Neutron activation analysis: A primary method of measurement

Neutron activation analysis (NAA), based on the comparator method, has the potential to fulfill the requirements of a primary ratio method as defined in 1998 by the Comité Consultatif pour la Quantité de Matière — Métrologie en Chimie (CCQM, Consultative Committee on Amount of Substance — Metrology in Chemistry). This thesis is evidenced in this paper in three chapters by: demonstration that the method is fully physically and chemically understood; that a measurement equation can be written down in which the values of all parameters have dimensions in SI units and thus having the potential for metrological traceability to these units; that all contributions to uncertainty of measurement can be quantitatively evaluated, underpinning the metrological traceability; and that the performance of NAA in CCQM key-comparisons of trace elements in complex matrices between 2000 and 2007 is similar to the performance of Isotope Dilution Mass Spectrometry (IDMS), which had been formerly designated by the CCQM as a primary ratio method.     

Synthesis of silver nanoparticles using dl-alanine for ESR dosimetry applications

The potential use of alanine for the production of nanoparticles is presented here for the first time. Silver nanoparticles were synthesized using a simple green method, namely the thermal treatment of silver nitrate aqueous solutions with dl-alanine. The latter compound was employed both as a reducing and a capping agent. Particles with average size equal to 7.5 nm, face-centered cubic crystalline structure, narrow size distribution, and spherical shape were obtained. Interaction between the silver ions present on the surface of the nanoparticles and the amine group of the dl-alanine molecule seems to be responsible for reduction of the silver ions and for the stability of the colloid. The bio-hybrid nano-composite was used as an ESR dosimeter. The amount of silver nanoparticles in the nanocomposite was not sufficient to cause considerable loss of tissue equivalency. Moreover, the samples containing nanoparticles presented increased sensitivity and reduced energetic dependence as compared with pure dl-alanine, contributing to the construction of small-sized dosimeters.     

Formation of oligomeric alkenylperoxides during the oxidation of unsaturated fatty acids: an electrospray ionization tandem mass spectrometry study

This study reports the identification of oligomeric alkenylperoxides by electrospray ionization mass spectrometry (ESI‐MS) and tandem mass spectrometry (ESI‐MS²), during the oxidation of oleic, linoleic and linolenic acids with Fenton's (Fe²⁺/H₂O₂) and Fe²⁺/O₂ systems. The reactions were followed by ferrous oxidation‐xylenol orange method together with GC‐MS and GC‐FID, allowing to observe that both oxidation systems are different in terms of hydroperoxide evolution, probably due to the presence of different intermediate reactive species: perferryl ion and OH^· radical responsible for the decomposition of lipid hydroperoxides and formation of new compounds. The analysis of ESI‐MS in the negative mode, obtained after oxidation of each fatty acid, confirmed the presence of the monomeric oxidation products together with other compounds at high mass region above m/z 550. These new ions were attributed to oligomeric structures, identified by the fragmentation pathways observed in the tandem mass spectra. Copyright © 2012 John Wiley & Sons, Ltd.     

Bioaccumulation pattern of lanthanides in pteridophytes and magnoliophytes species from Atlantic Forest

The availability of chemical elements for plants is mainly dependent on the nature of the soil and characteristics of each species. The transfer factors of lanthanides from the soil to the tree leaves of the Atlantic Forest, Brazil, were calculated for one fern species (Alsophila sternbergii—Pteridophyta division) and four magnoliophytes species (Bathysa australis, Euterpe edulis, Garcinia gardneriana and Guapira opposita—Magnoliophyta division) obtained in two areas of Serra do Mar State Park and collected in two different seasons. Samples were analyzed by instrumental neutron activation analysis (INAA). The soil-to-plant transfer factor (TF = C_plant:C_soil) in magnoliophytes species was correlated to the mass fraction of lanthanides in the soil, described by a exponential model (TF = a.C_soil^−b). Despite the tree fern Alsophila sternbergii presented a hyperaccumulation of lanthanides, this species did not have a significant relationship between TF and mass fraction in soil. Results indicated that plants of Magnoliophyta division selected the input of lanthanides from the soil, while the same was not observed in Alsophila sternbergii.     

Fluorescence of a Benzothienopyridopyrimidone in Solution and in Lipid Vesicles

Fluorescence properties of a biologically active benzothienopyridopyrimidone in solution and in lipid vesicles are reported. Assays at different pH values (0.5–10) allowed the determination of pK _a = 2.0, showing that this compound may be useful as a pH indicator for pH ≤ 4. In lipid vesicles, benzothienopyridopyrimidone locates in a water-rich environment, indicating that it can be carried in the hydrophilic region of liposomes for drug delivery applications.     

Fluorescence Studies on Potential Antitumoral Heteroaryl and Heteroannulated Indoles in Solution and in Lipid Membranes

Fluorescence properties of three potential antitumoral compounds, a 3-(dibenzothien-4-yl)indole 1, a phenylbenzothienoindole 2 and a 3-(dibenzofur-4-yl)indole 3, were studied in solution and in lipid aggregates of dipalmitoyl phosphatidylcholine (DPPC), dioleoyl phosphatidylethanolamine (DOPE) and egg yolk phosphatidylcholine (Egg-PC). The 3-(dibenzofur-4-yl)indole 3 exhibits the higher fluorescence quantum yields in all solvents studied (0.32 ≤ Φ_F ≤ 0.51). All the compounds present a solvent sensitive emission, with significant red shifts in alcohols. The results point to an ICT character of the excited state, more pronounced for compound 1. Fluorescence (steady-state) anisotropy measurements of the compounds incorporated in lipid aggregates of DPPC, DOPE and Egg-PC indicate that the three compounds are deeply located in the lipid bilayer, feeling the difference between the rigid gel phase and fluid phases.     

Flow nephelometric analysis of protein-tannin interactions

The interaction of tannins from different sources (grape skin, grape seed and wine) with bovine serum albumin (BSA) was studied using a continuous flow method with nephelometric detection. The tannin samples were mixed in a reaction chamber with increasing BSA concentration and the resulting tannin-BSA insoluble aggregates passed through a flow cell where the turbidity was monitored. Based on this technique, the tannin specific activity (TSA) of wine can be directly determined from different wine flows without previous dilutions or any other treatment. The maximum amount of insoluble aggregates formed with BSA and wine or grape skin tannins seemed to remain constant even with the addition of an excess of protein, whereas a decrease in the amount of insoluble aggregates with an excess of BSA was observed in the case of grape seed tannins. It should be noted that BSA was used in these experiments as a model protein and only as an analytical reagent since bovine additives are not allowed in wine.     

Adsorption of detergent-solubilized and phospholipase C-solubilized alkaline phosphatase at air/liquid interfaces

To investigate the influence of a hydrophobic anchor on protein adsorption, equilibrium and dynamic aspects of the adsorption of two different solubilized forms of rat osseous plate alkaline phosphatase on Langmuir monolayers of dimyristoylphosphatidic acid (DMPA) were studied. Surface pressure and surface potential measurements at air/liquid interfaces were carried out using the detergent-solubilized form (DSAP) of alkaline phosphatase, which holds a glycosylphosphatidylinositol (GPI) hydrophobic anchor, and the glycosylphosphatidylinositol-specific phospholipase C-solubilized form (PLSAP), lacking the GPI anchor. Similar surface transitions observed for both DMPA and DMPA/PLSAP mixed monolayers indicate that the presence of PLSAP does not promote significant changes in surface packing of the DMPA monolayer. However, PLSAP interacts with the polar portion of the phospholipid even at high lateral compression. The presence of the GPI anchor increases the adsorption of DSAP at a plain air/liquid interface and also enables the penetration of the protein into the DMPA monolayers. The penetration is dependent on both time and surface pressure. Up to 20 mN/m, the surface pressure increases smoothly indicating a diffusion followed by an adsorption process. Above 20 mN/m, after a fast increase, the surface pressure slowly decays to equilibrium values quite close to the initial surface pressures. The results indicate that the molecular packing of the lipid layer drives the enzyme adsorption to the interface either through the GPI anchor or by the polypeptide moiety.