Copper(II) coordination compounds with ferulic acid

The first two molecular structures of the ferulic acid (3-(4-hydroxy-3-methoxyphenyl)-2-propenoic acid, C₁₀H₁₀O₄) coordination compounds are presented, namely, [Cu₂(C₁₀H₉O₄)₄(CH₃CN)₂] 1 and [Cu₂(C₁₀H₉O₄)₄(C₆H₆N₂O)₂]·4CH₃CN (C₆H₆N₂O = nicotinamide) 2. Both compounds were synthesised from the starting mixture of Cu₂O and CuCl upon copper oxidation in the acetonitrile solution. The single-crystal X-ray diffraction analysis of 1 and 2 reveals the binuclear structure of the ‘paddle–wheel’ type for both complexes. 1 and 2 are unstable outside mother liquid due to loosely bound acetonitrile molecules. The final products of decomposition are [Cu₂(C₁₀H₉O₄)₄] 1a and [Cu₂(C₁₀H₉O₄)₄(C₆H₆N₂O)₂] 2a, which were characterized by several physico-chemical methods. The triplet X-band EPR spectra of 1a and 2a, showing signals B_Z1  15 mT, B₂  460 mT and B_Z2  580 mT, are in agreement with the expected data for the binuclear tetracarboxylate units, found in the structures of the parent complexes 1 and 2. Together with the room temperature magnetic susceptibility data, μ_eff/B.M. 1.40 (1a), 1.48 (2a), the EPR spectra analysis confirm the antiferromagnetic interaction in 1a and 2a. This is suggesting preservation and stability of the paddle–wheel structures in 1a and 2a.     

An Eberhard-Like Theorem for Pentagons and Heptagons

Eberhard proved that for every sequence (p _k ), 3≤k≤r, k≠6, of nonnegative integers satisfying Euler’s formula ∑ _k≥3(6−k)p _k =12, there are infinitely many values p ₆ such that there exists a simple convex polyhedron having precisely p _k faces of size k for every k≥3, where p _k =0 if k>r. In this paper we prove a similar statement when nonnegative integers p _k are given for 3≤k≤r, except for k=5 and k=7 (but including p ₆). We prove that there are infinitely many values p ₅,p ₇ such that there exists a simple convex polyhedron having precisely p _k faces of size k for every k≥3. We derive an extension to arbitrary closed surfaces, yielding maps of arbitrarily high face-width. Our proof suggests a general method for obtaining results of this kind.     

Non-isothermal reduction of silica-supported nickel catalyst precursors in hydrogen atmosphere: a kinetic study and statistical interpretation

A series of silica-supported nickel catalyst precursors was synthesized with different SiO₂/Ni mole ratios (0.20, 0.80 and 1.15). Non-isothermal reduction of Ni catalyst precursors was investigated by temperature-programmed reduction at four different heating rates (2, 5, 10 and 20 °C min^?1), in a hydrogen atmosphere. Kinetic parameters (E _a, A) were determined using Friedman isoconversional method. It was found that for all mole ratios, apparent activation energy is practically constant in conversion range of α = 30–70 %. In considered conversion range, the following values of apparent activation energy were found: E _a = 129.5 kJ mol^?1 (SiO₂/Ni = 0.20), E _a = 133.8 kJ mol^?1 (SiO₂/Ni = 0.80) and E _a = 125.0 kJ mol^?1 (SiO₂/Ni = 1.15). Using two special functions (y(α) and z(α)), the kinetic model was determined. It was established that reduction of Ni catalyst precursors with different SiO₂/Ni mole ratios is a complex process and can be described by two-parameter ?esták–Berggren (SB) autocatalytic model. Based on established values of SB parameters for each mole ratio, the possible mechanism was discussed. It was found that for all investigated ratios, the Weibull distribution function fits very well the experimental data, in the wide range of conversions (α = 5–95 %). Based on obtained values of Weibull shape parameter (θ), it was found that experimentally evaluated density distribution functions of the apparent activation energies can be approximated by the unbalanced peaked normal distribution.     

Entropy viscosity method for nonlinear conservation laws

A new class of high-order numerical methods for approximating nonlinear conservation laws is described (entropy viscosity method). The novelty is that a nonlinear viscosity based on the local size of an entropy production is added to the numerical discretization at hand. This new approach does not use any flux or slope limiters, applies to equations or systems supplemented with one or more entropy inequalities and does not depend on the mesh type and polynomial approximation. Various benchmark problems are solved with finite elements, spectral elements and Fourier series to illustrate the capability of the proposed method.     

Composition of the essential oil of Geocaryum cynapioides (Guss.) L. Engstrand

Volatile constituents from two fresh samples of the subendemic Geocaryum cynapioides (Guss.) L. Engstrand (Apiaceae) obtained by hydrodistillation were analyzed by GC and GC-MS. Forty four and one hundred-twenty three constituents identified in the oils accounted for 98.7 % and 98.4 % of the total oils, respectively. The major component of both oils was (E)-β-farnesene (73.3 % and 57.7 %) while the other major contributors were: (E,E)-α-farnesene (4.8 % and 14.6 %) and trans-sesquisabinene hydrate (12.2 % and 3.0 %). The constituents endo-fenchyl acetate, and three sesquiterpene lactones belonging to the selinane (callitrisin) and guaiane (grilactone and jalcaguaianolide) series, with a rather restricted natural occurrence, were present in only one of the samples (4.7 %, trace amount, 0.1 %, 0.5 %, respectively) and completely absent from the other distinguishing so the two samples. A chemotaxonomic discussion of the results is presented.     

Phosphorescent excited state of [Au2[(Ph2Sb)2O]3]2+: Jahn-Teller distortion at only one gold(I) center

Dinuclear three-coordinate Au(I) complex [Au2{(Ph2Sb)2O}3](ClO4)2 1 displays an interesting phosphorescent behavior in which a large Stokes' shift is observed. Ab initio calculations show that the main distortion for the first triplet excited state, which is responsible for the luminescence behavior of complex 1, is a Jahn-Teller distortion for only one of the Au(I) centers together with a gold-gold distance shortening. This behavior could be extrapolated to other phosphorescent dinuclear three-coordinate Au(I) complexes.     

Folding–Unfolding Equilibrium of a Methylidene‐Substituted β‐Peptide

β‐Peptides possess the ability to fold into secondary structure elements, and this property, together with resistance to biodegradation, makes these compounds interesting for pharmaceutical applications. Recently, a novel class of β‐peptides containing methylidene moieties was described. The GROMOS 53A6 force field was used to simulate the folding equilibrium of a β³‐hexapeptide with methylidene (CH₂?) groups at all six CA‐atoms. Due to the rotational barriers induced by these methylidene groups, the helical secondary‐structure elements, normally found in β³‐peptides, are disfavored in this molecule. Simulations, started from fully extended and 3₁₄‐helical conformations, showed that the molecule adopts a complete 2₈‐helix for ca. 5% of the time and partial 2₈‐helical conformations for ca. 20% of the time. Yet, as suggested by experiments, the folding equilibrium is dominated by unfolded conformations.     

Cyanoamino compounds in synthesis syntheses of some heterocycles

Transformations of some heterocyclic cyanoamino compounds leading to various heterocyclic systems are described.s-Triazolo (1,5-α)azines are obtained either in a direct synthetic approach or via the substituted aminotetrazoles, substituted 3-amino-5-oxo-1,2,4-oxadiazolines, and fromN-ethoxycarbonylN′-heteroaryl thioureas orN-heteroarylN′-hydroxyguanidine. The cyanoamino group reacts also witho-difunctional benzenes to give the corresponding substituted derivatives of benzimidazole, benzoxazole or benzothiazole.     

Non-linear waves in heterogeneous elastic rods via homogenization

We consider the propagation of a planar loop on a heterogeneous elastic rod with a periodic microstructure consisting of two alternating homogeneous regions with different material properties. The analysis is carried out using a second-order homogenization theory based on a multiple scale asymptotic expansion.