An overview of analytical methodologies for the determination of antibiotics in environmental waters

The widespread occurrence of antibiotics as contaminants in the aquatic environment has increased attention in the last years. The concern over the release of antibiotics into the environment is related primarily to the potential for the development of antimicrobial resistance among microorganisms. This article presents an overview of analytical methodologies for the determination of quinolone (Qs) and fluoroquinolone (FQs), macrolide (MLs), tetracycline (TCs), sulfonamide (SAs) antibiotics and trimethoprim (TMP) in different environmental waters. The analysis of these antibiotics has usually been carried out by high-performance liquid chromatography (HPLC) coupled to mass spectrometry (MS) or tandem mass spectrometry (MS/MS) and to a lesser extent by ultraviolet (UV) or fluorescence detection (FD). A very important step before LC analysis is sample preparation and extraction leading to elimination of interferences and prevention of matrix effect and preconcentration of target analytes.     

Further Studies on Homo- and Copolymerization of Styrene through Metallocenic Initiator Systems

Summary: Binary metallocene-MAO and ternary diphenylzinc-metallocene-MAO initiator systems have been tested as initiators in the homopolymerization of styrene and also in its copolymerization with several diverse comonomers including substituted styrenes, styrene derivatives, α-olefins and dienes. Various titanocenes and zirconocenes and some exploratory experiment with hafnocene were carried out. The results indicate that titanocenes were more effective than zirconocenes in the homopolymerization of styrene while zirconocenes did better in α-olefin polymerization. It was found that titanocenes generated mainly syndiotactic polystyrene, s-PS, while zirconocenes yielded atactic polystyrene or, depending on the zirconocene, a low percentage of s-PS. For these types of initiators the polymerization process depends largely on the inductive effect of the substituents linked to the benzene ring of styrene and on its position (ortho, meta or para). Substituent multiplicity reduced markedly the effectiveness of these initiator systems. Styrene/isoprene polymerization was also studied using binary zirconocene-MAO initiator systems that yielded low conversions and also low molecular weight polymers.     

The unitarizability of the Aubert dual of strongly positive square integrable representations

Under a natural assumption, which holds in the generic case, we prove in this paper that, for the classical p-adic groups, the Aubert dual of an irreducible, strongly positive square-integrable representation (in the sense of Mœgl., in-Tadić classification), is unitarizable. In this way, for this important class of representations, we verify the conjecture which states that the Aubert involution preserves unitarity.     

Are the mixtures of homologous surfactants ideal?

The interaction between homologous surfactants in mixed micelles was studied by the Regular Solution Theory of mixed micelles. The interaction is independent of the nature of the polar head groups and attractive and the interaction parameter betaM depends linearly on the difference in chain length DeltanC. The interaction becomes ideal at DeltanC=0.75+/-0.06. Above DeltanC approximately 5, the dependence remains linear but the slope increased 2.7 times. The phenomenon is explained as the effect of the reduction of the hydrocarbon/water micelle interface and a better packing of the chains in the micelle core, caused by the inclusion of a shorter homologous surfactants. This reduction can be more effective when DeltanC>or=5.     

Light-induced flipping of a conserved glutamine sidechain and its orientation in the AppA BLUF domain

The AppA BLUF domain is a blue light photoreceptor containing flavin. Conserved glutamine 63 is necessary for the photocycle of the protein, and its side chain has been proposed to flip in response to blue light illumination. Recently published crystal structures of AppA WT and the AppA mutant C20S describe contradictory conclusions regarding the orientation of the conserved glutamine 63 side chain in the dark. Here, we present evidence from NMR spectroscopy confirming light-induced flipping of the glutamine side chain to form a strong hydrogen bond between the glutamine 63 side chain carbonyl group and the tyrosine 21 side chain hydroxyl proton in the light-induced state. Our conclusions are consistent with published data from UV/vis absorbance and FTIR spectroscopy, as well as the crystal structure of AppA WT.     

Functionalized magnetic micro- and nanoparticles: optimization and application to micro-chip tryptic digestion

The preparation of an easily replaceable protease microreactor for micro-chip application is described. Magnetic particles coated with poly(N-isopropylacrylamide), polystyrene, poly(2-hydroxyethyl methacrylate-co-ethylene dimethacrylate), poly(glycidyl methacrylate), [(2-amino-ethyl)hydroxymethylen]biphosphonic acid, or alginic acid with immobilized trypsin were utilized for heterogeneous digestion. The properties were optimized, with the constraint of allowing immobilization in a microchannel by a magnetic field gradient. To obtain the highest digestion efficiency, sub-micrometer spheres were organized by an inhomogeneous external magnetic field perpendicularly to the direction of the channel. Kinetic parameters of the enzyme reactor immobilized in micro-chip capillary (micro-chip immobilized magnetic enzyme reactor (IMER)) were determined. The capability of the proteolytic reactor was demonstrated by five model (glyco)proteins ranging in molecular mass from 4.3 to 150 kDa. Digestion efficiency of proteins in various conformations was investigated using SDS-PAGE, HPCE, RP-HPLC, and MS. The compatibility of the micro-chip IMER system with total and limited proteolysis of high-molecular-weight (glyco)proteins was confirmed. It opens the route to automated, high-throughput proteomic micro-chip devices.     

Numerical Analysis of Thermally Coupled Flow Problems with Interfaces and Phase-change Effects

In this work a fixed mesh finite element approach is presented to solve thermally coupled flow problems including moving interfaces between immiscible fluids and phase-change effects. The weak form of the full incompressible Navier-Stokes equations is obtained using a generalized streamline operator (GSO) technique that enables the use of equal order interpolation of the primitive variables of the problem: velocity, pressure and temperature. The interfaces are defined with a mesh of marker points whose motion is obtained applying a Lagrangian scheme. Moreover, a temperature-based formulation is considered to describe the phase-change phenomena. The proposed methodology is used in the analysis of a filling of a step mould and a gravity-driven flow of an aluminium alloy in an obstructed vertical channel.     

Optimized thermal desorption for improved sensitivity in trace explosives detection by ion mobility spectrometry

In this work we evaluate the influence of thermal desorber temperature on the analytical response of a swipe-based thermal desorption ion mobility spectrometer (IMS) for detection of trace explosives. IMS response for several common high explosives ranging from 0.1 ng to 100 ng was measured over a thermal desorber temperature range from 60 °C to 280 °C. Most of the explosives examined demonstrated a well-defined maximum IMS signal response at a temperature slightly below the melting point. Optimal temperatures, giving the highest IMS peak intensity, were 80 °C for trinitrotoluene (TNT), 100 °C for pentaerythritol tetranitrate (PETN), 160 °C for cyclotrimethylenetrinitramine (RDX) and 200 °C for cyclotetramethylenetetranitramine (HMX). By modifying the desorber temperature, we were able to increase cumulative IMS signal by a factor of 5 for TNT and HMX, and by a factor of 10 for RDX and PETN. Similar signal enhancements were observed for the same compounds formulated as plastic-bonded explosives (Composition 4 (C-4), Detasheet, and Semtex). In addition, mixtures of the explosives exhibited similar enhancements in analyte peak intensities. The increases in sensitivity were obtained at the expense of increased analysis times of up to 20 seconds. A slow sample heating rate as well as slower vapor-phase analyte introduction rate caused by low-temperature desorption enhanced the analytical sensitivity of individual explosives, plastic-bonded explosives, and explosives mixtures by IMS. Several possible mechanisms that can affect IMS signal response were investigated such as thermal degradation of the analytes, ionization efficiency, competitive ionization from background, and aerosol emission.     

Structural first-order transformation in La2/3Ba1/3MnO3: ESR study

We have studied by the electron-spin resonance (ESR) and static magnetic field techniques, the La_2/3Ba_1/3MnO₃ perovskite, which was previously shown to exhibit a martensitic phase transformation in the vicinity of T_s∼200 K [Physical Review B 68, 054109 (2003)], leading to its structural phase-segregated state. Resonant absorptions reveal that in the temperature interval from 100 K to 340 K the compound represents a mixture of two ferromagnetic phases possessing different magnetizations, in varying proportions depending on the temperature, and a small amount of a paramagnetic phase. The results agree well with the previous neutron diffraction study. Applied in the ESR experiments, magnetic fields (2–6 kOe) strongly affect the magnetization curves: even magnetic field as high as 700 Oe modifies the anomaly in the phase transformation region and removes the difference between the zero-field cooled and field-cooled magnetization curves, which implies that the difference in the magnetic susceptibility of the coexisting phases is small and the magnetic domain configuration can be easily changed.     

Influence of Catalyses on the Preparation of YVO<Subscript>4</Subscript>:Eu<Superscript>3+</Superscript> Phosphors by the Sol–gel Methodology

YVO(4):Eu(3+) phosphors have been prepared by the hydrolytic sol-gel methodology, with and without alkaline catalyst. The solid powder was obtained by reaction between yttrium III chloride and vanadium alkoxides; the europium III chloride was used as structural probe. The powder was treated at 100, 400, 600, or 800 °C for 4 h. The samples were characterized by X-ray diffraction, thermal analysis, and photoluminescence. The XRD patterns revealed YVO(4) crystalline phase formation for the sample prepared without the catalyst and heat-treated at 600 °C and for the sample prepared in the presence of ammonium as catalyst and heat-treated at 100 °C. The average nanosized crystallites were estimated by the Scherrer equation. The sample which was produced via alkaline catalysis underwent weight loss in two stages, at 100 and 400 °C, whereas the sample obtained without catalyst presented four stages of weight loss, at 150, 250, 400, and 650 °C. The excitation spectra of the samples treated at different temperatures displayed the charge transfer band (CTB) at 320 nm. PL data of all the samples revealed the characteristic transition bands arising from the (5)D(0) → (5)F(J) (J = 0, 1, 2, 3, and 4) manifolds under maximum excitation at 320, 394, and 466 nm in all cases. The (5)D(0) → (7)F(2) transition often dominates the emission spectra, indicating that the Eu(3+) ion occupies a site without inversion center. The long lifetime suggests that the matrix can be applied as phosphors. In conclusion, the sol-gel methodology is a very efficient approach for the production of phosphors at low temperature.