Nonlinear modelling of data in photomineralization kinetics of organic micropollutants by photocatalytic membranes immobilizing titanium dioxide in membrane reactors

Kinetic fitting of substrate disappearance and of total organic carbon (TOC) mineralization of organic micropollutants, in water and air, by photocatalytic membranes immobilizing titanium dioxide, was carried out. A model was used in which mineralization of substrate to CO₂ is supposed to occur, with kinetic constant k₁, through one single intermediate, mediating the behaviour of all the numerous real intermediates formed in the path to CO₂, kinetic constant of formation of the latter being k₂. A competitive Langmuirian‐type adsorption of both substrate and ‘intermediate’ was also supposed to be operative, as expressed by pseudo‐thermodynamic constants K₁ and K₂ respectively, these constants possessing a, partly at least, kinetic significance. Nonlinear models could be fitted to data by using the least‐squares method. The very satisfactory matching is shown for the laboratory‐scale mineralization kinetics of methane, as model molecule of aliphatic contaminants, both in the gas phase and in aqueous solution. Furthermore, in pilot plant experiments, using phenol, as model molecule of aromatics, modelling of quantum yields was carried out, as a function of concentration and of adsorbed radiant power. Kinetics of hydroxyl radicals reacting between themselves, leading to hydrogen peroxide, other than with substrate or intermediates leading to mineralization, was considered, paralleled by a second competition kinetics due to superoxide anion radical and its conjugate acid, equally leading to mineralization. In this model the contribution of hydroxyl radicals to mineralization decreases with irradiance, while the contribution of superoxide anion radical and its conjugate acid increases. If the regression equations of these two contributions are considered together, in a linear combination, the surface model perfectly fits the experimental data. Copyright © 2008 John Wiley & Sons, Ltd.     

Absolute Antioxidant Activity of Five Phenol-Rich Essential Oils

Essential oils (EOs) have promising antioxidant activities which are gaining interest as natural alternatives to synthetic antioxidants in the food and cosmetic industries. However, quantitative data on chain-breaking activity and on the kinetics of peroxyl radical trapping are missing. Five phenol-rich EOs were analyzed by GC-MS and studied by oxygen-uptake kinetics in inhibited controlled autoxidations of reference substrates (cumene and squalene). Terpene-rich Thymus vulgaris (thymol 4%; carvacrol 33.9%), Origanum vulgare, (thymol 0.4%; carvacrol 66.2%) and Satureja hortensis, (thymol 1.7%; carvacrol 46.6%), had apparent k_inh (30 °C, PhCl) of (1.5 ± 0.3) × 10⁴, (1.3 ± 0.1) × 10⁴ and (1.1 ± 0.3) × 10⁴ M⁻¹s⁻¹, respectively, while phenylpropanoid-rich Eugenia caryophyllus (eugenol 80.8%) and Cinnamomum zeylanicum, (eugenol 81.4%) showed apparent k_inh (30 °C, PhCl) of (5.0 ± 0.1) × 10³ and (4.9 ± 0.3) × 10³ M⁻¹s⁻¹, respectively. All EOs already granted good antioxidant protection of cumene at a concentration of 1 ppm (1 mg/L), the duration being proportional to their phenolic content, which dictated their antioxidant behavior. They also afforded excellent protection of squalene after adjusting their concentration (100 mg/L) to account for the much higher oxidizability of this substrate. All investigated EOs had k_inh comparable to synthetic butylated hydroxytoluene (BHT) were are eligible to replace it in the protection of food or cosmetic products.     

Bulk and shear mechanical loss of titania-doped tantala

We report on the mechanical loss from bulk and shear stresses in thin film, ion beam deposited, titania-doped tantala. The numerical values of these mechanical losses are necessary to fully calculate the Brownian thermal noise in precision optical cavities, including interferometric gravitational wave detectors like LIGO. We found the values from measuring the normal mode mechanical quality factors, Q's, in the frequency range of about 2000-10,000 Hz, of silica disks coated with titania-doped tantala coupled with calculating the elastic energy in shear and bulk stresses in the coating using a finite element model. We fit the results to both a frequency independent and frequency dependent model and find ${?}_{\mathrm{shear}}=(8.3\pm 1.1)\times {10}^{?4}$, ${?}_{\mathrm{bulk}}=(6.6\pm 3.8)\times {10}^{?4}$ with a frequency independent model and ${?}_{\mathrm{shear}}\left(f\right)=(5.0\pm 0.7)\times {10}^{?4}+(5.4\pm 1.1)\times {10}^{?8}f$, ${?}_{\mathrm{bulk}}\left(f\right)=(11\pm 2.8)\times {10}^{?4}?(8.7\pm 4.7)\times {10}^{?8}f$ with a frequency dependent (linear) model. The ratio of these values suggest that modest improvement in the coating thermal noise may be possible in future gravitational wave detector optics made with titania-doped tantala as the high index coating material by optimizing the coating design to take advantage of the two different mechanical loss angles.     

One-Dimensional Fluids with Positive Potentials

We study a class of one-dimensional classical fluids with penetrable particles interacting through positive, purely repulsive, pair-potentials. Starting from some lower bounds to the total potential energy, we draw results on the thermodynamic limit of the given model.     

Parallel transport and defects on nematic shells

Nematic shells are thin films of nematic liquid crystal deposited on the boundary of colloidal particles, where liquid crystal molecules may freely glide, while remaining tangent to the surface substrate. The surface nematic order is described here by an appropriate tensor field Q, which vanishes wherever a defect occurs in the molecular order. We show how the classical concept of parallel transport on a manifold introduced by Levi-Civita can be adapted to this setting to define the topological charge m of a defect. We arrive at a simple formula to compute m from a generic representation of Q. In a number of separate appendices, we revisit in a unified language several, apparently disparate applications of Levi-Civita’s parallel transport.     

Natural μ and Bμ in gauge mediation

We propose a natural solution to the μ problem in gauge mediation. It relies on the logarithmic dependence of the effective Kähler potential on the messenger threshold superfield X. Thus, μ and Bμ naturally arise at one and two loops, respectively. Moreover B has the same phase as the gaugino mass and the supersymmetric CP problem is solved as well.     

Molecular topology and QSAR multi-target analysis to boost the in silico research for fungicides in agricultural chemistry

The aim of the present study is to show how molecular topology can be a powerful in silico tool for the prediction of the fungicidal activity of several diphenylamine derivatives against three fungal species (cucumber downy mildew, rice blast and cucumber gray mold). A multi-target QSAR model was developed, and two strategies were followed. First is the construction of a virtual library of molecules using DesMol2 program and a subsequent selection of potential active ones. Second is the selection of molecules from the literature on the basis of molecular scaffolds. More than 700 diphenylamine derivatives designed and other 60 fluazinam’s derivatives with structural similarity higher than 80% were studied. Almost twenty percent of the molecules analyzed show potential activity against the three fungal species.

     

Cation dependence of chloride ion complexation by open-chained receptor molecules in chloroform solution

Seventeen peptides, most having the sequence GGGPGGG, but differing in the C- and N-terminal ends, have been studied as anion-complexing agents. These relatively simple, open-chained peptide systems interact with both chloride and the associated cation. Changes in the N- and C-terminal side chains appear to make little difference in the efficacy of binding. NMR studies suggest that the primary interactions involve amide NH contacts with the chloride anion, and CD spectral analyses suggest a concomitant conformational change upon binding. Changes in binding constants, which are expected in different solvents, also suggest selective solvent interactions with the unbound host that helps to preorganize the open-chained peptide system. Significant differences are apparent in complexation strengths when the heptapeptide chain is shortened or lengthened or when the relative position of proline within the heptapeptide is varied.     

Calix[4]arene-based Zn2+ complexes as shape- and size-selective catalysts of ester cleavage

[structures: see text] The kinetics of methanolysis of a number of esters endowed with a carboxylate anchoring group have been investigated in the presence of di- and trinuclear Zn2+ complexes of calix[4]arenes functionalized at the upper rim with nitrogen ligands. The results (i) emphasize the importance of a good match between ester size and intermetal distance, (ii) reveal a substrate independent superiority of the 1,2-vicinal dinuclear catalyst 1-Zn2 to its 1,3-distal regioisomer 2-Zn2, and (iii) provide further evidence for the concurrence of the three metal ions of 3-Zn3 in the catalytic mechanism.     

Time resolved ultraviolet photoluminescence of mesoporous silica

We studied the optical properties of sol-gel synthesized porous silica excited by synchrotron radiation in the 4-10 eV range. The spectral and temporal characteristics of the ultraviolet photoluminescence at about 3.7 eV are reported. The UV emission results from the contribution of two different centers: the first one centered at 3.7 eV with a decay time of 2.0 ns and the second one peaked at 3.9 eV with a decay time of 20 ns. We propose to assign the observed luminescence to different interacting surface silanols.