Synthesis of aromatic liquid crystals with asymmetric diester based on rod-like multi-ring system by two-step esterification method

<p>A novel method of two-step esterifications was developed to synthesize compounds with asymmetric double ester groups. By using this method, six rod-like double ester compounds were prepared with <i>p</i>-hydroxy benzaldehyde, <i>p</i>-hydroxy benzoic acid bicyclohexyl carboxylic acid, cyclohexyl benzoic acid and biphenyl carboxylic acid substituted by <i>n</i>-propyl and <i>n</i>-pentyl as main reactants. The structures and properties of target compounds were confirmed by IR, MS, ¹H NMR, elemental analysis, differential scanning calorimetry (DSC) and hot stage polarizing optical microscope (HS-POM). Typical yields of the target molecules were more than 70%. All the molecules have mesophases with the textures of nematic type, indicating a rod-like molecule with a longer rigid skeleton can keep its mesophases. There was no clearing point observed for any of the derivatives before they decomposed so that the temperature ranges of the mesophases could not be determined. The energy differences between frontier molecular orbitals (HOMO-LUMO) (<i>E</i>_g) of the compounds were calculated by cyclic voltammetry (CV). The terminal ring system has an obvious influence on the energy levels and the energy gaps (<i>E</i>_g).</p

Concave Cubic Pt–Sm Alloy Nanocrystals with High-Index Facets and Enhanced Electrocatalytic Ethanol Oxidation

Concave cubic Pt90Sm10 alloy nanocrystals (NCs) enclosed by high-index {310} facets were constructed by a facile electrochemical method in a choline chloride-urea (ChCl-U)-based deep eutectic solvent (DES). It was demonstrated that the concave cubic Pt90Sm10 alloy NCs with high-index {310} facets exhibit higher electrocatalytic activity and stability toward ethanol electrooxidation than those of pure concave cubic Pt NCs and commercial Pt/C catalysts because of the synergy of steric and electronic effects. Density functional theory (DFT) calculations indicated that Sm alloyed Pt{310} can significantly decrease the overall ethanol oxidation reaction barriers

Synthetic Strategy for Incorporating Carboxylate Ligands into Coordination Polymers under a Solvent-Free Reaction

Solvent-free synthesis is a powerful approach for obtaining elusive crystal structures of coordination polymers (CPs) and metal–organic frameworks (MOFs). However, carboxylic acids were hardly employed in solvent-free synthesis due to their high melting points (Tm’s). To employ carboxylates for the construction of CP/MOFs via solvent-free synthesis, we propose utilizing the melt state of organic cocrystals containing carboxylates as a reaction media. We prepared three organic cocrystals consisting of 1,4-benzenedicarboxylate (1,4-bdc2–) and azolates (imidazole, 2-methylimidazole, and 2-ethylimidazole). All of them have Tm’s below 200 °C, which is far lower than the Tm of 1,4-H2bdc (402 °C) studied by differential scanning calorimetry (DSC). The solvent-free reaction of corresponding azoles, 1,4-bdc2–, and ferrocene (Tm = 173 °C) in a sealed tube reactor provided new Fe2+-based CP structures constructed from 1,4-bdc2– and corresponding azolates with high purity

A Single-Crystal Open-Capsule Metal–Organic Framework

Micro-/nanocapsules have received substantial attention due to various potential applications for storage, catalysis, and drug delivery. However, their conventional enclosed non-/polycrystalline walls pose huge obstacles for rapid loading and mass diffusion. Here, we present a new single-crystal capsular-MOF with openings on the wall, which is carefully designed at the molecular level and constructed from a crystal-structure transformation. This rare open-capsule MOF can easily load the largest amounts of sulfur and iodine among known MOFs. In addition, derived from capsular-MOF and melamine through pyrolysis–phosphidation, we fabricated a nitrogen-doped capsular carbon-based framework with iron–nickel phosphide nanoparticles immobilized on capsular carbons interconnected by plentiful carbon nanotubes. Benefiting from synergistic effects between the carbon framework and highly surface-exposed phosphide sites, the material exhibits efficient multifunctional electrocatalysis for oxygen evolution, hydrogen evolution, and oxygen reduction, achieving well-qualified assemblies of an overall water splitting (low potential of 1.59 V at 10 mA·cm–2) and a rechargeable Zn–air battery (high peak power density of 250 mW·cm–2 and excellent stability for 500 h), which afford remarkably practical prospects over previously known electrocatalysts

A Single-Crystal Open-Capsule Metal–Organic Framework

Micro-/nanocapsules have received substantial attention due to various potential applications for storage, catalysis, and drug delivery. However, their conventional enclosed non-/polycrystalline walls pose huge obstacles for rapid loading and mass diffusion. Here, we present a new single-crystal capsular-MOF with openings on the wall, which is carefully designed at the molecular level and constructed from a crystal-structure transformation. This rare open-capsule MOF can easily load the largest amounts of sulfur and iodine among known MOFs. In addition, derived from capsular-MOF and melamine through pyrolysis–phosphidation, we fabricated a nitrogen-doped capsular carbon-based framework with iron–nickel phosphide nanoparticles immobilized on capsular carbons interconnected by plentiful carbon nanotubes. Benefiting from synergistic effects between the carbon framework and highly surface-exposed phosphide sites, the material exhibits efficient multifunctional electrocatalysis for oxygen evolution, hydrogen evolution, and oxygen reduction, achieving well-qualified assemblies of an overall water splitting (low potential of 1.59 V at 10 mA·cm–2) and a rechargeable Zn–air battery (high peak power density of 250 mW·cm–2 and excellent stability for 500 h), which afford remarkably practical prospects over previously known electrocatalysts

Boosting Electrocatalytic Hydrazine Oxidation Reaction on High-Index Faceted Au Concave Trioctahedral Nanocrystals

High-index faceted Au nanocrystals are explored as an efficient catalyst in the electrocatalytic hydrazine oxidation reaction (HzOR). Theoretical calculations reveal that the Au(551) surface is more active than the Au(111) surface toward HzOR with lower overpotentials, and the step atoms on the Au(551) surface serve as high-active sites to enhance HzOR. Experimentally, the as-prepared concave trioctahedral Au nanocrystals (TOH Au NCs) enclosed by {551} high-index facets (HIFs) exhibit excellent electrocatalytic performance of HzOR under both alkaline and acidic conditions. Particularly, the concave TOH Au NCs achieve very high activities of 272.3 mA cm–2 (mass activity, 1472.6 mA mg–1) and 329.5 mA cm–2 (mass activity, 1785.9 mA mg–1) for HzOR in 0.1 M HClO4 + 10 mM N2H4 and 0.1 M NaOH + 10 mM N2H4 solutions, respectively, which are superior to that of a commercial Au spheres catalyst. This study provides a new insight into electrocatalytic HzOR over Au high-index facets and presents a rational design and synthesis of high-performance electrocatalysts for HzOR

Concentration-Mediated Shape Evolution of Palladium Nanocrystals and Their Structure-Electrocatalytic Functionality

We reported a new insight into electrochemical shape evolution of Pd nanocrystals by controlling the concentration of Pd precursor, while the lower (EL) and upper (EU) potential limits of the square-wave potential were optimized at −0.8 and 0 V, respectively. It was found that the ratio (R) of the growth rate in the ⟨100⟩ to that of the ⟨111⟩ on a crystal increased with the concentration of PdCl2 getting higher in the reaction, leading to the shape transformation of Pd polyhedron from cubes to truncated octahedra, and finally to octahedra. The electrooxidation performances of CO and formic acid over the as-synthesized Pd polyhedrons were in the order of octahedra < truncated octahedra < cubes, indicating that the electrocatalytic activities of Pd polyhedrons were highly sensitive to the surface structure

Unique Proton Dynamics in an Efficient MOF-Based Proton Conductor

Recently, research on metal–organic frameworks (MOFs) serving as a new type of proton conductive material has resulted in many exciting achievements. However, direct observation of a well-established proton-transfer mechanism still remains challenging in MOFs and other crystalline compounds, let alone other conductive materials. Herein we report the solvothermal synthesis of a new proton-conducting MOF, (Me2NH2)­[Eu­(L)] (H4L = 5-(phosphonomethyl)­isophthalic acid). The compound consists of a layered anionic framework [Eu­(L)]− and interlayer-embedded counter cations (Me2NH2)+, which interact with adjacent uncoordinated O atoms of phosphonate groups to form strongly (N–H···O) hydrogen-bonded chains aligned parallel to the c-axis. Facile proton transfer along these chains endows the compound with single-crystal anhydrous conductivity of 1.25 × 10–3 S·cm–1 at 150 °C, and water-assisted proton conductivity for a compacted pellet of microcrystalline crystals attains 3.76 × 10–3 S·cm–1 at 100 °C and 98% relative humidity (RH). Proton dynamics (vibrating and transfer) within N–H···O chains of the compound are directly observed using a combination of anisotropic conductivity measurements and control experiments using large single-crystals and pelletized samples, in situ variable-temperature characterization techniques including powder X-ray diffraction (PXRD), single-crystal X-ray diffraction (SCXRD), diffuse reflectance infrared Fourier transform spectrum (DRIFTS), and variable-temperature photoluminescence. In particular, a scarce single-crystal to single-crystal (SCSC) transformation accompanied by proton transfer between an anionic structure (Me2NH2)­[Eu­(L)] and an identical neutral framework [Eu­(HL)] has been identified

Dracotangusions A and B, two new sesquiterpenes from <i>Dracocephalum tanguticum</i> Maxim. with anti-inflammatory activity

Two new guaiane sesquiterpenoids were isolated from the dried aerial parts of Dracocephalum tanguticum Maxim., named as dracotangusions A (1) and B (2), together with four known sesquiterpenoids, which were identified as Curcumenone (3), (4Z,7Z,9Z)-11-Hydroxy-4,7,9-germacratriene-1,6-dione (4), Kobusone (5), and (1S,10S), (4S, 5S)—(+)-germacrone-1(10)-4-diepoxide (6). The structures of isolates were determined by UV, IR, HR-ESI-MS, and NMR analysis. What is noteworthy is that four known sesquiterpenoids were isolated for the first time from the genus of Dracocephalum L. All compounds inhibited the extremely significant difference (p < 0.01) in anti-inflammatory activity, suggesting that these compounds may be promising candidates as an anti-inflammatory agent.</p