Estabilidad de la glucosa oxidasa en sistemas amorfos formados por los disacáridos sacarosa, maltosa y trehalosa

Glucose-oxidase (GOD), suffers conformational change during freeze-drying. In order to determine the protection level granted by amorphous matrices (AM) of saccharose, maltose, trehalose and their combinations, the thermal inactivation constants (K D) of GOD trapped in these systems were determined. For its evaluation, GOD samples were balanced at different water activities and heated up to 30, 50 and 70 ºC. The best AM found for GOD stability was saccharose-trehalose (5/10% p/v). The K D values (K D.10-4) at a w = 0.0 were 3 at 30 ºC and 6 at 70 ºC. For non-protected GOD under the same conditions these values were 48 at 30 ºC and 257 at 70 ºC.

Microencapsulação do agente quelante sulfoxina em microesferas de quitosana preparadas por spray drying como novo adsorvente para íons metálicos

In this work, a new adsorbent was prepared by microencapsulation of sulfoxine into chitosan microspheres by the spray drying technique. The new adsorbent was characterized by Raman spectroscopy, scanning electron microscopy and microanalysis of energy dispersive X-rays. The Cu(II) adsorption was studied as a function of pH, time and concentration. The optimum pH was found to be 6.0. The kinetic and equilibrium data showed that the adsorption process followed the pseudo second-order kinetic model and the Langmuir isotherm model over the entire concentration range. An increase of 8.0% in the maximum adsorption capacity of the adsorbent (53.8 mg g-1) was observed as compared to chitosan glutaraldehyde cross-linked microspheres.

Imobilização da lacase em micropartículas de quitosana obtidas por spray drying e usadas na construção de biossensores

Biosensors based on laccase immobilized on microparticles of chitosan crosslinked with tripolyphosphate (biosensor I) and glyoxal (biosensor II) obtained by spray drying for the determinations of rutin in pharmaceutical formulations were developed. Under optimized operational conditions (pH 4.0, frequency of 30 Hz, pulse amplitude of 40 mV and scan increment of 2.0 mV) two analytical curves were obtained for both biosensors showing a detection limit of 6.2x10-8 mol L-1 for biosensor (I) and 2.0x10-8 mol L-1 for biosensor (II). The recovery of rutin from pharmaceutical sample ranged from 90.7 to 105.0% and the lifetime of these biosensors were 4 months (at least 400 determinations).

An expeditious and consistent procedure for tetrahydrofuran (THF) drying and deoxygenation by the still apparatus

Despite the availability of alternative methods for drying tetrahydrofuran (THF), the use of the still apparatus, wherein a THF solution containing Na-bezophenone ketyl is heated to reflux, remains widespread. We herein propose a set of procedures to solve the problems usually faced in applying this drying technique. Moreover, a discussion is made on the chemical knowledge underlying such procedures. Safety and economy issues concerned with the operation of the THF still apparatus are also discussed.

Characterization of the antibiotic doripenem using physicochemical methods: chromatography, spectrophotometry, spectroscopy and thermal analysis

Doripenem was characterized through physicochemical and spectroscopic techniques, as well as thermal analysis. TLC (Rf = 0.62) and HPLC (rt = 7.4 min) were found to be adequate to identify the drug. UV and infrared spectra showed similar profile between doripenem bulk and standard. The ¹H and 13C NMR analysis revealed chemical shifts that allowed identifying the drug. Thermal analysis demonstrated three steps with mass loss, at 128, 178 and 276 ºC. The work was successfully applied to qualitative analysis of doripenem, showing the reported methods can be used for physicochemical characterization of doripenem

Rheological and thermal characteristics of wheat gluten biopolymers plasticized with glycerol

The objective this work was to obtain bioplastics from mixtures of wheat gluten and glycerol by two different processes and evaluate their respective rheological properties. The mixtures and their respective bioplastics were obtained through direct batch mixing under approximately adiabatic and isothermal conditions. The bioplastics showed high values for the storage (G') and loss (G") moduli, suggesting a stronger protein network formed in both processes. The temperature onset and the percentage of weight loss to be estimated were found to be near in both bioplastics. The bioplastics have demonstrated to be materials of interesting potential of use as biodegradable barrier materials.

Preparation of association compound between rhodium(II) citrate and β-cyclodextrin

Inclusion compound of rhodium(II) citrate with β-cyclodextrin in a 1:1 molar ratio was prepared using freeze-drying method. X-ray diffactometry, thermal analysis (TG/DTG/DSC), infrared and ¹H-NMR with ¹H spin lattice relaxation (¹H T1) measurements and 13C techniques were used to characterize the system prepared. The results indicated the formation of inclusion or association compounds between rhodium(II) citrate and β-cyclodextrin.

A new approach to evaluate immobilization of β-galactosidase on Eupergit® C: structural, kinetic, and thermal characterization

This study aimed to evaluate β-galactosidase immobilization. For this purpose, the ionic strength of the buffer, reaction time, amount of the immobilization support, and pH were evaluated by a central composite design. Assay 8, which consisted of 1.5 mol L-1 phosphate buffer (pH 7.5) and a reaction time of 2 h, produced the maximum yield. Eupergit® C (400 mg) was subsequently used as an immobilization support. Immobilization kinetics wereinvestigated, and a significant increase in the yield was obtained after immobilization compared with that obtained from assay 8 (22.0 U mL-1 vs. 15.6 U mL-1). The enzyme efficiency of actuation was evaluated using o-nitrophenyl-β-D-galactopyranoside and lactose, with lactose providing better results. The reuse of β-galactosidase was evaluated, and more than 50% of the initial enzyme activity was maintained after five cycles of use. Enzyme characterization revealed that immobilization improved some aspects of the thermostability of β-galactosidase.

Síntese, liofilização e caracterização de acetato de 57Fe(III)

Iron(III) acetate was synthesized by the reflux method using iron enriched in the 57Fe isotope and the compound processed by freeze-drying. The as-synthesized and freeze-dried acetates were characterized regarding their structural, thermal, vibrational and hyperfine properties. Similar diffractometric and spectroscopic results were found for both materials and also for an industrial acetate made with natural iron. However, the microstructures differed: the as-synthesized compound showed flake morphology with micrometric dimensions, whereas the freeze-dried showed flake morphology with sub-micrometric dimensions. The activation energies for thermal decomposition, calculated from the exothermic events occurring in differential scanning calorimetry measurements, were 100.9 kJ/mol (as-synthesized) and 114.7 kJ/mol (freeze-dried).

TUNGSTOPHOSPHORIC ACID HETEROGENIZED ONTO NH4ZSM5 AS AN EFFICIENT AND RECYCLABLE CATALYST FOR THE PHOTOCATALYTIC DEGRADATION OF DYES

Materials based on tungstophosphoric acid (TPA) immobilized on NH4ZSM5 zeolite were prepared by wet impregnation of the zeolite matrix with TPA aqueous solutions. Their concentration was varied in order to obtain TPA contents of 5%, 10%, 20%, and 30% w/w in the solid. The materials were characterized by N2 adsorption-desorption isotherms, XRD, FT-IR, 31P MAS-NMR, TGA-DSC, DRS-UV-Vis, and the acidic behavior was studied by potentiometric titration with n-butylamine. The BET surface area (SBET) decreased when the TPA content was raised as a result of zeolite pore blocking. The X-ray diffraction patterns of the solids modified with TPA only presented the characteristic peaks of NH4ZSM5 zeolites, and an additional set of peaks assigned to the presence of (NH4)3PW12O40. According to the Fourier transform infrared and 31P magic angle spinning-nuclear magnetic resonance spectra, the main species present in the samples was the [PW12O40]3- anion, which was partially transformed into the [P2W21O71]6- anion during the synthesis and drying steps. The thermal stability of the NH4ZSM5TPA materials was similar to that of their parent zeolites. Moreover, the samples with the highest TPA content exhibited band gap energy values similar to those reported for TiO2. The immobilization of TPA on NH4ZSM5 zeolite allowed the obtention of catalysts with high photocatalytic activity in the degradation of methyl orange dye (MO) in water, at 25 ºC. These can be reused at least three times without any significant decrease in degree of degradation.

Thermal modelling of semiconductor switches in three-level Neutral Point Clamped Medium Voltage DTC-inverter

The aim of this thesis is to investigate the thermal loading of medium voltage three-level NPC inverter’s semiconductor IGCT switches in different operation points. The objective is to reach both a fairly accurate off-line simulation program and also so simple a simulation model that its implementation into an embedded system could be reasonable in practice and a real time use should become feasible. Active loading limitation of the inverter can be realized with a thermal model which is practical in a real time use. Determining of the component heating has been divided into two parts; defining of component losses and establishing the structure of a thermal network. Basics of both parts are clarified. The simulation environment is Matlab-Simulink. Two different models are constructed – a more accurate one and a simplified one. Potential simplifications are clarified with the help of the first one. Simplifications are included in the latter model and the functionalities of both models are compared. When increasing the calculation time step a decreased number of considered components and time constants of the thermal network can be used in the simplified model. Heating of a switching component is dependent on its topological position and inverter’s operation point. The output frequency of the converter defines mainly which one of the switching components is – because of its losses and heating – the performance limiting component of the converter. Comparison of results given by different thermal models demonstrates that with larger time steps, describing of fast occurring switching losses becomes difficult. Generally articles and papers dealing with this subject are written for two-level inverters. Also inverters which apply direct torque control (DTC) are investigated rarely from the heating point of view. Hence, this thesis completes the former material.

Thermal behaviour study of solid state compounds of manganese (II), zinc (II) and lead (II) with cinnamic acid

Compounds of cinnamic acid with manganese, zinc and lead have been prepared in aqueous solution. Thermogravimetry, derivative thermogravimetry (TG, DTG), differential scanning calorimetry (DSC), X-ray diffraction and complexometry have been used in the characterization as well as in the study of the thermal stability and interpretation concerning the thermal decomposition.

Preparation and thermal decomposition of solid state cinnamates of alkali earth metals, except beryllium and radium

Solid state compounds of general formula ML2.nH2O [where M is Mg, Ca, Sr or Ba; L is cinnamate (C6H5 -CH=CH-COO-) and n = 2, 4, 0.8, 3 respectively], have been synthetized. Thermogravimetry (TG), derivative thermogravimetry (DTG), differential scanning calorimetry (DSC) and X-ray diffraction powder patterns have been used to characterize and to study the thermal stability and thermal decomposition of these compounds.

Preparation and thermal behavior of mixture of basic carbonate and 4-dimethylaminocinnamylidenepyruvate with lanthanides (III) and yttrium (III) in the solid state

Solid Ln-OHCO3-DMCP compounds, where Ln represents lanthanides (III) and yttrium (III) ions and DMCP is the anion 4-dimethylaminocinnamylidenepyruvate, have been prepared. Thermogravimetry, derivative thermogravimetry (TG, DTG), differential scanning calorimetry (DSC), x-Ray diffraction powder patterns and elemental analysis have been used to characterize the compounds. The thermal stability as well as the thermal decomposition of these compounds were studied using an alumina crucible in an air atmosphere.