NMR studies of carbon dioxide and methane self-diffusion in ZIF-8 at elevated gas pressures

Self-diffusion measurements with methane and carbon dioxide adsorbed in the Zeolitic Imidazolate Framework-8 (ZIF-8) were performed by ¹H and ¹³C pulsed field gradient nuclear magnetic resonance (PFG NMR). The experiments were conducted at 298 K and variable pressures of 7 to 15 bar in the gas phase above the ZIF-8 bed. Via known adsorption isotherms these pressures were converted to loadings of the adsorbed molecules. The self-diffusion coefficients of carbon dioxide measured by PFG NMR are found to be independent of loading. They are in good agreement with results from molecular dynamic (MD) simulations and resume the trend previously found by IR microscopy at lower loadings. Methane diffuses in ZIF-8 only slightly slower than carbon dioxide. Its experimentally obtained self-diffusion coefficients are about a factor of two smaller than the corresponding values determined by MD simulations using flexible frameworks.     

Effect of pH on the photophysical and redox properties of a ruthenium(II) mixed chelate derived from imidazole-4,5-dicarboxylic acid and 2,2'-bipyridine: an experimental and theoretical investigation

Combined experimental and DFT-TD-DFT computational studies were utilized to investigate the structural and electronic properties of mixed-ligand monometallic ruthenium(II) complexes of compositions [(bpy)(2)Ru(H(2)Imdc)](+) (1(+)), its N-H deprotonated form [(bpy)(2)Ru(HImdc)] (1), and COOH deprotonated form [(bpy)(2)Ru(Imdc)](-) (1(-)), where H(3)Imdc = imidazole-4,5-dicarboxylic acid and bpy = 2,2'-bipyridine. The optimized geometrical parameters for the complexes computed both in the gas phase and in solution are reported and compared with the previously reported X-ray data. The influence of pH on the absorption, emission, and redox properties of [(bpy)(2)Ru(H(2)Imdc)](+) (1(+)) has been thoroughly investigated. The absorption titration data were used to determine the ground state pK values, whereas the luminescence data were utilized for the determination of excited state acid dissociation constants. The proton-coupled redox activity of 1(+) has been studied over the pH range 2-12 in acetonitrile-water (3:2). From the E(1/2) versus pH profile, the equilibrium constants of the variously deprotonated complex species in Ru(II) and Ru(III) oxidation states have been determined. As compared to the protonated complex (1(+)), which undergoes reversible oxidation at 0.96 V (vs Ag/AgCl) in acetonitrile, the redox potential of the fully deprotonated complex (1(-)) is shifted to a much lower value, viz., 0.52 V. Density functional theory (DFT) and time-dependent DFT (TD-DFT) study provides insight into the nature of the ground and excited states with resulting detailed assignments of the orbitals involved in absorption and emission transitions. In particular, the red-shifts of the absorption and emission bands and the cathodic shift in the oxidation potential of 1(+) compared to 1 and 1(-) are also reproduced by our calculations.     

Eigensolutions of cyclopolyacene graphs

A graph of {X, Y}-cyclopolyacene with n of hexagonal rings has been presented that contains four orbits, of which orbits 1 and 4 are occupied by the X-type of vertex and orbits 2 and 4 are occupied by the Y-type, or vice versa. Eigensolutions for such a graph have been derived in analytical form through the use of rotational symmetry followed by a plane of symmetry. Varying X ( = C, N, B, …) and Y ( = C, N, B, …) several types of cyclopolyacene graph may be obtained. Eigenvalue-expressions for such systems containing C, N and B have been shown in analytical form and their total π-electron energies with 2–6 hexagonal rings have been calculated with the help of the expressions developed.     

Measurement of improved pressure dependence of superconducting transition temperature

We describe a technique for making electrical transport measurements in a diamond anvil cell at liquid helium temperature having in situ pressure measurement option, permitting accurate pressure determination at any low temperature during the resistance measurement scan. In general, for four-probe resistivity measurements on a polycrystalline sample, four fine gold wires are kept in contact with the sample with the help of the compression from the soft solid (usually alkali halides such as NaCl, KCl, etc.) acting as a pressure-transmitting medium. The actual pressure on the sample is underestimated if not measured from a ruby sphere placed adjacent to the sample and at that very low temperature. Here, we demonstrate the technique with a quasi-four-probe resistance measurement on an Fe-based superconductor in the temperature range 1.2–300 K and pressures up to 8 GPa to find an improved pressure dependence of the superconducting transition temperature.     

Observation of Griffiths phase in antiferromagnetic La(0.32)Eu(0.68)MnO3

We report the Griffiths phase (GP) scenario for isovalent doping in antiferromagnetic La(0.32)Eu(0.68)MnO(3). Rietveld refinement of structural data displays strong crystal structural distortion. The dc and ac magnetic studies nicely demonstrate unambiguous aspects of robust GP. The presence of ferromagnetically correlated spin clusters is found above the transition temperature, T(N). The disorder-driven phase inhomogeneity is correlated to strong structural distortion, giving rise to the GP. This is an unique example in manganite where double exchange interaction does not play any role for the observed phenomenon.     

Universality of the plastic instability in strained amorphous solids

By comparing the response to external strains in metallic glasses and in Lennard-Jones glasses we find a quantitative universality of the fundamental plastic instabilities in the athermal, quasistatic limit. Microscopically these two types of glasses are as different as one can imagine, the latter being determined by binary interactions, whereas the former is determined by multiple interactions due to the effect of the electron gas that cannot be disregarded. In spite of this enormous difference the plastic instability is the same saddle-node bifurcation. As a result, the statistics of stress and energy drops in the elastoplastic steady state are universal, sharing the same system-size exponents.     

Convergecast tree management from arbitrary node failure in sensor network

The efficiency and reliability of convergecast in sensor network depends on the correct and efficient accumulation of data to the sink. A tree, rooted at the sink, that utilizes sensor resources properly is an ideal topology for data gathering. Resource constrained sensor nodes are highly prone to sudden crash. So the application demands a quick and efficient repairing of the tree when a node dies. The proposed scheme builds a data gathering tree rooted at the sink. The tree eventually becomes a Breadth First Search (BFS) tree where each node maintains the shortest hop-count to the root to reduce the routing delay. Each node collects some extra neighborhood information during the tree construction. Thus a little pre-processing at each node helps in taking prompt actions to repair the tree through local adjustment if any arbitrary single or multiple nodes fail in future. On failure of a node, each affected node in its vicinity fixes the parent through a pair of control message transmissions. Simulation results show that the repairing delay is significantly less in average and the convergecast messages are delivered with minimum data loss and no redundancy even in presence of node crash.     

A mild and expedient one-pot synthesis of substituted benzimidazoles in water using a phase-transfer catalyst

Abstract  1-Alkyl/phenyl-2-arylbenzimidazoles have been synthesized in very good to excellent yields by a one-pot condensation of N-alkyl/phenyl-o-phenylenediamines with aryl aldehydes in water at room temperature using cetylpyridinium bromide as a cheap and eco-friendly catalyst. Graphical abstract        

A synthetic route to 1,3-dihydroisobenzofuran natural products: the synthesis of methyl ethers of pestacin

A synthetic route to 1-(2,6-dihydroxyphenyl)phthalan natural products is described. It is typified by the synthesis of permethyl and monomethyl ethers (21 and 22) of pestacin (1), a 1,3-dihydroisobenzofuran natural product. The key step is hydrodeoxygenation of the corresponding isobenzofuranone 19 in 2 steps: reduction and intramolecular etherification. A route involving hydrodesulfurization of a thionophthalide to a phthalan (e.g., 8) is also reported.     

A stereodivergent route to two epimeric 2-pyrrolidinylglycine derivatives

A new route to two epimeric 2-pyrrolidinylglycine derivatives is developed, which features Mitsunobu amination of a chiral allyl alcohol and ring-closing metathesis as key steps.