Scielo RSS <![CDATA[Journal of the Chilean Chemical Society]]> vol. 59 num. 2 lang. pt <![CDATA[SciELO Logo]]> <![CDATA[<b>Obituary</b>   <strong>Prof. Dr. Luis J. Núñez-Vergara</strong>]]> <![CDATA[<b>DEVELOPMENT OF VALIDATED HPTLC METHOD FOR QUANTIFICATION OF TRAZODONE IN HUMAN SERUM</b>]]> A high performance thin-layer chromatographic (HPTLC) method for quantitative analysis of trazodone in human serum has been developed and validated. Trazodone was extracted with n-hexane: isoamyl alcohol (99:1). Chromatographic separation was performed on silica gel 60 F 254 HPTLC plates, with toluene: acetone: ethanol: ammonium (9:7:2:0.5, v/v/v/v) as mobile phase. Densitometric evaluation was carried out at 290 nm. There was no chromatographic interference between trazodone and its major metabolite, m-chlorophenilpiperazine (Rf 0.82 and 0.39, respectively). Regression analysis of the calibration plot revealed good linearity (r=0.999) over the range of 20.00 and 200.00 ng/band, corresponding to 0.20 and 2.00 ng/µL of trazodone in human serum after extraction process and applying 10 µL to the chromatographic plates. The % RSD of intra-assay and inter-assay precision, were in the range of 0.98% to 2.97% (n=3) and 1.06% to 3.54% (n=9), respectively. LOD and LOQ were found to be 0.016ng/µL, and 0.048ng/µL, and the recovery values, of trazodone from serum, were between 92.52 % and 96.73 %. This method was successfully applied to quantify trazodone in patient serum samples. In conclusion, the developed method might be useful for the quantitative determination of trazodone in human serum, as a tool to evaluate patient adherence to their pharmacotherapy with this drug. <![CDATA[<b>DEVELOPMENT OF AN ACTIVE FILM WITH NATURAL ZEOLITE AS ETHYLENE SCAVENGER</b>]]> Ethylene (C2H4) acts as a plant hormone, growth regulator that has a number of effects on the growth. Ethylene accelerates respiration, leading to maturity and also softening and ripening of many kinds of fruits. Although ethylene has some positive effects, it is often hazardous to the quality and shelf-life of fruits and vegetables. The removal of ethylene and/or inhibition of the effect of ethylene in stored environments is fundamental to maintaining postharvest quality of climacteric produce. In this study, the efficiency of a Chilean natural zeolite (NZ-Ch) against a commercial Na+ montmorillonite (Cloisite Na+) was studied. The aluminosilicate characterization (XDR, FTIR, EGME, CEC, chemical composition) indicates that natural Chilean zeolite belongs to mordenite group. Elemental chemical analysis indicated that compensating ions, were sodium for MTNa+ and calcium, sodium and potassium for NZ-Ch, and in both aluminosilicates copper was present in their composition. Ethylene adsorption kinetics were fitted to a pseudo-second order model. The rate constant of the ethylene adsorption was nearly double for NZ-Ch compared with MtNa+. Langmuir-Freundlich isotherm allowed to determine maximum adsorption capacity that reached values of 5.4 µl g-1 for NZ-Ch and 1.28 µl g-1 for MtNa+. Films of low density polyethylene (LDPE) were obtained with different NZ-Ch concentrations. After 50 hours, a removal of 37% of ethylene present on headspace was achieves with 10% of ZN-Ch in LDPE active films. <![CDATA[<b>CHITOSAN-COPPER PAINT TYPES AS ANTIFOULING</b>]]> A prototype of antifouling paints was prepared with a Qs-Cu (I)-Fe (II) complex as a possible replacement for traditional antifouling net paints, which contain a large concentration of copper, finding them in an order of 10-30 % depending on the company, and either in water or solvent based. A Qs-Cu complex was prepared, with a solution at 3% with acetic acid, and then Fe2O3 was added to the solution. FT IR analysis was carried out, as well as analysis of the TGA at the Qs and the complex with Qs-Cu, and with the solution, three different paints were prepared. Those that varied volume of diethylene glycol added to them. The analysis of the paints was carried out, once the paint was pervaded in a network of polyamide, through SEM with EDX and TEM, which was purchased with the commercial paints, water based and solvent based. One of the objectives is to be able to compare the coverage of the network with the commercial paint, and that of the complex Qs-Cu. The results showed that the best paint obtained was paint #2, found to be similar to that pervaded with water based paint. <![CDATA[<b>POLY(ACRYLAMIDE-<em>co</em>-STYRENE SODIUM SULFONATE) AND POLY(2-ACRYLAMIDE-2-METHYL-1-PROPANESULFONIC ACID-<em>co</em>-ACRYLIC ACID) RESINS WITH REMOVAL PROPERTIES FOR Hg(II), Pb(II), Cd(II), and Zn(II)</b>]]> The water-insoluble polymers poly(acrylamide-co-styrene sodium sulfonate) (P(AAm-co-ESS)) and poly(2-acrylamide-2-methyl-1-propanesulfonic acid-co-acrylic acid) (P(APSA-co-AAc)) were synthesized by radical polymerization. Parameters including the water sorption capacity, effect of the pH and reaction time, maximum retention capacity of the metal ions, elution, regeneration, and selectivity were studied. The commercial resin Amberlite IRP-64 was used for comparative purposes. Laboratory tests showed that both of the resins had better capacities to remove Pb(II), Cd(II), Zn(II), and Hg(II) from an aqueous solution by the batch method. P(AAm-co-ESS) and P(APSA-co-AAc) resins remove the metal ions faster and had better regeneration than commercial Amberlite IRP-64 resin. <![CDATA[<b>TEMPERATURE AS THUMB RULE PREDICTOR OF OZONE LEVELS IN SANTIAGO DE CHILE GROUND AIR</b>]]> Ozone concentrations in the urban air of Santiago de Chile frequently surpass the air quality standard in summertime, particularly in the eastern part of the city (Las Condes). The main parameter that determines ozone episodes is the ground level daily maximum temperature. In the present work we propose that this single parameter can be employed as a simple predictor of the expected ozone levels. In particular, it is found that high ozone episodes takes place in Las Condes when the maximum daily temperature is higher than 30 °C. This single criterion applies during all the summer period (from December to March) and for weekdays and weekends. On the other hand, ozone episodes in downtown take place only when the maximum daily temperature reaches values higher than 32.5 °C. These simple relationships imply that weather forecast could be employed by the citizens to estimate the risk associated to carry out outdoors activities. <![CDATA[<b>METHODOLOGICAL VALIDATION FOR THE DETERMINATION OF TOXIC ARSENIC SPECIES IN HUMAN URINE USING HPLC WITH ICP-MS</b>]]> There is a significant amount of arsenic species in the environment and in biological systems; however, the toxicity and possibly the carcinogenicity of ingested arsenic depend on the species and the oxidation state. Therefore, analytical methodologies and techniques that are fast and robust, that involve highly efficient separation and are powerful tools of detection are necessary for the correct quantification of individual arsenic species. The field of speciation analysis of arsenic in this area has grown rapidly in recent years, especially with the application of liquid chromatography and mass spectrometry with inductively coupled plasma. This study aimed to develop and apply this technique to human urine samples in order to reduce the treatment needed for speciation, maintain maximum recovery and avoid interconversion and / or degradation between species. In order to optimize the separation of species, several experiments were performed by preparing the mobile phase at different pH values. The optimal pH value and the linearity of the method were determined and the methodology was validated using a Certified Reference Material. Student's t-test and Fisher F-test for determination of accuracy and precision were applied. A simple, rapid and reliable method for the separation and quantification of several species of arsenic, As III (Arsenite), As V (Arsenate), MMA (Monomethyl Arsonic Acid), DMA (Dimethyl Arsinic Acid), AB (Arsenobetaine) was developed in human urine samples with minimal prior sample preparation. The time required for sample processing and isocratic chromatographic analysis is about 15 minutes. Detection limits of 0.020 μgL-1 of AsB, 0.020 μgL-1 of As III, 0.040 μgL-1 of DMA, 0.060 μgL-1 of MMA and 0.060 μgL-1 of As V were achieved under the analytical conditions mentioned above. <![CDATA[<b>SOLID STATE SYNTHESIS OF MICRO AND NANOSTRUCTURED METAL OXIDES USING ORGANOMETALLIC-POLYMERS PRECURSORS</b>]]> The organometallic derivatives of poly(styrene-co-4vinylpyridine), PS-co-4-PVP, of the general formula: {[CH2CH(C6H J)]0.1[CH2CH(C5H4N•MLn)]0.9}n; MLn = W(CO)5 , (1), CpRu(PPh3)2 (2), CpFe(dppe) (3), Cp2TiCl (4) and CH3-C5H4-Mn(CO)2 (5) were prepared from the respective organometallic and the ' co-polymer {[CH2CH(C6H5)]0.1[CH2CH(C5H4N]0.9}n. The solid state pyrolysis of these derivatives under air and at 800 °C give rise to micro and nanostructured powder metal oxides WO3, RuO2, TiO2 Mn2O3 and the iron (III) phosphate (FePO4) in the case of the iron precursor. The pyrolytic products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray scattering (EDX) and infrared spectroscopy (IR). From the TG (thermal gravimetric) and DSC (differential scanning calorimetry) data a possible mechanism for the formation of the solid nanostructured materials is discussed. The method appears to be a reliable and general way to obtain nanostructured metal oxide in solid-state which could be potentially and easily incorporated in solid-state electronics, catalysts and sensor devices. <![CDATA[<b>LOW DENSITY POLYETHYLENE (LDPE) NANOCOMPOSITES WITH PASSIVE AND ACTIVE BARRIER PROPERTIES</b>]]> Nanocomposites based on Low Density Polyethylene (LDPE) containing organically modified montmorillonite (OMMT) and polyethylene grafted with maleic anhydride (PE-g-MA) were obtained by the mixing molten state method at 130 °C (LDPE / PE-g-MA / Cv / OMMT). Furthermore, in order to obtain a material with active barrier properties, carvacrol (Cv) was incorporated into the nanocomposite (LDPE / PE-g-MA / Cv / OMMT). Carvacrol is an essential oil component with a high antimicrobial, antifungal, and antiparasitic capability. The nanocomposites were characterized by XRD, DSC, TGA, oxygen permeability, and tensile test. The nanocomposites without Cv (LDPE / PE-g-MA / OMMT) showed an intercalated morphology (confirmed by the X ray diffraction analysis), an improved percentage of crystallinity and a reduced permeability to oxygen (25%) as compared with LDPE . The rigidity of the resulting material correlated with the clay content as expected. The nanocomposite containing Cv (LDPE / PE-g-MA / Cv / OMMT) also show intercalated morphology with a greater displacement between the clay layers as compared with the nanocomposite without Cv produced by intercalation of the antimicrobial agent between the layers. The antimicrobial activity of (LDPE / PE-g-MA / Cv / OMMT) was observed by the reduction or inhibition on bacterial (Escherichia coli and Staphylococcus aureus) growth. <![CDATA[<b>TEMPLATE ASSISTED ELECTRODEPOSITION OF HIGHLY ORIENTED ZnO NANOWIRE ARRAYS AND THEIR INTEGRATION IN DYE SENSITIZED SOLAR CELLS</b>]]> Dye sensitized solar cell (DSSC) based on N719 dye sensitized zinc oxide nanowires prepared by template assisted electrodeposition was investigated. The morphology and crystalline structure of highly oriented nanowires were characterized by scannnig electron microscopy and X-ray diffraction, respectively. The photovoltaic performance of the DSSC was characterized at full sun intensity of 100 mW/cm² obtaining a shortcircuit current of 4.8 mA/cm², an open circuit voltage of 0.64 V and energy conversion efficiency of 1.23 %. <![CDATA[<b>SOLUBILIZATION OF P-ALKYLPHENOLS IN PLURONICS F-68 AND F-127 MICELLES</b>: <b>PARTITION COEFFICIENTS AND EFFECT OF SOLUTE ON THE AGGREGATE STRUCTURE</b>]]> The partition of a series of substituted phenols between water and polymer micelles formed by Pluronic F-68 and F-127 has been studied. The formation of micelles by these block copolymers has been evidenced by steady-state fluorescence and dynamic light scattering. The data show that micelles and larger aggregates are formed above the critical micelle concentration. In presence of p-alkylphenols a micelle rearrangement occurs that leads to the formation of just one and large aggregate. This effect depends both on polymer and phenols structures. The partition coefficients and the standard free energies of transfer from the aqueous to the micellar phases were determined. The incremental free energy for a methylene group are 2.88 kJ mol-1 and 1.65 kJ mol-1 for F-127 and F-68, respectively. This difference is explained in terms of the core sizes that are determined by the length of the PPO block. <![CDATA[<b>GREEN SYNTHETIC APPROACHES TO FUROYLNAPHTHOHYDROQUINONE AND JUGLONE</b>]]> The synthesis of two valuable precursors of biological active compounds named 2-(furan-2-yl)-1,4-dihydroxynapthohydroquinone 2 and 5-hydroxy-1,4-naphthoquinone (4, juglone) via solar photo-induced reactions from 1,4-naphthoquinone 1 and 1,5-dihydroxynaphthalene 3 in green solvent media is reported. When t-butyl alcohol and the binary t-ButOH/DMK and ternary i-PrOAc/DMK/MEK solvent mixtures were used, acylhydroquinone 2 was isolated in yields of 80, 83 and 77%, respectively. The sensitized photooxygenation of 3 "on water" and in water containing sodium dodecyl sulfate produce juglone 4 in 81 and 39% yields respectively. <![CDATA[<b>SENSING IMMOBILIZED MOLECULES OF STREPTAVIDIN ON A SILICON SURFACE BY MALDI-TOF MASS SPECTROMETRY AND FLUORESCENCE MICROSCOPY</b>]]> A hydrogen-terminated Si (111) surface was modified to form an aminoterminated monolayer for immobilization of streptavidin. Cleavage of an N-(ω-undecylenyl)-phthalimide covered surface using hidrazine yields an amino group-modified surface, which serves as a substrate for the attachment of biotin and subsequently streptavidin. We used surface analytical techniques to characterize the surface and to control the course of functionalization before the immobilization of streptavidin. To confirm the presence of the streptavidin Texas red on the surface two powerful techniques available in a standard biochemical laboratory are used, Fluorescence Microscopy and MALDI-TOF that allow us to detect and determine the immobilized streptavidin. This work provides an avenue for the development of devices in which the exquisite binding specificity of biomolecular recognition is directly coupled to a biosensor. In addition, we have demonstrated that MALDI-TOF and fluorescence microscopy are useful techniques for the characterization of silicon functionalized surfaces. <![CDATA[<b>PYRIDINE BASED POLYMERS</b>: <b>SYNTHESIS AND CHARACTERIZATION</b>]]> Two new conjugated polymers, poly(2,3-di(thiophen-2-yl)pyrido[2,3-b]pyrazine) and poly(2,3-di(thiophen-2-yl)pyrido[3,4-b]pyrazine), based on thiophene and pyridine rings were chemically and electrochemically synthesized and characterized by IR, UV-Vis and elemental analysis. Monomers were chemically synthesized at high yield percentages and characterized by FTIR and NMR. Polymers showed p- and n-type doping as well as low bandgap, making them potential candidates for the development of electronic devices. <![CDATA[<b>SYNERGIC EFFECT OF TWO INORGANIC FILLERS ON THE MECHANICAL AND THERMAL PROPERTIES OF HYBRID POLYPROPYLENE COMPOSITES</b>]]> Inorganic fillers such as CaCO3 and clays are widely used as fillers to improve the mechanical and physical properties of polypropylene (PP). With the aim of improving simultaneously the stiffness and yield stress of PP, hybrid nanocomposites comprising PP/CaCO3/clay (montmorillonite) were prepared and their thermal and mechanical properties were investigated and compared with those of PP/CaCO3 and PP/clay composites. Morphological characterizations of the composites were performed by SEM and XRD analyses. The results showed exfoliated clay in the hybrid composite with a much higher degree than in PP/clay composite. Increase in modulus and yield stress and better thermal stability was attained for hybrid composites as a result of the clay exfoliation. The toughening effect of two different types of CaCO3 particles was also observed in hybrid composites, where an effective enhancement of the mechanical and thermal properties were achieved depending on the origin, specific area, particle and pore size of the CaCO3 used. <![CDATA[<b>SYNTESIS AND CRYSTALLINE STRUCTURE OF THE EXO-3,6-DIMETHYL-3,6-EPOXI-1,2,3,6-TETRAHYDROPHTLALIMIDE AND ITS N-BROMODECYL ANALOG</b>: <b>TWO THERMALLY LABILE DIELS-ALDER ADDUCTS</b>]]> The molecular structure of the exo-3,6-dimethyl-3,6-epoxi-1,2,3,6-tetrahydrophthalimide (1), determined by X-ray diffraction analysis, as well as, its complete spectroscopic characterization and the synthesis and complete spectroscopic characterization of its N-(10-bromodecyl) analog (2) are presented. <![CDATA[<b>EXTRACTION OF POLYCYCLIC AROMATIC HYDROCARBONS FROM WATER SAMPLES INTO A ROTATING-DISK MICROEXTRACTOR AND THE SUBSEQUENT DETERMINATION BY GAS CHROMATOGRAPHY-MASS SPECTROMETRY</b>]]> The rotating disk sorptive extraction (RDSE) technique was applied in this study to the extraction of 16 polycyclic aromatic hydrocarbons (PAHs) in real water samples. The sorptive and desorptive behavior of the analytes were studied by using a rotating disk coated with polydimethylsiloxane (PDMS) on one of its surfaces. The optimal conditions for extractions of all analytes were: rotational velocity of the disk: 1250 rpm; sample volume: 20 mL; matrix modifier: 20 % MeOH and extraction time: 30 min. A desorption time of 10 min at 1250 rpm was used for the analytes using 5 mL of methanol. PAHs were measured in the extract by gas chromatography coupled to mass spectrometry (GC-MS). Under these conditions, recoveries ranging from 84 to 100 % were obtained in drinking water enriched with the analytes, and the precision, expressed as relative standard deviation, was between 2 and 20%. The detection limit of the method was between 8 and 115 ng L-1 depending on the analyte. The method was applied to the analysis of water samples obtained from a lagoon in Curauma, Chile, obtaining quantitative recoveries. <![CDATA[<b>DESIGN AND EVALUATION OF A Hg(II) SENSOR BASED ON THE RESPONSE OF A POLY(3,4-ETHYLENEDIOXYTHIOPHENE) MODIFIED ELECTRODE</b>]]> The electro-synthesis of poly(3,4-ethylenedioxythiophene), PEDOT, has been widely studied due to its different and important applications. Considering that one of the most important electrochemical characteristics of this polymer is its ability to undergo p- and n-doping/undoping, our research group has tested its potential usefulness for cations extraction based on the n-doping/undoping process, hitherto almost unexplored. Therefore, in a first stage, EDOT was electropolymerized on AISI 316 stainless steel, SS, and the SS|PEDOT modified electrode was then obtained. Applying the n-doping potential to these SS|PEDOT electrodes immersed in Hg(II) solution at physiological pH (PBS) it was verified that the cation was incorporated into the polymeric matrix and, depending on the area of the working electrode and removal method (n-doping/undoping), its quantitative extraction was possible. It was also found that the charge recorded during the process is proportional to Hg(II) concentration, hence the assembly is now proposed as sensor for this cation. To this end, in the current paper the amperometric response of the SS|PEDOT electrode toward Hg(II) in PBS, prepared under the optimum conditions previously established and described, was studied. First of all, it is noteworthy establishing that the response obtained with a freshly prepared SS|PEDOT electrode prior to each measurement is highly reproducible. Having this in mind, the modified electrode can be thought as a sensor that may be utilized as a disposable device. Once the electrode response was optimized, analytical parameters were established, namely linear response between 66.6 nmol•L-1-1.0 mmol•L-1 Hg(II), 1s response time, and quantification and detection limit 10 and 15 nmol•L-1, respectively. It is possible thus to have at our disposal a suitable and inexpensive sensor that would enable quick and economical quantification of this toxic element using electrochemical methods. <![CDATA[<b>DETERMINATION AND CO-ESTIMATE OF THE CHLORMADINONE ACETATE AND 17</b>α<b>-ETHINYL ESTRADIOL IN PHARMACEUTICAL FORMULATION AND DRINKING WATER SAMPLES BY DIGITAL DERIVATIVE SPECTOPHOTOMETRY</b>]]> In this work are presented two methods for the simultaneous determination of 17α-ethinylestradiol (EEL) and chlormadinone acetate (CMA) by second order derivative spectrophotometry. The first analytical method proposed is based in the dissolution and extraction of both drugs in acetonitrile. The solution was directly evaluated by second order derivative spectrophotometry with a smoothing factor of 8,000 and a scale factor of 10,000. The determination of EEL and CMA was carried out to 296,6 and 291.8 nm, respectively. The detection limits (3.3 σ criterion) for EEL and CMA were 6.9 x 10-7 and 9.8 x 10-8 mol/L, respectively. Furthermore, a study of the effect of the excipients containing in the pharmaceutical formulation was included. Polyvidone presents greater tendency to produce interference, but its spectral bands are located between 215 and 240 nm, so these bands do not interferes spectrally in the simultaneous determination of EEL and CMA. Both drugs were extracted from the pharmaceutical formulation with acetonitrile, obtaining a good recovery relative to the nominal content. The second method is a screening method and was applied in fortified drinking water. In this method, drugs were extracted in chloroform, which was then removed with N2 and the residue was redissolved in acetonitrile. Due to the difference in the procedure in relation to the pharmaceutical formulation a new analytical parameters were obtained. For EEL this parameters were very similar to those obtained directly in solution, however these were higher for CMA, which could be attributed to that under these conditions was found a higher standard deviation of the blank. Recoveries of fortified samples were 81.8 ± 1.5% and 101.1 ± 0.73% for EEL and CMA, respectively. <![CDATA[<b>ZINC ELECTROWINNING USING REACTIVE ELECTRODIALYSIS (RED)</b>]]> This paper presents an alternative process for the conventional zinc electrowinning, which consists of a cell of two compartments separated by a anion exchange membrane. One of them contains a zinc sulphate catholyte and sulfuric acid while the anolyte solution contains ferrous sulfate and sulfuric acid. By using a membrane the classical lead anode may be replaced, as well as the main oxidation reaction of water, for that of the ferrous ion to ferric ion. This leads to significant savings in specific energy consumption of the overall process and eliminates the classic problem of acid mist in electrowinning cells. The results show that the proposed process consumes 30% less cell potential compared to conventional electrowinning cell. <![CDATA[<b>ELECTROOXIDATION OF DNA AT GLASSY CARBON ELECTRODES MODIFIED WITH MULTI-WALLED CARBON NANOTUBES WITH DIFFERENT OXIDATION DEGREE</b>]]> For the first time, the study of the effect of length and degree of oxidation of multi-walled carbon nanotubes (CNTs) on the electroanalytical DNA sensing properties of modified glassy carbon electrodes (GCEs) is reported. GCE/CNT electrodes were prepared using chitosan (CHI) as a dispersing agent. Short (S-NCs) and long (L-NCs) carbon nanotubes, as well as unoxidized and 3 or 6 hour oxidized samples were used. Cyclic voltammetry indicated that S-NCs exhibited larger capacitance values than L-NCs, and that these values increased when the CNTs were oxidized. Using Scanning Electrochemical Microscopy (SECM), an increase in the surface homogeneity was determined when oxidized CNTs were used as electrode modifiers. dsDNA electrooxidation showed the highest response using GCEs/CHI-L-NCs, and a clear decrease in the current intensity was observed when the oxidation time was increased. This result correlates with the higher BET surface area of L-NCs. In conclusion, the electrochemical performance of GCE/CNT electrodes against DNA increase when the length of CNTs is higher and decrease at higher oxidation state. <![CDATA[<b>MULTIWALLED CARBON NANOTUBES MODIFIED ELECTRODES WITH ENCAPSULATED 1,4-DIHYDRO-PYRIDINE-4-NITROBENZENE SUBSTITUTED COMPOUNDS</b>]]> We report a voltammetric study of several nitroaromatic compounds such as the drugs: Nifedipine, Nitrendipine, Furnidipine and Nisoldipine in multiwalled carbon nanotubes (MWCNT) modified electrodes. All the compounds are strongly encapsulated in the three dimensional structure of the MWCNT and then reduced to the corresponding hydroxylamine derivatives. In the case of the modified electrode with MWCNT the answer in current are remarkably increased (approximately 40 times). This current multiplier effect is due to the nitro compounds are not only superficially adsorbed but this really encapsulated in the nanotube network covering the GCE. The nitro reduction peak was linearly dependent with the concentration of the nitroaromatic compound with detection limit (LOD) of 1.2·0-8 mol•L-1 and a quantification limits (LOQ) of 3.9•10-8 mol•L-1 for the case of Nitrendipine. All the studied nitrocompounds followed equivalents behaviours. Obviously from this result it is possible to postulate this technology as a very useful tool to develop analytical methods to determine these nitroaromatic drugs in real samples such as biological fluids. From the obtained results it is possible to conclude that for the studied 1,4-dihydropyridine-4-nitrobenzene substituted compounds a greater difficulty of reduction implies a greater ability to encapsulation. <![CDATA[<b>OXYGEN REDUCTION ON Cu<sub>1</sub> ,Mn<sub>16</sub>O<sub>4</sub> SPINEL PARTICLES COMPOSITE ELECTRODES EFFECT OF PARTICLES SIZE</b>]]> The oxygen reduction reaction (orr) was studied on CG/PPy/PPy(Ox)/PPy and CG/paint/CC(Ox)PPy composite electrodes, CG representing conducting glass, PPy polypyrrole, CC carbon cloth and Ox mixed valence spinel oxide particles of transition metals Cu14Mn16O4 in 0.2 M KCl pH = 9.2, at room temperature. PPy is electrochemically polymerized and serves as a protective layer to dispersed oxide particles in the carbon cloth. Oxide particles size varied from 7.6 to 11.2 μm. The orr takes place on the oxide particles with formation of hydrogen peroxide which diffuses to electrolyte solution. The amount of peroxide ions produced was detected using the rotating ring-disk electrode technique and determined indirectly by iodine spectroscopy. The peroxide ions production depends strongly on the oxide particle size. <![CDATA[<b>DEGRADATION OF A VETERINARY PHARMACEUTICAL PRODUCT IN WATER BY ELECTRO-OXIDATION USING A BDD ANODE</b>]]> The electrochemical oxidation (EO) treatment in water of Fantetra a veterinary drug widely used in Chile, and its components: oxytetracycline hydrochloride, phtalylsulfathiazole and diphenhydramine, has been carried out at constant current using a BDD/Stainless steel system. First, solutions of each drug were electrolyzed following the decay of the absorbance of each compound and total organic carbon abatement. The mineralization of the Fantetra commercial formulation was also studied. An analysis of the degradation by-products was made by high performance liquid chromatography. Thus, during the degradation of each pharmaceutical by the electrochemical oxidation process, aliphatic carboxylic acids were detected prior to their complete mineralization to CO2 and nitrogen ions, while NO3- and NH4+ remain in the treated solution. This is an essential preliminary step towards the applicability of the EO processes for the treatment of wastewater containing pharmaceutical compounds. <![CDATA[<b>EFFECT OF LOW CONCENTRATION OF DHPC ON THE DPPC/SM BILAYER</b>]]> The organization of bilayers depends on the physicochemical and structural properties of the molecules that compose the membrane. The phospholipid molecular shape depends on the relative volumes of their polar headgroups and non-polar acyl chains. In this work, we study the effect of DHPC concentration over the bilayer of large unilamellar vesicles (LUV) prepared with different proportions of dipalmitoylphosphatidylcholine / sphingomyelin / dihexanoylphosphatidylcholine (DPPC/SM/DHPC) using fluorescence spectroscopy and molecular dynamics (MD) simulations. In this work, we use Laurdan's generalized polarization (GP) and 1,6-diphenyl-1,3,5-hexatriene (DPH) fluorescence anisotropy to observe the effect of DHPC concentration on dynamic properties of both, the interface and hydrophobic region. Detailed information, at atomistic scale, was obtained by trajectory calculations of accessible solvent area (ASA), partial densities and order parameters using Molecular Dynamics (MD). The results indicate that DHPC induces global packing defects in the membrane, favoring the liquid crystalline state for the system with higher concentration of DHPC. <![CDATA[<b>DEVELOPMENT OF A MODIFIED CARBON ELECTRODE WITH IONIC LIQUID AND ITS APPLICATION FOR ELECTROCATALYTIC OXIDATION AND VOLTAMMETRIC DETERMINATION OF LEVODOPA</b>]]> A carbon paste electrode was modified with the ionic liquid 1-butyl-4-methylpyridinium hexafluoro phosphate and applied for the study of the electrocatalytic oxidation and voltammetric determination of the drug levodopa. The developed modified electrode was characterized using cyclic voltammetry and scanning electron microscopy. The oxidation of levodopa at the surface of a modified electrode occurs at lower potentials than that of an unmodified carbon paste electrode and both an enhancement of the anodic peak current and a signal narrower and better defined with the modified electrode were observed. Accordingly, a method for the determination of levodopa was developed using differential pulse voltammetry, at pH 4 and with an accumulation time of 4 min. The oxidation of levodopa exhibited a dynamic range between 2.4 - 16.6 μg/mL and detection and quantitation limits of 0.63 and 1.4 μg/mL, respectively. The method was applied to the determination of levodopa in capsules. <![CDATA[<b>ELECTROCHEMICAL CHARACTERIZATION OF NEW 1,5-BENZODIAZEPINE DERIVATIVES</b>]]> Cyclic voltammetry was used to study the electrochemical behavior of new 1,5-benzodiazepine derivatives on a glassy carbon electrode. Well-defined oxidation peaks were observed in DMSO. The Electrochemical response of the glassy carbon electrode was evaluated as function of the scan rate, showing that the electron transfer process for compound (5) and (6) resulted to be controlled by diffusion. <![CDATA[<b>IS THE DETERMINATION OF THE ASSOCIATION CONSTANT OF CYCLODEXTRIN INCLUSION COMPLEXES DEPENDENT ON THE TECHNIQUE</b>]]> Differences in association constants values of cyclodextrin inclusion complexes can be found in the literature. Most of the times, different experimental conditions have been used leading to different results. This paper reports the association constants (Ka) values of two different cyclodextrins (CD), namely native beta-CD (PCD) and hydroxypropyl-PCD (HP-PCD) with bentazon (BTZ, herbicide used in control of broadleaf weeds and sedges in many crops). These constants were determined by spectrophotometric and fluorescence measurements carried out under the same experimental conditions, and they were compared with those previously obtained by electrochemical techniques. The association constant values for the BTZ/HP-PCD inclusion complex obtained by fluorescence measurements were lower than those expected taking into account the values obtained from the other techniques. Differences in the complexation of the guest with CD in the excited and basal state could explain these results. <![CDATA[<b>FAST ELECTROCHEMICAL DETECTION OF NON-DESIRABLE AGING IN BOTTLED WHITE WINE</b>]]> Oenologists and wine exporters know that a serious problem is to determine the quality of wine after it travels to final market. In fact the last quality controls are made after the bottling and before the trip. Chile is an important exporter of wine and Asiatic markets are a common destination for this exportation, taking long times of traveling. If wine changes it quality due to different stressing situations during the trip, the final costumer will receive a low-quality beverage in spite of the high quality of the original wine. This fact can reduce the interest of the costumer to consume Chilean wine and diminishes the importations of this product. <![CDATA[<b>ELECTROCATALYTIC ACTIVITY FOR O<sub>2</sub> REDUCTION OF UNSUBSTITUTED AND PERCHLORINATED IRON PHTHALOCYANINES ADSORBED ON AMINO-TERMINATED MULTIWALLED CARBON NANOTUBES</b><b> </b><b>DEPOSITED ON GLASSY CARBON ELECTRODES</b>]]> Amino-functionalized multiwalled carbon nanotubes (MWCNT-NH2) were modified with Fe phthalocyanine (FePc) and perchlorinated Fe phthalocyanine (16(Cl)FePc) and deposited on glassy carbon electrodes (GCE). The electrocatalytic activity of these hybrid electrodes was examined for the reduction of molecular oxygen in alkaline media (0.2 M NaOH) using stationary and rotating disk electrodes. Electrodes containing 16(Cl)FePc are more active than those containing FePc. Electrodes containing CNTs are more active than electrodes without CNTs but the higher activity can be attributed to a greater real surface area, compared CGEs and not necessarily to a catalytic effect.