Dynamic cylindrical assembly of triblock copolymers by a hierarchical process of covalent and supramolecular interactions

We have developed a hierarchical process that combines linear triblock copolymers into concentric globular subunits through strong chemical bonds and is followed by their supramolecular assembly via weak noncovalent interactions to afford one-dimensionally assembled, dynamic cylindrical nanostructures. The molecular brush architecture forces triblock copolymers to adopt intramolecular interactions within confined frameworks and then drives their intermolecular interactions in the mixtures of organic solvent and water. In contrast, the triblock copolymers, when not preconnected into the molecular brush architectures, organize only into globular assemblies.     

Phosphorescent sensor for biological mobile zinc

A new phosphorescent zinc sensor (ZIrF) was constructed, based on an Ir(III) complex bearing two 2-(2,4-difluorophenyl)pyridine (dfppy) cyclometalating ligands and a neutral 1,10-phenanthroline (phen) ligand. A zinc-specific di(2-picolyl)amine (DPA) receptor was introduced at the 4-position of the phen ligand via a methylene linker. The cationic Ir(III) complex exhibited dual phosphorescence bands in CH(3)CN solutions originating from blue and yellow emission of the dfppy and phen ligands, respectively. Zinc coordination selectively enhanced the latter, affording a phosphorescence ratiometric response. Electrochemical techniques, quantum chemical calculations, and steady-state and femtosecond spectroscopy were employed to establish a photophysical mechanism for this phosphorescence response. The studies revealed that zinc coordination perturbs nonemissive processes of photoinduced electron transfer and intraligand charge-transfer transition occurring between DPA and phen. ZIrF can detect zinc ions in a reversible and selective manner in buffered solution (pH 7.0, 25 mM PIPES) with K(d) = 11 nM and pK(a) = 4.16. Enhanced signal-to-noise ratios were achieved by time-gated acquisition of long-lived phosphorescence signals. The sensor was applied to image biological free zinc ions in live A549 cells by confocal laser scanning microscopy. A fluorescence lifetime imaging microscope detected an increase in photoluminescence lifetime for zinc-treated A549 cells as compared to controls. ZIrF is the first successful phosphorescent sensor that detects zinc ions in biological samples.     

Surfactant-free water-processable photoconductive all-carbon composite

Heterojunctions between different graphitic nanostructures, including fullerenes, carbon nanotubes and graphene-based sheets, have attracted significant interest for light to electrical energy conversion. Because of their poor solubility, fabrication of such all-carbon nanocomposites typically involves covalently linking the individual constituents or the extensive surface functionalization to improve their solvent processability for mixing. However, such strategies often deteriorate or contaminate the functional carbon surfaces. Here we report that fullerenes, pristine single walled carbon nanotubes, and graphene oxide sheets can be conveniently coassembled in water to yield a stable colloidal dispersion for thin film processing. After thermal reduction of graphene oxide, a solvent-resistant photoconductive hybrid of fullerene-nanotube-graphene was obtained with on-off ratio of nearly 6 orders of magnitude. Photovoltaic devices made with the all-carbon hybrid as the active layer and an additional fullerene block layer showed unprecedented photovoltaic responses among all known all-carbon-based materials with an open circuit voltage of 0.59 V and a power conversion efficiency of 0.21%. The ease of making such surfactant-free, water-processed, carbon thin films could lead to their wide applications in organic optoelectronic devices.     

Total synthesis of the potent androgen receptor antagonist (-)-arabilin: a strategic, biomimetic [1,7]-hydrogen shift

The first total synthesis of (-)-arabilin, a Streptomyces metabolite that inhibits hormone activation of the androgen receptor, has been completed. The key step, a [1,7]-hydrogen shift, establishes the enol ether-containing skipped-tetraene substructure. This nonenzymatic pericyclic reaction is considered to be biomimetic.     

Tetrahedral atom ordering in a zeolite framework: a key factor affecting its physicochemical properties

Three gallosilicate natrolites with closely similar chemical composition but differing in the distribution of Si and Ga over crystallographically different tetrahedral sites (T-sites) show striking differences in their cation exchange performance. The ability to exchange Na(+) by the larger alkali metal cations decreases upon increasing the size of the cation, as expected, but also with the degree of T-atom ordering. To seek an insight into this phenomenon, the crystal structures of 11 different zeolites, which show variations in degree of T-atom ordering, nature of countercation, and hydration state, have been refined using synchrotron diffraction data. While the three as-made sodium materials were characterized to have a low, medium, and high degree of ordering, respectively, their pore sizes are close to the size of the bare Na(+) cation and much smaller than that of the larger alkali cations, which are nonetheless exchanged into the materials, each one at a different level. Interestingly, large differences are also manifested when the Na(+) back-exchange is performed on the dehydrated K(+) forms, with crystallographic pore sizes too small even to allow the passage of Na(+). Although the thermodynamic data point to small differences in the enthalpy of the Na(+)/K(+) exchange in the three materials, comparison of the "static" crystallographic pore sizes and the diameter of the exchanged cations lead us to conclude that during the exchange process these zeolites undergo significant deformations that dynamically open the pores, allowing cation traffic even for Cs(+) in the case of the most disordered material. In addition to the very large topological flexibility typical of the natrolite framework, we propose as a hypothesis that there is an additional flexibility mechanism that decreases the rigidity of the natrolite chain itself and is dependent on preferential siting of Si or Ga on crystallographically different T-sites.     

New Dammarane‐Type Saponins from the Rhizomes of Panax japonicus

Phytochemical investigation of the rhizomes of Panax japonicus C. A. Meyer (Araliaceae) resulted in the isolation of two new dammarane‐type triterpenoid saponins, yesanchinoside R₁ ( 1 ) and yesanchinoside R₂ ( 2 ), together with one new natural product, 6′′′‐O‐acetylginsenoside Re ( 3 ). In addition, 25 known compounds, including 23 triterpenoid saponins, 4 – 26 , β‐sitosterol 3‐O‐β‐D ‐glucopyranoside ( 27 ), and ecdysterone ( 28 ), were also identified. The known saponins 12, 15 , and 18 – 22 were reported for the first time from the title plant. Their structures were elucidated on the basis of detailed spectroscopic analyses, including 1D‐ and 2D‐NMR techniques, as well as acidic hydrolysis.     

Porous magnetic manganese oxide nanostructures: synthesis and their application in water treatment

Magnetic manganese oxide nanostructures are fabricated at room temperature by mixing a KMnO(4) solution and oleic acid capped Fe(3)O(4) particles. Oleic acid molecules capped Fe(3)O(4) particles are oxidized by potassium permanganate (KMnO(4)) in an aqueous solution to produce porous magnetic manganese oxide nanostructures. The synthesis technique can be extended to other MnO(x) structures with composition of different nanocrystals, such as quantum dots, noble metal crystals which may have important applications as catalysts, adsorbents, electrodes and advanced materials in many scientific disciplines. Transmission electron microscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy, and nitrogen adsorption-desorption measurements are employed to characterize the structures. As an adsorbent in water treatment, the nanostructures possess a large adsorption capability and high organic pollutant removal rates due to the large surface area and pore volume. The nanostructures are recyclable as their adsorption capability can be recovered by combustion. Furthermore, the strong magnetism exhibited by the structures provides an easy and efficient separation means in wastewater treatment under an external magnetic field.     

Speciation analysis of arsenic compounds in edible oil by ion chromatography-inductively coupled plasma mass spectrometry

An inductively coupled plasma mass spectrometer (ICP-MS) was used as an ion chromatographic (IC) detector for the speciation analysis of arsenic in edible oil. The arsenic species studied include arsenite, arsenate, monomethylarsonic acid, dimethylarsinic acid, arsenobetaine and arsenocholine. Gradient elution using (NH(4))(2)CO(3) and methanol at pH 8.5 allowed the chromatographic separation of all species in less than 8 min. Effluents from the IC column were delivered to the nebulizer of ICP-MS for the determination of arsenic. The concentrations of arsenic species have been determined in several used and fresh vegetable oil samples. In this study, a microwave-assisted extraction method was used for the extraction of arsenic species from oil samples. The extraction efficiency was better than 92% and the recoveries from spiked samples were in the range of 90-105%. The precision between sample replicates was better than 8% for all determinations. The limits of detection were in the range of 0.008-0.024 ng mL(-1) for various arsenic species based on peak height, which corresponded to 0.08-0.24 ng g(-1) in the original oil sample. The major arsenic species in the used oil samples varied based on the food items cooked.     

Novel calcium-alginate capsules with aqueous core and thermo-responsive membrane

Novel calcium-alginate (Ca-alginate) capsules with aqueous core and thermo-responsive membrane are successfully prepared by introducing a co-extrusion minifluidic approach, and the thermo-responsive gating characteristics of Ca-alginate capsule membranes embedded with poly(N-isopropylacrylamide) (PNIPAM) microspheres are investigated systematically. The experimental results show that the prepared Ca-alginate capsules are highly monodisperse, and the average diameter and membrane thickness of Ca-alginate capsules are about 2.96 mm and 0.11 mm respectively. The Ca-alginate capsule membranes exhibit desired thermo-responsive gating property. With increasing the content of PNIPAM microspheres embedded in the Ca-alginate capsule membranes, the thermo-responsive gating coefficient of the capsule membranes increases simply. When solute molecules diffuse through the capsule membrane, the thermo-responsive gating coefficient is significantly affected by the molecular weight of solute molecules.