inflammation of rheumatoid arthritis: role of toll-like receptor 3 signaling.

BACKGROUND: Innate immunity is known to be implicated in the etiology of synovitis in rheumatoid arthritis (RA). However, details of the molecular mechanisms have not been fully clarified. DExD/H-box helicase 60 (DDX60), a putative RNA helicase, is of consequence in anti-viral innate immune reactions followed by inflammation. Although DDX60 is involved in the pathogenesis of autoimmune diseases such as systemic lupus nephritis, the role of DDX60 in RA has not been elucidated. The objective of this study was to examine the expression and the role of DDX60 in RA synovial inflammation. METHODS AND RESULTS: DDX60 protein expression was investigated by immunohistochemistry in synovial tissues resected from 4 RA and 4 osteoarthritis (OA) patients. We found that synovial DDX60 expression was more intense in RA than in OA. Treatment of human rheumatoid fibroblast-like synoviocytes in culture with polyinosinic-polycytidylic acid, a Toll-like receptor 3 (TLR3) ligand, increased DDX60 protein and mRNA expression. A knockdown experiment of DDX60 using RNA interference revealed a decrease in the expression of poly IC-induced C-X-C motif chemokine ligand 10 (CXCL10) which induces lymphocyte chemotaxis. CONCLUSIONS: The synovial DDX60 was more expressed in RA patients than in OA. In human RFLS, DDX60 stimulated by TLR3 signaling affected CXCL10 expression. DDX60 may contribute to synovial inflammation in RA.

TMEM2 suppresses TLR3-mediated IFN-ß/ISG56/CXCL10 expression in BEAS-2B bronchial epithelial cells.

BACKGROUND: Bronchial epithelial cells are at the front line of viral infections. Toll-like receptor 3 (TLR3) cascade causes the expression of interferon (IFN)-ß and IFN-stimulated genes (ISGs), which in turn induce an antiviral response. Members of the transmembrane protein (TMEM) family are expressed in various cell types. Although the prognostic value of TMEM2 in various cancers has been reported, its association with infectious diseases remains unknown. In this study, we investigated the effects of TMEM2 on antiviral immunity in BEAS-2B bronchial epithelial cells. METHODS AND RESULTS: TMEM2 protein was found in the cytoplasm of normal human bronchial epithelial cells and differed between organs using immunohistochemistry. Cultured BEAS-2B cells were transfected with TMEM2 siRNA, followed by administration of TLR3 ligand polyinosinic-polycytidylic acid (poly IC) or recombinant human (r(h)) IFN-ß. The expression of TMEM2, IFN-ß, ISG56, C-X-C motif chemokine ligand 10 (CXCL10) and hyaluronan were evaluated appropriately by western blotting, quantitative reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay. TMEM2 expression was not altered by poly IC stimulation. Knockdown of TMEM2 increased poly IC-induced expression of IFN-ß, CXCL10, and ISG56, while IFN-ß-induced expression of ISG56 and CXCL10 were not changed by TMEM2 knockdown. The hyaluronan concentration in the medium was decreased by either TMEM2 knockdown or poly IC, but additive or synergistic effects were not observed. CONCLUSIONS: TMEM2 knockdown enhanced TLR3-mediated IFN-ß, CXCL10, and ISG56 expression in BEAS-2B cells. This implies that TMEM2 suppresses antiviral immune responses and prevents tissue injury in bronchial epithelial cells.

A Three-Dimensionally Extended Metal-Organic Ladder Compound Exhibiting Proton Conduction.

Ladder systems situated in the dimensional crossover region have attracted much attention because their electronic states and physical properties depend strongly on the electronic correlations among the constituent legs. Generally, two-/three-legged transition metal-oxide ladder compounds are studied as representative ladder systems, but two-/three-dimensional (2D/3D) extensions based on such ladder systems with a few numbers of legs are difficult because of the extreme synthesis conditions. Here, for the first time, we report the successful creation of a 3D extended two-legged ladder compound, [Pt(en)(dpye)I]2(NO3)4 ⋅ 2H2O (en=ethylenediamine; dpye=1,2-Di(4-pyridyl)ethane), which is obtained by simple oxidative polymerization of a small Pt macrocyclic complex using elemental I2. The unique 3D extended lattice consists of 1D mixed-valence halogen-bridged metal chains (⋅⋅⋅Pt-I-Pt-I⋅⋅⋅) and helically arranged macrocyclic units as the constituent legs and rungs, as confirmed by single-crystal X-ray diffraction. Diffuse X-ray scattering analyses and optical measurements revealed that the out-of-phase mixed-valence Pt2+/Pt4+ arrangement arises from the weak interchain correlation among adjacent legs. In addition, this compound shows an increase in proton conductivity by a factor of up to 1000, depending on humidity.

Self-Assembled Crystalline Bundles in Soluble Metal-Organic Nanotubes.

The use of nanotubes in the solution state is crucial not only for the exploration of physical and chemical behaviors at the molecular level but also for application such as thin-film fabrication. Surface modification is generally used to solubilize carbon nanotubes (CNTs) and various synthetic nanotubes; however, this method may affect the surface properties of the original nanotubes, and the detailed crystal structure obtained after modification is unclear. Here, we report the synthesis of a crystalline and soluble metal-organic nanotube consisting of a cationic tubular framework and an anion with a long alkyl chain. The nanotubular structures are formed not only in the solid state but also in the solution state, as confirmed by an X-ray structural analysis, optical measurements, and electron microscopy studies. This nanotube system is realized in different states without any surface modification, which is quite different from typical CNTs and synthetic nanotubes. In addition, self-assembled crystalline bundles are directly observed using transmission electron microscopy (TEM) for the first time in a metal-organic nanotube system. The bundle structures are also confirmed by atomic force microscopy (AFM) observations of thin nanotube films. We envisage a systematic design of such soluble metal-organic nanotubes that will enable direct observation of mass transport behavior in channels of bundles or a single nanotube, as well as a wide range of thin-film applications.

Continuous-Flow Chemical Synthesis for Sub-2 nm Ultra-Multielement Alloy Nanoparticles Consisting of Group IV to XV Elements.

Multielement alloy nanoparticles have attracted much attention due to their attractive catalytic properties derived from the multiple interactions of adjacent multielement atoms. However, mixing multiple elements in ultrasmall nanoparticles from a wide range of elements on the periodic table is still challenging because the elements have different properties and miscibility. Herein, we developed a benchtop 4-way flow reactor for chemical synthesis of ultra-multielement alloy (UMEA) nanoparticles composed of d-block and p-block elements. BiCoCuFeGaInIrNiPdPtRhRuSbSnTi 15-element alloy nanoparticles composed of group IV to XV elements were synthesized by sequential injection of metal precursors using the reactor. This methodology realized the formation of UMEA nanoparticles at low temperature (66 °C), resulting in a 1.9 nm ultrasmall average particle size. The UMEA nanoparticles have high durability and activity for electrochemical alcohol oxidation reactions and high tolerance to CO poisoning. These results suggest that the multiple interactions of UMEA efficiently promote the multistep alcohol oxidation reaction.

Molybdenum-Ruthenium-Carbon Solid-Solution Alloy Nanoparticles: Can They Be Pseudo-Technetium Carbide?

Technetium (Tc), atomic number 43, is an element that humans cannot freely use even in the 21st century because Tc is radioactive and has no stable isotope. In this report, we present molybdenum-ruthenium-carbon solid-solution alloy (MoxRu1-xCy) nanoparticles (NPs) that are expected to have an electronic structure similar to that of technetium carbide (TcCy). MoxRu1-xCy NPs were synthesized by annealing under a helium/hydrogen atmosphere following thermal decomposition of metal precursors. The obtained NPs had a solid-solution structure in the whole composition range. MoxRu1-xCy with a cubic structure (down to 30 atom % Mo in the metal ratio) showed a superconducting state, and the transition temperature (Tc) increased with increasing Mo composition. The continuous change in Tc across that of TcCy indicates the continuous control of the electronic structure by solid-solution alloying, leading to pseudo-TcCy. Density functional theory calculations indicated that the synthesized Mo0.53Ru0.47C0.41 has a similar electronic structure to TcC0.41.

Fe Site Order and Magnetic Properties of Fe1/4NbS2.

Transition-metal dichalcogenides (TMDs) have long been attractive to researchers for their diverse properties and high degree of tunability. Most recently, interest in magnetically intercalated TMDs has resurged due to their potential applications in spintronic devices. While certain compositions featuring the absence of inversion symmetry such as Fe1/3NbS2 and Cr1/3NbS2 have garnered the most attention, the diverse compositional space afforded through the host matrix composition as well as intercalant identity and concentration is large and remains relatively underexplored. Here, we report the magnetic ground state of Fe1/4NbS2 that was determined from low-temperature neutron powder diffraction as an A-type antiferromagnet. Despite the presence of overall inversion symmetry, the pristine compound manifests spin polarization induced by the antiferromagnetic order at generic k points, based on density functional theory band-structure calculations. Furthermore, by combining synchrotron diffraction, pair distribution function, and magnetic susceptibility measurements, we find that the magnetic properties of Fe1/4NbS2 are sensitive to the Fe site order, which can be tuned via electrochemical lithiation and thermal history.

Expression of interferon-stimulated gene 20 (ISG20), an antiviral effector protein, in glomerular endothelial cells: possible involvement of ISG20 in lupus nephritis.

BACKGROUND: In addition to regulating the antiviral response, increased expression of Toll-like receptor 3 (TLR3) in resident renal cells plays a role in developing some forms of glomerulonephritis. TLR3 activation leads to type I interferon (IFN) production, which induces the expression of IFN-stimulated genes (ISGs). However, the role of ISG20 expression in resident renal cells remains unclear. METHODS: Cultured normal human glomerular endothelial cells (GECs) were treated with polyinosinic-polycytidylic acid (poly IC), Escherichia coli lipopolysaccharide (LPS), R848, and CpG (TLR3, TLR4, TLR7, and TLR9 agonists, respectively). The mRNA levels of ISG20, CX3CL1/fractalkine, and CXCL10/IP-10 were measured by quantitative reverse transcription-polymerase chain reaction. ISG20 protein expression was assessed by Western blotting. RNA interference was used to knockdown IFN-ß and ISG20 expression. CX3CL1 protein levels were assessed by enzyme-linked immunosorbent assay. We performed immunofluorescence to examine endothelial ISG20 expression in biopsy specimens from patients with lupus nephritis (LN). RESULTS: In GECs, the expression of ISG20 mRNA and protein was increased by polyIC, not by LPS, R848, or CpG treatment. Moreover, ISG20 knockdown prevented poly IC-induced CX3CL1 expression but had no effect on CXCL10 expression. Intense endothelial ISG20 immunoreactivity was observed in biopsy specimens obtained from patients with proliferative LN. CONCLUSION: In GECs, ISG20 was regulated via TLR3 but not via TLR4, TLR7, or TLR9 signaling. Moreover, ISG20 was involved in regulating CX3CL1 production. In addition to regulating antiviral innate immunity, ISG20 may act as a mediator of CX3CL1 production, thereby inducing glomerular inflammation, particularly in patients with LN.

Crossover Sorption of C2 H2 /CO2 and C2 H6 /C2 H4 in Soft Porous Coordination Networks.

Porous sorbents are materials that are used for various applications, including storage and separation. Typically, the uptake of a single gas by a sorbent decreases with temperature, but the relative affinity for two similar gases does not change. However, in this study, we report a rare example of "crossover sorption," in which the uptake capacity and apparent affinity for two similar gases reverse at different temperatures. We synthesized two soft porous coordination polymers (PCPs), [Zn2 (L1)(L2)2 ]n (PCP-1) and [Zn2 (L1)(L3)2 ]n (PCP-2) (L1= 1,4-bis(4-pyridyl)benzene, L2=5-methyl-1,3-di(4-carboxyphenyl)benzene, and L3=5-methoxy-1,3-di(4-carboxyphenyl)benzene). These PCPs exhibits structural changes upon gas sorption and show the crossover sorption for both C2 H2 /CO2 and C2 H6 /C2 H4 , in which the apparent affinity reverse with temperature. We used in situ gas-loading single-crystal X-ray diffraction (SCXRD) analysis to reveal the guest inclusion structures of PCP-1 for C2 H2 , CO2 , C2 H6 , and C2 H4 gases at various temperatures. Interestingly, we observed three-step single-crystal to single-crystal (sc-sc) transformations with the different loading phases under these gases, providing insight into guest binding positions, nature of host-guest or guest-guest interactions, and their phase transformations upon exposure to these gases. Combining with theoretical investigation, we have fully elucidated the crossover sorption in the flexible coordination networks, which involves a reversal of apparent affinity and uptake of similar gases at different temperatures. We discovered that this behaviour can be explained by the delicate balance between guest binding and host-guest and guest-guest interactions.

Integrated Soft Porosity and Electrical Properties of Conductive-on-Insulating Metal-Organic Framework Nanocrystals.

A one-stone, two-bird method to integrate the soft porosity and electrical properties of distinct metal-organic frameworks (MOFs) into a single material involves the design of conductive-on-insulating MOF (cMOF-on-iMOF) heterostructures that allow for direct electrical control. Herein, we report the synthesis of cMOF-on-iMOF heterostructures using a seeded layer-by-layer method, in which the sorptive iMOF core is combined with chemiresistive cMOF shells. The resulting cMOF-on-iMOF heterostructures exhibit enhanced selective sorption of CO2 compared to the pristine iMOF (298 K, 1 bar, S CO 2 / H 2 ${{_{{\rm CO}{_{2}}/{\rm H}{_{2}}}}}$ from 15.4 of ZIF-7 to 43.2-152.8). This enhancement is attributed to the porous interface formed by the hybridization of both frameworks at the molecular level. Furthermore, owing to the flexible structure of the iMOF core, the cMOF-on-iMOF heterostructures with semiconductive soft porous interfaces demonstrated high flexibility in sensing and electrical "shape memory" toward acetone and CO2 . This behavior was observed through the guest-induced structural changes of the iMOF core, as revealed by the operando synchrotron grazing incidence wide-angle X-ray scattering measurements.

Crystal Structure Control of Binary and Ternary Solid-Solution Alloy Nanoparticles with a Face-Centered Cubic or Hexagonal Close-Packed Phase.

The crystal structure significantly affects the physical and chemical properties of solids. However, the crystal structure-dependent properties of alloys are rarely studied because controlling the crystal structure of an alloy at the same composition is extremely difficult. Here, for the first time, we successfully demonstrate the synthesis of binary Ru-Pt (Ru/Pt = 7:3) and Ru-Ir (Ru/Ir = 7:3) and ternary Ru-Ir-Pt (Ru/Ir/Pt = 7:1.5:1.5) solid-solution alloy nanoparticles (NPs) with well-controlled hexagonal close-packed (hcp) and face-centered cubic (fcc) phases, through the chemical reduction method. The crystal structure control is realized by precisely tunning the reduction speeds of the metal precursors. The effect of the crystal structure on the catalytic performance of solid-solution alloy NPs is systematically investigated. Impressively, all the hcp alloy NPs show superior electrocatalytic activities for the hydrogen evolution reaction in alkaline solution compared with the fcc alloy NPs. In particular, hcp-RuIrPt exhibits extremely high intrinsic (mass) activity, which is 3.1 (3.2) and 6.7 (6.9) times enhanced compared to that of fcc-RuIrPt and commercial Pt/C.