Search results for "Names"

Application of headspace analysis to the study of aroma compounds-lipids interactions

1998

Taking into account interactions between aroma compounds and food components is necessary to better manage the flavoring of food products. These interactions occur at a molecular level and reflect changes, at a macroscopic level, in thermodynamic equilibria, such as solubility or volatility. The rate of transfer of an aroma compound from the liquid to the vapor phase can be affected as well. The behavior of aroma compounds in water and lipid solutions was studied in two complementary ways, a thermodynamic and a kinetic approach (head-space analysis). The transfer rate of volatiles at the liquid-water interface does not only depend on the hydrophobicity of the aroma compounds. Vapor-liquid p…

1991

Tracer diffusion coefficients D* of both components were measured in mixtures of polystyrene (PS) and polymethylstyrene (PMS), a random copolymer from 60 wt.-% of m-methylstyrene and 40 wt.-% of p-methylstyrene. The results are interpreted in terms of the free-volume theory which yields master curves even for “asymmetric” mixtures of oligomer and polymer chains, if D* is drawn versus the distance from the glass transition temperature, T–Tg. Whereas D* was measured by the forced Rayleigh scattering technique, we also studied photon correlation spectroscopy in these mixtures and observed “slow modes” with decay constants that correspond to diffusion coefficients 2–3 decades smaller than the i…

Extruded Expanded Polystyrene Sheets Coated by TiO2 as New Photocatalitic Materials for Foodstuffs Packaging

2012

Nanostructured, photoactive anatase TiO2 sol prepared under very mild conditions using titanium tetraisopropoxide as the precursor is used to functionalise extruded expanded polystyrene (XPS) sheets by spray-coating resulting in stable and active materials functionalised by TiO2 nanoparticles. Photocatalytic tests of these sheets performed in a batch reactor in gas-solid system under UV irradiation show their successful activity in degrading probe molecules (2-propanol, trimethylamine and ethene). Raman spectra ensure the deposition of TiO2 as crystalline anatase phase on the polymer surface. The presence of TiO2 with respect to polymer surface can be observed in SEM images coupled to EDAX …

Immobilization of vegetable tannins on tannery chrome shavings and their use for the removal of hexavalent chromium from contaminated water

2011

Abstract Chestnut (C) and mimosa (M) tannins immobilized on chrome shavings (CS) as an adsorbent have been proposed to be an efficient and economical alternative in hexavalent chromium removal from aqueous solutions. The adsorption of hexavalent chromium onto chrome shavings-tannin (CS-T) adsorbents was performed using batch equilibrium technique at 25 ± 2 °C. The effect of pH is highly important especially in the case of high concentrations of hexavalent chromium. The maximum chromium uptake was obtained at pH 4. Two hours of contact time are enough to reach equilibrium. Sorption of chromium on CS-T was found to follow a pseudo-second order kinetic model (with correlation coefficients grea…

A truncated driven Overhauser effect study of Adriamycin in water: Conformation of the glycosidic linkage

1991

Abstract Truncated driven nuclear Overhauser effect difference spectra have been used to ascertain the conformational characteristics of the glycosidic linkage of Adriamycin in aqueous solution. The “two-spin approximation” has been employed to evaluate the cross-relaxation rates between nearby protons and to obtain the relative internuclear distances. The rotational angles φ1 = C(7)−O(7)−C(1′)−(H1′) and φ2 = H(7)−C(7)−O(7)−C(1′) have also been calculated.

Structure of e-beam sculptured poly(N-vinylpyrrolidone) networks across different length-scales, from macro to nano

2013

Abstract Study of macromolecular structure and dynamics of networks formed by pulsed electron-beam irradiation of poly(N-vinyl pyrrolidone) (PVP) aqueous solutions, at relatively low energy per pulse and across different concentration regimes, provides the basis for the understanding of a new generation of functional nanostructures. Networks are the result of the follow–up reactions initiated by a continuous series of electron pulse-generated hydroxyl radicals, which may have a different fate at the variance of polymer concentration. Different spectroscopic techniques, FT-IR, 13 C { 1 H} CP-MAS NMR and Raman, applied to characterize the formed networks, describe a profound modification of t…

Apparent activation energies and apparent frequency factor in polarographic waves of paludrine-Zn(II)

1993

Abstract Arrhenius and Vlcek plots of ac 1 and dp polarograms of paludrine-Zn complexes are tested in order to understand the apparent activation energies and pre-exponential factor, and their dependence on the potential. These empirical treatments are useful for obtaining information about the energetic contributions of the elemental processes associated with the Zn(II) and paludrine ligands in the overall mechanism of reduction of the complex 2:1 on the mercury interface.

Kinetic Investigation on Metal Free Anionic Polymerization of Methyl Methacrylate Using Tetraphenylphosphonium as the Counterion in Tetrahydrofuran

1997

The anionic polymerization of methyl methacrylate using tetraphenylphosphonium triphenylmethanide as an initiator proceeds in a living manner even at room temperature. The rate constants of propagation were measured between -20 and +20 °C using a flow tube reactor. At 0 °C the reaction half-lives range from 0.3 to 1 s. The polymerization follows first-order kinetics with respect to monomer conversion (with a short induction period) and shows a linear dependence of the number-average degree of polymerization on conversion with high initiator efficiencies and narrow molecular weight distributions (M w /M n < 1.1). The dependence of the measured rate constants on the active center concentratio…

Configurational effects in17O NMR chemical shifts of hydroxyl-substituted, bicyclo [2.2.1]heptenes and -heptanes, their methylated derivatives and so…

1993

Well resolved natural abundance 17O NMR spectra of 27 mono-, di-, tri- and tetrahydroxybicyclo[2.2.1]heptenes and -heptanes (norbornenes or norbornanes), their methylated derivatives and some related compounds were measured for 0.5 M or saturated solutions in acetonitrile at 65°C. In addition, the 17O NMR chemical shifts of 14 aliphatic and alicyclic alcohols were also determined for reference purposes. The 17O NMR chemical shifts of all compounds were assigned. Both methyl- and hydroxyl-induced deshielding β-effects were consistent with those reported in the literature. Similarly, observed shielding γ-effects were in agreement with the earlier observations and characteristic especially for…

Calculation of phase diagrams not requiring the derivatives of the Gibbs energy for multinary mixtures

1996

A method for the calculation of phase diagrams (tie lines and binodal, spinodal, critical points and their stability) based exclusively on the Gibbs energy of mixing with no need of its derivatives with respect to the composition variables is extended to multinary mixtures for any number of components. The mathematical description of the (K-1)-dimensional phase diagram of a K-component mixture is presented. The method is demonstrated for a quinternary blend of five polymers exhibiting a closed miscibility gap; all binary, ternary and quaternary subsystems are completely miscible. The phase separation in the quinternary system is caused by very favorable interactions in the ternary subsystem…