Determination of oxygen and nitrogen derivatives of polycyclic aromatic hydrocarbons in fractions of asphalt mixtures using liquid chromatography coupled to mass spectrometry with atmospheric pressure chemical ionization

Liquid chromatography coupled to mass spectrometry with atmospheric pressure chemical ionization was used for the determination of polycyclic aromatic hydrocarbon derivatives, the oxygenated polycyclic aromatic hydrocarbons and nitrated polycyclic aromatic hydrocarbons, formed in asphalt fractions. Two different methods have been developed for the determination of five oxygenated and seven nitrated polycyclic aromatic hydrocarbons that are characterized by having two or more condensed aromatic rings and present mutagenic and carcinogenic properties. The parameters of the atmospheric pressure chemical ionization interface were optimized to obtain the highest possible sensitivity for all compounds. The detection limits of the methods ranged from 0.1 to 57.3 μg/L for nitrated and from 0.1 to 6.6 μg/L for oxygenated derivatives. The limits of quantification were in the range of 4.6–191 μg/L for nitrated and 0.3–8.9 μg/L for oxygenated derivatives. The methods were validated against a diesel particulate extract standard reference material (National Institute of Standards and Technology SRM 1975), and the obtained concentrations (two nitrated derivatives) agreed with the certified values. The methods were applied in the analysis of asphalt samples after their fractionation into asphaltenes and maltenes, according to American Society for Testing and Material D4124, where the maltenic fraction was further separated into its basic, acidic, and neutral parts following the method of Green. Only two nitrated derivatives were found in the asphalt sample, quinoline and 2‐nitrofluorene, with concentrations of 9.26 and 2146 mg/kg, respectively, whereas no oxygenated derivatives were detected.     

Dynamical changes in hydration water accompanying lysozyme thermal denaturation

We study the dynamics of the first hydration shell of lysozyme to determine the role of hydration water that accompanies lysozyme thermal denaturation. We use nuclear magnetic resonance spectroscopy to investigate both the translational and rotational contributions. Data on proton self-diffusion and reorentational correlation time indicate that the kinetics of the lysozyme folding/unfolding process is controlled by the dynamics of the water molecules in the first hydration shell. When the hydration water dynamics change, because of the weakening of the hydrogen bond network, the three-dimensional structure of the lysozyme is lost and denaturation is triggered. Our data indicates that at temperatures above approximately 315 K, water behaves as a simple liquid and is no longer a good solvent.     

一种HBV多聚酶基因检测系统的光学系统设计

基于荧光偏振理论,设计了一套HBV多聚酶基因检测光学系统。该光学系统包括荧光激发系统和荧光检测系统。使用荧光激发系统对激发样品产生荧光,由荧光检测系统对荧光进行水平和垂直两个方向的荧光强度检测,从而获得荧光的偏振度。通过更换该套系统中的滤光片可实现对400～550nm范围内的样品荧光偏振度的检测。运用该光学系统进行了临床实验,结果表明,系统测试方法具有简单易行、灵敏度高、精确可靠、抗干扰能力强的特点。     

Adsorption-induced surface stresses in alkanethiolate-au self-assembled monolayers

First-principles calculations were employed to elucidate the origin of adsorption-induced surface stresses in alkanethiolate self-assembled monolayers on an Au(111) surface. Our results suggest a mechanism that accounts for the huge relief of the tensile stress compared to the bare surface in terms of a local rearrangement of surface Au atoms accompanying charge removal from the surface towards the Au-S bond. A purely interadsorbate interaction model is shown to be inconsistent with the anisotropy and the magnitude of the calculated stress.     

Enhancement of antibiotic activity by phytocompounds of Turnera subulata

Abstract

The present study aimed to evaluate the antibacterial and modulatory activity of the Turnera subulate methyl extract in isolation or in combination with aminoglycoside antibiotics, using the microdilution method. The Turnera subulata methyl extract was used in isolation in the antibacterial assays and in combination with antibiotics in the modulation assays. All tests were performed in triplicates. The Turnera subulata methyl extract presented both antibacterial and antibiotic-modulatory effects in vitro, in isolation and in association with aminoglycosides. The extract activity depends on the bacterial strain and may be associated with the presence of tannins and flavonols. However, further studies are required to characterize the Turnera subulata potential for the development of new drugs against multiresistant bacteria.     

Water confined in nanotubes and between graphene sheets: a first principle study

Water confined at the nanoscale has been the focus of numerous experimental and theoretical investigations in recent years, yet there is no consensus on such basic properties as diffusion and the nature of hydrogen bonding (HB) under confinement. Unraveling these properties is important to understand fluid flow and transport at the nanoscale, and to shed light on the solvation of biomolecules. Here we report on a first principle, computational study focusing on water confined between prototypical nonpolar substrates, i.e., single-wall carbon nanotubes and graphene sheets, 1-2.5 nm apart. The results of our molecular dynamics simulations show the presence of a thin, interfacial liquid layer (approximately 5 A) whose microscopic structure and thickness are independent of the distance between confining layers. The properties of the HB network are very similar to those of the bulk outside the interfacial region, even in the case of strong confinement. Our findings indicate that the perturbation induced by the presence of confining media is extremely local in liquid water, and we propose that many of the effects attributed to novel phases under confinement are determined by subtle electronic structure rearrangements occurring at the interface with the confining medium.     

On an evolution equation with acoustic boundary conditions

In this paper, we analyze from the mathematical point of view a model for small vertical vibrations of an elastic string with weak internal damping and quadratic term, coupled with mixed boundary conditions of Dirichlet type and acoustic type. Our goal is to extend some of the results of Frota‐Goldstein work in the sense of considering a weaker internal damping and one more quadratic nonlinearity in the elastic string equation. Copyright © 2011 John Wiley & Sons, Ltd.     

Potential effects of climate change on the chemical quality of aquatic biota

Climate changes can alter and modify the distribution and the partitioning of contaminants in water bodies through several factors (e.g., rise in temperature, decrease in oxygen through water scarcity, acidification and remobilization of pollutants in sediments due to flooding). Other indirect effects can be linked to climate changes (e.g., increased use of pesticides due to the rise of plant diseases caused by new vectors and erosion of coastal areas due to rise in sea level). All these factors have the potential to enhance the bioavailability of dangerous pollutants with bioaccumulative properties with an increasing risk of transfer in the food chain.The data available on aquatic species for compounds such as, polychlorinated biphenyls, dioxins and mercury show that the legislative standards for food are exceeded in some areas. These data also show that levels in aquatic biota of other emerging compounds with bioaccumulative properties (such as, perfluorinated octane sulfonate, polybrominated diphenyl ethers and hexabromocyclododecane can be relevant in some areas and at some trophic levels. In particular, the effect of climate changes can be relevant in vulnerable water bodies (e.g., estuaries of rivers or coastal lagoons), where fishing, extensive and intensive aquaculture activities and sites of high biodiversity value are often present.For these reasons, there is a need to change the water-monitoring strategies with a focus on analytical methods for biota determination and to have monitoring programs that include detection of long-term trends and share procedures for the setting of quality criteria for biota.     

On the geometry of linear Weingarten hypersurfaces in the hyperbolic space

In this paper, we apply some forms of generalized maximum principles in order to study the geometry of complete linear Weingarten hypersurfaces with nonnegative sectional curvature immersed in the hyperbolic space. In this setting, under the assumption that the mean curvature attains its maximum, we prove that such a hypersurface must be either totally umbilical or isometric to a hyperbolic cylinder.