M.L.P. da Silva

Use of plasma polymerized highly hydrophobic hexamethyldissilazane (HMDS) films for sensor development

Hexamethyldissilazane (HMDS) plasma polymerized films can be used in a wide variety of applications due to the facility on plasma polymerization of HMDS molecule and the high resistance to acid or basic corrosion of the formed film. Nonetheless, the hydrophobic character, as well as the possibility of adsorption of organic molecules, did not receive attention yet. In this work HMDS plasma polymerized films, presenting high organic character, were obtained in order to analyze their properties as sensors for organic compounds in N2 and aqueous solutions. The films showed to be not only highly resistant to corrosion in a wide scan of pH, but also presented high water contact angle (approximately 908). The organic character of the films leads to a high adsorption characteristic for polar and non-polar compounds. The water contact angle measurements vary for 2-propanol aqueous solutions from 908 (0% of 2-propanol) to about 08 (50% of 2-propanol). When HMDS films were deposited on two different substrates, dielectric and porous silicon (PS), two main issues were found. The films suffered degradation by heating and porous silicon was planarized by the plasma deposition, as shown by infrared spectroscopy, optical and Raman microscopy. Deposition on piezoelectric quartz crystal (PQC) showed adsorption of polar and non-polar organic compounds carried by N2 and chloroform aqueous solutions. HMDS films deposited on silicon were electrically characterized showing quickly and reversible response for 2-propanol carried by N2 .I n saturated environment, the electrical current increases about five times when a range of � 5 to 0 V was applied. For n-hexane drops, no reversible electrical characteristics were found. Although some issues were revealed, HMDS highly hydrophobic films showed promising characteristics for sensor development. # 2003 Elsevier Science B.V. All rights reserved.

HYPERTONICITY INCREASES NO PRODUCTION TO MODULATE THE FIRING RATE OF MAGNOCELLULAR NEURONS OF THE SUPRAOPTIC NUCLEUS OF RATS

Increases in plasma osmolality enhance nitric oxide (NO) levels in magnocellular neurosecretory cells (MNCs) of the supraoptic nucleus (SON) and modulate the secretion of both vasopressin (VP) and oxytocin (OT). In this paper, we describe the effects of hypertonicity on the electrical properties of MNCs by focusing on the nitrergic modulation of their activity in this condition. Membrane potentials were measured using the patch clamp technique, in the presence of both glutamatergic and GABAergic neurotransmission blockers, in coronal brain slices of male Wistar rats. The recordings were first made under a control condition (295 mosm/kg H2O), then in the presence of a hypertonic stimulus (330 mosm/kg H2O) and, finally, with a hypertonic stimulus plus 500 μM L-Arginine or 100 μM N-nitro-L-Arginine methyl ester hydrochloride (L-NAME). Hypertonicity per se increased the firing frequency of the neurons. L-Arginine prevented the increase in fire frequency induced by hypertonic stimulus, and L-NAME (inhibitor of nitric oxide synthase) induced an additional increase in frequency when applied together with the hypertonic solution. Moreover, L-Arginine hyperpolarizes the resting potential and decreases the peak value of the after-hyperpolarization; both effects were blocked by L-NAME and hypertonicity and/or L-NAME reduced the time constant of the rising phase of the after-depolarization. These results demonstrate that an intrinsic nitrergic system is part of the mechanisms controlling the excitability of MNCs of the SON when the internal fluid homeostasis is disturbed.

Adsorção de íons fosfato nos compósitos celulose/ZrO2.nH2O preparados pelos métodos da precipitação convencional e em solução homogênea

This work describes the preparation and characterization of cellulose/hydrous zirconium oxide composites prepared by conventional precipitation (PC) and homogeneous solution (PSH) from cellulose of the sugarcane bagasse and subsequent adsorption of phosphate ions. The composite obtained by the PC method was prepared using an ammonium solution as precipitating agent, whereas the composite obtained by the PSH method was prepared using urea as precipitating agent. The adsorption of phosphate ions was carried out reacting a KH2PO4 solution with ammonium molibdate under acid conditions to form an ammonium phosphomolybdic complex. The analyses to determine the concentration after adsorption were performed using UV-Vis at 880 nm. The results were satisfactory showing that the Cell/ ZrO2.nH2O composites obtained for both the methods presented good adsorption capacity.

Estudo da adsorção de íons fosfato em matriz inorgânica

This work reports the preparation, characterization and adsorption study of phosphate on hydrous tungsten oxides prepared by acid lixiviation of sodium tungstate. Part of this material (S1) was heated at 100 °C resulting in a material with differentiated characteristics (S1/D). The materials prepared were characterized by X-ray diffraction, thermal analysis, scanning electron microscopy and energy dispersive spectroscopy. Through the Q0 constant, related with the capacity of maximum adsorption, it was observed that the S1 sample presented better adsorption capacity than the S1/D. The DG values show that PO4-3 had been adsorbed through favorable reactions for all range of studied concentration.

Efeito da temperatura na síntese de óxidos hidratados de nióbio e zircônio e adsorção de íons Ag+ e Pb2+

This work reports the digestion temperature effect of precipitating agent on the physical and chemical characteristics of Nb2O5.nH2O and ZrO2.nH2O. The compounds were obtained by homogeneous solution precipitation method with thermal decomposition of (NH4)2CO3 at 45 oC and 90 oC. The X-ray diffraction analysis showed crystalline materials with interlamelar space for both Nb2O5.nH2O, whereas ZrO2.nH2O is amorphous. By thermal analysis a similar hydration grade was observed for all materials. The Langmuir adsorption isotherms show that the materials prepared at 90 oC, in both cases, have the best results.

In vitro differentiation between oxytocin- and vasopressin-secreting magnocellular neurons requires more than one experimental criterion

The phenotypic differentiation between oxytocin (OT)- and vasopressin (VP)-secreting magnocellular neurosecretory cells (MNCs) from the supraoptic nucleus is relevant to understanding how several physiological and pharmacological challenges affect their electrical activity. Although the firing patterns of OT and VP neurons, both in vivo and in vitro, may appear different from each other, much is assumed about their characteristics. These assumptions make it practically impossible to obtain a confident phenotypic differentiation based exclusively on the firing patterns. The presence of a sustained outward rectifying potassium current (SOR) and/or an inward rectifying hyperpolarization-activated current (IR), which are presumably present in OT neurons and absent in VP neurons, has been used to distinguish between the two types of MNCs in the past. In this study, we aimed to analyze the accuracy of the phenotypic discrimination of MNCs based on the presence of rectifying currents using comparisons with the molecular phenotype of the cells, as determined by single-cell RT-qPCR and immunohistochemistry. Our results demonstrated that the phenotypes classified according to the electrophysiological protocol in brain slices do not match their molecular counterparts because vasopressinergic and intermediate neurons also exhibit both outward and inward rectifying currents. In addition, we also show that MNCs can change the relative proportion of each cell phenotype when the system is challenged by chronic hypertonicity (70% water restriction for 7 days). We conclude that for in vitro preparations, the combination of mRNA detection and immunohistochemistry seems to be preferable when trying to characterize a single MNC phenotype.

Thermal characterization of hydrous tungsten oxides and their behavior as ion exchanger

The preparation, and thermal characterization and ion exchanger behavior of hydrous tungsten oxides obtained from purified tungsten trioxide, by processing of a Brazilian scheelite ore were described. By an alkaline fusion of tungsten trioxide with an excess of sodium carbonate at 900°C an intermediate tungstate product is obtained. Acid lixiviation of the tungstate intermediary in different experimental conditions produces two different hydrous tungsten oxides I and II respectively. A third material was produced by thermal treatment of II, yielding the material IIA, a monohydrate species. The materials prepared were characterized by TG/DTG, X-ray diffractometry and by surface area measurements. Their ion exchange behavior was studied too, using Na+ and K+ ions as the exchanged species. The inorganic exchanger materials were partially regenerated and may be used consecutively.

Effects of nitric oxide on magnocellular neurons of the supraoptic nucleus involve multiple mechanisms

Physiological evidence indicates that the supraoptic nucleus (SON) is an important region for integrating information related to homeostasis of body fluids. Located bilaterally to the optic chiasm, this nucleus is composed of magnocellular neurosecretory cells (MNCs) responsible for the synthesis and release of vasopressin and oxytocin to the neurohypophysis. At the cellular level, the control of vasopressin and oxytocin release is directly linked to the firing frequency of MNCs. In general, we can say that the excitability of these cells can be controlled via two distinct mechanisms: 1) the intrinsic membrane properties of the MNCs themselves and 2) synaptic input from circumventricular organs that contain osmosensitive neurons. It has also been demonstrated that MNCs are sensitive to osmotic stimuli in the physiological range. Therefore, the study of their intrinsic membrane properties became imperative to explain the osmosensitivity of MNCs. In addition to this, the discovery that several neurotransmitters and neuropeptides can modulate their electrical activity greatly increased our knowledge about the role played by the MNCs in fluid homeostasis. In particular, nitric oxide (NO) may be an important player in fluid balance homeostasis, because it has been demonstrated that the enzyme responsible for its production has an increased activity following a hypertonic stimulation of the system. At the cellular level, NO has been shown to change the electrical excitability of MNCs. Therefore, in this review, we focus on some important points concerning nitrergic modulation of the neuroendocrine system, particularly the effects of NO on the SON.

Nanofibers and thin films as a selective membrane for sensors and microTAS

A composite material of PAN (polyacrylonitrile), starch granules and dimethylformamide as solvent was used as a selective membrane for volatile organic compounds (VOCs) in gaseous phase. This composite was produced as a thin film obtained by spin-casting and as a fiber mat produced by electrospinning. The fiber mat was tested for adsorption of VOCs and water. Characterization used microscopy (electron scanning and optical) in order to evaluate the fiber morphology and the starch incorporation in the PAN matrix. Infrared spectroscopy was intended to determine the starch presence. Relative viscosity of the starch/PAN suspensions was measured in order to provide a model of composite fiber formation. Quartz crystal microbalance experiments determined VOCs and water adsorption. Fibers incorporated the starch granules, making the composite sensible to water; but VOCs were not detected. Therefore, the composite was found to be a good choice as selective barrier on sensors or microTAS protection purposes.

Estudo da adsorção de surfactante catiônico em uma matriz inorgânica preparada via óxido de nióbio

One of the applications that have been studied for niobium is the adsorption process, in the form of hydrous phosphates. These materials are constituted of lamellar crystals, what make them possible to be used in adsorption processes and polar molecules intercalation as the cationic as the cationic surfactant cetyltrimethyammonium bromide (CTAB). This work describes the adsorption study for cationic cetytrimetlyl ammonium bromide (CTAB) surfactant in the niobium oxide matrix. The material was characterized by X-ray diffraction, thermogravimetry, scanning electron microscopy and surface area measurements. The Langmuir and Freundlich isotherm models were used for the CTAB adsorption study. In the adsorption process the pH effect has been studied and it could be observed that the largest adsorption value was in pH 3.0 with Qo 16.52 mg/g. The adsorption process was favorable for the Langmuir model and not favorable for the Freundlich one.