Short range order and glass transition in AgIAg2OB2O3 vitreous electrolytes

Several experimental techniques are used to study the short range order, the dynamics and the glass transition in AgIAg₂B₂O₃ compounds. Addition of Ag₂O to B₂O₃, up to [Ag₂O]/[B₂O₃] ?0.5 modifies the borate network by creating a BO₄ unit for each silver added. Addition of AgI decreases the glass transition temperature (T_g) but has only minor effects on the short range structure of the borate network. Silver iodide is partially accomodated in the interstices of the glass network. The relationship among a tentative structural picture, the ion transport phenomena and the low temperature dynamics are discussed.An investigation of the dynamics in the AgI·Ag₂O·2B₂O₃ glass near and above T_g is presented. With NMR techniques, we monitor the onset of tumbling of the borate units and the dynamical effects of crystallization and/or aging of the glass. Hysteresis effects in the ionic conductivity (σ) temperature dependence and the non-Arrhenian behavior of σT near T_g are interpreted in terms of structural modifications occurring at elevated temperatures in the glass.     

Delineation of agonist binding to the human histamine H4 receptor using mutational analysis, homology modeling, and ab initio calculations

A three-dimensional homology model of the human histamine H 4 receptor was developed to investigate the binding mode of a series of structurally diverse H 4-agonists, i.e. histamine, clozapine, and the recently described selective, nonimidazole agonist VUF 8430. Mutagenesis studies and docking of these ligands in a rhodopsin-based homology model revealed two essential points of interactions in the binding pocket, i.e. Asp3.32 and Glu5.46 (Ballesteros-Weinstein numbering system). It is postulated that Asp3.32 interacts in its anionic state, whereas Glu5.46 interacts in its neutral form. The hypothesis was tested with the point mutations D3.32N and E5.46Q. For the D3.32N no binding affinity toward any of the ligands could be detected. This is in sharp contrast to the E5.46Q mutant, which discriminates between various ligands. The affinity of histamine-like ligands was decreased approximately a 1000-fold, whereas the affinity of all other ligands remained virtually unchanged. The proposed model for agonist binding as well as ab initio calculations for histamine and VUF 8430 explain the observed differences in binding to the H 4R mutants. These studies provide a molecular understanding for the action of a variety of H 4 receptor-ligands. The resulting H 4 receptor model will be the basis for the development of new H 4 receptor-ligands.     

A label-free method based on MALDI-TOF mass spectrometry for the absolute quantitation of troponin T in mouse cardiac tissue

A label-free absolute quantitation method based on matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has been developed. This methodology was applied to mouse heart in order to quantify cardiac troponin T (cTnT), which is considered to be a sensitive marker of heart damage. The cTnT was extracted, isolated by reversed-phase high-performance liquid chromatography, digested, and analyzed by MALDI-TOF MS. The MS-based quantitation was performed using matrix-matched calibration curves (due to a matrix effect) of two synthetic peptides, one cTnT-specific peptide and one internal standard peptide, respectively. Recoveries at three spiking levels ranged from 87–96%, with relative standard deviations of below 10%. The method detection limit and the method quantitation limit, expressed as the amount of cTnT for the amount of total sarcomeric protein extract, were 0.03 mg g⁻¹ and 0.15 mg g⁻¹, respectively. This method appears to be accurate and generally suitable for improving absolute protein quantitation.     

Photochromic,Thermochromic, and Fluorescent Spirooxazines and Naphthopyrans: A Spectrokinetic and Thermodynamic Study

The photochromic and thermochromic behavior of four commercially available Reversacol dyes are presented. The compounds studied belong to the class of spirooxazines and naphthopyrans, which are typically thermoreversible photochromic molecules. On stimulation with UV light, these compounds become colored and exhibit spectra which extend over the whole visible region. Increasing the temperature causes spontaneous coloration (thermochromism). Herein, absorption and fluorescence spectra, molar absorption coefficients of the colorless and colored forms, fluorescence and photochemical quantum yields, and kinetic parameters of thermal bleaching (rate constant, frequency factor, and activation energy) are determined in acetonitrile solution. The thermal ground‐state reaction is exhaustively described in terms of thermodynamic parameters (equilibrium constant, free energy, enthalpy, and entropy). Temperature effects on photochemical and thermal colorabilities are evaluated. The results indicate that the two spirooxazines are good photochromes below room temperature, whereas they are efficient thermochromic compounds above room temperature. Naphthopyrans are better photochromes but worse thermochromic compounds than spirooxazines.     

Determination of aflatoxins in hazelnuts by various sample preparation methods and liquid chromatography-tandem mass spectrometry

A sensitive and reliable liquid chromatography-tandem mass spectrometric with electrospray ionization method for determining aflatoxins in hazelnuts has been developed. Three different extraction techniques, such as homogenization, ultrasonic extraction, and matrix solid phase dispersion have been tested and compared in terms of recovery, matrix effect, accuracy and precision. Ultrasound extraction was the most performing sample preparation method. Absolute recoveries for analytes and I.S. ranged from 93 to 101%. Accuracy and precision were calculated using matrix matched calibration, and ranged 91-102% and 2-11%, respectively. CC alpha and CC beta for aflatoxin B1 (EU limit=2 microg/kg) were 2.15 and 2.33 microg/kg, respectively. A ruggedness test performed on three other matrices demonstrated that sonication time was critical and a matrix matched calibration must be constructed for every sort of matrix.     

Highly enantioselective desymmetrization of meso anhydrides by a bifunctional thiourea-based organocatalyst at low catalyst loadings and room temperature

Bifunctional (thio)urea-based cinchona alkaloid derivatives have been shown to promote highly efficient enantioselective desymmetrization reactions of meso anhydrides. The most selective of these catalysts is capable of the enantioselective methanolysis of succinic and glutaric anhydride derivatives to form hemiester products with >90% yield and enantiomeric excess at 1 mol % loading and ambient temperature.     

Do computed crystal structures of nonpolar molecules depend on the electrostatic interactions? The case of tetracene

We present a strategy for comparing the global properties of competing potential models. By systematically sampling the potential energy surface of crystalline tetracene, we assess how the number, energy and structure of its minima are modified by switching on (or off) the Coulombic interactions. The increased complexity of the Coulombic potential leads to a more "rugged" potential energy surface with a larger number of minima, but the effect is not large. In fact, we find a subset of minima stable only in presence of the Coulombic interactions, a smaller subset stable only in their absence, and a large majority stable in both cases. Among these, there is a very good, but not perfect, correlation between the energies and the structures computed with and without the electrostatic interactions. Although electrostatic interactions play a role even in a rigid nonpolar molecule such as tetracene, they are not as crucial as often believed, because altering the electrostatic model (or switching it off completely) leads, in most cases, to equivalent results.     

Fabrication, structural characterization, and applications of langmuir and langmuir-blodgett films of a poly(azo)urethane

The synthesis of a poly(azo)urethane by fixing CO(2) in bis-epoxide followed by a polymerization reaction with an azodiamine is presented. Since isocyanate is not used in the process, it is termed "clean method" and the polymers obtained are named "NIPUs" (non-isocyanate polyurethanes). Langmuir films were formed at the air-water interface and were characterized by surface pressure vs mean molecular area per mer unit (Pi-A) isotherms. The Langmuir monolayers were further studied by running stability tests and cycles of compression/expansion (possible hysteresis) and by varying the compression speed of the monolayer formation, the subphase temperature, and the solvents used to prepare the spreading polymer solutions. The Langmuir-Blodgett (LB) technique was used to fabricate ultrathin films of a particular polymer (PAzoU). It is possible to grow homogeneous LB films of up to 15 layers as monitored using UV-vis absorption spectroscopy. Higher number of layers can be deposited when PAzoU is mixed with stearic acid, producing mixed LB films. Fourier transform infrared (FTIR) absorption spectroscopy and Raman scattering showed that the materials do not interact chemically in the mixed LB films. The atomic force microscopy (AFM) and micro-Raman technique (optical microscopy coupled to Raman spectrograph) revealed that mixed LB films present a phase separation distinguishable at micrometer or nanometer scale. Finally, mixed and neat LB films were successfully characterized using impedance spectroscopy at different temperatures, a property that may lead to future application as temperature sensors. Principal component analysis (PCA) was used to correlate the data.     

A New Recurrence Relation and Related Determinantal form for Binomial Type Polynomial Sequences

For polynomial sequence of binomial type we propose a new recurrence formula equivalent to a determinantal form of the sequence, from which known and unknown properties are deducted. Relationships whit \({\delta}\)–functionals, \({\delta}\)–operators and generating function are pointed out. Finally, some classical examples are studied, highlighting interesting determinantal identities.     

A-priori upper bounds for the set covering problem

A matrix M∈R^n×n is said to be a column sufficient matrix if the solution set of LCP(M,q) is convex for every q∈Rⁿ. In a recent article, Qin et al. (Optim. Lett. 3:265–276, 2009) studied the concept of column sufficiency property in Euclidean Jordan algebras. In this paper, we make a further study of this concept and prove numerous results relating column sufficiency with the Z and Lypaunov-like properties. We also study this property for some special linear transformations.