Characterization of oxygenated derivatives of isoprene related to 2-methyltetrols in Amazonian aerosols using trimethylsilylation and gas chromatography/ion trap mass spectrometry

In the present study, we have tentatively identified the structures of three oxygenated derivatives of isoprene in Amazonian rain forest aerosols as the C(5) alkene triols, 2-methyl-1,3,4-trihydroxy-1-butene (cis and trans) and 3-methyl-2,3,4-trihydroxy-1-butene. The formation of these oxygenated derivatives of isoprene can be explained by acid-catalyzed ring opening of epoxydiol derivatives of isoprene, namely, 1,2-epoxy-2-methyl-3,4-dihydroxybutane and 1,2-dihydroxy-2-methyl-3,4-epoxybutane. The structural proposals of the C(5) alkene triols were based on chemical derivatization reactions and detailed interpretation of electron and chemical ionization mass spectral data, including data obtained from first-order mass spectra, deuterium labeling of the trimethylsilyl methyl groups, and MS(2) ion trap experiments. The characterization of 2-methyl-1,3,4-trihydroxy-1-butene (cis and trans) and 3-methyl-2,3,4-trihydroxy-1-butene in forest aerosols is important from an atmospheric chemistry viewpoint in that these compounds hint at the formation of intermediate isomeric epoxydiol derivatives of isoprene and as such provide mechanistic insights into the formation of the previously reported 2-methyltetrols through photooxidation of isoprene.     

Ein einfaches Mikrocoulometer

Zusammenfassung Es wird ein einfaches Gas-Coulometer beschrieben, das aus einer Bürette und einem Glasansatzgefäß mit zwei Platinelektroden herstellbar ist. Mit dessen Hilfe sind kleine Strommengen und Stromstärken mit hoher Genauigkeit meßbar.

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Summary A simple gas coulometer is described, which can be constructed from a burette and a glass extension piece with two electrodes. Small amounts of current and current strengths can be measured with high accuracy by its aid.

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Résumé On décrit un coulomètre à gaz qui est fabriqué avec une burette et un dispositif de verre avec deux électrodes de platine. On peut mesurer avec lui de petites quantités de courant et des intensités avec une grande précision.

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Mit 1 Abbildung.     

Drag of a Solid Particle Trapped in a Thin Film or at an Interface: Influence of Surface Viscosity and Elasticity

We propose a theoretical model for the motion of a spherical particle entrapped in a thin liquid film or in a monolayer of insoluble surfactant at the air/water interface. Both surface shear and dilational viscosity, surface diffusion, and elasticity of the film are taken into consideration. The drag force acting on the particle is analytically calculated and asymptotic expressions of the problem are provided. The relevance of the model is discussed by comparing the calculated "viscoelastic" drag, gamma(vel), to the one predicted by Saffman's theory, gamma(S), for cylindrical inclusions in membranes. Numerical analyses are performed to evaluate the contributions of the surface viscosity and the diffusion coefficient of the layer on the hydrodynamical resistance experienced by the particle. Copyright 2000 Academic Press.     

Photogeneration and transport of charge carriers in polysilylenes

The attachment of π-conjugated chromophores that absorb the radiation with long wavelengths to poly(methylphenylsilylene) ( 1 ) via reactions of its formylated derivative is described. Some of the polymers obtained show improved photostability and higher quantum photogeneration efficiency in comparison with the parent polymer. Photoconductive ultra-thin layers can be prepared from polar derivatives of ( 1 ) by the Langmuir–Blodgett technique.     

Note on the Coulson integral formula

Let P be a polynomial of degree n, whose zeros λ₁, λ₂, ..., λ _n are real-valued. The Coulson integral formula (first reported in 1940) is an expression for the sum of the positive–valued zeros of P, in terms of P. We show that the Coulson formula holds if and only if the condition λ₁+λ₂+...+λ _n =0 is obeyed. We also show how the formula has to be modified, so that it be applicable in the case when λ₁+λ₂+...+λ _n ≠ 0. Ams Classification (2000): primary: 92E10, secondary: 32A27, 81Q99     

Kinetic studies and analytical application of cholesterol oxidase and peroxidase immobilized to synthetic polymer

A method for individual and simultaneous covalent immobilization of cholesterol oxidase and peroxidase to copolymer of acrylonitrile with acrylamide is described. The effect of immobilization on the catalytic properties of the covalently bound enzymes was studied. The immobilized enzymes showed no change in pH optima and an increase in temperature optima, activation energy, and K _m , compared to data received from experiments with soluble enzymes. A small glass column packed with immobilized multienzyme complex was used to develop a method for manual determination of cholesterol in foodstuffs (e.g., in mayonnaise “Olinease”). The method was characterized by high analytical precision (coefficient of variation = 2.67%). The results show high correlation with those obtained by the Kageyama method (r=0.986). The method is economical (the enzyme-carrier conjugate may be used more than 300 times), precise, easy to perform, and less time-consuming than the manual methods utilizing soluble enzymes. The established manual method can be proposed for cholesterol determination in foodstuffs.     

Detection of hydrogen atom adduct of spin-trap DEPMPO. The relevance for studies of biological systems

We proposed EPR spectroscopy using spin-trap DEPMPO as a novel method for the detection of a hydrogen atom (*H) produced by chemical and biological systems. In complex EPR spectra of DEPMPO adducts in biological systems, spectral lines of unknown origin have been observed. We have assumed (Baci?, G.; Mojovi?, M. Ann. N. Y. Acad. Sci. 2005, 1048, 230-243) that those lines represent the spectrum of a hydrogen atom (*H) adduct i.e., DEPMPO/H. An electrochemical system known to produce only *H radicals was used here in order to obtain a separate spectrum of the DEPMPO/H adduct. An acquired spectrum as well as a computer spectral simulation of the DEPMPO/H adduct showed considerable resemblance with additional lines in the EPR spectra of DEPMPO adducts in biological systems-plant plasma membranes and cell walls. This shows that such a radical is produced by plants as well as that DEPMPO is suitable for detection in both electrochemical and biological systems.     

The UHF-CNDO/2 study of tetra-atomic radicals containing silicon and phosphorus

The UHF-CNDO/2 calculations have been performed for several radicals containing C, Si or P. The equilibrium geometries found by the minimization of the total energies and calculated spin densities are compared with results from ESR experiments and INDO calculations. The electronic structure of the radicals is discussed for their equilibrium geometries.