Possibility of increasing the efficiency of spin injection by current in magnetic junctions

The nonequilibrium spin polarization of electrons is calculated under the conditions of spin injection by current passing from one ferromagnetic film to another in a magnetic junction. It is shown that the nonequilibrium spin concentration may substantially increase with an appropriate choice of parameters of the films and operation conditions. This leads to a decrease in the threshold current density required for switching the magnetic junction by several orders of magnitude.     

Umwandlungen des Polyacrylnitrils und Acrylnitril/Isobutylen-Copolymerisats in Gegenwart der Schwefels?ure

Ohne Zusammenfassung     

A study on the mechanism of polyvinyl chloride stabilization by lead salts

Infrared spectroscopic and DTA measurements and chemical analysis have shown that during stabilization of PVC with organic and inorganic basic lead salts various reactions occur: (a) binding of the evolved HCl, by these salts with the formation of lead chloride and complexes, including HCl, which catalyze the PVC degradation; (b) complex-forming reaction with the reactive PVC groups, which decreases the intensity of color of the polymer. In addition, with weak-organic-acid basic lead salts, exchange of labile Cl atoms for acid residues in PVC occurs, which results in an increase in inherent polymer stability.     

Oxygen and hydrogen profiles and electrical properties of unintentionally doped gallium nitride grown by hydride vapor phase epitaxy

Commercially available hydride vapor phase epitaxy gallium nitride (GaN) is characterized with the aim to correlate the oxygen and hydrogen secondary ion mass spectrometry profiles of a GaN wafer with the electrical properties of the sample. A GaN layer model, including doping profile and mobility, is derived, utilizing electrical (capacitance–voltage, Hall), structural (high resolution X‐ray diffraction) and optical (polarized infrared spectroscopy) methods. Oxygen and hydrogen are easily incorporated during hydride vapor phase epitaxy growth of GaN. Oxygen is an n‐type dopant in GaN, whereas hydrogen may passivate some of the donors. Electrical and optical properties correlate with a low defect concentration top GaN layer and a high defect concentration GaN interlayer.     

Theoretical studies of [FeFe]-hydrogenase: infrared fingerprints of the dithiol-bridging ligand in the active site

An unresolved structural issue for [FeFe]-hydrogenases is the nature of the dithiol-bridging ligand in the diiron subcluster of the active site. The two most probable candidates are 1,3-dithiopropane (propane dithiol, PDT) and di-(thiomethyl)-amine (DTN). In the latter case, the dithiol-bridging ligand is assumed to play a major role in the reaction cycle. We report density-functional theory studies of the differing roles of these dithiol-bridging ligands in the infrared spectra of synthetic models and of computational representations of the diiron cluster of the active site. Our analysis shows distinct spectral features associated with the dithiol-bridging NH mode for compounds having a DTN bridge, which, however, would have been obscured by the H2O vibrations in existing measurements. However, if indeed nitrogen is present in the dithiol-bridging ligand, a combination of selective deuteration and chemical inactivation with CO would create a unique signature in an accessible region of the infrared spectrum, whose position and intensity are predicted.     

Large-scale semidefinite programming via a saddle point Mirror-Prox algorithm

In this paper, we first demonstrate that positive semidefiniteness of a large well-structured sparse symmetric matrix can be represented via positive semidefiniteness of a bunch of smaller matrices linked, in a linear fashion, to the matrix. We derive also the “dual counterpart” of the outlined representation, which expresses the possibility of positive semidefinite completion of a well-structured partially defined symmetric matrix in terms of positive semidefiniteness of a specific bunch of fully defined submatrices of the matrix. Using the representations, we then reformulate well-structured large-scale semidefinite problems into smooth convex–concave saddle point problems, which can be solved by a Prox-method developed in [6] with efficiency . Implementations and some numerical results for large-scale Lovász capacity and MAXCUT problems are finally presented.      

Tubular conjugated polymer for chemosensory applications

In this paper, we present the concept of a soluble tubular conjugated polymer (TCP). We report on a fluorescent 5,5'-Bicalixarene-based polymer where the calixarene units are seamlessly incorporated in the conjugated polymeric chain that can respond to a small molecule complexation inside the hydrophobic cavity. In particular, our system demonstrated a reversible rapid fluorescence quenching upon interaction of gaseous nitric oxide with the calixarene moiety.     

Fluorescent Calixarene Scaffolds for NO Detection in Protic Media

We present the first fluorescent water‐soluble conjugated calixarene scaffolds that are capable of NO gas detection. Two different scaffolds, one based on a 5,5′‐bicalixarene structure and its isomer bearing two distantly conjugated calixarene moieties, were synthesized. While the fluorescence of both isomers is quenched upon either passing of NO gas or generating it in situ from diethylamine NONOate, the bicalixarene‐based scaffold showed a significantly stronger response. We also present an example of a dye encapsulation strategy to achieve the detection of NO at longer wavelengths than in the parent calixarene host. Finally, a conjugated polymer bearing a 5,5′‐bicalixarene scaffold has also been prepared and demonstrated enhanced sensitivity compared to the monomer due to the molecular wire effect.     

Cationic Graft Copolymers as Carriers for Delivery of Antisense‐Oligonucleotides

Self‐assembling systems based on ionic complexes of DNA fragments (36 base pairs), bcl‐2 antisense oligonucleotides (octadecamer), oligophosphates (25 phosphate groups) or acrylic oligomers (18 groups of phosphonic acid) with poly(L ‐lysine) (PLL) ( = 130 000 and 88 000) grafted with short poly[N‐(2‐hydroxypropyl)methacrylamide] (PHPMA) chains ( = 4 300 or 8 600) were studied by static and dynamic light scattering methods as systems suitable for gene therapy applications. The graft copolymers (GPLLs) with shorter PHPMA grafts ( = 4 300) provide polyelectrolyte complexes (PECs) with smaller and R_H than the corresponding GPLLs with longer grafts ( = 8 600) and the same content of PLL. The lowest aggregation number of 2 was observed for PECs prepared from the GPLL with short grafts and 40 wt.‐% of PLL. The complexes of oligonucleotides and DNA fragments with GPLLs showed quite similar behavior to that with oligophosphates and acrylic oligomer. The complexes prepared from GPLLs containing 40 wt.‐% of PLL and at excess of oligophosphate were stable for at least 48 h under physiological conditions (0.15 M NaCl) and in bovine serum albumin solutions (1 mg · mL^?1). Additionally, polyanion exchange reactions of the PECs in contact with poly(styrenesulfonate) and DNA were studied in 0.15 M NaCl solutions. The oligophosphates in complexes were at least partially substituted with high‐molecular‐weight polyanions. The structure of the initial PECs dominated the PEC structure after the exchange reaction.

The dependence of the molecular weight (a) and the hydrodynamic radius R_H (b) of complexes of the oligophosphate (OPP) and four graft copolymers (GPLLi, i = 0–3) on the mixing ratio X.     

Simulation of novel soy protein‐based systems for tissue regeneration applications

In the present research, molecular modeling methods were used to study novel porous soy protein conjugates with gelatin or alginate, which were recently developed as potential scaffolds for tissue engineering applications. Gelatin (protein) and alginate (polysaccharides) were chemically crosslinked to soy protein isolates (SPI) in order to obtain a porous 3D network. Computational tools were applied to estimate the crosslinking degree and compare the degradation rate of soy–gelatin or soy–alginate conjugates. Soy protein 3D structure was obtained from the Protein Data Bank (PDB). Alginate and gelatin structures were built and subjected to dynamic simulation using the molecular modeling package Material Studio 7.0. The crosslinking degree was estimated by the miscibility of the two reactants and the interaction with the crosslinking agents 1‐ethyl‐3‐(3‐dimethylaminopropyl) carbodiimide (EDC) or glyoxal. The calculations revealed that soy protein mixes well with gelatin but not with alginate. Radial distribution function (RDF) calculations showed that the interaction distance between alginate and EDC is significantly shorter than between gelatin and EDC, probably because of ionic attraction between the ammonium groups of EDC and the carboxylate groups in alginate, which facilitates the crosslinking reaction. The degradation rate of soy protein conjugates was related to their interaction with water. It was found that the solubility of soy–gelatin in water is higher than soy–alginate and that water molecules form more hydrogen bonds with soy–gelatin than with soy–alginate. These findings might be the reason for the observed difference in degradation rate of the two conjugates; the soy–gelatin degrades faster than soy–alginate. Copyright © 2016 John Wiley & Sons, Ltd.