Metal-chelating nanoparticles as selective fluorescent sensor for Cu2+

A fluorescent sensor for Cu(2+) at the nanomolar level in water has been designed by associating a BODIPY fluorophore and a selective ligand (cyclam) in ultrafine polymer nanoparticles.     

Cross-linking of polyolefins: a study by thermoporosimetry with benzene derivatives as swelling solvents.

The solvents o-, m-, p-xylene, p-dichlorobenzene, 1,2,4-trichlorobenzene, and naphthalene were calibrated as condensates used in the thermoporosimetry technique. Exponential relationships were found connecting the pore radii R(p) (in nm) and the freezing-point depression of the swelling solvent deltaT (in degrees C) on the one hand and the apparent energy of crystallization W(a) (in J cm(-3)) and deltaT on the other hand: R(p) = t exp[-1/(c deltaT)]; W(a) = W0 exp(deltaT/f). Pore- or mesh-size distributions can be derived from differential scanning calorimetry results by using the following equation: dV(p)/dR(p) = k{[cY(T)deltaT2]/[W(a)R(p)]}. All the numerical parameters were determined. Polyethylene and polypropylene samples, cross-linked with high-energy electrons or gamma-rays, were submitted to thermoporosimetry study. Relative mesh-size distributions, which depend on the polymer/solvent pair, were calculated for these polyolefins with o-, m-, and p-xylene as solvent and were found to be in the same sequence as those of their degrees of swelling and the irradiation doses received.     

Control of the evolution of iron peroxide intermediate in superoxide reductase from Desulfoarculus baarsii. Involvement of lysine 48 in protonation

Superoxide reductase is a nonheme iron metalloenzyme that detoxifies superoxide anion radicals O(2)(?-) in some microorganisms. Its catalytic mechanism was previously proposed to involve a single ferric iron (hydro)peroxo intermediate, which is protonated to form the reaction product H(2)O(2). Here, we show by pulse radiolysis that the mutation of the well-conserved lysine 48 into isoleucine in the SOR from Desulfoarculus baarsii dramatically affects its reaction with O(2)(?-). Although the first reaction intermediate and its decay are not affected by the mutation, H(2)O(2) is no longer the reaction product. In addition, in contrast to the wild-type SOR, the lysine mutant catalyzes a two-electron oxidation of an olefin into epoxide in the presence of H(2)O(2), suggesting the formation of iron-oxo intermediate species in this mutant. In agreement with the recent X-ray structures of the peroxide intermediates trapped in a SOR crystal, these data support the involvement of lysine 48 in the specific protonation of the proximal oxygen of the peroxide intermediate to generate H(2)O(2), thus avoiding formation of iron-oxo species, as is observed in cytochrome P450. In addition, we proposed that the first reaction intermediate observed by pulse radiolysis is a ferrous-iron superoxo species, in agreement with TD-DFT calculations of the absorption spectrum of this intermediate. A new reaction scheme for the catalytical mechanism of SOR with O(2)(?-) is presented in which ferrous iron-superoxo and ferric hydroperoxide species are reaction intermediates, and the lysine 48 plays a key role in the control of the evolution of iron peroxide intermediate to form H(2)O(2).     

Comparison of solvent mixtures for pressurized solvent extraction of soil fatty acid biomarkers

The extraction and transesterification of soil lipids into fatty acid methyl esters (FAMEs) is a useful technique for studying soil microbial communities. The objective of this study was to find the best solvent mixture to extract soil lipids with a pressurized solvent extractor system. Four solvent mixtures were selected for testing: chloroform:methanol:phosphate buffer (1:2:0.8, v/v/v), chloroform:methanol (1:2, v/v), hexane:2-propanol (3:2, v/v) and acetone. Soils were from agricultural fields and had a wide range of clay, organic matter and microbial biomass contents. Total lipid fatty acid methyl esters (TL-FAMEs) were the extractable soil lipids identified and quantified with gas chromatography and flame ionization detection. Concentrations of TL-FAMEs ranged from 57.3 to 542.2 n mole g⁻¹ soil (dry weight basis). The highest concentrations of TL-FAMEs were extracted with chloroform:methanol:buffer or chloroform:methanol mixtures than with the hexane:2-propanol or acetone solvents. The concentrations of TL-FAMEs in chemical groups, including saturated, branched, mono- and poly-unsaturated and hydroxy fatty acids were assessed, and biological groups (soil bacteria, mycorrhizal fungi, saprophytic fungi and higher plants) was distinguished. The extraction efficiency for the chemical and biological groups followed the general trend of: chloroform:methanol:buffer ≥ chloroform:methanol > hexane:2-propanol = acetone. Discriminant analysis revealed differences in TL-FAME profiles based on the solvent mixture and the soil type. Although solvent mixtures containing chloroform and methanol were the most efficient for extracting lipids from the agricultural soils in this study, soil properties and the lipid groups to be studied should be considered when selecting a solvent mixture. According to our knowledge, this is the first report of soil lipid extraction with hexane:2-propanol or acetone in a pressurized solvent extraction system.     

Influence of the Metal Ion on the Two‐Photon Absorption Properties of Lanthanide Complexes Including Near‐IR Emitters

The synthesis of tris(2‐thenoyltrifluoroacetonate)lanthanide(III) complexes featuring a diethylaminostyryl‐2,2′‐bipyridine coligand was achieved for lanthanum; the near‐infrared (NIR) emitters neodymium, erbium, and ytterbium; and the transition‐metal yttrium. The photophysical properties were thoroughly studied, and it was demonstrated that the conjugated bipyridine ligand acts as a good antenna for the sensitization of the NIR emitters. The two‐photon absorption (TPA) properties of all five complexes were investigated by using both two‐photon excited fluorescence and the Z‐scan method. We demonstrate that the nature of the rare earth ion has almost no influence on the TPA properties centered on the conjugated bipyridyl ligand. Finally, we show that Yb^III is sensitized by a two‐photon antenna effect, and that Nd^III is mostly sensitized by a one‐photon process involving direct excitation of forbidden f–f transitions.     

Ion-Molecule reaction in the gas phase part VI Regioselective SN2 reaction from terpenoid diastereoisomeric diols using CI/NH

A stereospecific and regioselective S_N2 mechanism (Walden inversion) is observed during studies involving modified terpenoid epimeric diols in a high-pressure ion source using ammonia as a reagent gas.     

Immobilization of biotinylated biomolecules onto electropolymerized poly(pyrrole-nitrilotriacetic acid)–Cu2+ film

A novel and simple immobilization strategy for biotinylated biological macromolecules onto electropolymerized poly(pyrrole-nitrilotriacetic acid)(NTA)–Cu²⁺ films without avidin as connecting bridge is reported. After complexation of Cu²⁺ by the polymerized NTA chelator, biotinylated biomolecules were immobilized by coordination of the biotin groups on the NTA–Cu²⁺ complex. The anchoring of biotinylated glucose oxidase was demonstrated by fluorescent characterization via FITC-labeled avidin and amperometric measurement of glucose. The resulting calibration curve led to a sensitivity and maximum current density values of 0.6 mA mol^?1 L cm^? 2 and 13.2 μA cm^? 2, respectively. Thus, biotinylated polyphenol oxidase was fixed leading to a catechol sensor with a sensitivity of 656 mA mol^?1 L cm^? 2 and maximum current density of 25.4 μA cm^? 2. This system was also applied to the efficient immobilization of biotinylated DNA, illustrated by impedimetric detection of the formation of the DNA duplex.     

Goal achieving probabilities of cone‐constrained mean‐variance portfolios

In this paper, we establish closed‐form formulas for key probabilistic properties of the cone‐constrained optimal mean‐variance strategy, in a continuous market model driven by a multidimensional Brownian motion and deterministic coefficients. In particular, we compute the probability to obtain to a point, during the investment horizon, where the accumulated wealth is large enough to be fully reinvested in the money market, and safely grow there to meet the investor's financial goal at terminal time. We conclude that the result of Li and Zhou [Ann. Appl. Prob., v.16, pp.1751–1763, (2006)] in the unconstrained case carries over when conic constraints are present: the former probability is lower bounded by 80% no matter the market coefficients, trading constraints, and investment goal. We also compute the expected terminal wealth given that the investor's goal is underachieved, for both the mean‐variance strategy and the aforementioned hybrid strategy where transfer to the money market occurs if it allows to safely achieve the goal. The former probabilities and expectations are also provided in the case where all risky assets held are liquidated if financial distress is encountered. These results provide investors with novel practical tools to support portfolio decision‐making and analysis. Copyright © 2013 John Wiley & Sons, Ltd.