The Antioxidative Activity of Riboflavin in the Presence of Antipyrin. Spectroscopic Studies

The effect of Antipyrin upon the antioxidant activity of the riboflavin has been evidenced using chemiluminescent system luminol–hydrogen peroxide, in Tris–HCl buffer, pH 8.5. It was found that riboflavin antioxidant activity depends on the reaction time and the Antipyrin concentration. Using ESR spectroscopy the hydroxyl radical generation, in the mentioned chemiluminescent system, was evidenced. The interaction between reactants was also investigated by UV-VIS and fluorescence spectroscopy. The effect of Antipyrin concentration upon the riboflavin fluorescence has also been investigated. The fluorescence quenching by Antipyrin is not significant and subsequently the riboflavin fluorescence quenching doesn’t indicate an electron transfer process through diffusion-controlled mechanism. The results are discussed with relevance to the redox processes of riboflavin.     

Detection of Allergenic Lysozyme during Winemaking with an Electrochemical Aptasensor

In this work we investigate the performance of a simple, disposable electrochemical aptasensor for lysozyme and its usefulness for monitoring the allergen risk along wine production. The sensor relies on screen‐printed gold electrodes modified with gold nanoparticles as the electrochemical transducer, with detection by cyclic voltammetry. This simple method is characterized by a detection limit of 0.32 μg.mL^?1 lysozyme and a linear range of 1–10 μg.mL^?1, being appropriate for the analysis of lysozyme‐treated wines. Several white wines where sulphur dioxide was partially replaced by lysozyme were produced and analyzed with the aptasensor at critical stages during wine production. The results obtained with the aptasensor were moreover compared with those recorded in parallel by a standard method, high performance liquid chromatography (HPLC). The specific advantages brought by the use of nanomaterial and the limitations of the sensor are discussed. The sensor allowed evaluating the effect of various technological steps along wine production on the content of lysozyme.     

Heterocyclic organoboron compounds—XVI : Chelated compounds with α,β-unsaturated β-aminoketones

The reaction of β-aminoenones 4 with diphenylborinic acid or 2-alkoxy-1,3,2-benzodioxaborole affords chelated compounds whose UV, IR and NMR spectra are discussed.     

The Künneth formula for Hilbert complexes

A variant of the Künneth formula for tensor products of Fredholm complexes of Hilbert spaces is given.     

The properties of aqueous solutions of some short chain cosurfactants used for radical polymerization of vinyl acetate

 The refractive index and excess molar volume, of the following short hydrocarbon chain co-surfactants were studied: ethylene glycol, ethylene glycol monomethyl ether, ethanol, n-, i-propanol, acrylic acid, ethyl monomethylmaleate and acrylamide. The refractive indexes of the aqueous solutions of these compounds vary nonlinearly with composition. The maximum variation of refractive indexes occurs up to a cosurfactant/water molar ratio equal to 1 5. The fluorescence probe method was successfully used to evidence the structure modifications of the alcohol–water mixtures. The intensity ratio of pyrene fluorescence vibrational bands varies nonlinearly with the composition of the systems; in case of 1-propanol, the sudden decrease of the ratio is similar to that of micellar solutions, so that a critical concentration of association can be determined at a 0.88 water mole fraction. It was shown, in good agreement with data in literature, that the compounds mentioned penetrate into the cluster structure of water and associate. At concentrations higher than critical, restructuring of aqueous solutions continues and structures of bicontinuous or w/o type may arise. The excess volume of the first six compounds is negative owing to the restructuring just mentioned. Vinyl acetate may penetrate in the struc-tures of binary systems to form homogeneous systems. The number of homogeneous systems decreases in the sequence: ethanol, i-propanol, acrylic acid, n-propanol, the mono-methylether of ethyleneglycol, methyl monomaleate. The vinyl acetate over cosurfactant molar ratio of limiting homogeneous systems varies in inverse sequence at the same monomer/water ratio. After radical polymerization of VAc in homogeneous samples transparent systems were obtained only when the polymer was solubilized in cosurfactant water mixtures. Received: 16 July 1996 Accepted: 14 January 1997     

Structural factors influencing the reaction rates of 4-aryloxy-7-nitrobenzofurazans with amino acids

An interesting observation was made when studying the S _N Ar reaction between several 4-aryloxy-7-nitrobenzofurazans (2) and several amino acids leading to the apparition of detectable fluorescence from the substitution products3. Acidic amino acids reacted very slowly=while basic amino acids react fastest with2 having an unsubstituted phenyl or a 4-formyl-phenyl Ar group. Amongst neutral amino acids, proline reacts fastest at room temperature after 100 min. With2 having a methoxy-subtituted Ar group.