Utilization of Sc3N@C80 in long-range charge transfer reactions

Electron accepting Sc(3)N@C(80) promotes long-range charge transfer events evolving from photoexcited metalloporphyrins to afford radical ion pair states with lifetimes in the range of μs.     

Bimetallic Pd/Sn-based Nanoparticles and their Catalytic Properties in the Semihydrogenation of Diphenylacetylene

Multimetallic nanoparticles often enhance the catalytic performance of their monometallic counterparts by increasing reaction rates, catalyst selectivity, and/or stability. A prerequisite for understanding structure- and composition-associated properties, however, is the careful design of multimetallic nanoparticles with various structures and compositions. Here, bimetallic Pd/Sn-based nanoparticles are prepared with a tunable composition and structure exploiting ionic liquids (ILs) as reaction medium (i. e., methyltrioctylammonium bis(trifluoromethylsulfonyl)imide). The nanoparticles are obtained in a one-pot synthetic procedure by reducing the metal salt precursors with triethylborohydride in the IL. The results show that the reaction parameters, in particular the nature and ratio of the Pd²⁺/Sn²⁺ precursors as well as the reaction temperature, influence NP formation and composition. X-ray diffraction with Rietveld analysis and transmission electron microscopy are employed to determine NP size and phase composition. Under optimized reaction conditions Pd₂Sn or PdSn nanocrystals are formed as single-phase products after introducing an additional annealing step at 200 °C. Nanocrystals with intermetallic composition reveal enhanced catalytic properties in the semihydrogenation of diphenylacetylene which was used as a model reaction.     

Entangling strings of neutral atoms in 1D atomic pipeline structures

We study a string of neutral atoms with nearest neighbor interaction in a 1D beam splitter configuration, where the longitudinal motion is controlled by a moving optical lattice potential. The dynamics of the atoms crossing the beam splitter maps to a 1D spin model with controllable time dependent parameters, which allows the creation of maximally entangled states of atoms by crossing a quantum phase transition. Furthermore, we show that this system realizes protected quantum memory, and we discuss the implementation of one- and two-qubit gates in this setup.     

On the shape of bottle-brush macromolecules: systematic variation of architectural parameters

We measured the form factor of bottle-brush macromolecules under good solvent conditions with small-angle neutron scattering and static light scattering. The systems under investigation are brushes, synthesized via the grafting-from route, built from a poly(alkyl methacrylate) backbone to which poly(n-butyl acrylate) side chains are densely grafted. The aim of our work is to study how the systematic variation of structural parameters such as the side chain length and backbone length change the conformation of the polymer brushes in solution. All spectra can be consistently described by a model, considering the bottle-brush polymers as flexible rods with internal density fluctuations. Parameters discussed are (1) the contour length per main chain monomer l(b), (2) the fractal dimension of the side chains Ds, as well as (3) the fractal dimension D, and (4) the Kuhn length lambdak of the overall brush. l(b)=0.253+/-0.008 nm is found to be independent of the side chain length and equal to the value found for the bare main chain, indicating a strongly stretched conformation for the backbone due to the presence of the side chains. The fractal dimension of the side chains is determined to be Ds=1.75+/-0.07 which is very close to the value of 10.588 approximately 1.70 expected for a three-dimensional self-avoiding random walk (3D-SAW) under good solvent conditions. On larger length scales the overall brush appears to be a 3D-SAW itself (D=1.64+/-0.08) with a Kuhn-step length of lambdak=70+/-4 nm. The value is independent of the side chain length and 46 times larger than the Kuhn length of the bare backbone (lambdak=1.8+/-0.2 nm). The ratio of Kuhn length to brush diameter lambda(k)d>or=20 determines whether lyotropic behavior can be expected or not. Since longer side chains do not lead to more persistent structures, lambda(k)d decreases from 8 to 4 with increasing side chain length and lyotropic behavior becomes unlikely.     

Ba6Ge25: low-temperature Ge-Ge bond breaking during temperature-induced structure transformation

In order to find the optimal conditions for sample preparation of the binary germanide Ba₆Ge₂₅, the germanium-rich part of the Ba-Ge phase diagram was redetermined by means of metallography, X-ray powder diffraction and differential thermal analysis. The temperature behavior of cubic Ba₆Ge₂₅ was investigated both on polycrystalline samples and single crystals. The temperature dependence of the lattice parameter exhibits two anomalies at about 180 and 230 K, respectively, which are caused by a structure transformation in two steps with hysteresis. Powder (T=10-295 K) and single-crystal (T=95-295 K) X-ray diffraction studies confirm that the symmetry of Ba₆Ge₂₅ (space group P4₁32) remains unchanged within the entire temperature range. A reconstructive behavior of the structural transformation is observed, involving Ge-Ge bond breaking and barium cation displacements. Some Ge4 type atoms (∼28%) are so significantly displaced during cooling that Ge4-Ge6 bonds break and new three-bonded (3b)Ge⁻ species (electron acceptors) are formed. Consequently, the number of charge carriers is reduced, affecting the physical properties. The reversible bond breaking involved in this process is a typical characteristic of a solid-state chemical reaction.     

Supported Intermetallic PdZn Nanoparticles as Bifunctional Catalysts for the Direct Synthesis of Dimethyl Ether from CO‐Rich Synthesis Gas

The single‐step syngas‐to‐dimethyl ether (STD) process entails economic and technical advantages over the current industrial two‐step process. Pd/ZnO‐based catalysts have recently emerged as interesting alternatives to currently used Cu/ZnO/Al₂O₃ catalysts, but the nature of the active site(s), the reaction mechanism, and the role of Pd and ZnO in the solid catalyst are not well established. Now, Zn‐stabilized Pd colloids with a size of 2 nm served as the key building blocks for the methanol active component in bifunctional Pd/ZnO‐γ‐Al₂O₃ catalysts. The catalysts were characterized by combining high‐pressure operando X‐ray absorption spectroscopy and DFT calculations. The enhanced stability, longevity, and high dimethyl ether selectivity observed makes Pd/ZnO‐γ‐Al₂O₃ an effective alternative system for the STD process compared to Cu/ZnO/γ‐Al₂O₃.     

A Boron‐Fluorinated Tris(pyrazolyl)borate Ligand (FTp*) and Its Mono‐ and Dinuclear Copper Complexes [Cu(FTp*)2] and [Cu2(FTp*)2]: Synthesis,Structures, and DFT Calculations

Reaction of [Si(3,5‐Me₂pz)₄] ( 1 ) with [Cu(MeCN)₄][BF₄] ( 2 ) gave the mono‐ and dinuclear copper complexes [Cu₂(^FTp*)₂] ( 3 ) and [Cu(^FTp*)₂] ( 4 ). Both complexes contain the so‐far unprecedented boron‐fluorinated ^FTp* ligand ([FB(3,5‐Me₂pz)₃]^? with pz=pyrazolyl) originating from 1 , acting as a pyrazolyl transfer reagent, and the [BF₄]^? counter anion of 2 , serving as the source of the {BF} entity. The solid‐state structures as well as the NMR and EPR spectroscopic characteristics of the complexes were elaborated. Pulsed gradient spin echo (PGSE) experiments revealed that 3 retains (almost entirely) its dimeric structure in benzene, whereas dimer cleavage and formation of acetonitrile adducts, presumably [Cu(^FTp*)(MeCN)], is observed in acetonitrile. The short Cu???Cu distance of 269.16 pm in the solid‐state is predicted by DFT calculations to be dictated by dispersion interactions between all atoms in the complex (the Cu?Cu dispersion contribution itself is only very small). As revealed by cyclic voltammetry studies, 3 shows an irreversible (almost quasi‐reversible at higher scan rates) oxidation process centred at E^pa=?0.23 V (E⁰_1/2=?0.27 V) (vs. Fc/Fc⁺). Oxidation reactions on a preparative scale with one equivalent of the ferrocenium salt [Fc][BF₄] (very slow reaction) or air (fast reaction) furnished blue crystals of the mononuclear copper(II) complex [Cu(^FTp*)₂] ( 4 ). As expected for a Jahn–Teller‐active system, the coordination sphere around copper(II) is strongly distorted towards a stretched octahedron, in accordance with EPR spectroscopic findings.     

Simultaneous quantitation of Aspergillus flavus/A. parasiticus and aflatoxins in peanuts

A method was developed for simultaneous quantitation of Aspergillus flavus/A. parasiticus and aflatoxins in peanuts. Peanut samples were ground with an equal weight of water in a vertical cutter mixer to produce a slurry. Separate subsamples were taken for dilution-plating to determine total colony forming units (CFU)/g of A. flavus/A. parasiticus and for liquid chromatographic analysis to determine aflatoxin concentrations. Dry-grinding peanuts for homogenization of aflatoxins produced high temperatures that killed most of the A. flavus/A. parasiticus propagules. Addition of water to produce a slurry kept the temperature from rising above levels that killed the fungi. A 7 min grind time provided optimal homogenization for both the fungi and aflatoxins, so long as the temperature of the slurry did not exceed 45 degrees C. In the analysis of 60 shelled peanut samples, total aflatoxin concentrations ranged from 0 to 10,000 ng/g and total A. flavus/A. parasiticus ranged from 1.4 x 10(3) to 3.2 x 10(6) CFU/g. Regression analysis showed a significant positive correlation (p < 0.0001) between the quantities of A. flavus/A. parasiticus and aflatoxin (R2 = 0.82).