Wavelet-based method for noise characterization and rejection in high-performance liquid chromatography coupled to mass spectrometry

We present a new method for rejecting noise from HPLC-MS data sets. The algorithm reveals peptides at low concentrations by minimizing both the chemical and the random noise. The goal is reached through a systematic approach to characterize and remove the background. The data are represented as two-dimensional maps, in order to optimally exploit the complementary dimensions of separation of the peptides offered by the LC-MS technique. The virtual chromatograms, reconstructed from the spectrographic data, have proved to be more suitable to characterize the noise than the raw mass spectra. By means of wavelet analysis, it was possible to access both the chemical and the random noise, at different scales of the decomposition. The novel approach has proved to efficiently distinguish signal from noise and to selectively reject the background while preserving low-abundance peptides.     

The influence of the synthesis routes of MgAl2O4 on its properties and behavior as support of dehydrogenation catalysts

In order to synthesize MgAl₂O₄, three methods were used: (a) a solid phase reaction of MgO and γ-Al₂O₃ oxides at 900 °C for 24 h (ceramic method), (b) wet milling during 24 h of the mixture of oxides followed by the reaction at 900 °C for 12 h (mechanochemical synthesis), and (c) coprecipitation of Mg(NO₃)₂·6H₂O and Al(NO₃)₃·9H₂O with ammonia solution followed by a calcination in a flow of air at 800 °C during 4 h (coprecipitation method). The synthesized materials were characterized by XRD, BET isotherm, isopropanol dehydration reaction, TGA/DTA and SEM. The results indicate that in all the cases the MgAl₂O₄ spinel was formed. Besides, a residue of MgO in the samples obtained by the ceramic method and mechanochemical synthesis was found, which was eliminated by purification. The surface area of MgAl₂O₄ obtained by mechanochemical synthesis and coprecipitation method are much higher than that of the spinel synthesized by the ceramic method. Pt (0.3%) catalysts were prepared by impregnating the three supports with H₂PtCl₆. The metallic dispersion of Pt/MgAl₂O₄ obtained by mechanochemical synthesis was higher than that of Pt catalysts supported on the other spinels, in agreement with the catalytic behavior observed in n-butane dehydrogenation reaction and test reactions of the metallic phase.     

Calcium Addition,pH, and High Hydrostatic Pressure Effects on Soybean Protein Isolates—Part 1: Colloidal Stability Improvement

Calcium addition to soybean protein dispersions increases nutritional value but harms functional properties, such as protein solubility and colloidal stability. The high hydrostatic pressure (HHP) treatment can reverse those effects. The aims of this work were to evaluate the influence of pH and protein and calcium concentration on HHP solubilizing/stabilizing effect and to characterize the physicochemical properties of HHP-stabilized species. Proteins without calcium addition were stabilized by HHP at both pHs. However, calcium-added proteins behaved differentially: at pH 5.9, the effect was verified only at low protein concentration, whereas at pH 7.0, the effect was verified under both assayed protein concentrations (5 and 10 g L^?1) and with a higher magnitude in calcium-added samples. Moreover, at pH 7.0, the effect was independent of the order of calcium addition and HHP treatment, whereas at pH 5.9, the effect was smaller when calcium was added after HHP treatment. At both pHs, the solubilizing/stabilizing effect of HHP on soybean proteins seemed to be largely dependent on the decrease in the size of protein species. The smaller the size, the greater the amount of protein that remained in dispersion after intense centrifugation (10,000g, 20 min, 4 °C). Although the effect of HHP consisted, at least in part, of stabilizing insoluble protein, turbidity decreased in all samples after HHP treatment. By combining different levels of pH, calcium, and protein concentrations, translucent or turbid colloidal-stable dispersions can be obtained by HHP treatment.     

Mechanism of binding of fluoroquinolones to the quinolone resistance-determining region of DNA gyrase: towards an understanding of the molecular basis of quinolone resistance

We have studied the bacterial resistance to fluoroquinolones that arises as a result of mutations in the DNA gyrase target protein. Although it is known that DNA gyrase is a target of quinolone antibacterial agents, the molecular details of the quinolone-gyrase interaction remain unclear. The mode of binding of ciprofloxacin, levofloxacin, and moxifloxacin to DNA gyrase was analyzed by means of docking calculations over the surface of the QRDR of GyrA. The analysis of these binding models allows study of the resistance mechanism associated with gyrA mutations more commonly found in E. coli fluoroquinolone-resistant strains at the atomic level. Asp87 was found to be critical in the binding of these fluoroquinolones because it interacts with the positively charged nitrogens in these bactericidal drugs. The role of the other most common mutations at amino acid codon Ser83 can be explained through the contacts that the side chain of this residue establishes with fluoroquinolone molecules. Finally, our results strongly suggest that, although Arg121 has never been found to be associated with fluoroquinolone resistance, this residue makes a pivotal contribution to the binding of the antibiotic to GyrA and to defining its position in the QRDR of the enzyme.     

Reaction of chlorine dioxide with emergent water pollutants: product study of the reaction of three beta-lactam antibiotics with ClO(2)

This work deals with the chlorine dioxide (ClO(2)) reactivity with three representative beta-lactam antibiotics (penicillin, amoxicillin and cefadroxil) that can be present in natural aquatic resources. Due to the wide use of ClO(2) as disinfection agent our work is of interest to determine the fate of these antibiotics during the water treatment process. Our study shows that antibiotics react stoichiometrically with ClO(2) because increasing amounts of ClO(2) lead to increasing antibiotic disappearance. Concerning the influence of antibiotic structure, penicillin reacts sluggishly with ClO(2), whereas amoxicillin and cefadroxil are highly reactive at either neutral or basic pH. For both reactive antibiotics, hydroquinone together with a wide range of 4-substituted phenols were detected as products. Pretreatment with ClO(2) before chlorination of aqueous solutions of antibiotics reduces the trihalomethane formation as compared with analogous chlorination without ClO(2) pretreatment.     

Identification of precancerous lesions by multispectral gastroendoscopy

Gastric cancer is one of the fifth most deadly cancers worldwide. Nowadays the diagnosis is performed through gastroendoscopy under white light and histological analysis. However, the precancerous lesions are multifocalized and present low differences with respect to healthy tissue. Several systems have been proposed based on light tissue interaction to improve the visualization of malignancies. However, these systems are limited to few wavelengths. In this paper, we propose a minimally invasive technique based on multispectral imaging and a methodology to identify malignancies in the stomach. We developed a multispectral gastroendoscopic system compatible with current gastroendoscopes, where only the illumination is changed. The spectra are extracted from the acquired multispectral images in order to compute statistical features that are used to classify the data in two classes: healthy and malignant. The features are ranked by pooled variance t test to train three classifiers. Neural networks using generalized relevance learning vector quantization, support vector machine (SVM) with a Gaussian kernel and k-nn are evaluated using leave one patient out cross-validation. Taking into consideration the data collected in this work, the quantitative results from the classification using SVM show high accuracy and sensitivity using a low number of features. These results show the ability to discriminate malignancies of the gastric tissue. Therefore, multispectral imaging could help in the identification of malignancies during gastroendoscopy.     

Silver contamination on abiotic and biotic compartments of Nahuel Huapi National Park lakes, Patagonia, Argentina

The Ag contents of abiotic and biotic compartments of different lakes of Nahuel Huapi National Park, Patagonia, Argentina were analyzed. The water bodies studied were lakes Nahuel Huapi, Moreno, Escondido, Espejo Chico and Traful, the latter chosen as a reference lake. The Ag concentration profiles of short sediment cores, dated by (210)Pb and (137)Cs techniques, were analyzed, as well as suspended load collected from three sites of lake Nahuel Huapi. The biota studied were the native mussel Diplodon chilensis (digestive gland and total soft tissues pooled samples) and five species of fish, two native and three introduced (liver and muscle pooled samples). Ag contents were determined by Instrumental Neutron Activation Analysis (INAA). The upper layers of the sediment cores sampled in lake Nahuel Huapi were enriched in Ag contents compared to deep layers in accumulation periods corresponding to the second half of the 20th century, but this enrichment was neither observed in the reference lake Traful, nor in lakes Espejo Chico and Escondido. Ag was enriched over background level (0.1 microg g(-1)) also in suspended load collected in lake Nahuel Huapi. Ag fluxes to sediments were computed for suspended load and enriched sediment core layers. Highest Ag fluxes, from 350 to 470 microg m(-2) year(-1), were measured in Nahuel Huapi near the site where the liquid effluents of the Bariloche city sewage treatment plant are released to the lake. The spatial distribution of the other Ag fluxes suggests that this is the main source of Ag to lake Nahuel Huapi and lateral transport occurs within the water body. Ag concentrations on biota samples were consistent with these conclusions. Mussels collected in lake Nahuel Huapi showed higher Ag concentrations than in the other lakes, especially when compared to lake Traful. Ag contents in mussels were strongly associated with sediment intake, but enriched probably due to sediment grain size sorting during the intake processes. Evidence of food chain biomagnification of Ag in fish liver was observed. Ag contents in fish liver were higher at lake Nahuel Huapi even considering the high intra-specific variability, with highest values ranging from 10 to 29 microg g(-1) dry weight for brown trout and rainbow trout.     

Functional properties of thermoformed wheat gluten/montmorillonite materials with respect to formulation and processing conditions

Wheat gluten (WG)/montmorillonite (MMT) films were prepared by a thermomechanical process consisting of first mixing the components in a two‐blade, counter‐rotating device and second thermoforming the obtained dough. A significant loss in protein solubility due to the formation and rearrangement of disulfide bonds was observed upon mixing and thermoforming. In the range of studied glycerol contents (25–42.8 wt %), it was shown that glycerol had no significant effect on the mechanical properties or water sensitivity of WG‐based films. Increasing the thermoforming temperature from 60 to 120°C led to considerable improvements of the mechanical properties (increases in both the stress and strain at break) and a significant reduction of the water sensitivity. The introduction of MMT (up to 5 wt %) allowed the achievement of mechanical properties that were not possible by just the variation of the glycerol content and the processing temperature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008