Preliminary study on the monitoring of glutathione S-tranferase activity toward styrene oxide by electromigration methods

A new method has been developed for the monitoring of glutathione S-tranferase (GST) detoxification activity toward styrene oxide (SO). The enzymatic reaction was carried out directly in a thermostatted autosampler vial and the formation of conjugates between glutathione (GSH) and SO was monitored by sequential MEKC runs. The determinations were performed in a 50-microm fused silica capillary using 50 mM SDS in 20 mM phosphate 20 mM tetraborate buffer (pH 8.3) as a background electrolyte; separation voltage 28 kV (positive polarity), temperature of capillary 25 degrees C, and detection at 200 nm. The method is rapid, amenable to automation, and requires only small amounts of samples, which is especially important in the case of GST isoenzyme analyses.     

On the photochemical dimerization of some 5‐substituted 2‐styryl‐4‐pyrones. The effect of 5‐hydroxy‐/ 5‐methoxy‐substitution

Irradiation of styryl‐4‐pyrones 1a‐1d or 2a‐2e (6‐9 × 10^?3 M, methanol solution) with filtered (RAYONET photochemical reactor, 300 nm) or unfiltered uv‐light (high‐pressure mercury arc lamp) under aerobic conditions led mainly to dimeric products. Parent 5‐hydroxy‐substituted compounds 1a‐1d yielded exclusively “half‐cage” dimers 3a‐d characteristic for 4‐pyrone dimerization. 5‐Methoxy‐analogues 2a‐2e behave like typical stilbene structures and the mixture of tetrasubstituted cyclobutanes 4 and 5 accompanied with minor amount of phenanthrene‐like compound 6 were the only isolable products of the irradiation. The structure elucidation of products is based on spectral data obtained from MS, IR, ¹H NMR and ¹³C NMR spectra applying COSY, APT, HETCOR, HMBC and NOESY techniques.     

Amination of naphthoquinones with azidotrimethylsilane

A new method for the synthesis of aminonaphthoquinones from 1,2- or 1,4-naphthoquinones and azidotrimethylsilane is described. In a similar manner 2,3-epoxy-2,3-dihydro-1,4-naphthoquinone was transformed into 2-amino-3-hydroxy-1,4-naphthoquinone. The mechanism of these transformations and the formation of by-products are discussed.

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Aminierung von Naphthochinonen mit Azidotrimethylsilan

Zusammenfassung Eine neue Methode zur Herstellung von Aminonaphthochinonen aus 1,2- oder 1,4-Naphthochinonen und Azidotrimethylsilan wird beschrieben. In analoger Weise wurde 2,3-Epoxy-2,3-dihydro-1,4-naphthochinon in 2-Amino-3-hydroxy-1,4-naphthochinon umgewandelt. Eine mechanistische Deutung dieser Umsetzung und die Bildung von Nebenprodukten wird diskutiert.

     

Optimization of Affinity Chromatography of Pepsins on Iodinated <Emphasis Type="SmallCaps">l</Emphasis>-Tyrosine–Sepharose

Iodinated l-tyrosine–Sepharose was used as an affinity sorbent for the separation of porcine and human pepsins. The optimized conditions for pepsin adsorption as well as enzyme desorption were investigated. The following basic characteristics of the prepared affinity sorbent were determined: the recovery of the loaded enzyme, capacity of the affinity sorbent, concentration range of the linear dependence of bound pepsin on the applied enzyme, and the reproducibility of the experiments. The method described here cannot only be used for pepsin separation but also for analytical purposes.     

Development of a selective sample clean-up method based on immuno-ultrafiltration for the determination of deoxynivalenol in maize

This paper describes the development of a highly selective analytical method for the determination of deoxynivalenol (DON) in maize. The developed method is based on immuno-ultrafiltration (IUF) and is the first application of IUF as a clean-up strategy in food analysis. Quantification of DON was carried out by high-performance liquid chromatography with ultraviolet detection. In contrast to immunoaffinity chromatography, in IUF the antibodies are not bound to a solid support material but used in free form, thus making it possible to avoid the critical immobilisation step. Sample clean-up by IUF proved to be as selective as clean-up using commercially available immunoaffinity columns. The limit of detection (S/N=3) of the analytical method was found to be 74 ng DON/g maize. Repeated analysis of a certified maize reference material on four different days resulted in a mean recovery of 93% with a standard deviation of 10%.     

An overview on the application of ultrasound in extraction,separation and purification of plant polysaccharides

In view of the recent emphasis on non-conventional chemistry, application of ultrasound in isolation of plant polysaccharides represents a viable alternative to traditional extraction processes. This review presents an extensive literature survey of ultrasound-assisted extraction of polysaccharides from different plant materials, particularly herbal plants and secondary agricultural plant sources. Targeted, multistep methods were applied with respect to differences in the types of polysaccharides and their location in plant cell walls. The effectiveness of the methods was evaluated according to yield and properties of the isolated polysaccharides in comparison to classical extraction methods. Substantial shortening of extraction time, reduction of reagent consumption and/or extraction temperature are the most important advantages of the ultrasonic treatment. In combination with sequential extraction steps using different solvents, sonication was shown to be effective in separation and/or purification of polysaccharides. The disadvantages of the sonication treatment, such as degradation and compositional changes of the polysaccharide preparations are discussed as well.     

Co-isolation of deoxynivalenol and zearalenone with sol–gel immunoaffinity columns for their determination in wheat and wheat products

The paper describes a sample clean-up method for the co-isolation of deoxynivalenol (DON) and zearalenone (ZON), two mycotoxins naturally co-occurring in wheat. The method is based on immunoaffinity columns prepared by co-immobilising anti-DON and anti-ZON antibodies in a porous sol–gel glass. The main task in developing the method consisted in finding a loading medium allowing retention of both analytes as well as a common elution medium for the dissociation of both antigen–antibody complexes formed. This can be achieved by co-extracting DON and ZON with ACN–water (60:40, v/v), reducing the acetonitril concentration to 2.5% before loading an aliquot of the diluted sample extract onto the DON/ZON column. The columns are washed with 5 ml of MeOH–water (10:90, v/v) before DON and ZON are co-eluted with 4 ml of ACN–water (50:50, v/v). Concentrations of DON and ZON are determined with HPLC-UV and HPLC-fluorescence detection, respectively. The sample clean-up method was shown to be applicable to wheat and wheat products, e.g., cornflakes, milk wheat mash and rusk. Spiking experiments (spike level 500 μg DON/kg and 50 μg ZON/kg) resulted in recovery rates from 82% to 111%.     

Synthesis of 5-Arylamino-4-pyrone Carboxamides. A Contribution to the Knowledge About the Reaction of Aromatic Amines and 5-Hydroxy-4-pyrones.

The reaction of aromatic amine and 5-hydroxy-4-pyrone carboxylates in glacial acetic acid gave new type of 4-pyrone derivatives, that is 5-arylamino-4-pyrone carboxanilides (3-9).