Water-soluble silica-overcoated CdS:Mn/ZnS semiconductor quantum dots

Highly luminescent and photostable CdS:Mn/ZnS core/shell quantum dots are not water soluble because of their hydrophobicity. To create water-soluble quantum dots by an appropriate surface functionalization, CdS:Mn/ZnS quantum dots synthesized in a water-in-oil (W/O) microemulsion system (reverse micelles) were consecutively overcoated with a very thin silica layer ( approximately 2.5 nm thick) within the same reverse micellar system. The water droplet serves as a nanosized reactor for the controlled hydrolysis and condensation of a silica precursor, tetraethyl orthosilicate (TEOS), using an ammonium hydroxide (NH4OH) catalyst. Structural characterizations with transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS) indicate that the silica-quantum dot nanocomposites consist of a layered structure. Owing to the amorphous, porous nature of a silica layer, the optical and photophysical properties of silica-overcoated CdS:Mn/ZnS quantum dots are found to remain close to those of uncoated counterparts.     

Nonfactorization and the decaysD s +→φπ +,φρ + andφl + ν l

Using the experimentally measured values ofx=A ₂(0)/A ₁(0) andy=V(0)/A ₁(0) and the measured ratiosR _st=Γ(D _s ⁺ →φl ⁺ ν _l)/Γ(D _ins ⁺ →φπ ⁺) andR _h=Γ(D _s ⁺ →φρ ⁺)/Γ(D _s ⁺ →φπ ⁺), we present evidence for significant nonfactorization contribution in the decay amplitude forD _s ⁺ →φπ ⁺. We analyze the role of nonfactorization inD _s ⁺ →φρ ⁺ and conclude that present data onR _h are consistent with factorization inD _s ⁺ →φρ ⁺. A measurement of polarization inD _s ⁺ →φρ ⁺ would greatly assist our analysis.     

Production of Bioactive Compounds with Broad Spectrum Bactericidal Action,Bio-Film Inhibition and Antilarval Potential by the Secondary Metabolites of the Endophytic Fungus Cochliobolus sp. APS1 Isolated from the Indian Medicinal Herb Andrographis paniculata

Endophytes, being the co-evolution partners of green host plants, are factories of pharmaceutically valuable novel natural products. Cochliobolus sp. APS1, an endophyte of Andrographis paniculata (Green Chiretta), produces a plethora of natural bioactive compounds and the multipotent alkaloid Aziridine, 1-(2-aminoethyl)-, is the prime one among them. The isolate exhibited antibacterial, anti-biofilm, and antilarval potency. The MIC and MBC values of the ethyl-acetate culture extract ranged from 15.62 to 250 µg/mL against ten pathogenic microorganisms (including MRSA and VRSA). Killing kinetics data along with the leakage of macromolecules into the extracellular environment supports the cidal activity of the antibacterial principles. The broad spectrum antibacterial activity of Aziridine, 1-(2-aminoethyl)-, was optimized by a one-variable-at-a-time system coupled with response surface methodology, which led to a 45% enhancement of the antibacterial activity. The maximum response (22.81 ± 0.16 mm of zone of inhibition against MRSA) was marked in 250 mL Erlenmeyer flask containing 90 mL potato dextrose broth supplemented with (g%/L) glucose, 9.7; urea concentration, 0.74; with medium pH 6.48; after 8.76 days of incubation at 26 °C. APS1 strongly inhibited biofilm formation in the tested pathogenic microorganisms and acts as a larvicidal agent against the Dengue-vector Aedes aegypti. This is probably the first report of Aziridine, 1-(2-aminoethyl)-, from any endophytic source. Cochliobolus sp. APS1 possesses industrial importance for the production of bioactive alkaloids.     

Profile of the least energy solution of a singular perturbed Neumann problem with mixed powers

We consider the problem ${\varepsilon^{2}\Delta u - u^q + u^p = 0\,{\rm in}\,\Omega,\,u > 0\,{\rm in}\,\Omega,\,\frac{\partial u}{\partial \nu} = 0\,{\rm on}\,\partial\Omega }$ where Ω is a smooth bounded domain in ${\mathbb{R}^N}$ , ${1 < q < p < {N+2\over N-2}}$ if N ≥ 2 and ${\varepsilon}$ is a small positive parameter. We determine the location and shape of the least energy solution when ${\varepsilon \rightarrow 0.}$      

Use of allylzinc halide as a source of halide: Differential addition of nucleophiles to Ts-aziridines and aldehydes under similar reaction conditions

We have observed that the allylic zinc halide under identical reaction conditions acts in different modes for different electrophiles. For Ts-aziridines the halide part of the allylic halide has been introduced as a nucleophile and for the carbonyl compounds the simple allylation reaction occurs. To the best of our knowledge this is the first report where the allylic zinc halide is the source of halide acting as nucleophile. The main advantages of the present procedure are easy to handle, no need of inert atmosphere, mild reaction conditions, and applicability to a wide variety of substrates for aziridines and carbonyl compounds.     

Ru(II)‐based antineoplastic: A “wingtip” N‐heterocyclic carbene facilitates access to a new class of organometallics that are cytotoxic to common cancer cell lines

The syntheses, structures, and chemotherapeutic activities of Ag(I)‐, Au(I)‐, and Ru(II)‐complexes ligated to a novel N‐heterocyclic carbene ligand, 2‐(4‐nitrophenyl)imidazo[1,5‐a]pyridin‐2‐ylidene ( 1 ), are described. The corresponding complexes, [Ag( 1 )₂][PF₆], [Au( 1 )₂][PF₆] ( 3 ), and [Ru( 1 )(p‐cymene)Cl][PF₆] ( 4 ), were prepared using convenient transmetallation chemistry and characterized using a range of spectroscopic and analytical techniques. X‐ray crystallography revealed that complexes 2 and 3 adopted linear structures whereas 4 exhibited a prototypical “piano‐stool”‐like geometry; the structural assignments were further supported by DFT calculations. A series of in vitro studies revealed that while the aforementioned Ag(I), Au(I) and Ru(II) complexes exhibited significant cytotoxicities against the human colon adenocarcinoma (HCT 116), lung cancer (A549), and breast cancer (MCF7) cell lines, the Ru derivative was most prominent.     

Single-crystal X-ray diffraction analysis of arylamine-containing 2,2′-bipyridine derivatives

The structures of six 2,2′-bipyridine derivatives containing aromatic amine moieties, namely N-aryl-4-aryl-1-(pyridin-2-yl)-6,7-dihydro-5H-cyclopenta[c]pyridine-3-amines, were studied by single-crystal X-ray diffraction. The molecular structures and the effect of the substituents of these compounds on the crystal packing are discussed.

     

Oxidase‐Like Activity of Polymer‐Coated Cerium Oxide Nanoparticles

Inorganic enzyme? Ceria nanoparticles exhibit unique oxidase‐like activity at acidic pH values. These redox catalysts can be used in immunoassays (ELISA) when modified with targeting ligands (see picture; light blue and yellow structures are nanoparticles with attached ligands). This modification allows both for binding and for detection by the catalytic oxidation of sensitive colorimetric dyes (e.g. TMB).