Binding of environmental pollutants to the corn protein zein studied by high-performance liquid chromatography

The interaction of 16 ring-substituted phenols and anilines with the corn protein zein was studied by reversed-phase high-performance liquid chromatography by preparing silica- and alumina-based stationary phases coated with various concentrations of zein. The relationship between the strength of interaction and the physicochemical parameters of solutes was elucidated by principal component analysis followed by the nonlinear mapping technique. The binding of each phenol and aniline derivative to zein has been demonstrated. It was established that the electrostatical parameters of solutes exert the highest influence on the interaction and the involvement of hydrophobic binding forces is of secondary importance. The binding characteristics of phenol and aniline derivatives were different.     

Molecular recognition by β-cyclodextrin derivatives: molecular dynamics, free-energy perturbation and molecular mechanics/ Poisson–Boltzmann surface area goals and problems

 The complexation of p-tert-butylphenyl p-tert-butylbenzoate and N-(p-tert-butylphenyl)-p-tert-butylbenzamide with a β-cyclodextrin derivative formed by two cyclodextrin units linked by a disulfide bridge on one of the C6 atoms has been studied by computational methods. The better amide solubility and the better internal interactions of the ester complex explain the experimentally observed better association constant for the ester. The free-energy perturbation methodology and molecular mechanics/Poisson–Boltzmann surface area analysis have been used to explain the problem and to compare the results. Received: 14 April 2002 / Accepted: 11 August 2002 / Published online: 4 November 2002 Acknowledgements. The Kollman group at the University of California San Francisco is gratefully acknowledged for support and encouragement throughout all this study. The authors thank UAB for inland and outland fellowships to I.B.. Financial support was obtained from grant no. PPQ2000-0369 from the “Ministerio de Ciencia y Tecnologia” (Spain). Intensive computations were performed either with the computers of the Kollman group or with those of CESCA-C⁴ (Catalonia, Spain). Correspondence to: C. Jaime e-mail: carlos.jaime@uab.es     

Vapor-liquid equilibria for the system water + tert.-pentanol at 4 temperatures

Precise isothermal vapor-liquid equilibrium data at 10, 30, 55 and 70°C for the system water + tert.-pentanol were measured using a computer-operated differential static apparatus. Activity coefficients at infinite dilution were derived from the experimental P − x data in the dilute region using a flexible Legendre polynomial, and the vapor-liquid-liquid locus was derived directly from the P − x data near the liquid-liquid phase boundary. Heteroazeotropic points were measured directly by distillation using a rotating band column. Furthermore the UNIQUAC and the NRTL models were used to correlate the experimental P − x data and to derive the azeotropic data.

Experimental H^E data were taken from literature and used together with the experimental P − x data to simultaneously fit temperature dependent interaction parameters for UNIQUAC and NRTL. The parameters were used to predict the azeotropic composition over a large temperature range. The results were compared with those of a simple analytical thermodynamic equation using only the pure component vapor pressure data, heats of mixing in the heterogeneous region and the azeotropic composition at one temperature.

Heats of mixing were measured at 140°C with the help of a flow calorimeter in order to determine the slope of H^E vs. x₁ in the heterogeneous region. The H^E data were used to check the reliability of the G^E model parameters and the equation to calculate the temperature dependence of the heteroazeotropic composition.     

Multinuclear NMR Study of the Structure and Intramolecular Dynamics of (eta(2)-Acetone phenylhydrazonato)tetrafluorooxotungsten(VI)

Using one- and two-dimensional techniques of (1)H, (13)C, (15)N, and (19)F NMR spectroscopy, it was proved that acetone phenylhydrazone (H-aph) acts as a two-center N,N-donor ligand in the complex [WOF(4)(aph)](-). As a result of the coordination to tungsten, the ligand conformation changes from E to Z, and at the same time the phenyl ring is turned out of the >N-N=C< plane. At low temperatures (-30 degrees C), the equatorial plane of the pentagonal-bipyramidal tungsten polyhedron comprises two donor nitrogen atoms of hydrazone and three fluoro ligands. At elevated temperatures, stereoisomeric interconversion caused by hindered intramolecular rotation of the aph(-) ligand occurs. The mechanism of this process was elucidated on the basis of the dynamic effects in (19)F spectra and line-shape analysis of the trans-CH(3) resonance in (13)C spectra split due to direct "through-space" coupling with the proximate fluoro ligand.     

A dimeric cobalt(II)–suberate complex with 3‐amino­pyridine

The title complex, μ‐octane‐1,8‐dioato‐bis[bis(3‐aminopyridine)chloro(methanol)cobalt(II)], [Co₂(C₈H₁₂O₄)Cl₂(C₅H₆N₂)₄(CH₄O)₂], is located on a crystallographic centre of inversion. The coordination around each of the Co centres is distorted octa­hedral, involving two N, three O and one Cl atom. Discrete dimers are connected in a three‐dimensional arrangement through N—H⋯O, N—H⋯Cl and O—H⋯O hydrogen‐bond inter­actions.     

Spectroscopic investigation of a new hybrid glass formed by the interaction between croconate ion and calcium polyphosphate

In this work, a new organic-inorganic hybrid material has been synthesized by the incorporation of croconate ion into a calcium polyphosphate coacervate. The hybrid so obtained was characterized by means of electronic and vibrational spectroscopies. The material is a homogeneous mixture described by a structural model, which includes helical chains of polyphosphate ions, where the calcium ion occupies the internal vacancies of the structure. The croconate ion appears to be occupying the regions outside the polymeric structure, surrounded by several water molecules. The electronic spectrum of the incorporated material shows a broad band peaking at the same wavelength region (363 nm) observed for the aqueous solution of croconate ion, and manifesting the Jahn-Teller effect as evidenced by the doublet structure of the band. The infrared spectrum is widely dominated by the absorption bands of the polyphosphate ion and the appearance of the carbonyl stretching band at ca. 1550 cm(-1) indicates the presence of croconate ion incorporated in the structure. The Raman spectrum of the material shows several vibrational bands related to the oxocarbon moiety; most of them are shifted in comparison with the free ion. These shifts can be understood in terms of strong hydrogen bonding interactions between water molecules and the oxocarbon moiety. The low temperature methodology proposed here can be well used in the preparation of new phosphate glasses containing organic moieties opening the route to an entirely new class of hybrid glasses.     

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.