A doubly bridged isodicyclopentadienyl zirconium complex: bis{N‐(3,5‐dimethylphenyl)‐N‐[(η5‐isodicyclopentadien‐2‐yl)dimethylsilyl]amido‐κN}zirconium(II) diethyl ether solvate

Transmetallation of the dilithium salt of (3,5‐dimethyphenyl­amino)(isodicyclopentadienyl)dimethylsilane by treatment with zirconium tetrachloride in a 2:1 ratio leads to the substitution of all four chloride ligands. With the applied stoichiometry, the title complex, [Zr(C₂₀H₂₅NSi)₂]·C₄H₁₀O, was obtained and crystallized from diethyl ether. X‐ray diffraction characterization showed that both isodi­cyclo­penta­dienyl ligands (alternatively called 4,5,6,7‐tetrahydro‐4,7‐methano‐1H‐indene) are complexed to the metal on their exo face in a completely stereoselective manner and that they are η⁵‐bonded to the Zr atom.     

Synergistic Properties of Arabinogalactan (AG) and Hyaluronic Acid (HA) Sodium Salt Mixtures

The properties of mixtures of two polysaccharides, arabinogalactan (AG) and hyaluronic acid (HA), were investigated in solution by the measurement of diffusion coefficients D of water protons by DOSY (Diffusion Ordered SpectroscopY), by the determination of viscosity and by the investigation of the affinity of a small molecule molecular probe versus AG/HA mixtures in the presence of bovine submaxillary mucin (BSM) by ¹HNMR spectroscopy. Enhanced mucoadhesive properties, decreased mobility of water and decreased viscosity were observed at the increase of AG/HA ratio and of total concentration of AG. This unusual combination of properties can lead to more effective and long-lasting hydration of certain tissues (inflamed skin, dry eye corneal surface, etc.) and can be useful in the preparation of new formulations of cosmetics and of drug release systems, with the advantage of reducing the viscosity of the solutions.     

Thermodynamic study of transthyretin association (wild‐type and senile forms) with heparan sulfate proteoglycan: pH effect and implication of the reactive histidine residue

The tetramer destabilization of transthyretin into monomers and its fibrillation are phenomena leading to amyloid deposition. Heparan sulfate proteoglycan (HSPG) has been found in all amyloid deposits. A chromatographic approach was developed to compare binding parameters between wild‐type transthyretin (wtTTR) and an amyloidogenic transthyretin (sTTR). Results showed a greater affinity of sTTR for HSPG at pH 7.4 compared with wtTTR owing to the monomeric form of sTTR. Analysis of the thermodynamic parameters showed that van der Waals interactions were involved at the complex interface for both transthyretin forms. For sTTR, results from the plot representing the number of protons exchanged vs pH showed that the binding mechanism was pH‐dependent with a critical value at a pH 6.5. This observation was due to the protonation of a histidine residue as an imidazolium cation, which was not accessible when TTR was in its tetrameric structure. At pH >6.5, dehydration at the binding interface and several contacts between nonpolar groups of sTTR and HSPG were also coupled to binding for an optimal hydrogen‐bond network. At pH <6.5, the protonation of the His residue from sTTR monomer when pH decreased broke the hydrogen‐bond network, leading to its destabilization and thus producing slight conformational changes in the sTTR monomer structure. Copyright © 2014 John Wiley & Sons, Ltd.     

Crystal and molecular structure of calcium L(–)-malate trihydrate

The new crystal and molecular structures of a less common hydrated calcium L(–)-malate (calcium (2S) 2-hydroxybutanedioate trihydrate) Ca(C₄H₄O₅)3H₂O, are reported. X-ray crystallographic data are as follows: a = 6.6460(3) Å, b = 8.3795(3) Å, c = 8.2707(4) Å, = 112.640(2)°, V = 425.1(4) ų, space group P2₁ (No. 4), Z = 2, D _calc = 1.767 g cm^–3. The calcium ion coordination number is seven. One of the three water molecules present in the unit cell is less strongly bound, only interacting with a calcium ion. In aqueous or hydroalcoholic solution, both di- and trihydrated species crystallize simultaneously.     

The Bending-Gradient Theory for Thick Plates: Existence and Uniqueness Results

This paper is devoted to the mathematical justification of the Bending-Gradient theory which is considered as the extension of the Reissner-Mindlin theory (or the First Order Shear Deformation Theory) to heterogeneous plates. In order to rigorously assess the well-posedness of the Bending-Gradient problems, we first assume that the compliance tensor related to the generalized shear force is positive definite. We define the functional spaces to which the variables of the theory belong, then state and prove the existence and uniqueness theorems of solutions of the Bending-Gradient problems for clamped and free plates, as well as for simply supported plates. The obtained results are afterward extended to the general case, i.e., when the compliance tensor related to generalized shear forces is not definite.     

Cellular rubber: Dependency between relaxation time and pretreatment

In this contribution we investigate experimentally a porous carbon-filled rubber. The main focus is on the dependency of the mechanical behaviour using different pretreatments. Therfore, cyclic tests and relaxation tests with different pretreatment are performed. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Simultaneous measurement of proline and related compounds in oak leaves by high-performance ligand-exchange chromatography and electrospray ionization mass spectrometry for environmental stress studies

A mass spectrometer was coupled to high-performance ligand-exchange liquid chromatography (HPLEC) for simultaneous analysis of stress associated solutes such as proline, hydroxyproline, methylproline, glycine betaine and trigonelline extracted from leaves of drought stressed oaks and an internal standard namely N-acetylproline. Methanol/chloroform/water extracts were analyzed using an Aminex HPX-87C column and specifically quantified by the positive ion mode of an electrospray ionisation-mass spectrometry (ESI-MS) in single ion monitoring (SIM) mode. The recovery of N-acetyl proline added to oak leaf extracts ranged from 85.2 to 122.1% for an intra-day study. Standard calibration curves showed good linearity in the measured range from 0.3125 to 10 μmol L⁻¹ with the lowest correlation coefficient of 0.99961 for trigonelline. The advantages of this alternative procedure, compared to previously published methods using fluorescence or amperometric detections, are the simultaneous and direct detection of osmoprotectants in a single chromatographic run, a minimal sample preparation, a good specificity and reduced limits of quantification, ranging from 0.1 to 0.6 μmol L⁻¹. Fifty-six days of water deficit exposure resulted in increased foliar free proline levels (2.4-fold, P < 0.001, 155 μmol g⁻¹ FW) and glycine betaine contents (2.5-fold, P < 0.05, 175 μmol g⁻¹ FW) of drought stressed oak compared to control.     

Safety and Quality Aspects of Acrylic Monomers

Summary : Acrylic monomers are important intermediates for the chemical industry. Especially acrylic acid (AA) is the basis for various reactions, such as polymerizations and esterifications and is, therefore, responsible for high product diversity. Spontaneous polymerization is a safety problem during the transportation and storage of acrylic monomers. In the production process, polymerization leads to blockages in the apparatus. For the prevention of these issues, special stabilizer systems are used such as hydroquinone monomethyl ether (MeHQ)/oxygen and phenothiazine (PTZ). The reactions of these stabilizer systems are not well understood at the moment. Therefore a lot of expertise and experience are necessary to guarantee safe handling. In this paper some methods for the investigation of stability related reaction kinetics are presented. A better comprehension of the mechanism of the polymerization inhibition is generated by the kinetic simulation with these data.     

Real Interpolation of Sobolev Spaces Associated to a Weight

We hereby study the interpolation property of Sobolev spaces of order 1 denoted by \(W^{1}_{p,V}\), arising from Schrödinger operators with positive potential. We show that for 1?≤?p ₁?p?p ₂?q ₀ with p?>?s ₀, \(W^{1}_{p,V}\) is a real interpolation space between \(W_{p_1,V}^{1}\) and \(W_{p_2,V}^{1}\) on some classes of manifolds and Lie groups. The constants s ₀, q ₀ depend on our hypotheses.     

Facilitating access to the most easily ionized molecule: an improved synthesis of the key intermediate, W2(hpp)4Cl2, and related compounds

A far superior synthesis is reported for W(2)(hpp)(4)Cl(2), a key intermediate in the synthesis of the most easily ionized closed-shell molecule W(2)(hpp)(4) (hpp = the anion of the bicyclic guanidine compound 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine). At 200 degrees C, the one-pot reaction of the air-stable and commercially available compounds W(CO)(6) and Hhpp in o-dichlorobenzene produces W(2)(hpp)(4)Cl(2) in multigram quantities with isolated yields of over 90%. At lower temperatures, the reaction can lead to other compounds such as W(Hhpp)(2)(CO)(4) or W(2)(mu-CO)(2)(mu-hpp)(2)(eta(2)-hpp)(2), which are isolable in good purity depending upon the specific conditions employed. These compounds provide insight into the reaction pathway to W(2)(hpp)(4)Cl(2) and W(2)(hpp)(4). Two additional derivatives, W(2)(hpp)(4)X(2) where X is PF(6)(-) or the anion tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB), have also been synthesized and structurally characterized. A comparison of the electrode potentials of W(2)(mu-CO)(2)(mu-hpp)(2)(eta(2)-hpp)(2) and the di-p-anisylformamidinate analogue shows that oxidation of the hpp compound is significantly displaced (1.12 V) and shows that the bicyclic guanidinate ligand is considerably better than the formamidinate anion at stabilizing high oxidation states. A differential pulse voltammogram of W(2)(hpp)(4)(TFPB)(2) in THF shows two reduction processes with an E(1/2) of -0.97 V for the first and -1.81 V (vs Ag/AgCl) for the second. DFT calculations on the W(2)(hpp)(4)(2+) units in W(2)(hpp)(4)X(2) compounds show that the metal-metal bonding orbitals are destabilized by the axial ligands, which accounts for significant variations in the W-W distances. The low-energy gas-phase ionizations of W(2)(hpp)(4) are also reported and discussed.