Absence of skew scattering in two-dimensional systems: testing the origins of the anomalous Hall effect

We study the anomalous Hall conductivity in spin-polarized, asymmetrically confined two-dimensional electron and hole systems, taking into account the intrinsic, side-jump, and skew-scattering contributions to the transport. We find that the skew scattering, principally responsible for the extrinsic contribution to the anomalous Hall effect, vanishes for the two-dimensional electron system if both chiral Rashba subbands are partially occupied, and vanishes always for the two-dimensional hole gas studied here, regardless of the band filling. Our prediction can be tested with the proposed coplanar two-dimensional electron-hole gas device and can be used as a benchmark to understand the crossover from the intrinsic to the extrinsic anomalous Hall effect.     

Experimental device for study of the thermal stimulated direct current in the composite materials

Journal of Thermal Analysis and Calorimetry - Presents the device for analysis the thermally stimulated electrical conductivity of composites in the wide temperature range. The main advantage of...     

Sequential and selective hydrogenation of the C(alpha)-C(beta) and M-C(alpha) double bonds of an allenylidene ligand coordinated to osmium: new reaction patterns between an allenylidene complex and alcohols

Complex [OsH(=C=C=CPh2)(CH3CN)2(PiPr3)2]BF4 (1) reacts with primary and secondary alcohols to give the corresponding dehydrogenated alcohols and the hydride-carbene derivative [OsH(=CHCH=CPh2)(CH3CN)2(PiPr3)2]BF4 (2), as a result of hydrogen transfer reactions from the alcohols to the Calpha-Cbeta double bond of the allenylidene ligand of 1. The reactions with phenol and t-butanol, which do not contain any beta-hydrogen, afford the alkoxy-hydride-carbyne complexes [OsH(OR)(CCH=CPh2)(CH3CN)(PiPr3)2]BF4 (R = Ph (3), tBu (4)), as a consequence of the 1,3-addition of the O-H bond of the alcohols to the metallic center and the Cbeta atom of the allenylidene of 1. On the basis of the reactions of 1 with these tertiary alcohols, deuterium labeling experiments, and DFT calculations, the mechanism of the hydrogenation is proposed. In acetonitrile under reflux, the Os-C double bond of 2 undergoes hydrogenation to give 1,1-diphenylpropene and [Os{CH2CH(CH3)PiPr2(CH3CN)3(PiPr3)]BF4 (11), containing a metalated phosphine ligand. This reaction is a first-order process with activation parameters of DeltaH = 89.0 +/- 6.3 kJ mol-1 and DeltaS = -43.5 +/- 9.6 J mol-1 K-1. The X-ray structures of 2 and 3 are also reported.     

Small-molecule fluorophores to detect cell-state switching in the context of high-throughput screening

A small molecule capable of distinguishing the distinct states resulting from cellular differentiation would be of enormous value, for example, in efforts aimed at regenerative medicine. We screened a collection of fluorescent small molecules for the ability to distinguish the differentiated state of a mouse skeletal muscle cell line. High-throughput fluorescence-based screening of C2C12 myoblasts and myotubes resulted in the identification of six compounds with the desired selectivity, which was confirmed by high-content screening in the same cell states. The compound that resulted in the greatest fluorescence intensity difference between the cell states was used as the screening agent in a pilot screen of 84 kinase inhibitors, each present in four doses, for inhibition of myogenesis. Of the kinase inhibitors, 17 resulted in reduction of fluorescence at one or more concentrations; among the "hits" included known inhibitors of myogenesis, confirming that this compound is capable of detecting the differentiated myotube state. We suggest that the strategy of screening for screening agents reported here may be extended more broadly in the future.     

An amperometric biosensor based on multiwalled carbon nanotube-poly(pyrrole)-horseradish peroxidase nanobiocomposite film for determination of phenol derivatives

An amperometric biosensor based on horseradish peroxidase (HRP) and carbon nanotube (CNT)/polypyrrole (PPy) nanobiocomposite film on a gold surface has been developed. The HRP was incorporated into the CNT/PPy nanocomposite matrix in one-step electropolymerization process without the aid of cross-linking agent. Amperometric response was measured as a function of concentration of phenol derivatives, at a fixed bias voltage of -50 mV. Optimization of the experimental parameters was performed with regard to pH and concentration of hydrogen peroxide. The linear range, sensitivity and detection limit of the biosensor were investigated for eighteen phenol derivatives. The sensitivity in the linear range increased in this order: 4-methoxyphenol>2-aminophenol>guaiacol=m-cresol>2-chlorophenol=4-chlorophenol=hydroquinone=pyrocatechol>2,6-dimethoxyphenol>3-chlorophenol>p-cresol>p-benzoquinone=4-acetamidophenol>catechol>phenol=pyrogallol=2,4-dimethylphenol. CNTs was shown to enhance the electron transfer as a mediator and capable to carry higher bioactivity owing to its intensified surface area. The biosensor exhibited low detection limits with a short response time (2s) for the tested phenolics compared to the reported working electrodes. It retained 70% of its initial activity after using for 700 measurements in 1 month.     

Preparation of ribavirin analogues by copper- and ruthenium-catalyzed azide-alkyne 1,3-dipolar cycloaddition

In this study, we described the synthesis of 1,4- and 1,5-disubstituted-1,2,3-triazolo-nucleosides from various alkynes with 1′-azido-2′,3′,5′-tri-O-acetylribose using either copper-catalyzed azide-alkyne cycloaddition (CuAAC) or ruthenium-catalyzed azide-alkyne cycloaddition (RuAAC), respectively. Optimized RuAAC conditions were realized with the commercially available [Cp^∗RuCl(PPh₃)₂] under microwave heating, which allows a significant acceleration of the reaction times (from 6 h to 5 min). This reaction can work under water-containing system. RuAAC and CuAAC are useful tools for the synthesis of 1,2,3-triazolyl-nucleosides small libraries.     

Tetranitromethane as an efficient reagent for the conversion of epoxides into β-hydroxy nitrates

A convenient regioselective method for the preparation of β-hydroxy nitrates based on the ring opening reaction of epoxides by tetranitromethane in the presence of triethylamine is described. A series of substituted β-hydroxy nitrates were obtained in high yields under mild conditions.     

Kinetics of the β-picoline oxidation to nicotinic acid over vanadia-titania catalyst. 2. Effect of dioxygen and β-picoline

The effect of the dioxygen and β-picoline concentrations on the oxidation of β-picoline to nicotinic acid was studied at 270°C over a 20% V₂O₅-80% TiO₂ (wt. %) catalyst. The study was performed in a differential reactor at constant concentrations of water and nicotinic acid. A considerable excess of dioxygen was shown to be necessary for the formation of nicotinic acid. It was found that the rates of β-picoline transformation into nicotinic acid, pyridine-3-carbaldehyde, pyridine-3-nitrile, pyridine and carbon oxides as well as selectivities to products and the catalyst state depend strongly on the ratio of dioxygen to β-picoline concentrations. The minimum admissible ratio of these concentrations under industrial conditions was determined.     

Intramolecular sensitization of photocleavage of the photolabile 2-(2-nitrophenyl)propoxycarbonyl (NPPOC) protecting group: photoproducts and photokinetics of the release of nucleosides

Novel photolabile protecting groups based on the 2-(2-nitrophenyl)propoxycarbonyl (NPPOC) group with a covalently linked thioxanthone as an intramolecular triplet sensitizer exhibit significantly enhanced light sensitivity under continuous illumination. Herein we present a detailed study of the photokinetics and photoproducts of nucleosides caged with these new protecting groups. Relative to the parent NPPOC group, the light sensitivity of the new photolabile protecting groups is enhanced by up to a factor of 21 at 366 nm and is still quite high at 405 nm, the wavelength at which the sensitivity of the parent compound is practically zero. A new pathway for deprotection of the NPPOC group proceeding through a nitroso benzylalcohol intermediate has been discovered to complement the main mechanism, which involves beta elimination. Under standard conditions of lithographic DNA-chip synthesis, some of the new compounds, while maintaining the same chip quality, react ten times faster than the unmodified NPPOC-protected nucleosides.