Characterization of the oxidation products of styryl-substituted terthiophenes and sexithiophenes using electronic absorption spectroscopy and time-dependent DFT

The electronic absorption spectra of a series of alkoxy-styryl substituted terthiophenes, their corresponding sexithiophenes, and the oxidation products of both have been measured. The terthiophenes studied sigma-dimerize to sexithiophenes during the oxidation process and there is clear evidence of sexithiophene radical cations, dications, and pi-dimers in the electronic absorption spectra. The oxidation of concentrated solutions produces predominantly pi-dimer bands, as expected. The absorption spectrum of the styryl-functionalized sexithiophene dication without alkoxy substitution closely resembles that of unsubstituted sexithiophene, while alkoxy substitution induces changes in the wavelength of the dication band maximum and the overall band shape. Time-dependent density functional theory (TDDFT) calculations have shown that styryl-based molecular orbitals are important in the transitions of the neutral molecules as well as the charged species, the dication in particular. Kinetics analyses confirm the stabilization effect induced by the alkoxy substituents. The presence of a reversible pi-dimer equilibrium was verified by cyclic voltammetry. It is clear from the experimental observations and the theoretical calculations that both the styryl and alkoxy groups are influencing the electronic properties of this class of molecules.     

A study of the shear viscosity of human whole saliva

Summary A model R-18 Weissenberg Rheogoniometer operating in the continuous shear mode was used to generate shear viscosity vs. shear rate data on male and female human whole saliva. These data were found to accurately follow the Sisko model, , whereµ is the shear viscosity at shear rate is the asymptotic shear viscosity at infinite shear rate, andK andn are constants. Data were collected on the effects of food, coffee, caffeine, and aspirin as functions of time. Studies were also made on the effects of emotional stress, donor sex and age.The saliva viscosity increased with time and then decreased to the basal value for most ingested materials. Emotional stress was found to elevate the saliva viscosity. On the other hand, no significant difference was found between the average saliva viscosities of male and female groups. Also, no significant effect of donor age was detected.

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Zusammenfassung Mit Hilfe eines Weissenberg-Rheogoniometers (Typ R-18) wurden bei stationärem Betrieb Scherviskositätskurven in Abhängigkeit von der Schergeschwindigkeit für den Speichel von Männern und Frauen gemessen. Man fand, daß sich die Meßwerte hinreichend genau durch ein Sisko-Modell, , beschreiben lassen, woµ die Scherviskosität bei der Schergeschwindigkeit die asymptotische Scherviskosität bei unendlich großer Schergeschwindigkeit sowieK undn weitere Konstanten bedeuten. Diese Messungen verfolgten die Wirkung von Nahrung, Kaffee, Coffein und Aspirin als Funktion der Zeit. Untersucht wurde weiterhin der Einfluß von emotionaler Spannung, sowie Geschlecht und Alter der Spender.Die Speichelviskosität stieg bei den meisten eingenommenen Stoffen mit der Zeit zuerst an, um danach wieder auf den Normalwert abzusinken. Ebenso fand man, daß emotionale Spannung eine Viskositätserhöhung hervorruft. Dagegen wurden bei Gruppen von Männern und Frauen keine signifikanten Unterschiede gefunden, und ebenso wurde kein gesicherter Einfluß des Alters festgestellt.

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With 4 figures and 6 tables     

Species-specific and inhibitor-dependent conformations of LpxC: implications for antibiotic design

LpxC is an essential enzyme in the lipid A biosynthetic pathway in gram-negative bacteria. Several promising antimicrobial lead compounds targeting LpxC have been reported, though they typically display a large variation in potency against different gram-negative pathogens. We report that inhibitors with a diacetylene scaffold effectively overcome the resistance caused by sequence variation in the LpxC substrate-binding passage. Compound binding is captured in complex with representative LpxC orthologs, and structural analysis reveals large conformational differences that mostly reflect inherent molecular features of distinct LpxC orthologs, whereas ligand-induced structural adaptations occur at a smaller scale. These observations highlight the need for a molecular understanding of inherent structural features and conformational plasticity of LpxC enzymes for optimizing LpxC inhibitors as broad-spectrum antibiotics against gram-negative infections.     

Concrete models and dynamic instruments as early technology tools in classrooms at the dawn of ICMI: from Felix Klein to present applications in mathematics classrooms in different parts of the world

Most national curricula for both primary and secondary grades encourage the active involvement of learners through the manipulation of materials (either concrete models or dynamic instruments). This trend is rooted in the emphasis given, at the dawn of ICMI, to what might be called an experimental approach: the links between mathematics, natural sciences and technology were in the foreground in the early documents of ICMI and also in the papers of its first president, Felix Klein. However, the presence of this perspective in teaching practice is uneven. In this paper, we shall reconstruct first an outline of what happened in three different parts of the world (Europe, USA and Japan) under the direct influence of Klein. Then, we shall report classroom activities realized in the same regions in three different research centres: the Laboratory of Mathematical Machines at the University of Modena and Reggio Emilia, Italy (http://www.mmlab.unimore.it); the pedagogical space of Kinematical Model for Design Digital Library at Cornell, USA (http://kmoddl.library.cornell.edu/); and the Centre for Research on International Cooperation in Educational Development at Tsukuba University, Japan (http://math-info.criced.tsukuba.ac.jp/). They have maintained the reference to concrete materials (either models or instruments), with original interpretations that take advantage of the different cultural conditions. Although in all cases the reference to history is deep and systematic, the synergy with mathematical modelling and with information and communication technologies has been exploited, not to substitute but to complement the advantages of the direct manipulations.     

Coprecipitation study of As(III), Cu(II) and Cd(II) from aqueous solution using 5-bromo and 2-methylthioquinoline-8-thiol

Oxidation products of 5-bromo and 2-methylthio-quinoline-8-thiol are used for the quantitative coprecipitation of As(III), Cu(II) and Cd(II) from water solutions in a wide range of acidity. The recovery is >95%.     

Vapor–liquid equilibria and density measurement for binary mixtures of toluene,benzene, o-xylene,m-xylene,sulfolane and nonane at 333.15 K and 353.15 K

Isothermal vapor–liquid equilibria at 333.15 K and 353.15 K for four binary mixtures of benzene + nonane, toluene + o-xylene, m-xylene + sulfolane and o-xylene + sulfolane have been obtained at pressures ranged from 0 to 101.3 kPa over the whole composition range. The Wilson, NRTL and UNIQUAC activity coefficient models have been employed to correlate experimental pressures and liquid mole fractions. The non-ideal behavior of the vapor phase has been considered by using the Peng–Robinson equation of state in calculating the vapor mole fraction. Liquid and vapor densities of these solutions were measured by using two vibrating tube densitometers. The excess molar volumes of the liquid phase were also determined. The P–x–y phase behavior indicates that mixtures of m-xylene + sulfolane, o-xylene + sulfolane and benzene + nonane present large positive deviations from the ideal solution and belong to endothermic mixings because their excess Gibbs energies are positive.     

Attracting cavities for docking. Replacing the rough energy landscape of the protein by a smooth attracting landscape

Molecular docking is a computational approach for predicting the most probable position of ligands in the binding sites of macromolecules and constitutes the cornerstone of structure‐based computer‐aided drug design. Here, we present a new algorithm called Attracting Cavities that allows molecular docking to be performed by simple energy minimizations only. The approach consists in transiently replacing the rough potential energy hypersurface of the protein by a smooth attracting potential driving the ligands into protein cavities. The actual protein energy landscape is reintroduced in a second step to refine the ligand position. The scoring function of Attracting Cavities is based on the CHARMM force field and the FACTS solvation model. The approach was tested on the 85 experimental ligand–protein structures included in the Astex diverse set and achieved a success rate of 80% in reproducing the experimental binding mode starting from a completely randomized ligand conformer. The algorithm thus compares favorably with current state‐of‐the‐art docking programs. © 2015 The Authors. Journal of Computational Chemistry Published by Wiley Periodicals, Inc.     

Tris(2‐methyl­quinoline‐8‐seleno­lato‐κ2N,Se)antimony(III)

The title complex, [Sb(C₁₀H₈NSe)₃], has a 3Se+3N distorted octa­hedral geometry at the Sb atom. The structure is stabilized by weak inter­molecular C—H⋯π(arene) inter­actions.