Surface redox induced bipolar switching of transition metal oxide films examined by scanning probe microscopy

The bipolar resistive switching mechanisms of a p-type NiO film and n-type TiO₂ film were examined using local probe-based measurements. Scanning probe-based current–voltage (I–V) sweeps and surface potential/current maps obtained after the application of dc bias suggested that resistive switching is caused mainly by the surface redox reactions involving oxygen ions at the tip/oxide interface. This explanation can be applied generally to both p-type and n-type conducting resistive switching films. The contribution of oxygen migration to resistive switching was also observed indirectly, but only in the cases where the tip was in (quasi-) Ohmic contact with the oxide.     

New Potassium- and Cesium-selective Ionophoric Bis(crown ether)s Derived from Xanthene-4,5-dicarboxylic Acid

A series of bis(crown ether)sbased-upon a xanthene-4,5-dicarboxylic acid skeletonwas prepared and their ionophoric properties towardalkali metal cations were investigated. Bis(crownether)s bearing 15-crown-5 and 18-crown-6 moietiesexhibited pronounced extraction efficiencies towardK⁺ and Cs⁺ ions, respectively, and theextraction constant estimated by solvent extractionstudies was as high as 10⁹ for the 2-K⁺ and 3-Cs⁺ systems. Using UVtitration of potassium picrate with 2 in THF, thecomplex was found to have a structure of a completelyencapsulated guest in the host. In transportexperiments, the bis(crown ether)s showed nosignificant selectivity pattern compared withextraction results, again implying the strongcomplexation of bis(crown ether)s. Ion-selectiveelectrode studies also demonstrated that the selectiveionophoric properties of 2 toward K⁺ werereminiscent of the natural antibiotic valinomycinexcept for a somewhat slow response.     

Involvement of mitogen-activated protein kinases and p21Waf1 in hydroxyurea-induced G1 arrest and senescence of McA-RH7777 rat hepatoma cell line

Hydroxyurea is commonly used to treat hematologic disorders and some type of solid tumors, but the mechanism for its therapeutic effect is not clearly known. In this study, we examined the effect of hydroxyurea on rat hepatoma McA-RH7777 cells, specifically, on the role of mitogen-activated protein (MAP) kinase signal transduction pathways and p21(Waf1), p27(Kip1) and p53. Rat hepatoma McA-RH7777 cells treated with hydroxyurea for 7 days, caused the inhibition of cell growth in a dose-dependent manner. But, this growth inhibition was not caused by necrosis or apoptosis but instead was associated with cell senescence-like change as evidenced by senescence associated-beta-galactosidase staining, and cells arrest at G1 phase of cell cycle. Phosphorylation of MAP kinases, such as ERK, JNK, and p38, was found to be decreased after treatment of cells with hydroxyurea. But, the expression of p21(Waf1) was increased, while p27(Kip1) and p53 were not detected in hydroxyurea treated rat hepatoma cells. Hydroxyurea treatment induced G1 arrest and a senescence-like changes in rat hepatoma McA-RH7777 cells may be the likely results of signal disruption of MAP kinases (ERK, JNK, and p38 MAP kinase) and p21(Waf1) over-expression.     

Asymmetry in electrical properties of Al‐doped TiO2 film with respect to bias voltage

The energy diagram of RuO₂/Al‐doped TiO₂/RuO₂ structures was estimated from the capacitance–voltage and leakage current density–voltage curves. The Al‐doping profile in TiO₂ film was varied by changing position of the atomic layer deposition cycle of Al₂O₃ during the atomic layer deposition of 9 nm‐thick TiO₂ film. The interface between the TiO₂ film and the RuO₂ electrode containing Al‐doping layer showed a higher Schottky barrier by 0.1 eV compared with the opposite interface without the doping layer. The evolution of various leakage current profiles upon increasing the bias with opposite polarity could be well explained by the asymmetric Schottky barrier. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Electrostatic Complementarity Drives Amyloid/Nucleic Acid Co-Assembly

Proteinaceous plaques associated with neurodegenerative diseases contain many biopolymers including the polyanions glycosaminoglycans and nucleic acids. Polyanion-induced amyloid fibrillation has been implicated in disease etiology, but structural models for amyloid/nucleic acid co-assemblies remain limited. Here we constrain nucleic acid/peptide interactions with model peptides that exploit electrostatic complementarity and define a novel amyloid/nucleic acid co-assembly. The structure provides a model for nucleic acid/amyloid co-assembly as well as insight into the energetic determinants involved in templating amyloid assembly.     

Viscoelastic effects in concentrated protein dispersions

Summary Shear viscosity and primary normal stress difference of ethanol dispersions of zein indicate that there is a characteristic concentration above which concentration and shear rate dependencies change. The characteristic time derived from shear viscosity of 35 to 45 wt% zein dispersions, 10^–1 sec, is five orders of magnitude greater than that reported for dilute solution. Recoverable shear, ranging from 0.2 to 3.5, decreases at higher shear rates, increases up to the characteristic concentration, and then decreases. It is estimated that the hydrodynamic volume of the globular protein at 35 to 45 wt% concentration reduces to 1/7 to 1/9 of that in the dilute solution.It is proposed that the hydrodynamic domain of a globular protein is compressed and overlapped. The degree of compression may represent the elastic characteristics of proteins in dispersions.

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Zusammenfassung Scherviskosität und erste Normalspannungsdifferenz von Zein-Dispersionen zeigen die Existenz einer charakteristischen Konzentration an, oberhalb derer sich die Abhängigkeit von Schergeschwindigkeit und Konzentration ändern. Die aus der Scherviskosität von 35–45 gew.-%igen Zein-Dispersionen abgeleitete charakteristische Zeit von 10^–1 s ist um fünf Größenordnungen größer als die in der Literatur für verdünnte Lösungen angegebene Zeit. Die reversible Scherung, welche Werte zwischen 0,2 und 3,5 annimmt, wird zu höheren Schergeschwindigkeiten hin kleiner; sie wächst bis zu einer charakteristischen Konzentration, um danach wieder abzufallen. Es wird abgeschätzt, daß das hydrodynamische Volumen von globulärem Protein bei einer Konzentration von 35 bis 45 Gew.-% auf 1/7 bis 1/9 desjenigen in verdünnter Lösung abnimmt. Daher wird angenommen, daß die hydrodynamischen Bereiche der globulären Proteine zusammengedrückt sind und sich überlappen. Der Kompressionsgrad stellt möglicherweise die entscheidende elastische Kenngröße der Proteine in Dispersionen dar.

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With 6 figures and 5 tables     

Mesh-integrated microdroplet array for simultaneous merging and storage of single-cell droplets

We constructed a mesh-grid integrated microwell array which enables easy trapping and consistent addition of droplets. The grid acts as a microchannel structure to guide droplets into the microwells underneath, and also provides open access for additional manipulation in a high-throughput manner. Each droplet in the array forms a stable environment of pico-litre volume to implement a single-cell-based assay.     

Electrostatic Complementarity Drives Amyloid/Nucleic Acid Co‐Assembly

Proteinaceous plaques associated with neurodegenerative diseases contain many biopolymers including the polyanions glycosaminoglycans and nucleic acids. Polyanion‐induced amyloid fibrillation has been implicated in disease etiology, but structural models for amyloid/nucleic acid co‐assemblies remain limited. Here we constrain nucleic acid/peptide interactions with model peptides that exploit electrostatic complementarity and define a novel amyloid/nucleic acid co‐assembly. The structure provides a model for nucleic acid/amyloid co‐assembly as well as insight into the energetic determinants involved in templating amyloid assembly.     

Profiling of In Vitro Bioaccessibility and Intestinal Uptake of Flavonoids after Consumption of Commonly Available Green Tea Types

The aim of this study was to profile the bioaccessibility and intestinal absorption of epicatechins and flavonols in different forms of green tea and its formulation: loose leaf tea, powdered tea, 35% catechins containing GTE, and GTE formulated with green tea-derived polysaccharide and flavonols (CATEPLUS™). The bioaccessibillity and intestinal absorption of epicatechins and flavonols was investigated by using an in vitro digestion model system with Caco-2 cells. The bioaccessibility of total epicatechins in loose leaf tea, powdered tea, GTE, and CATEPLUS™ was 1.27%, 2.30%, 22.05%, and 18.72%, respectively, showing that GTE and CATEPLUS™ had significantly higher bioaccessibility than powdered tea and loose leaf tea. None of the flavonols were detected in powdered tea and loose leaf tea, but the bioaccessibility of the total flavonols in GTE and CATEPLUS™ was 85.74% and 66.98%, respectively. The highest intestinal absorption of epicatechins was found in CATEPLUS™ (171.39 ± 5.39 ng/mg protein) followed by GTE (57.38 ± 9.31), powdered tea (3.60 ± 0.67), and loose leaf tea (2.94 ± 1.03). The results from the study suggest that formulating green tea extracts rich in catechins with second components obtained from green tea processing could enhance the bioavailability of epicatechins.