Effects of organic and inorganic additives on flotation recovery of washed cells of Saccharomyces cerevisiae resuspended in water

Separation of microbial cells by flotation recovery is usually carried out in industrial reactors or wastewater treatment systems, which contain a complex mixture of microbial nutrients and excretion products. In the present study, the separation of yeast cells by flotation recovery was carried out using a simple flotation recovery systems containing washed yeast cells resuspended in water in order to elucidate the effects of additives (defined amounts of organic and inorganic acids, ethanol, surfactants and sodium chloride) on the cellular interactions at interfaces (cell/aqueous phase and cell/air bubble). When sodium chloride, organic acids (notably propionic, succinic and acetic acids) and organic surfactants (sodium dodecyl sulphate (SDS), cetyltrimethylammonium bromide (CTAB) and Nonidet P40) were added to the flotation recovery system, significant increases in the cell recovery of yeast hydrophobic cells (Saccharomyces cerevisiae, strain FLT-01) were observed. The association of ethanol to acetic acid solution (a minor by-product of alcoholic fermentation) in the flotation recovery system, containing washed cells of strain FLT-01 resuspended in water, leading to an increased flotation recovery at pH 5.5. Thus, the association among products of the cellular metabolism (e.g., ethanol and acetic acid) can improve yeast cell recovery by flotation recovery. (c) 2006 Elsevier B.V. All rights reserved.

Doxorubicin biocompatible O/W microemulsion stabilized by mixed surfactant containing soya phosphatidylcholine

Microemulsions (ME) containing soya phosphatidylcholine (SPC/polyoxyethylenglycerol trihydroxystearate 40 (EU)/sodium oleate (SO) as surfactant cholesterol (CHO) as oil phase and aqueous buffer were studied. Pseudo-ternary phase diagrams of the investigated systems were obtained at constant SPC/EU/SO weight ratio 3.5:3.5:3.0 by titration, in order to characterize the proportions between the components to form clear systems. The dynamic light scattering results showed that the size of the oil droplets decreases significantly with the ratio of surfactant/oil phase added to system. Depending on the composition ME system could exhibit a thixotropic behavior. The apparent viscosity increased 25- and 13-folds with cholesterol concentration for drug-free and drug-load ME, respectively. It was also verified that the octanol/aqueous buffer partition coefficient (K-O/B) of doxorubicin (DOX) was pH dependent increasing abruptly above pH 6.0. It was possible to incorporate 2.24 mg/ml of DOX into ME. The incorporation of DOX in the ME systems increased the droplets size for all surfactant concentrations used in the system. The results suggest that DOX interacts with the microstructure of the ME at the studied pH increasing significantly the drug solubility. It was possible to conclude that the investigated ME can be a very promising vehicle as drug-carrier for administration of doxorubicin. (c) 2006 Elsevier B.V. All rights reserved.

Relationship between structural features and in vitro release of doxorubicin from biocompatible anionic microemulsion

In this work structural features of anionic microemulsions, containing the pharmaceutical biocompatible components soya phosphatidylcholine (SPC), eumulgin HRE 40 (EU) and sodium oleate (SO) as surfactant, cholesterol (CHO) as oil phase and aqueous buffer were studied. Microemulsions were formulated with and without the antitumor drug doxorubicin (DOX). The various microstructures characterized in the pseudo-temary phase diagram were analyzed by polarized light microscopy, small-angle X-ray scattering (SAXS) and X-ray diffraction (XRD) as well as by their ability to incorporate and release DOX. The experimental results demonstrated a correlation between the composition, the structural features and drug delivery. It was found that at higher cholesterol contents, the crystallization of CHO polymorph phases changed the mobility of DOX molecules. Droplets were formed with short-range spatial correlation from a microemulsion (ME) with a low surfactant:oil ratio. More ordered structures with lamellar arrangements formed by the increasing of the CHO proportions in the formulation may be due to CHO crystallization. The in vitro release of DOX showed that the presence of a high content of crystalline CHO prolongs the release of DOX from ME. The retention of DOX in the internal oil phase of the ME may modulate the drug release for a prolonged time. These results clearly demonstrate the potential of ME as a drug-delivery system. (c) 2007 Elsevier B.V. All rights reserved.

SAXS and UV-Vis combined to Quick-XAFS monitoring of ZnO nanoparticles formation and growth

Time-resolved X-ray absorption-fine structure (Quick-XAFS) and UV-Vis absorption spectroscopies were combined for monitoring simultaneously the time evolution of Zn-based species and ZnO quantum dot (Qdot) formation and growth during the sol-gel synthesis from zinc oxy-acetate precursor solution. The time evolution of the nanostructural features of colloidal suspension was independently monitored in situ by small angle X-ray scattering (SAXS). In both cases, the monitoring was initialized just after the addition of NaOH solution (B = [OH]/[Zn] = 0.5) to the precursor solution at 40 degrees C. Combined time-resolved Quick-XAFS and UV-Vis data showed that the formation of ZnO colloids from the zinc oxy-acetate consumption achieves a quasi-steady-state chemical equilibrium in less than 200s. Afterwards, the comparison of the ZnO Qdots size and Guinier gyration radius evidences a limited aggregation process coupled to the Qdots growth. The analysis of the experimental results demonstrates that the nanocrystal coalescence and Ostwald ripening control the kinetics of the Qdot growth.

Structural changes of biocompatible neutral microemulsions stabilized by mixed surfactant containing soya phosphatidylcholine and their relationship with doxorubicin release

Depending on the composition, the mixture of surfactant, oil and water, may form supramolecular aggregates with different structures which can significantly influence the drug release. In this work several microemulsion (ME) systems containing soya phosphatidylcholine (SPC) and eumulgin HRE40 (TM) (EU) as surfactant, cholesterol (O) as oil phase, and ultra-pure water as an aqueous phase were studied. MEs with and without the antitumoral drug doxorubicin (DOX) were prepared. The microstructures of the systems were characterized by photon correlation spectroscopy, rheological behavior, polarized light microscopy, small-angle X-ray scattering (SAXS) and X-ray diffraction (XRD). The results reveal that the diameter of the oil droplets was dependent on the surfactant (S) amount added to formulations. The apparent viscosity was dependent on the O/S ratio. High O/S ratio leads to the crystallization of cholesterol polymorphs phases which restricts the mobility of the DOX molecules into the ME structure. Droplets with short-range spatial correlation were formed from the ME with the low O/S ratio. The increase of the cholesterol fraction in the O/S mixture leads to the formation of ordered structures with lamellar arrangements. These different structural organizations directly influenced the drug release profiles. The in vitro release assay showed that the increase of the O/S ratio in the formulations inhibited the constant rate of DOX release. Since the DOX release ratio was directly dependent on the ratio of O/S following an exponential decay profile, this feature can be used to control the DOX release from the ME formulations. (C) 2008 Elsevier B.V. All rights reserved.

Oil-in-water lecithin-based microemulsions as a potential delivery system for amphotericin B

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

Well-Alloyed PtFe/C Nanocatalysts of Controlled Composition and Same Particle Size: Oxygen Reduction and Methanol Tolerance

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

Sol phase and sol-gel transition in SnO2 colloidal suspensions

The effect of concentration on the structure of SnO2 colloids in aqueous suspension, on their spatial correlation and on the gelation process was studied by small angle x-ray scattering (SAXS). The shape of the experimental SAXS curves varies with suspension concentration. For diluted suspensions ([SnO2] less than or equal to 0.13 mol L-1), SAXS results indicate the presence of colloidal fractal aggregates with an internal correlation length xi congruent to 20 Angstrom, without any noticeable spatial correlation between them. This suggests that the aggregates are spatially arranged without any significant interaction like in ideal gas structures. For higher concentrations ([SnO2] = 0.16, 0.32, and 0.64 mol L-1), the colloidal aggregates are larger (xi = 24 Angstrom) and exhibit a certain degree of spatial correlation between them. The pair correlation function corresponding to the sol with the highest concentration (0.92 mol L-1) reveals a rather strong short range order between aggregates, characteristic of a fluid-like structure, with an average nearest-neighbor distance between aggregates d(1) = 125 Angstrom and an average second-neighbor distance d(2) = 283 Angstrom. The pair distribution function remains essentially invariant during the sol-gel transition, suggesting that gelation involves the formation of a few points of connection between the aggregates resulting in a gel network constituted by essentially linear chains of clusters..

Yeast flotation viewed as the result of the interplay of supernatant composition and cell-wall hydrophobicity

Flotation is a process of cell separation based on the affinity of cells to air bubbles. In the present work, flotability and hydrophobicity were determined using cells from different yeasts (Hansenulla polymorpha, Saccharomyces cerevisiae, Candida albicans), which were propagated in different media and at different temperatures. Alterations to the supernatant of the cells were also carried out before the flotation assays. The results described here indicate that supernatants of the yeast cells can play a more important role on flotation than cell-wall hydrophobicity. For example, wall-hydrophobicity of strain FLT-01 of S. cerevisiae was high but flotation did not occur when their washed cells were resuspended in water. Additions of neopeptone to cultures of S. cerevisiae and H. polymorpha repressed flotation and increased the volume of foam. An additional task of the present work was to show that the relationship between cell-wall hydrophobicity and flotation performance was dependent on the method used for the measurement of hydrophobicity. Based on the assay procedure, two types of hydrophobicity were distinguished: (a) the apparent hydrophobicity for cells suspended in the medium and expressed by the degree of cell affinity to the organic solvent in the two-phase system supernatant/hexane; (b) the standard hydrophobicity, which was determined for cells suspended in a standard solution (acetate buffer, in the present work) within the acetate buffer/hexane system. Flotation of cells of S. cerevisiae and C albicans were best related to the degree of apparent hydrophobicity (varying with the supernatant composition at the cell/medium interface) rather than to the degree of standard hydrophobicity (varying with the alterations in the wall components, since the liquid phase was constant in the assay). However, depending on the yeast unpredictable results can be obtained. For example, cells of H. polymorpha exhibited good flotation associated to a high degree of standard hydrophobicity while having a lower degree of apparent hydrophobicity. Concerning growth temperature, flotation of cells of C albicans was strongly repressed when the temperature was raised from 30 to 38 degreesC while a similar effect was not observed in cultures of S. cerevisiae and H. polymorpha. It is difficult to understand and predict flotation of yeast cells but simple modifications made to the supernatant of cultures can activate or repress flotation. (C) 2003 Elsevier B.V. B.V. All rights reserved.

Preparation and characterization of spherical silica-porphyrin catalysts obtained by the sol-gel methodology

This work describes the synthesis of a first-generation iron porphyrin catalyst entrapped in a silica matrix by the sol-gel route, leading to spherical particles. The catalyst was synthesized by the method of Stober, through hydrolysis and condensation of the alkoxysilane TEOS in a mixture of alcohol, water and ammonia, in the presence of the iron porphyrin Fe(TPP)Cl. The relation between particle morphology and catalytic activity of the different Fe(TPP)-SiO2, obtained using different H2O/silane molar ratios and ammonia concentrations in the xerogel syntheses, was studied.The obtained catalysts were characterized by UV-vis spectroscopy, NMR Si-29. thermogravimetric analysis and transmission electron microscopy. Their ability to catalyze (Z)-cyclooctene epoxidation and cyclohexane oxidation was tested using iodosylbenzene as oxygen donor; the oxidation products were analyzed by gas chromatography and the catalysts obtained in a form of particles spherical and monodispersed showed to be a promising catalytic system for selective oxidation. (c) 2005 Elsevier B.V. All rights reserved.

Zirconia needles synthesized inside hexagonal swollen liquid crystals

We report the synthesis of zirconia microneedles by the direct nucleation of particles inside a hexagonal swollen liquid crystal (SLC) (cell parameter a = 27 nm) prepared by mixing with the proper ratio, an aqueous solution of sulfated zirconium colloids, a cationic surfactant (cetylpyridinium chloride), cychlohexane as swelling agent with an oil over water ratio of 2.5 (vol.), and 1-pentanol as cosurfactant. After a slow crystallogenesis that can be enhanced by an initial induction step under moderate temperature, particles in the centimeter range can be obtained, with a very high shape ratio (over 100). These particles are made of crystalline octahydrate zirconium oxychloride containing pores of 20 nm diameter, aligned along the main axis of the liquid crystal, as the fingerprint of the oil cylinders present in the hexagonal phase. The morphology of these particles confirms that the shaping mechanism is based on true liquid crystal templating (TLCT). Further thermal treatment of these particles, after extraction from the SLC, leads to the crystallization of zirconia with the same needlelike morphology as the zirconium oxychloride.

Preparation of ceramic membranes from surface modified tin oxide nanoparticles

The preparation of crack-free SnO2 supported membranes requires the development of new strategies of synthesis capable to allow controlled changes of surface chemistry and to improve the processability of supported layers. In this way, the controlled modification of the SnO2 nanoparticle surface by adding capping molecules like Tiron(R) ((OH)(2)C6H2(SO3Na)(2)) during the sol-gel process was studied, aiming to obtain high performance membranes. Colloidal suspensions were prepared by hydrolyzing SnCl4.5H(2)O aqueous solution with NH4OH in presence of Tiron(R). The effect of the amount of Tiro(R) (from I to 20 wt.%) on the structural features of nanoparticles, powder redispersability and particle-solution interface properties was investigated by X-ray powder diffraction (XRPD), extended X-ray absorption fine structure (EXAFS), quasi-elastic light scattering and electrophoretic mobility measurements. XRPD and EXAFS results showed that the addition of Tiron(R) up to 20 wt.% to colloidal suspensions does not affect the crystallite size of SnO2 primary particles, determined around 2-3 nm. This value is comparable to the hydrodynamic size measured after redispersion of powder prepared with amount of Tiro(R) higher than 7.5 wt.%, indicating the absence of condensation reactions between primary particles after the initial precipitation step. As a consequence the powder with amount of Tiron(R) > 7.5 wt.%, can be fully redispersed in aqueous solution at pH greater than or equal to I I until a nanoparticle concentration of 6 vol.%. The electrophoresis measurements showed a decrease of the isoelectric point by increasing the amount of grafted Tiron(R) at the SnO2 nanoparticle surface, resulting in negatively charged particle-solution interface in all the studied pH range (2-11). These features govern the gelation process favoring the preparation of crack-free SnO2 supported membranes. The control exercised by Tiron(R) modifying agent in the aggregation process allows the fine-tuning of the porosity, from 0.124 to 0.065 cm(3) g(-1), and mean pore size, from 6.4 to 1.9 nm, as the amount of grafted molecules increases from 0 to 10 wt.%. In consequence, the membrane cut-off determined by filtration of polyethylene glycol standard solutions can be screened from 1500 to 3500 g mol(-1). (C) 2002 Elsevier B.V. B.V. All rights reserved.

Surface-enhanced resonance Raman scattering as an analytical tool for single molecule detection

A perylene derivative, n-(n-butyl)-n'-(4-aminobutyl) perylene-3,4,9,10-tetracarboxylic acid diimide (simplified as nBu-PTCD-(CH2)(4)-NH2) has been chosen as the target molecule for studies involving single molecule detection (SMD) using Raman scattering. The enhancement of the Raman signal is the result of the multiplicative effects of two phenomena, resonance Raman scattering (RRS) and surface-enhanced Raman scattering (SERS), which leads to the resulting surface-enhanced resonance Raman scattering (SERRS) process. The SERRS spectra from a single molecule have been collected using both silver and gold colloids. The SMD detection of the fundamental vibrational frequencies characteristic of nBu-PTCD-(CH2)(4)-NH2 is complemented with the detection of some overtones and combinations from ring stretching modes at the single molecule level. The background characterization of the ensemble vibrational spectroscopy of the target perylene and its SERRS is also presented, which includes the UV-vis absorption, experimental and calculated Raman scattering and infrared absorption, and molecular organization using reflection-absorption infrared spectroscopy (RAIRS).

EVOLUTION PATTERNS OF THE SOIL ORGANIC-MATTER IN SOME AGRICULTURAL SYSTEMS IN THE BRAZILIAN CERRADO REGION

Several changes in the soil humus characteristics were observed after clearing the Central Brazil virgin forest. When compared with the original ''Cerrado'' forest, the soils from the agricultural systems showed increased values for cation exchange capacity, total organic matter and non-extractable humin. The humic acid fraction underwent some changes suggesting increased oxidation and decreased aliphatic content. The soil organic N tends to accumulate in the insoluble humus fractions.The above changes were much less intense when the virgin forest was transformed into pastures. Under these conditions, the most significant changes were the reduction of readily biodegradable soil organic matter fractions.In view of the intensity of the lixiviation processes in the area studied, the above changes may be connected with the reduction in aggregate stability observed in the cleared sites.In general, the characteristics of the humus formations in the ''Cerrado'' region suggested high resistance to external factors, which is in part attributed to the active insolubilization of humic colloids by the Al and Fe oxides. In the absence of erosive processes in the cleared sites, additional humus stability may conform both to selective biodegradation and/or lixiviation of the humic colloids, or to the effects of the fire used in soil management.