Validation of a digestion system using a digester block/cold finger system for the determination of lead in vegetable foods by electrothermal atomic absorption spectrometry

This paper presents the validation of a system for sample digestion using a digester block/cold finger to determine the lead content in vegetables by electrothermal atomic absorption spectrometry (ETAAS). After mineralization, lead contents were determined by ETAAS using a calibration curve based on aqueous standards prepared in 2.60 M nitric acid solutions containing 5 microg ammonium phosphate as chemical modifier. A pyrolysis temperature of 900 degrees C and atomization temperature of 2000 degrees C were used. This method allowed the determination of lead with a characteristic mass of 35 pg; LOD and LOQ of 0.6 and 2 nglg, respectively, were found. The precision was investigated in terms of reproducibility and repeatability. Reproducibility was estimated by analysis of nine different portions of a certified reference material (CRM) of spinach leaves, and the repeatability was determined through the analysis of nine aliquots of the same solution. The reproducibility and repeatability were found to be 4.27 and 2.94% RSD, respectively. The accuracy was confirmed by analysis of whole meal flour, spinach leaves, and orchard leaves CRMs, all furnished by the National Institute of Standards and Technology. Lead contents were measured using the newly developed technique in 11 different potato samples. The lead contents ranged from 12.80 to 69.27 ng/g, with an average value of 28.59 ng/g. These values were in agreement with data reported in the literature.     

Fixed point theorems for random pseudo-contractive mappings

Very recently in Fierro et al. (2009) [6], we obtained a general principle to prove the existence of Random Fixed Point Theorems. As a consequence of this, we have been able to obtain various generalizations for pseudo-contractive mappings with rather simple proofs. In addition, while we were deriving these extensions for random operators, some deterministic results arose, which also appear to be new.     

Highly polar carbohydrates stack onto DNA duplexes via CH/π interactions

Carbohydrate-nucleic acid contacts are known to be a fundamental part of some drug-DNA recognition processes. Most of these interactions occur through the minor groove of DNA, such as in the calicheamicin or anthracycline families, or through both minor and major groove binders such as in the pluramycins. Here, we demonstrate that carbohydrate-DNA interactions are also possible through sugar capping of a DNA double helix. Highly polar mono- and disaccharides are capable of CH/π stacking onto the terminal DNA base pair of a duplex as shown by NMR spectroscopy. The energetics of the carbohydrate-DNA interactions vary depending on the stereochemistry, polarity, and contact surface of the sugar involved and also on the terminal base pair. These results reveal carbohydrate-DNA base stacking as a potential recognition motif to be used in drug design, supramolecular chemistry, or biobased nanomaterials.     

Antibacterial action of Ag-containing MFI zeolite at low Ag loadings

We show that Ag-containing zeolites are highly effective against Staphylococcus aureus (SA) bacteria even at low Ag loadings and in the presence of high (10(9) CFU per mL) bacterial concentrations. At short contact times the bactericidal efficiency correlates strongly with Ag(+) release. At longer times data dispersion is higher, probably as a consequence of bacterial metabolism.     

Enantioselective organocatalytic formal allylation of α-branched aldehydes

Heteroarylvinyl sulfone 1 has been successfully used as a new sulfonyl Michael acceptor in aminocatalytic reactions with branched aldehydes. Subsequent one-pot Julia-Kocienski olefination allows the challenging preparation of enantiomerically pure α-allylated aldehydes bearing C-α quaternary carbons.     

Asymptotics of solutions to the periodic problem for a Burgers type equation

We study large time asymptotic behavior of solutions to the periodic problem for the nonlinear Burgers type equation

An Integrated Market for Electricity and Natural Gas Systems with Stochastic Power Producers

In energy systems with high shares of weather-driven renewable power sources, gas-fired power plants can serve as a back-up technology to ensure security of supply and provide short-term flexibility. Therefore, a tighter coordination between electricity and natural gas networks is foreseen. In this work, we examine different levels of coordination in terms of system integration and time coupling of trading floors. We propose an integrated operational model for electricity and natural gas systems under uncertain power supply by applying two-stage stochastic programming. This formulation co-optimizes day-ahead and real-time dispatch of both energy systems and aims at minimizing the total expected cost. Additionally, two deterministic models, one of an integrated energy system and one that treats the two systems independently, are presented. We utilize a formulation that considers the linepack of the natural gas system, while it results in a tractable mixed-integer linear programming (MILP) model. Our analysis demonstrates the effectiveness of the proposed model in accommodating high shares of renewables and the importance of proper natural gas system modeling in short-term operations to reveal valuable flexibility of the natural gas system. Moreover, we identify the coordination parameters between the two markets and show their impact on the system’s operation and dispatch.     

Long Distance Electronic Effects on the Rotational Potential Barriers Around the Caromatic-Cethylenic Bond

A systematic study of the rotational activation free energy around the C_aromatic-C_ethylenic bond of para-substituted styrene systems is carried out in the present work from a quantum chemistry point of view.

Calculations of the rotational potential barriers in the AM1 approach are developed as function of the electron-donor groups localized on the aromatic ring. Based on these calculations and thermodynamical data, we predict changes in the activation free energy barriers due to the long distance electronic effects of the substituents in acetophenones, cinnamaldehydes and benzalketones according to the following equation:

Our results agree the experimental measurements registered up to date and the standard deviations are similar to experimental determinations.     

Availability of Isoflavones (Genistin,Genistein and Daidzein) in Soybean ( Glycine Max ) Curd Treated under High Pressure

The article describes the concentration of isoflavones (genistin, genistein and daidzein) in a Spanish commercial tofu treated under high-pressure. The tofu was subjected to pressure of 400 MPa, in cycles of 10 min each with a total of 4 cycles with the progression of 10, 20, 30 and 40 min, and a temperature of about 10-12 °C. The isoflavones were extracted from tofu with aqueous methanol solution (80:20). The content of isoflavones went up directly proportional to the pressure applied for the first 30 minutes. Afterwards, at 40 min, the values dropped close to the control. Significant differences were found in genistein, genistin and daidzein treated for 20 and 30 min in comparison to control values. Finally, we came to the conclusion that, the isoflavones (genistin, genistein and daidzein) of treated tofu were not destroyed at 400 Mpa for 30 min and a major extraction was observed when compared with the untreated tofu.