Hierarchically Structured Porous Spinels via an Epoxide-Mediated Sol–Gel Process Accompanied by Polymerization-Induced Phase Separation

Enhancing the activity and stability of catalysts is a major challenge in scientific research nowadays. Previous studies showed that the generation of an additional pore system can influence the catalytic performance of porous catalysts regarding activity, selectivity, and stability. This study focuses on the epoxide-mediated sol–gel synthesis of mixed metal oxides, NiAl₂O₄ and CoAl₂O₄, with a spinel phase structure, a hierarchical pore structure, and Ni and Co contents of 3 to 33 mol % with respect to the total metal content. The sol–gel process is accompanied by a polymerization-induced phase separation to introduce an additional pore system. The obtained mixed metal oxides were characterized with regard to pore morphology, surface area, and formation of the spinel phase. The Brunauer–Emmett–Teller surface area ranges from 74 to 138 m²·g^–1 and 25 to 94 m²·g^–1 for Ni and Co, respectively. Diameters of the phase separation-based macropores were between 500 and 2000 nm, and the mesopore diameters were 10 nm for the Ni-based system and between 20 and 25 nm for the cobalt spinels. Furthermore, Ni–Al spinels with 4, 5, and 6 mol % Ni were investigated in the dry reforming of CH₄ (DRM) with CO₂ to produce H₂ and CO. CH₄ conversions near the thermodynamic equilibrium were observed depending on the Ni content and reaction temperature. The Ni catalysts were further compared to a noble metal-containing catalyst based on a spinel system showing comparable CH₄ conversion and carbon selectivity in the DRM

Synthesis, Crystal Structure and Catalytic Behavior of Homo- and Heteronuclear Coordination Polymers [M(tdc)(bpy)] (M²⁺ = Fe²⁺, Co²⁺, Zn²⁺, Cd²⁺; tdc^2– = 2,5-thiophenedicarboxylate)

A series of isostructural 3D coordination polymers ³_∞[M­(tdc)­(bpy)] (M²⁺ = Zn²⁺, Cd²⁺, Co²⁺, Fe²⁺; tdc^2– = 2,5-thiophenedicarboxylate; bpy = 4,4′-bipyridine) was synthesized and characterized by X-ray diffraction, thermal analysis, and gas adsorption measurements. The materials show high thermal stability up to approximately 400 °C and a solvent induced phase transition. Single crystal X-ray structure determination was successfully performed for all compounds after the phase transition. In the zinc-based coordination polymer, various amounts of a second type of metal ions such as Co²⁺ or Fe²⁺ could be incorporated. Furthermore, the catalytic behavior of the homo- and heteronuclear 3D coordination polymers in an oxidation model reaction was investigated

Synthesis, Crystal Structure and Catalytic Behavior of Homo- and Heteronuclear Coordination Polymers [M(tdc)(bpy)] (M²⁺ = Fe²⁺, Co²⁺, Zn²⁺, Cd²⁺; tdc^2– = 2,5-thiophenedicarboxylate)

A series of isostructural 3D coordination polymers ³_∞[M­(tdc)­(bpy)] (M²⁺ = Zn²⁺, Cd²⁺, Co²⁺, Fe²⁺; tdc^2– = 2,5-thiophenedicarboxylate; bpy = 4,4′-bipyridine) was synthesized and characterized by X-ray diffraction, thermal analysis, and gas adsorption measurements. The materials show high thermal stability up to approximately 400 °C and a solvent induced phase transition. Single crystal X-ray structure determination was successfully performed for all compounds after the phase transition. In the zinc-based coordination polymer, various amounts of a second type of metal ions such as Co²⁺ or Fe²⁺ could be incorporated. Furthermore, the catalytic behavior of the homo- and heteronuclear 3D coordination polymers in an oxidation model reaction was investigated

Antagonists for the Orphan G‑Protein-Coupled Receptor GPR55 Based on a Coumarin Scaffold

The orphan G-protein-coupled receptor GPR55, which is activated by 1-lysophosphatidylinositol and interacts with cannabinoid (CB) receptor ligands, has been proposed as a new potential drug target for the treatment of diabetes, Parkinson’s disease, neuropathic pain, and cancer. We applied β-arrestin assays to identify 3-substituted coumarins as a novel class of antagonists and performed an extensive structure–activity relationship study for GPR55. Selectivity versus the related receptors CB₁, CB₂, and GPR18 was assessed. Among the 7-unsubstituted coumarins selective, competitive GPR55 antagonists were identified, such as 3-(2-hydroxybenzyl)-5-isopropyl-8-methyl-2<i>H</i>-chromen-2-one (<b>12</b>, PSB-SB-489, IC₅₀ = 1.77 μM, p<i>A</i>₂ = 0.547 μM). Derivatives with long alkyl chains in position 7 were potent, possibly allosteric GPR55 antagonists which showed ancillary CB receptor affinity. 7-(1,1-Dimethyloctyl)-5-hydroxy-3-(2-hydroxybenzyl)-2<i>H</i>-chromen-2-one (<b>69</b>, PSB-SB-487, IC₅₀ = 0.113 μM, <i>K</i>_B = 0.561 μM) and 7-(1,1-dimethylheptyl)-5-hydroxy-3-(2-hydroxybenzyl)-2<i>H</i>-chromen-2-one (<b>67</b>, PSB-SB-1203, IC₅₀ = 0.261 μM) were the most potent GPR55 antagonists of the present series

Network Flexibility: Control of Gate Opening in an Isostructural Series of Ag-MOFs by Linker Substitution

An isostructural series of 15 structurally flexible microporous silver metal–organic frameworks (MOFs) is presented. The compounds with a dinuclear silver core as secondary building unit (Ag₂N₄) can be obtained under solvothermal conditions from substituted triazolyl benzoate linkers and AgNO₃ or Ag₂SO₄; they exhibit 2-fold network interpenetration with <b>lvt</b> topology. Besides the crystal structures, the calculated pore size distributions of the microporous MOFs are reported. Simultaneous thermal analyses confirm the stability of the compounds up to 250 °C. Interconnected pores result in a three-dimensional pore structure. Although the porosity of the novel coordination polymers is in the range of only 20–36%, this series can be regarded as a model system for investigation of network flexibility, since the pore diameters and volumes can be gradually adjusted by the substituents of the 3-(1,2,4-triazol-4-yl)-5-benzamidobenzoates. The pore volumes of selected materials are experimentally determined by nitrogen adsorption at 77 K and carbon dioxide adsorption at room temperature. On the basis of the flexible behavior of the linkers a reversible framework transformation of the 2-fold interpenetrated network is observed. The resulting adsorption isotherms with one or two hysteresis loops are interpreted by a gate-opening process. Due to external stimuli, namely, the adsorptive pressure, the materials undergo a phase transition confirming the structural flexibility of the porous coordination polymer

Bis(carboxyphenyl)-1,2,4-triazole Based Metal–Organic Frameworks: Impact of Metal Ion Substitution on Adsorption Performance

This work presents the syntheses and comprehensive characterization of six paddlewheel based metal–organic frameworks (MOFs) with the general formula _∞³[M₂L₂] (M = Cu, Co, Zn; L = bis­(carboxyphenyl)-1,2,4-triazole) forming an isoreticular series with rutile (<b>rtl</b>) topology. These microporous materials are suitable for a systematic investigation of structure–property relationships based on the impact of the metal ion. Depending on the metal ion, the calculated porosities and the pore diameters reach from 58% to 61% and 300 to 750 pm, respectively. Simultaneous thermal analysis and temperature dependent PXRD studies reveal varying thermal behavior with stabilities up to 400 °C. In the case of syntheses with various Co²⁺/Cu²⁺, Co²⁺/Zn²⁺, and Cu²⁺/Zn²⁺ ratios, ICP-OES analyses and SEM-EDX studies confirm the formation of mixed metal MOFs and the metal ion distribution in the bulk samples as well as within the crystals. For the systematic investigation of CO₂ (298 K) and N₂ (77 K) adsorption properties, all materials were previously subjected to extraction with supercritical CO₂. Depending on the metal ion, this procedure causes different phase transitions for each compound. As a result, adsorption studies reveal varying network flexibility for these MOFs. This study is one of the rare examples demonstrating that targeted modification of gate opening pressure, hysteresis shape, and adsorbed amounts of CO₂ or N₂ are possible by choice of the metal ion. This finding is supported by adsorption studies on the mixed metal MOF _∞³[(Cu_0.48Co_0.52)₂(<i>p</i>-L)₂)], showing CO₂ adsorption/desorption characteristics of both homonuclear copper and cobalt materials, whereas N₂ does not induce gate opening of the framework, as observed for the cobalt MOF. Furthermore, catalytic studies reveal that _∞³[Cu₂(<i>p</i>-L)₂)] is a suitable catalyst for the oxidation of cyclohexene with <i>tert</i>-butylhydroperoxide (TBHP) with high conversion of the starting materials and good selectivity. Its robustness under the applied catalysis conditions leads to similar conversions in repetition measurements

Improved Isolation of Microbiologically Produced (2<i>R</i>,3<i>S</i>)‑Isocitric Acid by Adsorption on Activated Carbon and Recovery with Methanol

A new, efficient method for the isolation of (2<i>R</i>,3<i>S</i>)-isocitric acid (ICA) from its fermentation solution was developed. It is noteworthy that this method is based on selective adsorption directly from the fermentation solution on activated carbon, followed by the release of both ICA and citric acid by means of elution with methanol and their final separation by known methods. Thereby, several disadvantages were overcome: Electrodialysis is no longer necessary to remove cations such as Na⁺ from the fermentation solution. Also, several hitherto accompanying dyestuffs were not observed with this method. Furthermore, removal of water by distillation is expendable. Eventually, the new crude product is of a quality that also avoids the use of a tedious slide vane rotary vacuum pump distillation of the trimethyl esters of both acids, which hitherto was the basis for the separation of ICA. In summary, the new method distinctly spares energy as well as time

Co-Registered Molecular Logic Gate with a CO-Releasing Molecule Triggered by Light and Peroxide

Co-registered molecular logic gates combine two different inputs and outputs, such as light and matter. We introduce a biocompatible CO-releasing molecule (CORM, <b>A</b>) as Mn­(I) tricarbonyl complex with the ligand 5-(dimethylamino)-<i>N</i>, <i>N</i>-bis­(pyridin-2-ylmethyl) naphthalene-1-sulfonamide (<b>L</b>). CO release is chaperoned by turn-on fluorescence and can be triggered by light (405 nm) as well as with hydrogen peroxide in aqueous phosphate buffer. Complex <b>A</b> behaves as a logic “OR” gate via co-registering the inputs of irradiation (light) and peroxide (matter) into the concomitant outputs fluorescence (light) and CO (matter). Cell viability assays confirm the low toxicity of <b>A</b> toward different human cell lines. The CORM has been used to track the inclusion of <b>A</b> into cancer cells

Platinum Group Metal Phosphides as Heterogeneous Catalysts for the Gas-Phase Hydroformylation of Small Olefins

A method for the synthesis of highly crystalline Rh₂P nanoparticles on SiO₂ support materials and their use as truly heterogeneous single-site catalysts for the hydroformylation of ethylene and propylene is presented. The supported Rh₂P nanoparticles were investigated by transmission electron microscopy and by infrared analysis of adsorbed CO. The influence of feed gas composition and reaction temperature on the activity and selectivity in the hydroformylation reaction was evaluated by using high throughput experimentation as an enabling element; core findings were that beneficial effects on the selectivity were observed at high CO partial pressures and after addition of water to the feed gas. The analytical and performance data of the materials gave evidence that high temperature reduction leading to highly crystalline Rh₂P nanoparticles is key to achieving active, selective, and long-term stable catalysts