Antioxidant Properties of Plant Extracts: an EPR and DFT Comparative Study of the Reaction with DPPH, TEMPOL and Spin Trap DMPO

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effect of dietary organic selenium and zinc on the internal egg quality of quail eggs for different periods and under different temperatures

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Sobre o limiar para a produção de pares e localização de partículas sem spin

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The Gerasimov-Drell-Hearn Sum Rule and the Spin Structure of the Proton

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Spin-1 particle in the light-front approach

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Quality of natural coffee subjected to different rest periods during the drying process

O parcelamento da secagem pode ser eficiente tanto no que diz respeito à qualidade final do café, quanto na redução do consumo específico de energia. Diante disso, objetivou-se, com o presente trabalho, avaliar o efeito do teor de água dos frutos no momento da interrupção da secagem e do período de repouso até a retomada da secagem na qualidade do café natural, por meio da análise sensorial e dos testes de condutividade elétrica e lixiviação de potássio. Frutos de café maduros foram colhidos manual e seletivamente e, em seguida, secados ao sol em terreiros de concreto por dois dias e, então, submetidos à secagem mecânica em secadores de camada fixa. Quando o café atingiu os teores de água de 20%, 17% e 14% (base úmida, bu), a secagem foi interrompida e o café permaneceu em repouso por cinco, quinze e trinta dias e, posteriormente, foi secado em secadores mecânicos até o teor de água de 11% (bu). O controle constituiu-se na secagem completa em terreiro. Observou-se que as combinações entre o menor teor de água e o maior período de repouso e entre o maior teor de água e o menor período de repouso, proporcionam menores valores de lixiviação de potássio. A qualidade da bebida melhora progressivamente com o aumento do período de repouso. A interrupção da secagem com teores de água de 17% e 20% (bu) não altera a qualidade do café natural, comparativamente à secagem completa em terreiro.

Asymmetrical penetration of microwave in a conducting media and determination of microwave conductivity for very thin samples using electron spin resonance

Dyson's theory of conduction electron spin resonance (CESR) has been used in the limit d less than or equal to delta (d being the thickness of the sample and delta the skin depth of the microwave field) to obtain the microwave conductivity from the (A/B) ratio of the CESR absorbed power derivative. In this work we calculate the CESR absorbed power derivative using Kaplan's approach and show that the (A/B) ratio can be enhanced if asymmetrical penetration of microwave is used, which means that the microwave field enters into the sample from one of the faces. Therefore, the determination of the microwave conductivity from the (A/B) ratio of the CESR line can be performed for thinner samples. Experimentally, asymmetrical penetration can be obtained if one of the sample's faces is covered with a thin gold layer. The determination of microwave conductivity in conducting polymers films is among the possible applications of this method. (C) 2001 Elsevier B.V. Ltd. All rights reserved.

Spin reversal and magnetization jumps in ErMexMn1-xO3 perovskites (Me = Ni, Co)

The erbium-based manganite ErMnO3 has been partially substituted at the manganese site by the transition-metal elements Ni and Co. The perovskite orthorhombic structure is found from x(Ni) = 0.2-0.5 in the nickel-based solid solution ErNixMn1-xO3, while it can be extended up to x(Co) = 0.7 in the case of cobalt, provided that the synthesis is performed under oxygenation conditions to favor the presence of Co3+. Presence of different magnetic entities (i.e., Er3+, Ni2+, Co2+, Co3+, Mn3+, and Mn4+) leads to quite unusual magnetic properties, characterized by the coexistence of antiferromagnetic and ferromagnetic interactions. In ErNixMn1-xO3, a critical concentration x(crit)(Ni) = 1/3 separates two regimes: spin-canted AF interactions predominate at x < x(crit), while the ferromagnetic behavior is enhanced for x > x(crit). Spin reversal phenomena are present both in the nickel- and cobalt-based compounds. A phenomenological model based on two interacting sublattices, coupled by an antiferromagnetic exchange interaction, explains the inversion of the overall magnetic moment at low temperatures. In this model, the ferromagnetic transition-metal lattice, which orders at T-c, creates a strong local field at the erbium site, polarizing the Er moments in a direction opposite to the applied field. At low temperatures, when the contribution of the paramagnetic erbium sublattice, which varies as T-1, gets larger than the ferromagnetic contribution, the total magnetic moment changes its sign, leading to an overall ferrimagnetic state. The half-substituted compound ErCo0.50Mn0.50O3 was studied in detail, since the magnetization loops present two well-identified anomalies: an intersection of the magnetization branches at low fields, and magnetization jumps at high fields. The influence of the oxidizing conditions was studied in other compositions close to the 50/50 = Mn/Co substitution rate. These anomalies are clearly connected to the spin inversion phenomena and to the simultaneous presence of Co2+ and Co3+ magnetic moments. Dynamical aspects should be considered to well identify the high-field anomaly, since it depends on the magnetic field sweep rate. (C) 2006 Elsevier B.V. All rights reserved.

Correlation between the mobility of spin-labeled peptide chains and resin solvation: An approach to optimize the synthesis of aggregating sequences

Resin solvation properties affect the efficiency of the coupling reactions in solid-phase peptide synthesis. Here we report a novel approach to evaluate resin solvation properties, making use of spin label electron paramagnetic resonance (EPR) spectroscopy. The aggregating VVLGAAIV and ING sequences were assembled in benzhydrylamine-resin with different amino group contents (up to 2.6 mmol/g) to examine the extent of chain association within the beads. These model peptidyl-resins were first labeled at their N-terminus with the amino acid spin label 2,2,6,6-tetramethylpiperidine-N-oxyl-4-amino-4-carboxylic acid (Toac). Their solvation properties in different solvents were estimated, either by bead swelling measurement or by assessing the dynamics of their polymeric matrixes through the analysis of Toac EPR spectra, and were correlated with the yield of the acylation reaction. In most cases the coupling rate was found to depend on bead swelling. Comparatively, the EPR approach was more effective. Line shape analysis allowed the detection of more than one peptide chain population, which influenced the reaction. The results demonstrated the unique potential of EPR spectroscopy not only for improving the yield of peptide synthesis, even in challenging conditions, but also for other relevant polymer-supported methodologies in chemistry and biology.

POTASSIUM ABSORPTION AND PARTITIONING IN COTTON AS AFFECTED BY PERIODS OF POTASSIUM-DEFICIENCY

Cotton (Gossypium hirsutum var. Latifolium) was grown in nutrient media, at two K levels: 58.5 mg/K and 11.7 mg/K. Potassium deficiency (11.7 mg K/g of K) was imposed upon cotton plants at different stages of plant development. A sequence of increasing sensitivity to K deficiency among cotton plant parts was observed: leaves < bolls < roots < stems. When K deficiency symptoms are clearly visible in the leaves, all the other plant parts are already affected. Bolls are a very important component in K partitioning within the cotton plant, but K is required most by the bur itself and is not translocated to seeds or fibers. Cotton could overcome a 30 day deficiency late in the season without significant losses in lint and seed cotton yields.

Characterization of BaTi1-xZrxO3 thin films obtained by a soft chemical spin-coating technique

Single-phase perovskite structure BaZrxTi1-xO3 (BZT) (0.05less than or equal toxless than or equal to0.25) thin films were deposited on Pt-Ti-SiO2-Si substrates by the spin-coating technique. The structural modifications in the thin films were studied using x-ray diffraction and micro-Raman scattering techniques. Lattice parameters calculated from x-ray data indicate an increase in lattice (a axis) with the increasing content of zirconium in these films. Such Zr substitution also result in variations of the phonon mode wave numbers, especially those of lower wave numbers, for BaZrxTi1-xO3 thin films, corroborate to the structural change caused by the zirconium doping. on the other hand, Raman modes persist above structural phase transition, although all optical modes should be Raman inactive in the cubic phase. The origin of these modes must be interpreted as a function of a local breakdown of the cubic symmetry, which could be a result of some kind of disorder. The BZT thin films exhibited a satisfactory dielectric constant close to 181-138, and low dielectric loss tan delta<0.03 at the frequency of 1 kHz. The leakage current density of the BZT thin films was studied at elevated temperatures and the data obey the Schottky emission model. Through this analysis the Schottky barrier height values 0.68, 1.39, and 1.24 eV were estimated to the BZT5, BZT15, and BZT25 thin films, respectively. (C) 2004 American Institute of Physics.