Challenges in the determination of aminoglycoside antibiotics,a review

Residues of antibiotics (ABs) in the aquatic environment and in food of animal origin represent a major concern, as prolonged exposure to ABs is a serious health hazard, related to both the side effects of prolonged use and the risk of developing bacterial resistance to various ABs. Given the low levels of the AB residues in complex matrices, the development of sensitive analytical methods represents a major challenge. This is certainly true for the aminoglycoside ABs (AGs) which lack a chromophore and show poor chromatographic properties in reversed-phase liquid chromatography. This paper reviews the current state of the art in the determination of AGs. Attention is paid to extraction, sample clean-up, chromatographic separation, and detection of AGs in both environmental and food samples and in plasma and serum. A general workflow for the analysis of AGs is presented which takes into account the matrix and required level of information.     

Separation of <Superscript>125</Superscript>IBZM and <Superscript>125</Superscript>ILIS using polyacrylamide-acrylic acid resin

Radioiodination of both S(−)BZM and LIS was carried out using n-bromosuccimide(NBS) as a mild oxidizing agent. The factors affecting on the radiochemical yield such as pH, reaction time, substrate concentration and oxidizing agent have been studied. The chromatographic separation of both ¹²⁵IBZM and ¹²⁵ILIS was carried out using HPLC and poly(acrylamide-acrylic acid) resin P(AAm-AA). The copolymer was prepared by a template polymerization of AA in aqueous solution on PAAm as a template polymer and in the presence of N,N-methylenebisacrylamide (NMBA) as a crosslinker using gamma rays as initiator. The purifications of tracers were carried out using prepared resin compared with TLC and HPLC. The effects of pH buffer, variable elution volumes, flow rate and temperature on the separation process of the resin efficiency have been studied.     

On the development of Taylor vortices in a vertical annulus with a heated rotating inner cylinder

A numerical study has been conducted to determine the heat transfer characteristics and flow patterns which develop around a rotating, heated vertical cylinder enclosed within a stationary concentric cylinder. A tall annulus (aspect ratio of 10) with fixed, adiabatic horizontal end-plates and a radius ratio of 0·5 has been considered. Furthermore, the effect that the introduction of buoyancy forces by heating the inner cylinder has on the development of the Taylor vortex flow is examined. It is observed that the formation of the Taylor vortices is delayed until the rotational parameter σ = Gr/Re² has a value below unity for any given Reynolds number Re which is above the critical value Re_crit for the formation of Taylor vortices in an isothermal flow. Also, the Taylor cells first appear at the top of the annulus. As σ is gradually decreased below unity, bifurcations to other states are observed. The final structure of the secondary flow is noticeably distorted in the mixed-convection mode, with the size of the Taylor cells varying greatly along the height of the annulus. This distortion diminishes as σ is further decreased, until the isothermal flow pattern is nearly recovered below σ = 0·01.     

Persistence of quantum correlations in a XY spin-chain environment

Quantum correlations in a physical system are usually degraded whenever there is aninteraction with the environment. Here we consider the action of a XY spin-chain interactingwith a system of two qubits. Results are surprising for particular families of statessince their evolution does not destroy the presence of either entanglement or nonlocality,that is, those correlations persist for any possible configuration of theenvironment. In addition, we unveil the form of those states which, although being mixed,their entanglement implies nonlocality and vice versa. This finding constitutes anextension of the well-known Gisin Theorem for pure states of two qubits.The ensuing form will enable us to find the evolved entanglement and nonlocality in ananalytical fashion.     

Acetylenic ketones. VII—Structural analyses by mass spectrometry of the products obtained from the reaction of acetylenic ketones with nucleophilic sulphur compounds

The mass spectra of β-hydroxy-α-thiobenzoylstyrene derivatives and (E, Z)- or (E, E)-β,β-di(α-aroylstyryl)sulphides as well as β,β′di(α-aroylstyryl)disulphides are discussed. The fragmentation patterns support their proposed structure and configuration.     

Reaction of α,β-unsaturated ketones with guanidine. Substituent effects on the protonation constants of 2-amino-4,6-diarylpyrimidines

1,3-Diaryl-2-propen-1-ones, I, reacted with guanidine hydrochloride (II) in the presence of 3 moles of sodium hydroxide to give the corresponding 2-amino-4,6-diarylpyrimidines, III. The structure and configuration of the products are based on chemical and spectroscopic evidence. The protonation constants of these compounds (series A and series B) have been determined in 50 volume percent ethanol-water medium. Excellent linear correlations are obtained when pK_a values of the two series of 2-amino-4,6-diarylpyrimidines, IIIa-j and IIIk-r, are plotted against the substituent constant, ^σx, and the polar substituent constant, ^σ* xC₆H₄, for substituted phenyl groups. The pK_a values have also been correlated with the extended Hammett equation. The correlation follows the equations: Series A; pK_a = 3.273 - 0.820σI,X - 0.662σR,X Series B; pK_a = 3.169 - 0.424σI,X - 0.137σR,X     

Study of the miscibility of poly(styrene-co-4-vinylbenzoic acid) with poly(ethyl methacrylate) or with poly[ethyl methacrylate-co-(2-N,N-dimethylaminoethyl) methacrylate] by inverse gas chromatography

Poly(styrene) is immiscible with poly(ethyl methacrylate). The introduction of a small amount of 4-vinylbenzoic acid units along poly(styrene) chains (PS-VBA) enhanced its miscibility with poly(ethyl methacrylate) (PEMA) or with poly[ethyl methacrylate-co-(2-N,N-dimethylaminoethyl) methacrylate] (PEMA-DAE), as observed from the appearance of a single composition dependent glass transition temperature for each binary system using inverse gas chromatography. The negative values of the apparent polymer-polymer interaction parameter, chi(23)app, determined with different families of molecular probes, for three blend compositions and over a range of temperature confirm quantitatively the miscibility of these blends. The chi(23)app values for PEMA(PS-VBA) and (PEMA-DAE)-(PS-VBA) blends are dependent of the chemical nature of the probes, the temperature and the blend composition.     

Diastereoselective alkynylation of N-p-tolylsulfinylimines with aluminum acetylides

The addition of alkynyl dimethyl aluminum compounds onto N-p-tolylsulfinylimines was investigated. The reaction was proved to be totally regioselective, leading to propargylamines with high diastereoselectivity (up to 99% de). Addition of aluminum derivatives gave a reversal of diastereoselectivity compared to the addition reaction of lithium acetylide.     

Pressure dependence of the contact angle

When a liquid and its vapor contact a smooth, homogeneous surface, Gibbsian thermodynamics indicates that the contact angle depends on the pressure at the three-phase line of an isothermal system. When a recently proposed adsorption isotherm for a solid-vapor interface is combined with the equilibrium conditions and the system is assumed to be in a cylinder where the liquid-vapor interface can be approximated as spherical, the contact-angle-pressure relation can be made explicit. It indicates that a range of contact angles can be observed on a smooth homogeneous surface by changing the pressure at the three-phase line, but it also indicates that the adsorption at the solid-liquid interface is negative, and leads to the prediction that the contact angle increases with pressure. The predicted dependence of the contact angle on pressure is investigated experimentally in a system that has an independent mechanism for determining when thermodynamic equilibrium is reached. The predictions are in agreement with the measurements. The results provide a possible explanation for contact angle hysteresis.     

Solid-phase microextraction and gas chromatography–mass spectrometry for analysis of phenols and nitrophenols in rainwater,as their <Emphasis Type="Italic">t</Emphasis>-butyldimethylsilyl derivatives

Solid-phase microextraction (SPME) coupled with gas chromatography–mass spectrometry has been used for analysis of four phenols and sixteen nitrophenols in rainwater samples. Analytes were extracted from the water in the immersion mode and derivatised for 5 min during direct desorption in the GC injector. Before desorption, 2 μL N-(t-butyldimethylsilyl)-N-methyltrifluoroacetamide (MDBSTFA) was introduced into the injector, which was maintained at 280 °C. Different conditions affecting extraction efficiency were studied, including temperature, type of microextraction fibre, and effect of pH and ionic strength. Five different fibre coatings were tested: 85-μm polyacrylate (PA), 100-μm polydimethylsiloxane (PDMS), 65-μm Carbowax–divinylbenzene (CW–DVB), 75-μm Carboxen–polydimethylsiloxane (CAR–PDMS), and 65-μm polydimethylsiloxane–divinylbenzene (PDMS–DVB). The best conditions were use of PA fibres for 40 min at ambient temperature (75 g NaCl per 100 mL, pH 3.0). MDBSTFA was used as derivatising agent because it enables analysis of phenols derivatives with high confidence in identification, because in electron-impact mode TBDMS–phenol derivatives produce the specific M–57 ion. Quantification was achieved by using 4-nitrophenol-d4, at 1 mg L⁻¹, as internal standard. Linearity was good, with correlation coefficients in the range 0.9888 (o-cresol) to 0.9987 (dinitro-o-cresol, DNOC). Detection limits varied between 0.208 and 99.3 μg L⁻¹ and quantification limits between 0.693 and 331 μg L⁻¹. Uncertainties varied between 8.7% (phenol) and 17.9% (4-methyl-2-nitrophenol). The method was successfully applied to the analysis of rainwater collected at urban and rural sites in Alsace (East of France). Because of derivatisation in the injector and the associated high temperature, the lifetime of the fibre is severely reduced.