Rearrangement, nucleophilic substitution, and halogen switch reactions of alkyl halides over NaY Zeolite: formation of the bicyclobutonium cation inside the zeolite cavity

Rearrangement and nucleophilic substitution of cyclopropylcarbinyl bromide over NaY and NaY impregnated with NaCl was observed at room temperature. The first-order kinetics are consistent with ionization to the bicyclobutonium cation, followed by internal return of the bromide anion or nucleophilic attack by impregnated NaCl to form cyclopropylcarbinyl, cyclobutyl, and allylcarbinyl chlorides. The product distribution analysis revealed that neither a purely kinetic distribution, similar to what is found in solution, nor the thermodynamic ratio, which favors the allylcarbinyl halide, was observed. Calculations showed that bicyclobutonium and cyclopropylcarbinyl carbocations are minimal over the zeolite structure, and stabilized by hydrogen bonding with the framework structure. A new process of nucleophilic substitution is reported, namely halogen switch, involving alkyl chlorides and bromides of different structures. The reaction occurs inside the zeolite pores, due to the confinement effects and is an additional proof of carbocation formation on zeolites. The results support the idea that zeolites act as solid solvents, permitting ionization and solvation of ionic species.     

Chaotic transient and the improvement of system flexibility

On this work it is addressed the problem of how to exploit the dynamic behind a chaotic transient behavior to improve system performance and adaptability to many operational conditions request. The phenomena of chaotic transient is explained as due to the presence of a chaotic saddle in the phase space. Different system operation points can be associated to the set of unstable periodic orbits that exist embedded in the chaotic saddle. A classical control procedure associated with a control of chaos strategy is proposed as a methodology to quickly guide system trajectories among different operation points and to keep the system on a particular operation point. The methodology is applied on an electronic circuit system.     

A rapid screening method for routine congener-specific analysis of polychlorinated biphenyls in human serum by high-resolution gas chromatography with mass spectrometric detection

A screening method using gas chromatography/mass spectrometry in the single ion monitoring (SIM) mode for the routine congener-specific analysis of polychlorinated biphenyls (PCBs) in human serum has been developed and validated. A fast procedure incorporating both liquid-liquid and solid-phase extraction was used for clean up and enrichment. Interday and intraday precision and accuracy were assessed for the 12 congeners having dioxin-like activity and PCBs #180 and #170 by analyzing spiked samples on three subsequent days and using (13)C(12)-labelled analogues as internal standards. Furthermore, the relative errors for six non-dioxin-like congeners (PCBs #28, #52, #101, #138, #153 and #180) were measured by using certified reference materials, providing good accuracy at two different concentration levels. The limits of quantification and of detection were 0.5 and 0.2 micro g/L in serum for each congener, respectively. The method allows the chromatographic separation of at least 35 congeners and can therefore be applied to the routine monitoring of the general population for both dioxin-like and non-dioxin-like PCB congeners.     

Determination of methotrexate in human urine at trace levels by solid phase extraction and high-performance liquid chromatography/tandem mass spectrometry

For biological monitoring of hospital personnel occupationally exposed to antineoplastic agents, highly sensitive and specific methods are required. In order to detect trace MTX urinary concentrations, a precise and accurate high-performance liquid chromatography/tandem mass spectrometry (HPLC-MS/MS) procedure, incorporating solid phase extraction, has been developed. Urine samples were purified by solid phase extraction (SPE) on octadecyl bonded, endcapped silica SPE columns. After eluting with methanol, the solvent was evaporated obtaining a 25-fold concentration of the analyte. This procedure was validated by using 7-OHMTX as internal standard. Calibration curves had correlation coefficients always higher than 0.999, and the limit of detection was assessed at 0.2 microg L(-1). High specificity of the HPLC-MS/MS technique assures that no interfering substances are detected rather than the analyte of interest.     

Vibrational and electronic spectroscopy of neutral antimony coordination compounds of the 1,3-dithiole-2-thione-4,5-dithiolate (dmit)

The S 1s X-ray absorption near edge structure (XANES) and X-ray photoelectron spectra (XPS) of the neutral complexes [SbL(dmit)] (L = Br or I; dmit =1,3-dithiole-2-thione-4,5-dithiolate) have been measured using tunable synchrotron radiation. The valence shell electronic excitation by ultraviolet-visible (UV-vis) spectroscopy and the infrared vibrational spectra are presented and analyzed. The UV-vis results lead to an assignment of bands at 400 nm as π(Sm) → π*(C═S), where S(m) is the thiolate sulfur. The corresponding S 1s → π*(C═S) transition was identified at 2468.3 eV. Ab initio calculations, within the improved virtual orbital (IVO) method, carried out with the GSCF3 program, were applied to establish a complete and accurate spectral assignment. It has been the first attempt to apply such methodology for dmit coordination compounds, and very consistent results were obtained.     

Preparation and Characterization of Insulin-Loaded Lipid-Based Microspheres Generated by Electrospray

Electrospray has been recognized as an efficient technique for the fabrication of polymer micro and nanosystems and recently it was applied to lipids. The objective of this study was to assess the potential of electrospray for the encapsulation of insulin into lipid particles. Spherical particles of about 1 µm were obtained jetting a propanolic solution of palmitic or stearic acid and ethylcellulose or Pluronic F127 in a 10:1 or 20:1 (w/w) ratio under an electric field of 30 kV. Insulin was entrapped into the particles with high encapsulation efficiency by the formation of an ion-pair with sodium dodecyl sulphate. Far-ultraviolet circular dichroism spectroscopy indicated that electrospray did not modify the secondary structure of insulin. An in vitro prolonged release over 24 hours was observed after an initial burst effect. This study demonstrates that electrospray represents a viable new alternative for preparing in a single step peptide-protein loaded lipid based microspheres directly in powder form.     

The iron-related molecular toxicity mechanism of synthetic asbestos nanofibres: a model study for high-aspect-ratio nanoparticles

Asbestos shares with carbon nanotubes some morphological and physico-chemical features. An asbestos-like behaviour has been recently reported by some authors, though the mechanism of toxicity may be very different. To identify at the atomic level the source of toxicity in asbestos, the effect of progressive iron loading on a synthetic iron-free model nanofibre previously found non-toxic in cellular tests was studied. A set of five synthetic chrysotile nanofibres [(Mg,Fe)3(Si2O5)(OH)4] has been prepared with Fe ranging from 0 to 1.78?wt?%. The relationship between fibre-induced free-radical generation and the physico-chemical characteristics of iron active sites was investigated with spin-trapping techniques on an aqueous suspension of the fibres and M?ssbauer and EPR spectroscopies on the solids, respectively. The fully iron-free fibre was inert, whereas radical activity arose with even the smallest amount of iron. Surprisingly, such activity decreased upon increasing iron loading. M?ssbauer and EPR revealed isolated iron ions in octahedral sites that undergo both axial and rhombic distortion and the occurrence of aggregated iron ions and/or extra-framework clustering. The isolated ions largely prevailed at the lowest loadings. Upon increasing the loading, the amount of isolated iron was reduced and the aggregation increased. A linear relationship between the formation of carbon-centred radicals and the amount of rhombic-distorted isolated iron sites was found. Even the smallest iron contamination imparts radical reactivity, hence toxicity, to any chrysotile outcrop, thereby discouraging the search for non-toxic chrysotile. The use of model solids that only differ in one property at a time appears to be the most successful approach for a molecular understanding of the physico-chemical determinants of toxicity. Such findings could also be useful in the design of safer nanofibres.     

Simultaneous determination of gemcitabine, taxol, cyclophosphamide and ifosfamide in wipe samples by high-performance liquid chromatography/tandem mass spectrometry: protocol of validation and uncertainty of measurement

Measurable levels of anticancer agents are still detected on work surfaces in health-care settings. However, application of recent guidelines for the protection of workers' safety and health has resulted in lowered contamination levels. To assess occupational exposure to antineoplastic agents, very sensitive and specific procedures for environmental sampling and analysis are therefore needed. In the present study an assay for simultaneous determination of gemcitabine, taxol, cyclophosphamide, and ifosfamide in wipe samples, using two internal standards (trofosfamide and cephalomannine), was developed and validated by high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS). Solid-phase extraction (SPE) was used for sample concentration and cleanup. The assay was found to be linear up to 1000 ng/wipe, with limits of quantitation of 25.0 ng/wipe for gemcitabine and taxol, and 12.5 ng/wipe for cyclophosphamide and ifosfamide. In order to investigate the effectiveness of the surface sampling, removal efficiency tests were repeated on different types of surfaces. Recovery rates of between 62 and 81% were obtained at two contamination levels (50.0 and 250 ng/100 cm2). Precision and trueness were determined on three different days. The within-day precision was found to be always less than 12.1% for all the analytes. The overall precision, expressed as relative standard deviation (RSD), was always less than 9.4%. Recoveries varying from 75.0 (gemcitabine) to 95.0% (taxol) were obtained at three levels. In order to obtain a quantitative indication of the quality of the result, the overall uncertainty of measurement (UOM) was evaluated according to the EURACHEM/CITAC guide. The relative combined uncertainty was found to be always less than 9.5%. The relative expanded uncertainty was also calculated, at three contamination levels.