Fe(II) hydrolysis in aqueous solution: A DFT study

Species arising from Fe(II) hydrolysis in aqueous solution have been investigated using density-functional methods (DFT). The different tautomers and multiplicities of each species have been calculated. The solvation energy has been estimated using the UAHF–PCM method. The hydrolysis free energies have been estimated and compared with the available experimental data. The different hydrolysis species have distinct geometries and electronic structures. The estimated ionization potential of the hydrolyzed species is linearly dependent to the number of hydroxyls present in the complex. The estimated Fe(II)/Fe(III) oxidation potential is in good agreement with previously published results about 0.29 V larger than the experimental value. The results highlight the importance of the chemical speciation in describing electron transfer processes at a molecular level. The PBE/TZVP/UAHF–PCM method has been found to describe correctly the hydrolysis free energies of Fe(II) with an average error about 5 kcal mol⁻¹ from the experimental values.     

A simple and rapid method to assess lycopene in multiple layers of skin samples

Topical application of lycopene is a convenient way to restore antioxidants depleted from the skin by UV radiation and achieve protection against premature aging and cancer. In this study, a simple, rapid and reproducible method to quantify lycopene in different skin layers was developed, validated and employed to assess this compound after skin penetration studies. Lycopene was extracted from the stratum corneum (SC) and viable epidermis and dermis (ED) by vortex homogenization and bath sonication in a mixture of acetonitrile and methanol (52:48, v/v). Lycopene was assayed by HPLC using a C₁₈ column, and acetonitrile:methanol (52:48, v/v) as mobile phase. The quantification limit of lycopene in samples of SC and ED was 35 ng/mL and the assay was linear from 35 to 2000 ng/mL. Within‐day and between‐days assays coefficients of variation and relative errors (indicative of precision and accuracy) were less than 15% (or 20% for the limit of quantification). Lycopene recovery from SC and ED was dependent on the spiked concentration: for 50 ng/mL, recoveries were 88.3 and 90.5%; for 100–1000 ng/mL, recoveries were 68.6–74.9%. This method has a potential application for lycopene quantification during formulation development and evaluation in the dermatological field. Copyright © 2009 John Wiley & Sons, Ltd.     

Multiobjective vehicle routing problem with fixed delivery and optional collections

We present an adaption on the formulation for the vehicle routing problem with fixed delivery and optional collections, in which the simultaneous minimization of route costs and of collection demands not fulfilled is considered. We also propose a multiobjective version of the iterated local search (MOILS). The performance of the MOILS is compared with the $\epsilon $ -constrained ( $P_{\epsilon }$ ) ILS, the NSGA-II and the indicator-based multi-objective local search methods in the solution of 14 problem instances containing between 50 and 199 customers plus the depot. The results indicate that the MOILS outperformed the other approaches, obtaining significantly better average values for coverage, hypervolume and cardinality.     

Development of a sequential injection chromatography (SIC) method for determination of simazine,atrazine, and propazine

This paper describes the development of a sequential injection chromatography (SIC) procedure for separation and quantification of the herbicides simazine, atrazine, and propazine exploring the low backpressure of a 2.5 cm long monolithic C₁₈ column. The separation of the three compounds was achieved in less than 90 s with resolution >1.5 using a mobile phase composed by ACN/1.25 mmol/L acetate buffer (pH 4.5) at the volumetric ratio of 35:65 and flow rate of 40 μL/s. Detection was made at 223 nm using a flow cell with 40 mm of optical path length. The LOD was 10 μg/L for the three triazines and the quantification limits were of 30 μg/L for simazine and propazine and 40 μg/L for atrazine. The sampling frequency is 27 samples per hour, consuming 1.1 mL of ACN per analysis. The proposed methodology was applied to spiked water samples and no statistically significant differences were observed in comparison to a conventional HPLC–UV method. The major metabolites of atrazine and other herbicides did not interfere in the analysis, being eluted from the column either together with the unretained peak, or at retention times well‐resolved from the studied compounds.     

Ion-exchange voltammetry of dopamine at Nafion-coated glassy carbon electrodes: quantitative features of ion-exchange partition and reassessment on the oxidation mechanism of dopamine in the presence of excess ascorbic acid

The incorporation/exclusion features of dopamine (DA), ascorbic acid (AA) and uric acid (UA) are evaluated for Nafion (NA)-coated glassy carbon electrodes (GCE) of different thicknesses. The ion-exchange partition of DA(+) between the NA film and the sodium phosphate electrolyte is evaluated by determining the partition coefficient (k(D)) and the apparent diffusion coefficient (D(app)) in thick NA films which were 401 and 1.5 x 10(-9) cm(2) s(-1), respectively. The solution diffusion coefficient was found to be 6.0 x 10(-6) cm(2) s(-1). Also, the effect of NA loading and of the voltammetric timescale on DA voltammetry in the presence of excess AA is assessed, at physiologic like conditions. It is demonstrated that, although AA is excluded at the NA coating, a catalytic regeneration of DA, induced by AA, occurs at the interface NA film/electrolyte resulting from the diffusion of the o-quinone product of DA oxidation from the electrode surface to that interface. The interference of AA in the voltammetric signal of DA is eliminated using 18 microg mm(-2) NA films and v> or =0.5 V s(-1). Therefore, fast, selective and sensitive voltammetric analysis of DA at concentrations<100 microM in the presence of excess AA, e.g., 1 mM is achieved.     

Invariant measures for systems of Kolmogorov equations

In this paper we provide sufficient conditions which guarantee the existence of a system of invariant measures for semigroups associated to systems of parabolic differential equations with unbounded coefficients. We prove that these measures are absolutely continuous with respect to the Lebesgue measure and study some of their main properties. Finally, we show that they characterize the asymptotic behaviour of the semigroup at infinity.     

Ethanol Production by Fermentation Using Immobilized Cells of Saccharomyces cerevisiae in Cashew Apple Bagasse

In this work, cashew apple bagasse (CAB) was used for Saccharomyces cerevisiae immobilization. The support was prepared through a treatment with a solution of 3% HCl, and delignification with 2% NaOH was also conducted. Optical micrographs showed that high populations of yeast cells adhered to pre-treated CAB surface. Ten consecutive fermentations of cashew apple juice for ethanol production were carried out using immobilized yeasts. High ethanol productivity was observed from the third fermentation assay until the tenth fermentation. Ethanol concentrations (about 19.82–37.83 g L^?1 in average value) and ethanol productivities (about 3.30–6.31 g L^?1 h^?1) were high and stable, and residual sugar concentrations were low in almost all fermentations (around 3.00 g L^?1) with conversions ranging from 44.80% to 96.50%, showing efficiency (85.30–98.52%) and operational stability of the biocatalyst for ethanol fermentation. Results showed that cashew apple bagasse is an efficient support for cell immobilization aiming at ethanol production.