Very long-distance magnetic coupling in a dicopper(II) metallacyclophane with extended π-conjugated diphenylethyne bridges

Self-assembly of the rigid rodlike ligand N,N'-4,4'-diphenylethynebis(oxamate) (dpeba) and Cu(2+) ions affords a novel dinuclear copper(II) metallacyclophane (nBu(4)N)(4)[Cu(2)(dpeba)(2)]·4MeOH·2Et(2)O (1) featuring a very long intermetallic distance (r = 15.0 ?). Magnetic susceptibility measurements for 1 reveal a moderately weak but nonnegligible intramolecular antiferromagnetic coupling between the two metal centers across the double para-substituted diphenylethynediamidate bridge (J = -3.9 cm(-1); H = -JS(1)S(2), where S(1) = S(2) = S(Cu) = (1)/(2)). Density functional electronic structure calculations on 1 support the occurrence of a spin polarization mechanism.     

Two step, hydrolytic-solvothermal synthesis of redispersible titania nanocrystals and their gas-sensing properties

A titanium chloromethoxide solution was prepared by reacting TiCl₄ with methanol, followed by water addition. The starting solutions were characterized by Fourier Transform Infrared (FTIR) spectroscopy, evidencing that the in situ generated water results in early hydrolysis of the chloroalkoxide. The solution was reacted with molten dodecylamine at room temperature, obtaining a white slurry of amorphous titania nanoparticles. Stable, redispersible TiO₂ nanocrystals could be prepared by subsequent solvothermal treatment in oleic acid at 250???C. The use of oleic acid was essential for obtaining crystalline structures, while other surfactants prevented crystallization. The nanocrystals were characterized by X-ray Diffraction and Transmission Electron Microscopy, confirming the formation of anatase TiO₂ nanocrystals with a mean size of 3.3?nm. The TiO₂ nanocrystals were used for fabricating gas-sensing devices, which were tested towards ethanol vapors. The initial small size of the nanocrystals, and the limited size growth during the high-temperature sensor operation, result in remarkable sensing performances if compared with bulk titania sensors.     

Biosynthesis of 4-methylproline in cyanobacteria: cloning of nosE and nosF genes and biochemical characterization of the encoded dehydrogenase and reductase activities

The biosynthesis of the unusual amino acid 4-methylproline in the Nostoc genus of cyanobacteria was investigated on the genetic and enzymatic level. Two genes involved in the biosynthesis were cloned and the corresponding enzymes, a zinc-dependent long-chain dehydrogenase and a Delta(1)-pyrroline-5-carboxylic acid (P5C) reductase homologue, were overexpressed in Escherichia coli and biochemically characterized. Putative substrates were synthesized to test enzyme substrate specificities, and deuterium labeling studies were carried out to reveal the stereospecificities of the enzymatic reactions with respect to the substrates as well as to the coenzymes.     

Structural analyses and magnetic properties of 3D coordination polymeric networks of nickel(II) maleate and manganese(II) adipate with the flexible 1,2-bis(4-pyridyl)ethane ligand

Two novel inorganic-organic hybrid 3D extended networks of Ni(II) and Mn(II) having molecular formulas [(maleate)(2)Ni(3)(bpe)(4)(H(2)O)(4)](NO(3))(2).H(2)O (1) and [(adipate)Mn(bpe)] (2) (bpe = 1, 2-bis(4-pyridyl)ethane), respectively, have been synthesized and characterized by single-crystal X-ray diffraction studies and low-temperature (300-2 K) magnetic measurements. Compound 1 crystallizes in the monoclinic system, space group C2/c (No. 15), with chemical formula C(56)H(62)N(10)Ni(3)O(19), a = 30.955(4) A, b = 12.705(3) A, c = 17.058(5) A, beta = 117.26(2) degrees, and Z = 4. Compound 2 crystallizes in the triclinic system, space group Ponemacr; (No. 2), with chemical formula C(18)H(20)MnN(2)O(4), a = 8.492(2) A, b = 9.444(2) A, c = 11.533(3) A, alpha = 97.19(1) degrees, beta = 94.64(1) degrees, gamma = 105.02(1) degrees, and Z = 2. The structure determination reveals for both a 3D network. Compound 1 contains two crystallographically independent Ni(II) ions in different octahedral environments. Ni(1) lies on an inversion center, and its coordination environment comprises two chelating maleate anions and two bpe nitrogen donors, while the Ni(2) ion is surrounded by meridionally disposed three bpe N atoms, two water molecules, and one oxygen donor from the dicarboxylate anion. Of the three crystallographic independent bpe ligand, one presents an anti and the others a gauche conformation. The corresponding N-to-N distances are 9.344, 6.543, and 6.187 A. Variable-temperature magnetic susceptibility measurement of the complex reveals the existence of a dominant ferromagnetic interaction within the molecule. Compound 2 is composed of Mn(2) dimer units linked by adipate anions to form corrugated 2D sheets which, on interconnection through bpe (anti conformation, N-to-N distance of 9.391 A), produces an interpenetrated 3D alpha-polonium-related type net. Complex 2 reveals to be antiferromagnetic fitting data using a dimeric Mn(II) model that considers negligible magnetic transmission through the carbon skeleton of adipate and the bpe pathway.     

Electrical conductivity in vinyl chloride during polymerization

Vinyl chloride of good polymerization quality showed a measurable electrical conductivity. The ionic strength of redistilled VCM appeared to be independent of temperature in the range from 20 to 50°C, and to decrease at higher temperatures. Conductivity measurements during bulk polymerization of VCM showed that the conductivity decreased with conversion. Other results indicated that electrolytically active species, formed during the polymerization, were trapped in the polymer matrix.     

A Quality Assurance Study for the Analysis of Hydrocarbons in Sediments

Abstract

Two exercises (MEDCAL I and II) were conducted in our Department during November 1984 and October 1986, with participants from the Mediterranean region, for testing the IOC Manual for the determination of petroleum hydrocarbons in sediments (IOC, Manuals and Guides, No. 11).

The gas chromatographic analysis of the saturated hydrocarbon fraction provided, at the best, a precision of 60% (relative standard deviation RSD) for n-alkanes (mean conc. 0.89 μg/g) and 56 % for the unresolved complex mixture (UCM) (mean conc. 16μg/g). The CPI and the pristane/phytane ratio provided better results (13% RSD). The aromatic fractions, analysed by UV-fluorescence, yielded in total a mean concentration of 10μg/g of chrysene equivalents with a 49% RSD.

The extraction-partition step was confirmed to be the main source of error in the analysis because when the results were corrected for recoveries, the RSD were reduced to 17, 30 and 6% for n-alkanes, UCM and total aromatics, respectively. Our reference intra-laboratory precision was, respectively, 18, 14 and 14%.     

2-Phospha-Allylic Systems

Abstract

Phosphamethincyanines prepared in 1964 by Dimroth and Hoffmann were among the first compounds with two-coordinate phosphorus. They are special cases of 2-phospha-allylic cations. Simple representatives of this type become available from the reaction of imidoyl chlorides with tris(trimethylsily1)phosphane.     

Residual‐based stabilization of the finite element approximation to the acoustic perturbation equations for low Mach number aeroacoustics

The acoustic perturbation equations (APE) are suitable to predict aerodynamic noise in the presence of a non‐uniform mean flow. As for any hybrid computational aeroacoustics approach, a first computational fluid dynamics simulation is carried out from which the mean flow characteristics and acoustic sources are obtained. In a second step, the APE are solved to get the acoustic pressure and particle velocity fields. However, resorting to the finite element method (FEM) for that purpose is not straightforward. Whereas mixed finite elements satisfying an appropriate inf–sup compatibility condition can be built in the case of no mean flow, that is, for the standard wave equation in mixed form, these are difficult to implement and their good performance is yet to be checked for more complex wave operators. As a consequence, strong simplifying assumptions are usually considered when solving the APE with FEM. It is possible to avoid them by resorting to stabilized formulations. In this work, a residual‐based stabilized FEM is presented for the APE at low Mach numbers, which allows one to deal with the APE convective and reaction terms in its full extent. The key of the approach resides in the design of the matrix of stabilization parameters. The performance of the formulation and the contributions of the different terms in the equations are tested for an acoustic pulse propagating in sheared‐solenoidal mean flow, and for the aeolian tone generated by flow past a two‐dimensional cylinder. Copyright © 2016 John Wiley & Sons, Ltd.     

and applications

We study an analogue of the classical theory of weights in without assuming that the underlying measure is doubling. Then, we obtain weighted norm inequalities for the (centered) Hardy-Littlewood maximal function and corresponding weighted estimates for nonclassical Calderón-Zygmund operators. We also consider commutators of those Calderón- Zygmund operators with bounded mean oscillation functions (), extending the main result from R. Coifman, R. Rochberg, and G. Weiss, Factorization theorems for Hardy spaces in several variables, Ann. of Math. 103 (1976), 611-635. Finally, we study self-improving properties of Poincaré-B.M.O. type inequalities within this context; more precisely, we show that if is a locally integrable function satisfying for all cubes , then it is possible to deduce a higher integrability result for , assuming a certain simple geometric condition on the functional .     

Synthesis and characterization of [Cu(Me2oxpn)Ni(NO2)(tmen)](ClO4): a single ferrimagnetic dinuclear CuII-NiII complex acting as weak molecule-based magnet

The new heterodinuclear complex [Cu(Me2oxpn)Ni(NO2)(tmen)](ClO4), that exhibits strong antiferromagnetic intramolecular coupling between CuII and NiII ions (ferrimagnetic behavior), shows ferromagnetic ordering at low temperature, due likely to a small canting phenomenon; it is one of the very few compounds made from isolated molecules that lead to cooperative magnetic behavior.