Magnetite nanoparticles as-prepared and dispersed in Copaiba oil: study using magnetic measurements and Mössbauer spectroscopy

Study of magnetite nanoparticles, as-prepared and dispersed in Copaiba oil as magnetic fluid, by means of magnetic measurement and Mössbauer spectroscopy at various temperatures demonstrated differences in the saturation magnetization and Mössbauer hyperfine parameters which were related to the interactions of Copaiba oil polar molecules with iron cations on magnetite nanoparticle’s surface.     

Chance and probability: What do they mean to university engineering students?

The great interest aroused by the incorporation of Statistics and Probability into curricular projects has been accompanied by considerable evidence of significant difficulties in the meaningful learning and application of the concepts. These difficulties have been the subject of many studies, mostly concerning secondary school students. This study seeks to investigate the level of understanding of random phenomena, in a group of university students, on the second year of a Technical and Industrial Engineering Degree at the University of the Basque Country, in Spain. The students, who had all undertaken an introductory course in Probability Theory, were tested through both written questionnaires and one-to-one interviews, where they were presented with situations that demanded the ability to apply the knowledge they had learnt, at a high level, to a range of situations and to justify their reasoning. The results show that the vast majority of students had a poor understanding of random phenomena, applying alternative ideas to the ones taught on their course in Probability. The need to improve teaching strategies in Probability and Statistics, so that students can develop skills in constructing probabilistic models, is highlighted.     

Analysis of polycyclic aromatic hydrocarbons in fish: evaluation of a quick,easy, cheap,effective, rugged,and safe extraction method

QuEChERS method was evaluated for extraction of 16 PAHs from fish samples. For a selective measurement of the compounds, extracts were analysed by LC with fluorescence detection. The overall analytical procedure was validated by systematic recovery experiments at three levels and by using the standard reference material SRM 2977 (mussel tissue). The targeted contaminants, except naphthalene and acenaphthene, were successfully extracted from SRM 2977 with recoveries ranging from 63.5–110.0% with variation coefficients not exceeding 8%. The optimum QuEChERS conditions were the following: 5 g of homogenised fish sample, 10 mL of ACN, agitation performed by vortex during 3 min. Quantification limits ranging from 0.12–1.90 ng/g wet weight (0.30–4.70 μg/L) were obtained. The optimized methodology was applied to assess the safety concerning PAHs contents of horse mackerel (Trachurus trachurus), chub mackerel (Scomber japonicus), sardine (Sardina pilchardus) and farmed seabass (Dicentrarchus labrax). Although benzo(a)pyrene, the marker used for evaluating the carcinogenic risk of PAHs in food, was not detected in the analysed samples (89 individuals corresponding to 27 homogenized samples), the overall mean concentration ranged from 2.52 ± 1.20 ng/g in horse mackerel to 14.6 ± 2.8 ng/g in farmed seabass. Significant differences were found between the mean PAHs concentrations of the four groups.     

Chromonic lyomesophases formed by the self-assembly of the cyclic dinucleotide d(cGpGp)

The cyclic dinucleotide d(cGpGp) undergoes a self-association process in water to give, first, columnar aggregates similar to the four-stranded helix of poly(G). Successively, at higher concentration, these aggregates self-organize to give a cholesteric and a hexagonal mesophase, the former of which appears only in biphasic systems. The self-assembly process in isotropic solution has been studied by CD spectroscopy and the structure of the mesophases was investigated by optical microscopy and X-ray diffraction.     

Attachment of water-soluble proteins to the surface of (magnetizable) phospholipid colloids via NeutrAvidin-derivatized phospholipids

The present work describes the incorporation of a functionalized phospholipid derivative into the phospholipid bilayer of both classical small unilamellar vesicles and recently developed magnetoliposomes, resulting in unique biocolloid structures onto which peripheral water-soluble enzymes can be immobilized on the surfaces. In the first part of this work, a synthesis protocol is outlined for a universal membrane anchor for water-soluble proteins. Dioleoylphosphatidylethanolamine-N-dodecanyl was used as the starting lipid molecule. After activation of the terminal -COOH group, alpha,omega-diamino-poly(ethylene glycol), used as a hydrophilic, flexible spacer arm, was coupled covalently. Subsequently, NeutrAvidin was bound, after blocking the free -NH(2) groups with citraconic anhydride. In the second part, the resulting lipid-NeutrAvidin derivative was incorporated into small unilamellar vesicles comprised of dimyristoylphosphatidylglycerol. FPLC with Superdex 200 as the column matrix clearly showed that biotinylated alkaline phosphatase, which served as a representative model of water-soluble proteins, was attached to the vesicles. Furthermore, magnetoliposomes, constructed of the same type of phospholipid molecules, were presented as interesting colloids to assess the degree of enzyme immobilization in a rapid and elegant manner. Potential applications that can emerge from this study are briefly discussed.     

Spectroscopic characterization of superparamagnetic particles of thermolytic products of ferric sulphate hydrates

Superparamagnetic particles of chemically pure samples, in the system Fe(OH)SO₄/Fe(OH)SO₄·(H₂O), are produced by thermal decomposition of ferric sulphate hydrates. The control of particle size distribution is achieved by successive hydration and dehydration processes monitored by X-ray diffraction, electron microscopy, Mössbauer and IR spectroscopy. The particle size modification is related for the particle growth and two mechanisms are suggested thereon.     

Spin - freezing phenomenon in pseudobrookite

The temperature dependence of EPR linewidth broadening in polycrystalline Fe₂TiO₅ is discussed. From the comparison between our EPR data and those reported in the literature we can conclude that our sample exhibits a true thermodynamic spin-glass transition at T_f=53.4±0.5 k. We present an expression to explain the behavior of the EPR linewidth broadening as a function of temperature.     

Electric field effect in the spin dynamics of self-assembled InAs/GaAs quantum dots

We identify fundamental mechanisms of electron and hole dynamics in self-organized InAs/GaAs quantum dots (QDs) subject to vertical electric fields by photocurrent investigations. We propose a spin–flip mechanism involving a spin exchange between neighboring QDs. The spin–flip process is revealed in the photocurrent dynamics when the exciton population increases unexpectedly with reverse bias.     

Automation of a heterogeneous enzyme immunoassay for atrazine. Comparison of three immobilization supports

Intensive agriculture associated with the use of large amounts of different pesticides, together with the growing concern about the potential contamination of ground water, have brought about the need for developing fast screening methods. This work presents the automation of an enzyme-linked immunosorbent assay for atrazine by means of a flow-through system. Three different solid supports for antibody immobilization were compared in a direct competitive assay format. Sensitivity reached in all cases was below the maximum level allowed in the EU (100 ng L^–1). Cross-reactivity of atrazine-related compounds was also studied. The performance of the different supports is discussed regarding sensitivity and immunosurface regeneration.