Ascorbic acid degradation kinetics in tomatoes at different drying conditions

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Refolding and purification of bothropstoxin-1, a Lys49 - Phospholipase A(2) homologue, expressed as inclusion bodies in Escherichia coli

Hydrolysis of phospholipids by Group II phospholipase A(2) enzymes involves a nucleophilic attack on the sn-2 ester bond by the His48 residue and stabilization of the reaction intermediate by a Ca2+ ion cofactor bound to the Asp49 residue in the protein active site region, Bothropstoxin-I (BthTX-I) is a PLA, variant present in the venom of the snake Bothrops jararacussu which shows a Asp49 to Lys substitution and which lacks hydrolytic activity yet damages artificial membranes by a noncatalytic Ca2+-independent mechanism. In order to better characterize this unusual mechanism of membrane damage, we have established an expression system for BthTX-I in Escherichia coli. The DNA-coding sequence for BthTX-I was subcloned into the vector pET11-d, and the BthTX-I was expressed as inclusion bodies in E, coli BL21(DE3). The native BthTX-I contains seven disulfide bonds, and a straightforward protocol has been developed to refold the recombinant protein at high protein concentration in the presence of surfactants using a size-exclusion chromatography matrix. After refolding, recovery yields of 2.5% (corresponding to 4-5 mg of refolded recombinant BthTX-I per liter of bacterial culture) were routinely obtained. After refolding, identical fluorescent and circular dichroism spectra were obtained for the recombinant BthTX-I compared to those of the native protein. Furthermore, the native and refolded recombinant protein demonstrated identical membrane-damaging properties as evaluated by measuring the release of an entrapped fluorescent marker from liposomes, (C) 2001 Academic Press.

Kinetics of osmotic dehydration and air-drying of pumpkins (Cucurbita moschata)

Kinetics of osmotic dehydration (OD) and effects of sucrose impregnation on thermal air-drying of pumpkin slices were investigated. A simplified model based on the solution of Fick's Law was used to estimate effective diffusion coefficients during OD and air-drying. In order to take into account shrinkage, average and variable thicknesses were considered. Pumpkin slices were dehydrated in sucrose solutions (40%, 50% and 60%, w/w, 27 degrees C. The effective water diffusion coefficients were higher than the sucrose, and low diffusivity dependence with solution concentration was observed. Samples non-treated and pre-treated in 60% osmotic solutions during one hour were dried in a hot-air-dryer at 50 and 70 degrees C (2 m/s) until equilibrium was achieved. Pre-treatment enhanced mass transfer during air-drying. Great volume reduction was observed in pre and non-treated dried samples. Using variable thickness in the model diminished the relative deviations between predicted and experimental OD and drying data. (C) 2007 Elsevier Ltd. All rights reserved.

Topography of funneled landscapes determines the thermodynamics and kinetics of protein folding

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

The Water Effect on the Kinetics of the Bovine Liver Catalase

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Statistics and kinetics of single-molecule electron transfer dynamics in complex environments: A simulation model study

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

Structure and Growth Kinetics of 3-Glycidoxypropyltrimethoxysilane-Derived Organic/Silica Hybrids at Different Temperatures

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

Dynamic Scaling and Growth Kinetics of 3-Glycidoxypropyltrimethoxysilane-Derived Organic/Silica Hybrids

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

Temperature Effect on the Structure and Formation Kinetics of Vinyltriethoxysilane-Derived Organic/Silica Hybrids

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

Structure and aggregation kinetics of vinyltriethoxysilane-derived organic/silica hybrids

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

Aging kinetics in the Cu-8 wt.% Al alloy with Ag additions

The influence of additions of 2, 4, 6, 8, 10 and 12 wt.% Ag in the isothermal aging kinetics of the Cu-8 wt.% Al alloy was studied using microhardness measurements, differential scanning calorimetry, optical and scanning electron microscopy and X-ray diffractometry. The results indicate that the presence of silver is responsible for the shift of the equilibrium concentration to higher Al contents, allowing the formation of the gamma(1) phase (Al4Cu9) in this alloy. For Ag additions up to 6% the dominant kinetic process is Ag precipitation and for additions from 8 to 12% Ag the nucleation of the perlitic phase dominates. (C) 2003 Elsevier B.V. B.V. All rights reserved.

Kinetics of Ag-rich precipitates formation in Cu-Al-Ag alloys

The kinetics of Ag-rich precipitates formation in the Cu-2 wt.% Al alloy with additions of 2, 4, 6, 8, 10 and 12 wt.% Ag was studied using microhardness changes with temperature and time, differential scanning calorimetry (DSC), differential thermal analysis (DTA), scanning electron microscopy (SEM), optical microscopy (OM), energy dispersive X-ray analysis (EDX) and X-ray diffractometry (XRD). The results indicated that an increase in the Ag content decreases the activation energy for Ag-rich precipitates formation, and that it is possible to estimate the values of the diffusion and nucleation activation energies for the Ag precipitates. (C) 2004 Elsevier B.V. All rights reserved.

Kinetics of martensite decomposition in the Cu-9Al-6Ag alloy

The non-occurrence of the beta' -> (alpha+ gamma(1)) decomposition reaction in the Cu-9 wt.% Al-6 wt.% Ag alloy, on ageing between 200 and 450 degrees C, is discussed considering the influence of Ag on point defects redistribution and energy difference between martensite and the ordered parent phase. (c) 2005 Elsevier B.V All rights reserved.

Isothermal decomposition kinetics in the Cu-9%Al-4%Ag alloy

The influence of 4 wt.%Ag addition on the isothermal decomposition kinetics of the beta' phase in the Cu-9wt.%Al alloy was studied by microhardness measurements, optical and scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, and X-ray diffractometry. The results showed that the presence of Ag decreases the beta' --> (alpha + gamma(1)) decomposition reaction rate in the Cu-9%Al-4%Ag alloy, an effect that may be associated to the gamma(1) phase which catalyses the Ag precipitation, making it faster than the decomposition reaction, and thus, stabilizing the martensitic phase. (C) 2003 Elsevier B.V. All rights reserved.