Maria Lucia Yoneama

Charging effects in thick insulating samples

In this paper we analyse the effects observed in X-ray spectra when thick insulating targets are irradiated with beams of light charged particles. Preliminary results show that the background yield due to charge buildup on mylar is larger for protons than for lithium ions, suggesting that particles with low energy loss tend to generate more background. Residual activity has been observed in several thick samples like resin, quartz and mylar. Two methods for suppressing the background due to charging effects have been studied. The first one was based on the use of a transverse magnetic field. The second one made use of a simple electric lamp of 6 V with its glass bulb removed. While the first method proved to be inefficient, the second one eliminated most of the background due to charge buildup in the sample.

Antioxidant Activity and Phenolic and Mineral Content of Rose Grape Juice

There are many studies related to the antioxidant activity of grape products; however, they concern only purple and white grape varieties. Up to now, there are no reports of studies on the Goethe rose grape variety, either on its antioxidant activity or on its phenolic and mineral quantification. Thus, the purpose of this study was to evaluate in vitro and in vivo antioxidant activity, as well as to quantify total phenolic compounds, ascorbic acid, and mineral content, in a Goethe rose grape juice. The results obtained showed that the Goethe rose grape juice is a great polyphenol source, which contains catechin, epicatechin, and procyanidins (B(1), B(2), B(3), and B(4)). Of all metals analyzed, potassium, calcium, magnesium, and iron showed the highest values. We found that this rose grape juice shows an important antioxidant activity in in vitro (2,2-diphenyl-1-picrylhydrazyl radical scavenging activity) and in vivo (using the Saccharomyces cerevisiae yeast cells) assays. The antioxidant activity could be explained by the significant phenolic content and ascorbic acid levels found in the juice. The results showed that rose grape juice is an excellent antioxidant source, which could contribute to the prevention of many diseases related to oxidative stress, such as atherosclerosis and Parkinsons disease.

PIXE analysis of urease isoenzymes isolated from Canavalia ensiformis (jack bean) seeds

Abstract The main goal of this work was to perform a stoichiometric analysis of metals, in particular Ni and Zn, in two isoforms of urease isolated from jack bean seeds. The urease isoforms were separated by immobilized metal affinity chromatography. The samples were prepared for PIXE by acetone precipitation of the proteins, which were deposited onto regenerated cellulose acetate membranes by filtration. The resulting mass of the samples was of the order of 0.20 mg (dry weight). The results show that urease contains two equivalents of Ni per 90 kDa monomer, in agreement with the results reported in the literature. For canatoxin, the other urease isoform, the presence of one equivalent of Zn per monomer was observed, besides Ni, previously detected by atomic absorption spectrometry as one equivalent per 90 kDa. Problems and further improvements concerning the preparation of the samples are discussed.

A PIXE study of elements transport in fluvial waters in the Candiota region, Rio Grande do Sul, Brazil

The transport of elements in fluvial waters within the Candiota region was evaluated by determining the elements associated with suspended particulate matter (SPM). To that end, SPM samples were collected at nine different locations five times from December 1999 to October 2000. The particle-induced X-ray emission technique was used to determine elements associated with SPM. Data interpretation was performed using factor analysis. Among the results explained by factor 1, the highest score was found to be due to the effect of local anthropogenic sources (coal mines) during the dry season. On the other hand, factor 2 was substantially heterogeneous, emphasising the sum of all anthropogenic contributions generated at the basin. Flux ratio and enrichment factor were calculated to elucidate the balance between weathering and solute transport. Results showed that Mn, Ni, Fe, Cu and Zn were carried by Candiota Stream particles, indicating that coal mining is presumably responsible for contamination of these elements in SPM.