Stereoselective synthesis of novel 4,5-epoxy-1,2-oxazin-6-ones and alpha,beta-epoxy-gamma-amino acids from beta-lithiated oxazolinyloxiranes and nitrones

[reaction: see text] A stereoselective synthesis of 9,10-epoxy-1,6-dioxa-4,7-diazaspiro[4,5]decanes has been developed on the basis of the addition of beta-lithiated oxazolinyloxiranes to nitrones. Conversion of these spirocyclic derivatives into 4,5-epoxy-1,2-oxazin-6-ones and successively into alpha,beta-epoxy-gamma-amino acids, alpha-hydroxy-gamma-amino acids, and gamma-butyrolactams is described.     

Biocatalytic nylon nanofibrous membranes

Nylon-6 nanofibrous membranes (NFM) have been prepared, characterized and used to build-up electrochemical biosensing devices. The assembly and the functioning of biocatalytic NFM are described in connection with the physical and the covalent immobilization of glucose oxidase for the detection of glucose. Effects of the enzyme loading, the mediator, the pH, the surface acidity and the kinetic of the catalysis have been thoroughly investigated. The results show that NFM allow the binding of proteins without the need for the hydrolysis step, in contrast to the nylon film. Furthermore, the high surface-to-volume ratio of the NFM allow superior loading of the enzyme with respect to thin film technology. The immobilization step does not affect the permeability of the coating to the mediator used. These results give evidence that NFM are a promising and inexpensive coating for a novel electrochemical transducer.     

Determination of Total Phenols in Foods by Boron Doped Diamond Electrode

A robust electrochemical method to measure the total phenol content in food samples is presented. Under optimal condition, BDD electrode showed excellent performance to detect the oxidation of several phenols and does not present the drawback due to electrode fouling. The analytical method used to perform such measurement has been optimized and successfully applied in different food samples. The results obtained were compared with the standard Folin–Ciocalteau method.     

White light transverse cooling of a helium beam

We report a study of transverse laser cooling on a metastable helium beam using spectrally broadened diode lasers (“white light") to increase its flux. For this purpose, beam profile and atomic flux versus laser power and other parameters have been characterized. We have performed experiments to compare this technique with other transverse cooling methods using monochromatic light. Best results are obtained with a “ziz-zag" configuration using “white light". Received 21 December 1998 and Received in final form 27 May 1999     

Inorganic by-products in waters disinfected with chlorine dioxide

The continuing diminishing sources of fresh waters has stimulated the search for unconventional water resources, such as effluents from municipal sewage treatment plants, which can be reused for purposes of irrigation in agriculture, cooling water in industry, groundwater aquifer recharge and in the long term even for drinking water. The main problem of using effluents is the presence of pathogenic bacteria and viruses that can affect human and animal health. Therefore, disinfection has been used for many years to control and reduce waterborne diseases.At the moment, most water treatment plants use sodium hypochlorite as their primary biocide. However, the toxicity of chlorinated organic compounds produced during the treatment has led to increased interest in the use of alternative agents. One possible candidate as viable substitute of free chlorine is chlorine dioxide. Before this disinfectant can be recommended for routine use, it is imperative that its safety be assessed.In this research we have investigated the presence of chlorite and chlorate in sewage disinfected with chlorine dioxide. The effect of initial concentration of biocide and contact time was evaluated using a pilot plant fed with the effluent of a municipal treatment plant. Moreover, the influence of ClO₂ generator performance was analyzed and discussed.     

A method for routine quantitation of urinary 8-hydroxy-2'-deoxyguanosine based on solid-phase extraction and micro-high-performance liquid chromatography/electrospray ionization tandem mass spectrometry

8-Hydroxy-2'-deoxyguanosine (8OHdG), one of the major oxidative DNA lesions induced by radical agents, is commonly used as a biomarker for oxidative stress, nowadays preferably in urine. In the absence of a commercially available internal standard a micro-high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (micro-HPLC/ESI-MS/MS) method, suitable for routine analysis of 8OHdG in human urine using external calibration, was developed. Evaluation of the matrix effect showed that the method allows highly sensitive and accurate quantitation despite the absence of an internal standard. HPLC analysis was performed using gradient elution at a flow rate of 10 microL min(-1) using a capillary reversed-phase column and an injection volume of 0.5 microL, with detection of 8OHdG in positive multiple reaction monitoring (MRM) mode. The absolute limit of detection was 0.35 fmol using m/z 168 as a quantifier (fragment) ion. A linear (R2> 0.999) calibration curve in urine was obtained over a range 0.2-10 ng mL(-1). This method is about 20 times more sensitive than previously described procedures, and is characterized by high accuracy (mean 90%) and good reproducibility (RSD <10%). The optimized method was applied to determination of 8OHdG in 18 urinary samples derived from three healthy volunteers. 8OHdG urinary excretion ranged from 3.0-7.9 microg/day, and a large intra-individual variation was found. This method, which effectively circumvents the need for isotopically labeled 8OHdG (internal standard), is suitable for routine monitoring of exposure to DNA-damaging factors in a large number of subjects.     

Synthesis and reactivity of 4-substituted-2,3-dihydrobenzo-1,4-thiazines

A series of derivatives of 4H-2,3-dihydrobenzo-1,4-thiazine has been prepared. 4-Acetyl-2,3-dihydrobenzo-1,4-thiazine undergoes self-condensation by n-butylmagnesium bromide affording the corresponding 4-aceto-acetyl-2,3-dihydrobenzo-1,4-thiazine, which, is converted to 5H-1,4-thiazino[2,3,4-if]quinolin-5-one. Halogena-tion of the acetyl derivative takes place at the position 2 of the heterocyclic ring and oxidation leads to 1-oxides and 1,1-dioxides.     

Influence of compatibilizer degradation on formation and properties of PA6/organoclay nanocomposites

Nanocomposites based on polyamide 6 (PA6) and commercial layered silicates have been prepared by both in situ polymerization and melt compounding. The main aim of the present work has been centred on compatibilizer degradation, caused by the preparation conditions, in terms of nanocomposite end features. Two montmorillonite (MMT)-type, organically-modified clays (OMLS), namely Cloisite 30B^® and Nanofil 784^®, and a sodium MMT (Cloisite Na^®) have been studied. Thermal properties of the layered silicates have been evaluated by TGA, IR, WAXD and pyrolysis-gas-mass. In order to better assess the influence of high temperature processes on clay modifications, a thermal treatment which mimics the conditions used during the in situ polymerization (4 h at 250 °C) has been applied on layered silicates. The above treatment, besides the elimination of absorbed water from all the clays, turned out to prove noteworthy differences in compatibilizer modification for the two organoclays. Indeed, in the case of Closite 30B^® only a removal of organic molecules outside the silicate galleries and a likely reorganization of those present inside the galleries have been detected, while a relevant chemical modification of Nanofil 784^® compatibilizer has been conversely found.As far as nanocomposite characteristics are concerned, the latter have been found to depend on both the preparation method and clay type. In the case of in situ polymerization, also thermally-treated layered silicates, coded (T), have been used, in order to put more clearly in evidence the role of compatibilizer decomposition on nanocomposite formation and properties. Indeed, nanocomposite samples containing Closite 30B^®(T) have been found to be completely exfoliated, while the same thermal treatment seems to make worse the properties of those based on Nanofil 784^®(T). Furthermore, with respect to nanocomposites based on pristine clays, samples containing thermally-treated silicates turned out to be different in terms of both molecular mass and crystal structure of the polymer matrix. Namely, PA6 γ-form seems to be promoted for all nanocomposites prepared in such a way, probably because of water removal at high temperature, which makes -OH groups of the layered silicate more free to interact with polyamide chains, thus causing a restriction of their mobility.     

Microchip capillary electrophoresis with amperometric detection for rapid separation and detection of phenolic acids

A microchip capillary-electrophoresis protocol for rapid and effective measurements of food-related phenolic acids (including chlorogenic, gentisic, ferulic, and vanillic acids) is described. Relevant parameters of the chip separation and amperometric detection are examined and optimized. Under optimum conditions, the analytes could be separated and detected in a 15 mM borate buffer (pH 9.5, with 10% of methanol) within 300 s using a separation voltage of 2000 V and a detection voltage of +1.0 V. Linear calibration plots are observed for micromolar concentrations of the phenolic acid compounds. The negligible sample volumes used in the microchip procedure obviates surface fouling common to amperometric measurements of phenolic compounds. The new microchip protocol offers great promise for a wide range of food applications requiring fast measurements and negligible sample consumption. An application on a commercial red wine was performed with minimal sample preparation and promising results.     

Analysis of a Distinguished Laplacian on Solvable Lie Groups

We study a class of kernels associated to functions of a distinguished Laplacian on the solvable group AN occurring in the Iwasawa decomposition G = ANK of a noncompact semisimple Lie group G. We determine the maximal ideal space of a commutative subalgebra of L¹, which contains the algebra generated by the heat kernel, and we prove that the spectrum of the Laplacian is the same on all L^p spaces, 1 ≤ p < ∞. When G is complex, we derive a formula that enables us to compute the L^p norm of these kernels in terms of a weighted L^p norm of the corresponding kernels for the Euclidean Laplacian on the tangent space. We also prove that, when G is either rank one or complex, certain Hardy-Littlewood maximal operators, which are naturally associated with these kernels, are weak type (1, 1).