Solvothermal synthesis and structural characterization of a new one-dimensional metal-organic framework [Co(Atibdc)(Dpa)] n (H2Tibdc = 5-amino-2,4,6-triiodoisophthalic acid, Dpa = 2,2′-dipyridylamine)

The title cobalt(II) coordination polymer, [Co(Atibdc)(Dpa)] _n (I) (H₂Atibdc = 5-amino-2,4,6-triiodoisophthalic acid, Dpa = 2,2′-dipyridylanine), has been synthesized under solvothermal conditions and characterized by elemental analysis, IR, and X-ray crystallography structural analysis. Complex I exhibits a one-dimensional chain structure in which 5-amino-2,4,6-triiodoisophthalate as a bridging ligand interconnects adjacent two Co(II) centers to form a helical chain structure. The asymmetric unit includes one Co(II) center, one atibdc ligand, and one Dpa ligand. Each Co(II) center is five-coordinated and surrounded by two nitrogen atoms and three oxygen atoms from one Dpa ligand and two individual Atibdc ligands, leading to distorted trigonal bipyramid geometry. Adjacent chains are further linked through hydrogen bonds, C-H-π and π-π stacking interactions to form a three-dimensional supramolecular framework.     

Silver and gold icosahedra: one-pot water-based synthesis and their superior performance in the electrocatalysis for oxygen reduction reactions in alkaline media

Much effort has gone into generating polyhedral noble metal nanostructures because of their superior electrocatalytic activities for fuel cells. Herein, we report uniform, high-yield icosahedral silver and gold nanoparticles by using a facile one-pot, seedless, water-based approach that incorporates polyvinyl pyrrolidone and ammonia. Electrocatalysis of the oxygen-reduction reaction was carried out in alkaline media to evaluate the performance of the icosahedral nanoparticles. They showed excellent stability and much higher electrocatalytic activity than the spherelike nanoparticles; they display a positive shift in reduction peak potential for O(2) of 0.14 and 0.05 V, while the reduction peak currents of the silver and gold icosahedra are 1.5- and 1.6-fold, respectively, better than the spherelike nanoparticles. More importantly, the icosahedral nanoparticles display electrocatalytic activities comparable with commercial Pt/C electrocatalysts. The facile preparation of icosahedral silver and gold nanoparticles and their superior performance in the oxygen reduction reaction render them attractive replacements for Pt as cathode electrocatalysts in alkaline fuel cells.     

A simple CdS nanoparticles cascading approach for boosting N3 dye/ZnO nanoplates DSSCs overall performance

Enhanced photosensitization in presence of CdS nanoparticles is achieved in electrochemically deposited ZnO nanoplates and N3 loaded dye-sensitized solar cells. Chemically embedded CdS nanoparticles act as a sandwiching layer between ZnO nanoplates and dye molecules by overcoming current limiting serious Zn²⁺/dye insulating complex formation and CdS photo-corrosion issues. The X-ray diffraction and the scanning electron microscopy confirm the ZnO with vertically aligned nanoplates, perpendicular to the substrate surface. Amorphous CdS is monitored using electron dispersive X-ray analysis. The low and high resolution transmission electron microscope images confirm the presence of CdS nanoparticles over ZnO nanoplates which later is supported by an increase in optical absorbance and shift in band edge. About 400% increase in solar conversion efficiency with this cascade arrangement is achieved when compared with without CdS which could be fascinating while designing solid state solar cells in presence of suitable p-type layer.     

Mechanistic Insights into the Ni‐Catalyzed Reductive Carboxylation of C−O Bonds in Aromatic Esters with CO2: Understanding Remarkable Ligand and Traceless‐Directing‐Group Effects

The mechanism of the Ni⁰‐catalyzed reductive carboxylation reaction of C(sp²)?O and C(sp³)?O bonds in aromatic esters with CO₂ to access valuable carboxylic acids was comprehensively studied by using DFT calculations. Computational results revealed that this transformation was composed of several key steps: C?O bond cleavage, reductive elimination, and/or CO₂ insertion. Of these steps, C?O bond cleavage was found to be rate‐determining, and it occurred through either oxidative addition to form a Ni^II intermediate, or a radical pathway that involved a bimetallic species to generate two Ni^I species through homolytic dissociation of the C?O bond. DFT calculations revealed that the oxidative addition step was preferred in the reductive carboxylation reactions of C(sp²)?O and C(sp³)?O bonds in substrates with extended π systems. In contrast, oxidative addition was highly disfavored when traceless directing groups were involved in the reductive coupling of substrates without extended π systems. In such cases, the presence of traceless directing groups allowed for docking of a second Ni⁰ catalyst, and the reactions proceed through a bimetallic radical pathway, rather than through concerted oxidative addition, to afford two Ni^I species both kinetically and thermodynamically. These theoretical mechanistic insights into the reductive carboxylation reactions of C?O bonds were also employed to investigate several experimentally observed phenomena, including ligand‐dependent reactivity and site‐selectivity.     

Mechanism of the Enhanced Electrochemical Properties of LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> Cathode Materials by a Pre-Sintering Process

α-NaFeO₂ layered LiNi_1/3Co_1/3Mn_1/3O₂ cathode materials were synthesized by mechanical milling accompanied by the solid phase sintering. The sample exhibited a good crystallinity and layered structure while sintered at 900°C, which can be further improved by adding a pre-sintering process at 500°C before high temperature sintering. The sample with a pre-sintering process presents an average particle size about 0.6 μm, and a hexagonal crystalline structure. The optimally fabricated sample showed a first charge capacity of 210.2 mA h/g, discharge capacity of 171.2 mA h/g with a current rate of 0.2 C within the voltage range of 2.7~4.5 V. With increasing the current rate to 1 C, the charge–discharge capacity faded quickly during the cycling process, which can be partially recovered while operated at a low current rate. However, the capacity fading at a current rate of 2 C was largely irreversible. The evolution of the surface chemical states was evaluated using X-ray photoelectron spectroscopy on the charged and discharged samples to understand the high rate capacity fading.     

Substituent effects on the redox potentials of dihydroxybenzenes: theoretical and experimental study

The redox reactions of p-hydroquinone and pyrocatechol undergo a two-proton-two-electron process in aqueous solution. We calculated their redox potentials at the B3LYP/6-311+G(d,p) level, and verified the values by employing cyclic voltammetry experiments. Then we selected seven substituent groups (–F, –Cl, –OH, –COOH, –CN, –NH₂, and –NO₂ groups) to systematically investigate the substituent effect, including the sort, position, and number of the substituent, on the redox potentials of p-hydroquinone and pyrocatechol. The calculated results show that –NH₂ and –OH groups can decrease the redox potentials, while –F, –Cl, –COOH, –CN, and –NO₂ groups increase the potential values of p-hydroquinone and pyrocatechol. The calculations can accurately predict the substituent effects on the redox potentials of pyrocatechol and p-hydroquinone. We would expect that the accurate calculation results for the model systems could be applied in the prediction of electrode potentials of other molecules.     

Design,synthesis, and insecticidal activities of novel diamide derivatives with alpha-amino acid subunits

A series of diamide derivatives containing α-amino acids were designed and synthesized. These compounds were evaluated for their insecticidal activities against Plutella xylostella, Mythimna separate, Myzus persicae, and Tetranychus cinnabarinus. Most of the title compounds containing an l -phenylglycine skeleton were endowed with good activities at the concentration of 500 mg·L⁻¹. Compounds ( R)-A6 showed a potential value for further optimization as an insecticidal lead with the LC₅₀ value of 86.8 mg·L⁻¹.     

Design,Synthesis, and Evaluation of Novel L-Pyroglutamic Acid Derivatives as Potent Antifungal Agents

Chemistry of Natural Compounds - A series of novel L-pyroglutamate containing 1,2,3-triazole ring substructures was synthesized and characterized by adopting an appropriate synthetic scheme. The...     

Group 4 complexes derived from o-carborane: synthesis, structures and ethylene polymerization properties

Nine thermally stable complexes (η⁵-Cp*)[η⁵-(C₅H₄)CMe₂CB₁₀H₁₀CR]MCl₂ (R=H and Me) and (η⁵-Cp*)[η⁵; η¹-(C₅H₄)CMe₂(CB₁₀H₁₀C)]MCl have been prepared via metathesis reactions of Cp*MCl₃ (M=Ti, Zr and Hf, Cp*=pentamethylcyclopentadienyl) with monolithium salts of (C₅H₅)CMe₂(CB₁₀H₁₀CR) (R=H and Me) and with dilithium salt of (C₅H₅)CMe₂(CB₁₀H₁₀CH), respectively. These compounds have been fully characterized by various spectroscopic methods and elemental analyses. All of the compounds except (η⁵-Cp*)[η⁵-(C₅H₄)CMe₂CB₁₀H₁₀CMe]HfCl₂ were additionally characterized by a single crystal X-ray diffraction study, establishing their monomeric bent metallocene structural feature with carborane acting as a substituent or an ancillary ligand. The titanium and zirconium complexes produce high-density polyethylenes with the activity range of about 10³-10⁴ g PE per mol of M bar h in the presence of modified methylaluminoxane cocatalyst.     

LIGHT-INDUCIBLE ABSORBANCE CHANGES AND VANADATE-SENSITIVE ATPase ACTIVITY ASSOCIATED WITH THE PRESUMPTIVE PLASMA MEMBRANE FRACTION FROM CAULIFLOWER INFLORESCENCES

Sucrose density gradient centrifugation of a microsomal membrane fraction of cauliflower inflorescences showed a strong correlation between a blue light mediated cytochrome b reduction (LIAC) and an ion stimulated nitrate-insensitive but a vanadate-sensitive ATPase activity at 38-40% sucrose. LIAC activity and vanadate-sensitive ATPase might be assigned to the same type of membrane different from ER, Golgi, tonoplast and mitochondria. The Mg²⁺-dependent ATP-hydrolytic activity obtained after purification of the microsomal fraction on an aqueous polymer two phase system was partially characterized. Temperature optimum (40°C), pH optimum (pH 7.0), vanadate inhibition (I₅₀ at 20 μ M ), substrate kinetics ( K _m= 1.37 m M Mg.ATP) and inhibitor studies all point to the presence of the frequently described plasma membrane ATPase. Potassium and Na⁺ stimulated the enzyme activity (20-40%). In general our data arc strongly in favour of the hypothesis that LIAC activity is localized on the plant plasma membrane. The cytochrome b involved in the light reaction has a midpoint potential near +150 mV. This cytochrome which has been previously shown in a cauliflower microsomal fraction is a constituent of the plasma membrane.