Scielo RSS <![CDATA[Journal of the Brazilian Chemical Society]]> http://www.scielo.br/rss.php?pid=0103-505320150005&lang=en vol. 26 num. 5 lang. en <![CDATA[SciELO Logo]]> http://www.scielo.br/img/en/fbpelogp.gif http://www.scielo.br <![CDATA[Flow Analysis]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000500831&lng=en&nrm=iso&tlng=en <![CDATA[Solventless and Mild Procedure to Prepare Organotellurium(IV) Compounds under Microwave Irradiation]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000500832&lng=en&nrm=iso&tlng=en Tellurium(IV) tetrachloride, p-methoxyphenyltellurium trichloride and the corresponding products of its reaction with alkynes were prepared under very mild reaction conditions, in absence of organic solvents and in short reaction times all assisted by microwave irradiation. <![CDATA[Recent Syntheses of Frog Alkaloid Epibatidine]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000500837&lng=en&nrm=iso&tlng=en Many natives from Amazon use poison secreted by the skin of some colorful frogs (Dendrobatidae) on the tips of their arrows to hunt. This habit has generated interest in the isolation of these toxins. Among the over 500 isolated alkaloids, the most important is undoubtedly (-)-epibatidine. First isolated in 1992, by Daly from Epipedobates tricolor, this compound is highly toxic (LD50 about 0.4 µg per mouse). Most remarkably, its non-opioid analgesic activity was found to be about 200 times stronger than morphine. Due to its scarcity, the limited availability of natural sources, and its intriguing biological activity, more than 100 synthetic routes have been developed since the epibatidine structure was assigned. This review presents the recent formal and total syntheses of epibatidine since the excellent review published in 2002 by Olivo et al.1 Mainly, this review is summarized by the method used to obtain the azabicyclic core. <![CDATA[Molecular Electronic Topology and Fragmentation Onset via Charge Partition Methods and Nuclear Fukui Functions: 1,1-Diamino-2,2-dinitroethylene]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000500851&lng=en&nrm=iso&tlng=en We investigated theoretically the ground state electronic structure and the onset of molecular fragmentation of 1,1-diamino-2,2-dinitroethylene (FOX-7) using density functional theory. The molecular charge density was analyzed via two partition methods: the distributed multipole analysis (DMA) and the deformed atoms in molecules (DAM). In this framework, the push-pull effect, hydrogen intra-molecular bonding and site acid-base properties of the molecule were discussed. Our analysis indicates that the molecular origin of the low measured impact sensitivity of FOX-7 is due to the magnitude of multipole values of the C-N bonds in the NO2 groups, the delocalized electrons over the central C-C bond and the hydrogen bonds. The onset of FOX-7 decomposition and acid-base properties were examined with the nuclear Fukui functions. The results support nitro to nitrite rearrangement and direct release of a NO2 as a possible initial step in FOX-7 decomposition process. The approach suggested is general and can be especially useful for very large molecules to examine in detail their electronic structure and to guide the search for the decomposition mechanisms. <![CDATA[Chemical Differentiation of Domestic Sewage Sludge and Cattle Manure Stabilized by Microbioreators: Study by Pyrolysis Coupled to Gas Chromatography Coupled to Mass Spectroscopy]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000500860&lng=en&nrm=iso&tlng=en The aim of the present study was to evaluate the chemical alterations in substrates of vermicomposts from domestic sewage sludge and from cattle manure, besides its quality as an organic fertilizer. Elemental and infrared analysis and UV-Vis spectroscopy were used for their characterizations. Chemical characteristics determined in the vermicomposts indicate that they can be used as organic fertilizers, mainly with regard to organic matter content, pH, C/N ratio, and nitrogen and phosphorus levels. The main constituents of the humic substances extracted from the vermicomposts were obtained by pyrolysis coupled to gas chromatography-mass spectrometry (GC/MS), showing that these compounds are quite similar, despite being produced by domestic sewage sludges or by cattle manure. <![CDATA[Determination of Aldrin Purity Using a Combination of the Mass Balance Approach and Quantitative NMR]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000500869&lng=en&nrm=iso&tlng=en This paper describes the studies performed to determine the purity of aldrin samples, an organochlorine pesticide, using the mass balance approach. The organic impurities were identified and quantified by gas chromatography-mass spectrometry (GC-MS), gas chromatography with flame ionization detection (GC-FID) and gas chromatography with electron capture detector (GC‑µECD) using two columns: DB-35ms (intermediate polarity) and DB-XLB (low polarity). The water content was determined by Karl Fischer coulometric titration, and the inorganics were analyzed by inductively coupled plasma mass spectrometry (ICP-MS). The aldrin contents determined by mass balance and quantitative nuclear magnetic resonance (qNMR) were compared. The obtained results were validated through the participation of the National Institute of Metrology, Quality and Technology (Inmetro) in the key-comparison CCQM-K55.b organized by the Organic Analysis Working Group/International Bureau of Weights and Measures (OAWG/BIPM). <![CDATA[Extraction and Separation of Molybdenum by Using Homogeneous Liquid-Liquid Microextraction via Flotation Assistance]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000500880&lng=en&nrm=iso&tlng=en Homogeneous liquid-liquid microextraction via flotation assistance (HLLME-FA) was investigated for the extraction of molybdenum from the water samples. Alizarin Red S and cetyl trimethylammonium bromide (CTAB) were used as a complexing ligand and ion-pairing reagent, respectively. The enriched analyte in the floated organic phase was determined by electrothermal atomic absorption spectrometry (ETAAS). In this work, low density organic solvent was used and no centrifugation was required in this procedure. A special extraction cell was designed to facilitate the collection of the low-density extraction solvent. By using air flotation, the organic solvent was collected at the conical part of the designed cell. Under the optimum conditions, the method performance was studied in terms of linear dynamic range (0.5-200 µg L-1), linearity (r2 &gt; 0.991), precision (repeatability &lt; 10.0 %). Also, the limit of detection (LOD) of 0.1 µg L-1 was obtained for molybdenum. The proposed method has been successfully applied for the determination of the molybdenum in water samples. <![CDATA[Optimization of an Electrolyte System for the Simultaneous Separation of Nelfinavir Mesylate and Two Impurities by Micellar Electrokinetic Chromatography]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000500887&lng=en&nrm=iso&tlng=en A methodology for the simultaneous determination of nelfinavir mesylate and the impurities 3-hydroxy-2-methylbenzoic acid and (2R,3R)-4-((3S,4aS,8aS)-3-(tert-butylcarbamoyl) octahydroisoquinolin-2(1H)-yl)-3-hydroxy-1-(phenylthio)butan-2-aminium benzoate by micellar electrokinetic chromatography, with an analysis time of 25 min, was proposed. An electrolyte composed of sodium tetraborate buffer (pH 9.24; 25 mmol L-1), sodium dodecyl sulphate (9 mmol L-1) and methanol (10%, v/v) was optimized using a mixed-level factorial design, with direct detection at 200 nm. After evaluating some figures of merit, such as selectivity, linearity, precision, limit of detection, limit of quantification, accuracy and robustness (using Youden's test), the method was successfully applied to the analysis of nelfinavir mesylate and its impurities in a pharmaceutical formulation. The optimized methodology is demonstrated to be useful in the determination of these analytes in a synthesis monitoring process, in raw materials and in pharmaceutical formulations, while offering low solvent consumption, requiring a small sample and using non-specific columns as advantages. <![CDATA[Kinetic Investigation of Thermal Formation Processes of SiOC Glasses Derived from C-Containing Hybrid Polymeric Networks]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000500899&lng=en&nrm=iso&tlng=en In this study, hybrid polymeric networks were prepared by hydrosilylation reaction as precursors to silicon oxycarbide (SiOC) glass. The polymeric networks were prepared from poly(methylsiloxane) (PMS) and divinylbenzene (DVB) in the 80:20 and 20:80 (PMS/DVB) compositions, with or without activated charcoal (AC), which was used as additional carbon source. Following, polymeric precursors were pyrolysed at 1000 °C, under Ar atmosphere, resulting in SiOC glasses. The effectiveness of the hydrosilylation reaction was evaluated by infrared spectroscopy. The degradation reactions and activation energy (Ea) obtained during polymer-to-glass conversion were investigated by thermogravimetric analysis applying Ozawa method for the determination of the Ea. In addition, the influence of the matrix composition and the presence of the C in both degradation processes and structure of the final products were reported. SiOC glasses were characterized by X-ray diffraction and Raman and 29Si nuclear magnetic resonance spectroscopies. <![CDATA[Microwave-Assisted Heck Arylations of Non-Activated <em>N</em>-Acyl-3-pyrrolines with Arenediazonium Tetrafluoroborates]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000500910&lng=en&nrm=iso&tlng=en Successful Heck-Matsuda arylations of non-activated olefins applying microwave irradiation as an alternative heating mode are presented. Cleaner reactions were performed with arenediazonium tetrafluoroborates bearing electron-donating and electron-withdrawing groups in good to excellent yields with reaction times reduced from 3.5-18 h to 12-30 min. <![CDATA[Cellulose Sulfuric Acid as an Eco-Friendly Catalyst for Novel Synthesis of Pyrido[2,3-<em>d</em>][1,2,4]triazolo[4,3-<em>a</em>]pyrimidin-5-ones]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000500916&lng=en&nrm=iso&tlng=en A novel synthesis of a series of pyrido[2,3-d][1,2,4]triazolo[4,3-a]pyrimidin-5-ones has been developed from reactions of 1-(5-methyl-1-phenyl-1H-pyrazol-4-yl)-3-arylprop-2-en-1-ones and 7-amino-1,3-disubstituted[1,2,4]triazolo[4,3-a]pyrimidin-5(1H)-ones in dioxane under thermal conditions, using cellulose sulfuric acid as an eco-friendly acid catalyst. The reaction mechanism was proposed and the structures of the newly synthesized compounds were established on the basis of spectral data (mass spectrometry, infrared, 1H and 13C nuclear magnetic resonance) and elemental analyses. <![CDATA[Application of Carbon Composite Adsorbents Prepared from Coffee Waste and Clay for the Removal of Reactive Dyes from Aqueous Solutions]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000500924&lng=en&nrm=iso&tlng=en A novel carbon composite was prepared from a mixture of coffee waste and clay with inorganic:organic ratio of 1.3 (CC-1.3). The mixture was pyrolysed at 700 °C. Considering the application of this adsorbent for removal of anionic dyes, the CC-1.3 was treated with a 6 mol L-1 HCl for 24 h to obtain ACC-1.3. Fourier transform infrared (FTIR), N2 adsorption/desorption curves, scanning electron microscope (SEM) and powder X-ray diffractometry (XRD) were used for characterisation of CC-1.3 and ACC-1.3 carbon adsorbents. The adsorbents were effectively utilised for removal of reactive blue 19 (RB-19) and reactive violet 5 (RV-5) textile dyes from aqueous solutions. The maximum amounts of RB-19 dye adsorbed at 25 °C are 63.59 (CC-1.3) and 110.6 mg g-1 (ACC-1.3), and 54.34 (CC-1.3) and 94.32 mg g-1 (ACC-1.3) for RV-5 dye. Four simulated dye-house effluents were used to test the application of the adsorbents for treatment of effluents. <![CDATA[Electrochemical Oxidation of Landfill Leachate: Investigation of Operational Parameters and Kinetics Using Graphite-PVC Composite Electrode as Anode]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000500939&lng=en&nrm=iso&tlng=en The preparation of a new carbon composite electrode constructed from graphite-polyvinyl chloride (graphite-PVC) compressed mixtures was used for the first time to treat landfill leachate in Malaysia under electrochemical oxidation. The electrochemical oxidation of landfill leachate was studied on graphite-PVC and Pt electrodes as anode and cathode, respectively, with the presence of NaCl electrolyte in a batch electrochemical reactor. The highest chemical oxygen demand (COD) and color removals of 87% and 97%, respectively, were achieved at pH 3, 0.58% (m/v) + 2078 mg L-1 electrolyte concentration, 15 V applied voltage, and 105 min electrolysis time. To confirm electrochemical oxidation, a field emission scanning electron microscopy (FESEM) was used to evaluate the surface of graphite-PVC electrode before and after treatment. The constant rate in terms of pseudo-first-order kinetics increased from 0.0015 min-1 to 0.0186 min-1 at 5 and 20 V applied voltage. The graphite-PVC composite exhibits favorable qualities as an electrode material because of its mechanical resistance, low cost, simple preparation, and easy renewal of the electrode surface. <![CDATA[Determination of Boron Isotope Ratios in Tooth Enamel by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) After Matrix Separation by Ion Exchange Chromatography]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000500949&lng=en&nrm=iso&tlng=en Boron isotopes in teeth has been a new proxy for dietary reconstructions and its resistance to diagenetic alteration. In this study a method using inductively coupled plasma source mass spectrometry (ICP-MS) for the measurement of boron isotope ratio in human dental enamel has been developed. Human dental enamel were digested with HNO3-H2O2 in a microwave system. Boron in solution was separated from the matrix components using Amberlite IRA-743 resin. The factors that may affect precision and accuracy in isotope ratio determination by ICP-MS, including memory effects, mass bias drift, and concentration effects, were investigated to obtain optimum conditions. Then, the 10B/11B ratios in teeth were measured. The results showed that 2% of HNO3 + 2% of NH3•H2O, selected as the diluent/rinse solution could be effective in the elimination of boron memory effect. There was no concentration effect on boron isotope ratios when the ratio of samples B concentration to standard B concentration (refers to Csample/Cstd) varied from 0.5 to 2. The result of 10B/11B ratios in tooth enamel by sex and age fluctuated over a broad range, ranged from 0.2007 to 0.2574. This method is expected to be used for boron isotope ratio analyses in archeometry, forensic identification, paleoecology, and other disciplines in the future. <![CDATA[Determination of Polycyclic Aromatic Hydrocarbons in Groundwater Samples by Gas Chromatography-Mass Spectrometry After Pre-Concentration Using Cloud‑Point Extraction with Surfactant Derivatization]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000500955&lng=en&nrm=iso&tlng=en A cloud-point extraction (CPE) method using the surfactant (30)p-tert-octylphenol polyoxyethylene (OPEO30) was proposed as the preceding step for the determination of polycyclic aromatic hydrocarbons (PAHs) by gas chromatography-mass spectrometry (GC-MS). Given the need for surfactant derivatization before the chromatographic analysis, the reaction conditions of coacervate derivatization were studied. The extraction process was also optimized, where surfactant concentration, temperature and time were analyzed as variables. The limits of detection obtained were between 0.02 and 0.05 µg L-1, and the recoveries of analytes were between 70 and 98%, with coefficient of variation better than 10.3%. The analytical method developed provides an efficient, precise and accurate method for the determination of the 16 priority PAHs, generating results in accordance with the USEPA 3510C method. The method was applied to the analysis of groundwater samples collected from artesian wells located at retail fuel stations. <![CDATA[Construction of a New Aluminum(III) Cation Selective Electrode Based on 12-Crown-4 as an Ionophore]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000500963&lng=en&nrm=iso&tlng=en This article describes the fabrication of a novel and selective polyvinylchloride (PVC) membrane potentiometric sensor for Al3+ cation based on 12-crown-4 (12C4) as an ionophore. The electrode was prepared by coating the surface of a graphite rod by a membrane containing PVC as a plastic matrix, dibutylphthalate (DBP) as plasticizer, 12C4 as an ionophore and oleic acid (OA) as an additive. Under optimized membrane composition, the constructed electrochemical sensor exhibited a Nernstian response for Al3+ cation concentration, ranging from 1.0 × 10-6 to 1.0 × 10-1 mol L-1 with a detection limit of 5.5 × 10-7 mol L-1 and a slope of 19.0 ± 0.4 mV per decade at 25 °C. The constructed potentiometric sensor showed a relatively fast response time (15 s), good reproducibility and stability, and high selectivity towards Al3+ cation in solutions. The proposed sensor was successfully used as an indicator electrode in potentiometric titration and also in the direct determination of this metal cation in real samples. <![CDATA[Intercalated 4-Aminobenzenethiol between Au and Ag Nanoparticles: Effects of Concentration and Nanoparticles Neighborhood on its SERS Response]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000500970&lng=en&nrm=iso&tlng=en In this work is reported the investigation of the 4-aminobenzenethiol (4-ABT) surface-enhanced Raman scattering (SERS) response for different 4-ABT concentrations as well as when this molecule is intercalated between Ag and Au nanoparticles (AgNP and AuNP). SERS substrates consisting of the individual AgNP or AuNP and bi-layer AgNP/4-ABT/AuNP or AuNP/4-ABT/AgNP were prepared on glass slides. It was observed a decreasing trend of the bands intensity ratios b2/a1 as a function of the 4-ABT solutions concentration. Since the b2 modes are enhanced through the charge transfer (CT) mechanism, this result indicates that this mechanism is less effective for low concentration of 4-ABT. Also, a dependence between a1 and b2-type bands intensities could be identified for the samples where 4-ABT molecules were intercalated between AgNP and AuNP. A significantly increase in the SERS intensities of the a1 mode around 1074 cm-1 and b2 mode around 1142 cm-1 is observed when AgNP are present in the samples. This result indicates that AgNP promote amplifications of the Raman signal thorough the CT and electromagnetic (EM) mechanisms, whereas for the AuNP the SERS effect is related manly to EM mechanism. These results show that the 4-ABT SERS response can provide more information than the SERS substrate activity. Its SERS signal pattern is rich in information, allowing investigations about the local where the molecule is, details about the substrate surface, and also on the mechanisms present in the system under study. <![CDATA[Facile Graphene Oxide Preparation by Microwave-Assisted Acid Method]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000500978&lng=en&nrm=iso&tlng=en Few-layered graphene oxide (GO) was prepared using a fast and energy-saving method by microwave-assisted acid technique. The oxygenated groups existing on the GO surface were determined using UV-Vis, X-ray photoelectron and Fourier-transform infrared spectroscopies. An oxygenated group percentage of 30% in mass for the GO was observed by thermogravimetric analysis. The reduced few-layered graphene oxide (rGO) film annealed at 110 °C deposited onto a silicon/silica wafer showed expanded graphite-like structure with 0.70 nm between the rGO sheets, as determined by X-ray diffraction. This rGO film exhibited a relatively high electrical conductivity value of 7.36 × 102 S m-1 confirming the good restoration of the π-conjugated system. The prepared GO sample exhibited good stability in water from pH 4 to 12, as determined by its zeta potential, and contained 5 to 9 layers, as determined by atomic force microscopy (AFM) and transmission electron microscopy (TEM). <![CDATA[Noteworthy Method for Direct Determination of Sb<sup>III</sup> and Total Inorganic Antimony in Natural Waters]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000500985&lng=en&nrm=iso&tlng=en A procedure was developed for the direct determination of SbIII and total inorganic Sb in water samples by hydride generation atomic absorption spectrometry (HG AAS), without pre-reduction of SbV. The NaBH4 concentration was maintained at 0.4% (m/v) to perform the selective generation of stibine from SbIII and online stibine generation was carried out with 5.0% (m/v) NaBH4 to obtain the total antimony concentration. SbV was calculated as the difference between the values obtained for total Sb and SbIII. In both cases, the procedure did not appear to be adversely affected by potential interferents such as SbV, AsIII, AsV, CaII, NaI, chloride and phosphate at a concentration of 0.5 mg L-1. For the proposed procedure, the detection limits were 0.2 µg L-1 for SbIII and 0.3 µg L-1 for total Sb, while the relative standard deviations were 0.1% for 10.0 µg L-1 SbIII and 0.4% for 10.0 µg L-1 total Sb. A sampling rate of approximately 30 determinations per hour was achieved, requiring 300 mL of NaBH4, and the amount of waste generated was in order of 960 mL, indicating that this analytical procedure can be considered as green. The method was shown to be satisfactory for the determination of trace levels of antimony in water samples. The result obtained for the assaying of certified drinking water samples was 9.7 ± 0.1 µg L-1 (certified value 10.0 ± 0.5 µg L-1). <![CDATA[New Flexible and Transparent Solution-Based Germanium-Sulfide Polymeric Materials]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000500992&lng=en&nrm=iso&tlng=en New flexible and transparent materials based on germanium sulfide were obtained using GeCl4 and 1,3-propanedithiol as precursors. These materials have transparency in the ultraviolet-visible (UV-Vis) spectral region (about 70%), thermal stability up to 200 °C and glass transition located at temperatures below 0 °C (-37 °C, -56 °C and -59 °C) as shown by differential scanning calorimetry (DSC) curves. Scanning electron microscopy (SEM) images showed that the polymer is homogeneous and presents formation of crystals in some regions of the surface. These polymers also exhibit Ge-S bonds in its structure, as can be observed through Fourier transform infrared (FTIR) (bands at 399, 401, 432 and 470 cm-1) and Raman (peaks at 361 and 430 cm-1) spectroscopies, and the diffraction patterns X-rays, which suggest the formation of a mixture of GeS2 and GeO2 phases (also confirmed through energy-dispersive X-ray analysis). The coupled thermogravimetric analysis / Fourier transform infrared (TG/FTIR) technique was used to investigate the degradation of the sample. Taken together, the results of these characterizations suggest optical applications, and usability at low temperatures. <![CDATA[Silver nanoparticle thin films deposited on glass surface using an ionic silsesquioxane as stabilizer and as crosslinking agent]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000501004&lng=en&nrm=iso&tlng=en Thin films containing silver nanoparticles homogeneously dispersed, with narrow size distribution below 10 nm, were synthesized on flat glass surface, by using an ionic silsesquioxane as stabilizer and crosslinking agent. The films can be prepared without previous functionalization of substrate surfaces and without addition of other components. The films were heat treated up to 200 ºC and characterized by ultraviolet-visible, transmission electron microscopy, atomic force microscopy, thermogravimetric analysis and ellipsometry. The films were thermally stable when heated up to 200 ºC, presenting the same thickness, and maintaining both optical and morphological properties of silver nanoparticles. The antibacterial activity of the films, containing the silver nanoparticles, was evaluated against Staphylococcus aureus by using the film applicator coating method, showing an excellent performance even after the third cycle of sterilization. <![CDATA[On the search for potential antimycobacterial drugs: synthesis of naphthoquinoidal, phenazinic and 1,2,3-triazolic compounds and evaluation against <em>mycobacterium tuberculosis</em>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000501013&lng=en&nrm=iso&tlng=en Fifteen naphthoquinones, sixteen phenazines and fifteen aryl triazoles were synthesized and evaluated against Mycobacterium tuberculosis. Twenty five substances are reported here for the first time and, among all of the compounds evaluated, six presented MIC (minimal inhibitory concentration) values &lt; 6.25 µg mL-1. These substances are promising antimycobacterial prototypes. <![CDATA[Theoretical Study of Molecular and Electronic Structures of 5<sub>1</sub> Knot Systems: Two‑Layered ONIOM Calculations]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000501028&lng=en&nrm=iso&tlng=en In this study we examine the electronic and molecular structures of the [51 knot···(PF6)10]+ pentafoil knot system and report calculated interaction energies that result from halides (X = F, Cl, Br, and I) localized at the center of the [51 knot···(PF6)9]X molecular structure. The equilibrium geometries were fully optimized at the ONIOM(M06/6-31G(2d,p):PM6) level of theory, starting from an initial geometry for the pentafoil knot obtained from experimental X-ray data. The molecular systems were divided into two layers, for which the M06/6-31G(2d,p) level of theory was used to describe the high layer ([C4H6]5X- structure) and the PM6 semiempirical method was employed for the low layer. The calculated electronic energies show that the interaction between the fluorine anion and the pentafoil knot produces the most stable structure, whereas an unfavorable interaction is observed for iodide due to the diffuse character of its electronic cloud. Using basis set superposition error (BSSE) correction techniques, the observed values of the interaction are -0.201 hartrees for the fluoride ion and -0.100 hartrees for iodide. <![CDATA[Amperometric Detection of Isoprenaline Based on Glassy Carbon Electrode Modified by Iridium Oxide Nanoparticles]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000501034&lng=en&nrm=iso&tlng=en A simple and sensitive electrochemical sensor by using a glassy carbon electrode modified by iridium oxide nanoparticles (GCE/IrOxNPs) was constructed and utilized to determine isoprenaline (IP). This sensor was used successfully for IP determination in human urine samples. IrOxNPs are grown on a GCE by electrodepositing method. Various experimental parameters influencing the electrochemical behavior of the modified electrode were optimized by varying the scan rates and pH. Compared with a bare GCE, the GCE/IrOxNPs exhibits a distinct shift of the oxidation potential of IP in the cathodic direction and a marked enhancement of the current response. The results showed that GCE/IrOxNPs exhibited excellent electrochemical activity towards IP in pH 7.0 phosphate buffer solution (PBS). The detection limit, sensitivity and catalytic rate constant (kcat) of the modified electrode toward IP were 90 nmol L-1, 17.3 nA µmol-1 L and 1.6 × 104 mol-1 L s-1, respectively, at linear concentration rang up to 2500 µmol L-1. The modified electrode displayed linear responses to IP in amperometry assays in real urine, with a detection limit of 120 nmol L-1. <![CDATA[Biotransformation of the Diterpene <em>Ent</em>-18,19-dihydroxytrachylobane by <em>Rhizopus stolonifer</em>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000501043&lng=en&nrm=iso&tlng=en The diterpene ent-18,19-dihydroxytrachylobane was biotransformed for the first time by Rhizopus stolonifer, and yielded the new ent-11β,18,19-trihydroxytrachylobane derivative besides the new ent-kaur-11-ene diterpenes ent-16α,18,19-trihydroxykaur-11-ene and ent-18,19-dihydroxy-16α-methoxykaur-11-ene. Their structures were determined by spectrometric methods. <![CDATA[Fluorescence Quenching of Two <em>meso</em>-Substituted Tetramethyl BODIPY Dyes by Fe(III) Cation]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532015000501048&lng=en&nrm=iso&tlng=en Ferric ion (Fe(III)) is a biologically and environmentally relevant cation so that its analysis in environmental and biological samples is often required. Borodiazaindacenes (BODIPYs) are known for their good photophysical properties; however, there are few BODIPY-based Fe(III) sensors reported. Herein, we show the characterisation of two BODIPY dyes whose fluorescence emission is diminished by such cation. Both "turn-off" probes, a catecholyl-substituted BODIPY and a pyridyl-substituted BODIPY, were synthetically obtained and an initial screening showed a relatively good specificity for Fe(III) when compared to other cations. Catecholyl-substituted BODIPY was more sensitive to Fe(III), however, with a pH-dependent analytical performance and low brightness. On the other hand, pyridyl-substituted BODIPY was very bright and its analytical performance was apparently pH-independent, however, it was less sensitive to the analyte. In conclusion, we show herein the obtainment and characterisation of two probes with promising analytical value in the analysis of Fe(III).