Photodegradation of butyl acrylate in the troposphere by OH radicals: kinetics and fate of 1,2‐hydroxyalcoxy radicals

The rate constant of the reaction of OH radicals with butyl acrylate was studied for the first time using an atmospheric simulation chamber at 298 K and ～750 Torr of air or nitrogen. The decay of the organics was followed using a gas chromatograph with a flame ionization detector (GC‐FID), and the rate constant was determined using a relative rate method with different references. The obtained average value of (1.80 ± 0.26) × 10^?11 cm³ molecule^?1 s^?1 is in agreement with previous determinations of the rate constants of OH radicals with acrylates and methacrylates in the literature. Additionally, product identification under atmospheric conditions was performed for the first time by the GC‐MS technique. Butyl glyoxalate was observed as the degradation product in accordance with the addition of OH to the less substituted carbon atom of the double bond, followed by decomposition of the 1,2‐hydroxyalkoxy radicals formed. Room temperature rate coefficient was used to estimate the atmospheric lifetime of the ester studied. Reactivity trends are discussed in terms of the substituent effects and the length of the hydrogenated chain of the ester. The atmospheric persistence of BUAC was calculated taking into account the experimental rate constant obtained. Copyright © 2008 John Wiley & Sons, Ltd.     

Cryopreservation of embryogenic cultures from mature Quercus suber trees using vitrification

Recent progress in somatic embryogenesis from selected mature trees of Quercus suber, has led to a demand for maintenance of a large number of selected embryogenic lines. To facilitate the management of this material a protocol for the long-term storage of this germplasm should be defined. This study reports on the use of a simple vitrification procedure for the successful cryopreservation of three cork oak embryogenic lines. High embryo recovery levels (88-93 percent) were obtained by first preculturing 2-4 mg clumps of two or three globular embryos on semisolid medium containing 0.3 M sucrose for three days, followed by incubation in PVS2 vitrification solution at 0 degree C for 60 min before direct immersion in liquid nitrogen. The mean number of embryos produced per explant was significantly greater for cryostored embryos than for untreated stock cultures, but the productivity of the latter was recovered in subsequent subcultures of the material produced by cryostored embryos. The germination and plant regeneration rates achieved by cultures derived from cryostored embryos, around 60 percent, were similar to those of non-cryopreserved stock cultures.     

Half-quadratic cost functions for phase unwrapping

We present a generic regularized formulation, based on robust half-quadratic regularization, for unwrapping noisy and discontinuous wrapped phase maps. Two cases are presented: the convex case and the nonconvex case. The unwrapped phase with the convex formulation is unique and robust to noise; however, the convex function solution deteriorates as a result of real discontinuities in phase maps. Therefore we also present a nonconvex formulation that, with a parameter continuation strategy, shows superior performance.     

Unstable Particles, Gauge Invariance and the Δ++ Resonance Parameters

The elastic and radiative ⁺ p scattering are studied in the framework of an effective Lagrangian model for the ⁺⁺ resonance and its interactions. The finite width effects of this spin-3/2 resonance are introduced in the scattering amplitudes through a complex mass scheme to respect electromagnetic gauge invariance. The resonant pole ( ⁺⁺) and background contributions ( ⁰, , , and neutron states) are separated according to the principles of the analytic S-matrix theory. The mass and width parameters of the ⁺⁺ obtained from a fit to experimental data on the total cross section are in agreement with the results of a model-independent analysis based on the analytic S-matrix approach. The magnetic dipole moment determined from the radiative ⁺ p scattering is nuclear magnetons.     

Determination of ethanol in beverages by flow injection, pervaporation and density measurements

A fast, clean and easy to automate flow injection-pervaporation method for the determination of ethanol in different beverages using density measurements is proposed. The method is based on separation of the ethanol from the sample using a pervaporation module; the analyte being collected in water as acceptor liquid. The density of this water-alcohol mixture is measured at the detector. After optimisation by either a univariate or multivariate approach as required, a linear range between 0 and 40% was established. Then, the assessment of the method versus a reference one was studied in terms of repeatability (0.12% v/v), reproducibility (0.32% v/v), detection limit (0.11% v/v) and traceability. The sample throughput was 15 samples h⁻¹. The method was in agreement with the reference methods used in the European Union.     

Transferability of fragmental contributions to the octanol/water partition coefficient: an NDDO-based MST study

This study examines the transferability of fragmental contributions to the octanol/water partition coefficient. As a previous step, we report the parameterization of the AM1 and PM3 versions of the MST model for n-octanol. The final AM1 and PM3 MST models reproduce the experimental free energy of solvation and the octanol/water partition coefficient (log P(ow)) with a root-mean-square deviation of around 0.7 kcal/mol and 0.5 (in units of log P), respectively. Based on this parameterization, an NNDO-based procedure is presented to dissect the free energy of transfer between octanol and water in contributions directly associated with specific atoms or functional groups. The application of this procedure to a set of representative molecular systems illustrates the dependence of the log P(ow) fragmental contribution due to electronic, hydrogen bonding, and steric effects, which cannot be easily accounted for in simple additive-based empirical schemes. The results point out the potential use of theoretical methods to refine the fragmental contributions in empirical methods.     

A novel organic-inorganic hybrid based on a dinuclear copper complex supported on a keggin polyoxometalate

The autoassembly process of copper-oxalate dimers and Keggin type polyoxometalates leads to the first example of a new family of organic-inorganic hybrids, K(14)[(Cu(2)(bpy)(2)(mu-ox))(SiW(11)O(39)Cu(H(2)O))](2)[SiW(11)O(39)Cu(H(2)O)]. approximately 55H(2)O. This compound crystallizes in the monoclinic space group C2/m, a = 37.932(6) A, b = 21.303(3) A, c = 12.546(2) A, beta = 106.16(1) degrees, Z = 2. The crystal structure reveals the presence of a polymeric hybrid built up of alternating dimer and polyoxometalate entities.     

Static pressurised liquid extraction of nitrated polycyclic aromatic hydrocarbons from soils with on-line filtration-preconcentration prior to gas chromatography-mass spectrometry detection

Nitrated polycyclic aromatic hydrocarbons have been extracted from both spiked and natural contaminated soils by using static pressurised liquid extraction. The variables governing the extraction (namely, pressure, extraction time, temperature and number of static extraction cycles) have been optimised using the experimental design methodology. A laboratory-made pressurised liquid extractor has been used allowing its coupling to a filtration-preconcentration system through a flow injection interface, thus providing a partially automated approach. Gas chromatography with MS-MS ion preparation mode has been used for individual separation-identification/quantification providing both high selectivity (no interferences were observed) and sensitivity (detection limits of low pg). The comparison of the proposed approach with the reference EPA Method 3540 has shown that both methods provide similar efficiencies but with dramatic saving of time by the former (30 min vs. 24 h). The use of water as leaching agent avoids the use of organic solvents, thus providing an environmentally friendly method.     

Use of supported liquid membranes incorporated in a flow system for the direct determination of eugenol in spice samples

A method for the determination of eugenol in spice samples based on the use of supported liquid membranes coupled to a flow system was developed. The solid sample is placed directly in the membrane unit without any treatment and the analyte is extracted from the sample, passes through the membrane and is conducted to the flow cell by the acceptor stream. This stream flows through the detector, allowing the measurement of the analyte by using a PVC-graphite composite electrode, versus Ag/AgCl/3 M KCl at +0.3 V, placed in a well-jet flow cell as amperometric detector. The method allowed the determination of eugenol in the range 0.5-30 micrograms ml-1 with a relative standard deviation of 5%. Results provided by the proposed procedure when applied to clove and seasoning samples agreed well with those obtained by a reference method.