Theoretical calculations of proton affinities of azines. Prediction of the relative basicities and preferred protonation sites

Theoretical calculations at the 3-21G and 3-21 + G ab initio levels and at the MNDO and AM1 semiempirical levels of several six-membered nitrogenated heterocycles and their protonated species have been carried out. The 3–21G calculated proton affinities are systematically too high, in relation to the available experimental data, and it is estimated that inclusion of electron correlation and zero-point corrections is not sufficient to reach the desired agreement; however, additional inclusion of diffuse functions (3-21 + G/3-21G calculations) lowers the calculated proton affinities by 5.4–6.8 kcal/mol, a good agreement being thus obtained, at least for 1–7 . On the other hand, semiempirical methods underestimate the repulsion between each pair of vicinal nitrogens; however, if a correction of ?9 kcal/mol is added to the AM1 results for each pair of neighboring nitrogens containing lone pairs of electrons, the corresponding proton affinities match fairly well the available exoerimental data and corrected 3-21 + G results. As expected, all methods predict that the introduction of additional nitrogens decreases the overall absolute basicity. Futhermore, comparison of the relative basicity of the isomers and of the preferred protonation site for each isomer indicates that nitrogen atoms with (only) one α-nitrogen and without a γ-nitrogen are more basic than any others. In benzazines, MNDO and AM1 suggest that the 2,3-diaza arrangement has a higher intrinsic basicity than the 1,2-diaza arrangement.     

Harmonic system in a random field

We study a model which may describe a dislocation-free commensurate phase in the presence of quenched impurities, or a vortex-freeXY model in a quenched random anisotropy. For a dimensionD between 2 and 4, we obtain an algebraic decay of the spin pair correlation function. This result was already obtained (without excluding vortices) by Aharony and Pytte, but our exponent is different and vanishes whenD approaches 4. ForD=2, a phase transition is obtained in agreement with previous theories, but without using the replica trick, and the low temperature phase is found to be more disordered than predicted by Cardy and Ostlund. Our conclusions disagree with the results of Dotsenko and Feigelman.     

Synthesis,characterization and a voltammetric study of (Bu4N)2[Mo2Br6]. Oxidation-reduction mechanism of related compounds

Summary The synthesis and characterization of (Bu₄N)₂[Mo₂Br₆], obtained from Mo(CO)₆, (Bu₄N)Br and 1,2-dibromoethane, is described. The electrochemical behaviour of [Mo₂Br₆]^–2 and related species is studied, and an oxidation-reduction mechanism is proposed.     

A representation of recursively enumerable sets through Horn formulas in higher recursion theory

We prove the existence of graphs with empty intersection of their longest paths or cycles as subgraphs of lattices on the torus and the Möbius strip.     

Crosslinking effects on hybrid organic–inorganic proton conducting membranes based on sulfonated polystyrene and polysiloxane

New hybrid semi‐interpenetrating proton‐conducting membranes were obtained using sulfonated polystyrene (SPS) and inorganic–organic polysiloxane phases with the aim of improving the mechanical and thermal characteristics of the pristine polymer and to study the effects of crosslinking in the latter phase in several of their properties, mainly proton conductivity. Siloxane phases were prepared using poly(dimethylsiloxane) (PDMS) and PDMS with tetraethoxysilane (TEOS) or phenyltrimethoxysilane (PTMS) as crosslinking agents. To study the crosslinking effect, membranes were prepared with different TEOS:PDMS and PTMS:PDMS mole ratios. The films obtained were characterized by FTIR, ²⁹Si‐HPDEC MAS‐NMR, ¹³C‐CP‐MAS NMR, elemental and thermal analyses. Certain properties, such as water uptake (WU), ion exchange capacity (IEC) and the state of the water, were determined. The proton conductivity was measured at different temperatures (30°C and 80°C) and relative humidities (50–95%). The water content of the hybrid membranes declined significantly, compared with the SPS membranes, depending on the nature and amount of siloxane phase added. Nonetheless, the conductivity values remained relatively high (>100 mS cm^?1 at 80°C and 95% RH) when compared to Nafion®117 presumably because of the formation of well developed proton channels, which makes them potentially promising as proton exchange membranes for fuel cells. These membranes proved to be thermally stable up to 350°C. Scanning electron microscopy (SEM) and scanning electrochemical microscopy (SECM) were used to characterize the hybrid membranes microstructures; the latter provided contrast for the conductive domains. Copyright © 2015 John Wiley & Sons, Ltd.     

Few‐Layer Antimonene by Liquid‐Phase Exfoliation

We report on a fast and simple method to produce highly stable isopropanol/water (4:1) suspensions of few‐layer antimonene by liquid‐phase exfoliation of antimony crystals in a process that is assisted by sonication but does not require the addition of any surfactant. This straightforward method generates dispersions of few‐layer antimonene suitable for on‐surface isolation. Analysis by atomic force microscopy, scanning transmission electron microscopy, and electron energy loss spectroscopy confirmed the formation of high‐quality few‐layer antimonene nanosheets with large lateral dimensions. These nanolayers are extremely stable under ambient conditions. Their Raman signals are strongly thickness‐dependent, which was rationalized by means of density functional theory calculations.     

Mitochondrially Targeted Nanoparticles Based on α‐TOS for the Selective Cancer Treatment

The aim of this work is the preparation of an active nanovehicle for the effective administration of α‐tocopheryl succinate (α‐TOS). α‐TOS is loaded in the core of nanoparticles (NPs) based on amphiphilic pseudo‐block copolymers of N‐vinyl pyrrolidone and a methacrylic derivative of α‐TOS. These well‐defined spherical NPs have sizes below 165 nm and high encapsulation efficiencies. In vitro activity of NPs is tested in hypopharynx squamous carcinoma (FaDu) cells and nonmalignant epithelial cells, demonstrating that the presence of additional α‐TOS significantly enhances its antiproliferative activity; however, a range of selective concentrations is observed. These NPs induce apoptosis of FaDu cells by activating the mitochondria death pathway (via caspase‐9). Both loaded and unloaded NPs act via complex II and produce high levels of reactive oxygen species that trigger apoptosis. Additionally, these NPs effectively suppress the vascular endothelial growth factor (VEGF) expression of human umbilical vein endothelial cells (HUVECs). These results open the possibility to use this promising nanoformulation as an α‐TOS delivery system for the effective cancer treatment, effectively resolving the current limitations of free α‐TOS administration.