Scielo RSS <![CDATA[Journal of the Brazilian Chemical Society]]> vol. 26 num. 9 lang. es <![CDATA[SciELO Logo]]> <![CDATA[Thought for Food]]> <![CDATA[Separation of the Glycerol-Biodiesel Phases in an Ethyl Transesterification Synthetic Route Using Water]]> Biodiesel is obtained by the transesterification of vegetable oil (or fat) and alcohol, with methanol being the most used alcohol. Methanol can be replaced by ethanol; however, this alcohol acts as a surfactant in the reaction mixture, promoting a stable dispersion of the glycerol in biodiesel, which hinders the separation of the glycerol-biodiesel phases. In this study, it was found that the addition of 1% v/v water relative to the total volume of the reaction mixture expedites the separation of the phases by interrupting the emulsifying action of ethanol with an immediate separation of glycerol from biodiesel. The characterization of the produced biodiesels was performed using hydrogen nuclear magnetic resonance (1H NMR) and gas chromatography (GC). 1H NMR indicated a 96.9% conversion of triglycerides to biodiesel. The fatty acid compositions of the synthesized ethyl and methyl biodiesels determined using GC are essentially the same. <![CDATA[New and Sensitive Electroquantification of Sulfentrazone in Soil by Differential-Pulse Voltammetry]]> In this work, a new and sensitive electroanalytical methodology was developed and validated to quantify sulfentrazone in soil samples. Sulfentrazone was initially characterized qualitatively using cyclic voltammetry (CV). Its oxidation occurred by diffusion (mass transport) on a glassy carbon electrode (GCE) via irreversible transfer of one electron close to a peak potential of +0.936 V vs. Ag|AgCl, 3.0 mol L-1 KCl, in 0.10 mol L-1 KOH. Differential-pulse voltammetry (DPV) was the most sensitive and selective technique, with limits of detection (LOD) of 1.94 and 2.19 mmol L-1 and limits of quantification (LOQ) of 6.46 and 7.31 mmol L-1, in the absence and presence of soil matrix, respectively. The reproducibility of the method ranged between 2.65 and 4.2%, with intermediate precision between 5.32 and 10.9%. The recovery rate ranged between 88.5 and 103%. Additionally, the accuracy of the electroanalytical method was validated by comparing the results with data from a standard analytical methodology of high-performance liquid chromatography (HPLC/UV-Vis). <![CDATA[Rietveld Method in the Analysis of Polymorphism in Mebendazole Tablets Acquired in Brazil’s Drugstores]]> Mebendazole (MBZ) is an anthelmintic medicine known to exhibit the polymorphs A, B and C, where polymorph C is the one indicated for tablets. Mebendazole commercial tablets (references, generics and similars) were analyzed in this work using X-ray powder diffraction data and the Rietveld method (RM) aiming at characterizing and quantifying crystal phases. Form C was found in mixture with form A in formulations of 500 mg (reference and generic). One of the generics presented a batch with form B and another one with form C. All the other tablets presented form A. <![CDATA[Layered Zinc Hydroxide Salts Intercalated with Anionic Surfactants and Adsolubilized with UV Absorbing Organic Molecules]]> Two anionic surfactants, dodecylsulfate (DDS) and dodecylbenzenesulfonate (DBS), were intercalated into layered zinc hydroxide salts (LHS) using the direct alkaline co-precipitation method, and characterized by powder X-ray diffraction (PXRD), Fourier-transform infrared (FTIR) and thermogravimetric analysis/differential thermal analysis (TGA/DTA). Different UV-absorbing organic molecules, like salicylates, cinnamates and benzophenones, were adsolubilized in the LHS interlayer following two different procedures (conventional microwave treatment and microwave with hydrothermal treatment). The adsolubilized products were investigated by PXRD, FTIR, diffuse reflectance UV-Vis (DRUV-Vis) and luminescence spectroscopies before and after exposure to UV radiation. Most of the products showed a good absorption in the UV region, from UVC to UVA, and good stability under UV radiation. The photodegradation tests showed that DDS-intercalated compounds were more stable than those intercalated with DBS. Adsolubilization in LHS can be an interesting alternative to immobilize neutral molecules with UV absorption capability, to prepare materials to be used in sunscreen formulations. <![CDATA[Solubility and Bioaccessibility of Ba, Ca, Cr, Cu, Fe, Mg, Mn, P, Sr and Zn in Slim Coffee Infusions by <em>in vitro</em> Gastrointestinal Digestion]]> Solubility and bioaccessibility of Ba, Ca, Cr, Cu, Fe, Mg, Mn, P, Sr and Zn in slim coffees were investigated using an in vitro method. Two different compositions of solutions simulating gastric and intestinal juices were tested: SGJ1 + SIJ1 (0.02% pepsin in 0.10 mol L-1 HCl; 0.015% pancreatin with 0.15% bile salts in 0.10 mol L-1 NaHCO3) and SGJ2 + SIJ2 (0.32% pepsin with 0.20% NaCl in 0.08 mol L-1 HCl; 0.40% pancreatin with 2.5% bile salts in 0.10 mol L-1 NaHCO3). Soluble and bioaccessible fractions (in %) in reference to total concentrations of studied elements in infusions were as follows: Ba (81.2, 34.2), Ca (84.4, 44.5), Cr (80.1, 44.8), Cu (69.2, 24.1), Fe (72.5, 6.6), Mg (89.5, 69.6), Mn (44.3, 28.4), P (96.6, 84.6), Sr (85.9, 46.8), Zn (80.8, 59.5). These results suggest that slim coffees are not a rich source of minerals. <![CDATA[Determination of Pesticides in Soil Using a Hyphenated Extraction Technique]]> A new method for the extraction of pesticide residues from soil was developed, optimized, validated and applied to real samples. The technique consisted of combining single-drop microextraction and solid-liquid extraction with low temperature partitioning (SLE/LTP-SDME) followed by analysis using gas chromatography with electron capture detection (GC/ECD). This method was used to determine the presence of alachlor, methyl parathion, trifluralin, endrin, lindane, dieldrin and dichloro-diphenyl-trichloroethane (4,4’-DDT) in soil samples. Recoveries ranging from 67.2 to 122.5% were achieved, coefficients of variation (repeatability) were lower than 22.4% and limits of detection ranged from 0.18 to 0.59 µg kg-1. Recovery from soils fortified with different concentrations of the pesticides ranged from 61.5 to 123.5%. The new method combines the primary advantages of the two techniques: purification of the sample using SLE/LTP and preconcentration using SDME. The new method also enables the determination of low volatility compounds without requiring the sample to be heated. <![CDATA[Effects from Gold Electrodes on the Electron-Phonon Coupling of Poly(p-phenylenevinylene) Films]]> Interface effects between metal electrodes and organic films are crucial for the overall performance of organic electronics devices. We investigate effects from gold electrodes deposited on spin-coated films of poly(p-phenylene vinylene) (PPV). While a thin Au layer (16 nm) did not affect the absorption and emission spectra of PPV, a 64 nm thick Au layer induced blue shifts in both spectra owing to the reduction in the effective conjugation degree of PPV segments. Upon combining photoluminescence and Raman scattering spectroscopies, we noted that the Au clusters interact preferentially with the phenyl rings of the polymer chain, leading to shifts in the vibrational modes at 1100 and 555 cm-1 and a significant change in the electron-phonon coupling inferred from the Huang-Rhys parameters. These results are consistent with theoretical predictions in ab initiocalculations, which imply that the final properties of polymeric devices may be tuned with adequate conditions for electrode deposition. <![CDATA[Synthesis, Antitumor Activity and Docking of 2,3-(Substituted)-1,4-Naphthoquinone Derivatives Containing Nitrogen, Oxygen and Sulfur]]> Eleven 2,3-(substituted)-1,4-naphthoquinone derivatives were synthesized in yields ranging from 52-89%. These derivatives were evaluated for their cytotoxic effects on human lungs (H460), triple-negative breast (MDA-MB-231) and ovarian (A2780) cancer cell lines. Compounds 5f and 8 showed IC50values of 3.048 × 10-5 mol L-1 and 4.24 × 10-6 mol L-1 for H460; 5c and 8showed IC50 values of 2.16 × 10-5 mol L-1 and 1.60 × 10-5 mol L-1 for MDA-MB-231, and 5gand 8 showed IC50 values of 2.68 × 10-6 mol L-1 and 3.89 × 10-6 mol L-1 for A2780. Additionally, we conducted a docking study with the four most active compounds and the therapeutic targets PI3K and topoisomerase II showing the pharmacophoric conformation of these compounds. <![CDATA[Dye Degradation Enhanced by Coupling Electrochemical Process and Heterogeneous Photocatalysis]]> In this study, we evaluated the combination between an electrochemical process, occurring in the dark, and a heterogeneous photocatalytic process for dye degradation, using the azo dye tartrazine as model of oxidizable substrate. TiO2 P25 and an Ag-doped TiO2 were used as photocatalysts in suspensions containing 50 mg L–1 of tartrazine. The best result, 74% of dye mineralization in 120 min of reaction, was obtained using TiO2 P25 as photocatalyst and a current density of 10 mA cm–2 in the electrochemical cell, a value 30% higher than the sum of the results obtained by heterogeneous photocatalysis (44%) and electrochemical oxidation (13%). The use of Ag-doped TiO2 did not result in significant improvement on tartrazine mineralization, due to the aggregation of these nanoparticles. Our results suggest that this process can be an alternative for a complete treatment (discoloration and mineralization) of tartrazine and most likely other azo dyes. <![CDATA[Photochemical and Electrochemical Study of the Release of Nitric Oxide from [Ru(bpy)<sub>2</sub>L(NO)](PF<sub>6</sub>)<sub>n</sub> Complexes (L = Imidazole, 1-Methylimidazole, Sulfite and Thiourea), Toward the Development of Therapeutic Photodynamic Agents]]> The development of NO photoreleaser compounds has important potential applications on medicine, particularly on preventing topic infections and controlling cancers. Due to these expectations, the photochemical release of nitric oxide from complexes of [Ru(bpy)2LX]n+, where L = imidazole, 1-methylimidazole, sulphite and thiourea and X = NO+ and NO2− was investigated employing spectroscopic and electrochemical techniques. The release of NO was confirmed by chronoamperometry using a NO selective electrode, while the other product, mainly [RuIIH2O], was detected by UV-Visible spectroscopy and electrochemical techniques for all complexes except for thiourea. The amount of NO released by these complexes upon irradiation was determined using a new developed method using square wave voltammetry. <![CDATA[Screening of By-Products of Esfenvalerate in Aqueous Medium Using SBSE Probe Desorption GC-IT-MS Technique]]> The pyrethroids, their metabolites and by-products have been recognized as toxic to environment and human health. Despite several studies about esfenvalerate toxicity and its detection in water and sediments, information about its degradation products is still scanty. In this work, esfenvalerate degradation products were obtained by chemical oxidation with hydrogen peroxide and their structure was elucidated using a procedure known as stir bar sorptive extraction (SBSE) probe desorption gas chromatography-ion trap mass spectrometry (GC-IT-MS) analysis. This procedure consists of the thermal desorption of analytes extracted from a SBSE stir bar introduced by a probe into a gas chromatograph (GC) coupled to an ion trap mass spectrometry (IT-MS) system. Based on IT-MS data, a degradation pathway of esfenvalerate is proposed with ten products of chemical oxidation of esfenvalerate that are fully identified. Among these compounds, 3-phenoxybenzoic acid and 3-phenoxybenzaldehyde were detected, reported as being environmental metabolites of some pyrethroids, with endocrine-disrupting activity. <![CDATA[Ruthenium(II) Complexes Containing Anti-Inflammatory Drugs as Ligands: Synthesis, Characterization and <em>in vitro</em> Cytotoxicity Activities on Cancer Cell Lines]]> The synthesis, characterization and cytotoxic activity of cis-[Ru(dicl)(dppm)2]PF6 and cis-[Ru(ibu)(dppm)2]PF6, (dppm = 1,1-bis(diphenylphosphine)methane; dicl = diclofenac anion and ibu = ibuprofen anion), are described in this work. Complexes were characterized by elemental analysis, Fourier transform infrared spectroscopy (FTIR), UV-Vis, 31P{1H} nuclear magnetic resonance (NMR) and high-resolution mass spectrometry (HRESIMS). X-ray structure of cis-[Ru(ibu)(dppm)2]PF6 is also described. Preliminary calf thymus DNA (ct-DNA) binding studies were carried out by UV-Vis and viscosity experiments, with results suggesting the existence of electrostatic interactions between ruthenium complexes and ct-DNA. Cytotoxicity assays were carried out on a panel of human cancer cell lines and a human normal cell line. Complexes displayed a high to moderate cytotoxicity with IC50 ranging from 5 to 47 µmol L-1. cis-[Ru(ibu) (dppm)2]PF6 was found to be the most active, with IC50 values lower than cisplatin. The degree of cytotoxicity was maintained for the normal cell line, although cis-[Ru(ibu)(dppm)2]PF6 exhibited a similar selectivity to that of cisplatin but with a higher activity for at least two tumor cell lines which evidences a promising anticancer candidate and selects this complex for further experiments. <![CDATA[Potentiometric Titration and Out-Of-Equilibrium pH Response of the Biotite‑Water System]]> Minerals in soils contribute significantly to the capacity of soils to buffer pH disturbance. In this paper, we present the pH buffering capacity of a common soil phyllosilicate mineral, biotite. We performed equilibrium potentiometric titrations and we also monitored the pH response kinetics of the mineral-water system in order to develop an out-of-equilibrium model able to capture the interactions between minerals and the surrounding aqueous fluid. During titrations, after each addition of titrant solution from pH 11 to ca. 3, the pH response patterns were monitored over time until reaching a pseudo-equilibrium pH value. Based on the potentiometric dataset Best7, equilibrium calculations were performed to obtain the concentrations and the equilibrium protonation constants of each deprotonable component that fit best our titration curve. In parallel, the out-of-equilibrium pH responses over time at each point of the titration were used in a simple first-order kinetic approach that allow for the determination of “slow” proton exchange [H+ex]t0(mol L-1) and the associated rate constants for the exchange reactions, k (s-1). Our results show a maximum in “slow” proton exchange [H+ex]t0 associated to a minimal value of k at pH &lt; 5 while at neutral and basic pH exhibits the opposite, i.e. , fast rate constant for a minimum value of the “slow” proton exchange. Expressing the observed “slow” proton exchange processes in terms of entropy production, our result demonstrate that the maximum resilience stability of biotite-water system to pH perturbation is in acidic pH, probably due to the consumption of proton associated with biotite dissolution reactions. <![CDATA[Synthesis and Characterization of Methylcellulose Produced from Bacterial Cellulose under Heterogeneous Condition]]> In this work, methylcellulose (MC) was produced from bacterial cellulose (BC), using dimethyl sulfate in a 3 h (MC3h) or 5 h (MC5h) reaction under heterogeneous conditions, with reagent substitution at each hour. MC3h showed a degree of substitution (DS) of 2.26 ± 0.13 and MC5h showed a DS of 2.33 ± 0.05. The two samples were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), differential thermal analysis (DTA), thermal gravimetric analysis (TGA), 13C nuclear magnetic ressonance (NMR) and 1H NMR techniques. The FTIR spectra of the BC and MC samples present significant differences in the regions from 3750 to 2750 cm−1 and from 1500 to 750 cm−1, which evidence the methylation of the samples. Solid state NMR spectroscopy of the MC samples was used to identify the 13C NMR signals of substitution at sites C-2, C-3 or C-6 in the glucopyranose units. The modification of bacterial cellulose produced a material with a high DS, determined by three different techniques (chemically and using the liquid 1H and solid 13C NMR spectra). These samples also demonstrate high crystallinity and thermal stability. With the MC samples synthesized in this work, transparent and resistant films were prepared and also a highly porous sponge like material. <![CDATA[Bifunctional Porous SiO<sub>2</sub> Complex Nanoparticles with Properties of Enzymatic Catalysis and Optical Oxygen Sensing]]> The porous fluorescent SiO2 nanoparticles encapsulating photosensitizer Ru(bpy)3Cl2were prepared by Stöber method and used as a carrier to immobilize glucose oxidase (GOD) to form the bifunctional porous SiO2 complex nanoparticles (BPSCNp) with the properties of enzymatic catalysis and optical oxygen sensing. The optimal immobilization conditions are as follows: hexadecyltrimethyl ammonium bromide (APTES) concentration of 2% (v/v), glutaraldehyde (GA) concentration of 1.0% (v/v), and pH of 6.5, GOD amount of 4.0 mg in 40 mg of carrier. BPSCNp showed maximal catalytic activity at pH 6.0 and 50 °C. After immobilization, the thermal storage and operation stability of GOD were improved remarkably. After kept at 4 °C for 30 days, BPSCNp and free GOD retained 68% and 35% of initial activity, respectively. BPSCNp maintained 58% of its initial activity after 7 consecutive operations and 30% after 15 consecutive operations. The fluorescence of BPSCNp could be quenched effectively by oxygen. There was a good linear relationship between tanΦ0/tanφ and O2 concentration in the range of 0 to ca. 90%. BPSCNp had a highly reproducible response to oxygen with the response time of 20 s. BPSCNp might be used as the sensing material and have potential application in multi parameter fiber optic biosensor based on enzyme catalysis and oxygen consumption. <![CDATA[Contributions on the Use of Bismuth as Internal Standard for Lead Determinations Using ICP-Based Techniques]]> Bismuth was evaluated as internal standard for Pb determinations and showed usefulness to minimize variations due to changes in the experimental conditions of the inductively coupled plasma optical emission spectrometry (ICP OES), inductively coupled plasma mass spectrometry (ICP-MS) and electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS). Thirty four samples were analyzed and the Pb contents obtained by ICP-MS and ETV-ICP-MS were in agreement at 95% confidence level. Plant, biological tissue and soil reference materials were also analyzed and the results were close to certified values upon the use of the internal standard. Recoveries for Pb spikes (ICP OES: 95-110%; ICP-MS: 95-106%; ETV-ICP-MS: 92-119%) were better than those obtained with external calibration (ICP OES: 56-91%; ICP-MS: 36-136%; ETV‑ICP-MS: 5-123%). The relative standard deviations (n = 12) was improved from 1-9% to 0.2-6% (ICP OES), from 0.5-11% to 0.1-7% (ICP-MS) and from 0.4-7% to 0.1-4% (ETV‑ICP‑MS) by using external and internal standard calibrations, respectively. <![CDATA[Nanomagnetite-Zeolite Composites in the Removal of Arsenate from Aqueous Systems]]> Composites based on nanosized particles of magnetite and natural microsized zeolite were prepared and their efficiency to adsorb arsenate from aqueous systems was evaluated through kinetic data and adsorption isotherms, considering the proportion of magnetic iron oxide, composite:solution ratio and zeolite particle size. A well-crystallized nanomagnetite with an averaged particle size of 50 nm when supported on zeolite was obtained; the nanomagnetite enhances the arsenate adsorption of zeolite. The composite prepared with a nanomagnetite:zeolite mass ratio of 0.43:1 and 0.30:1 presented on zeolite milled 20 and 120 min, respectively, showed a similar adsorption capacity as that observed for pure magnetite. Supported nanomagnetite prevents risks of the nanoparticles contamination. The smaller the mean particle size of zeolite the lower the mass proportion of nanomagnetite in the composite required to reach the maximum adsorptive efficiency. Acidic conditions improve arsenate remotion, in agreement with the development of positive surface charge in the composite. <![CDATA[Evaluation of the Effects of Hofmeister Series on Salting Out in the Determination of Organophosphorous Pesticides and Pyrethroids by LDS/DLLME]]> Various greener microextraction procedures have been proposed with low limits of detection to control of pesticides present in the environment, including the low-density solvent dispersive liquid‑liquid microextraction (LDS/DLLME) technique. The addition of electrolytes is important in order to induce the salting-out effect. Thus, it is possible to use the Hofmeister series and the Voet lyotropic number to study the effect of different ions on pesticide extraction in LDS/DLLME technique. Different anions were tested and a strong correlation was observed between the lyotropic number of the anion and the recovered volume of extraction solvent. The lyotropic numbers of the anions were successfully compared with the chromatographic peak areas normalized by the recovered solvent volumes, and similar empirical cubic relationships were obtained for all the pyrethroids evaluated. In the extraction of the organophosphorous pesticides, chlorpyrifos presented similarity with the pyrethroids, while correlation was observed between methyl parathion and profenofos. <![CDATA[Dispersive Liquid-Liquid Microextraction with Liquid Chromatography-Tandem Mass Spectrometry for the Determination of Triazine, Neonicotinoid, Triazole and Imidazolinone Pesticides in Mineral Water Samples]]> Mineral water is known for its high purity. Because mineral water is produced by the infiltration of water through the soil, there is the possibility of contamination with pesticides. The aim of this study was to develop a simple, rapid and efficient method for the extraction and preconcentration of different classes of pesticides in mineral water samples by dispersive liquid-liquid microextraction (DLLME) coupled with liquid chromatography tandem mass spectrometry. To optimize the DLLME conditions for the different classes of pesticides and access the effect of variables on the extraction, a central composite design (CCD) with a five-level fractional factorial design was used for the construction of a second order response surface model (RSM). The limits of quantification were between 0.005 and 0.5 μg L-1. Correlation coefficients (r) were higher than 0.999. Recoveries ranged from 102 to 120%, with relative standard deviations between 1 and 10%. Low matrix effect for all compounds was observed. The result showed that using a mixture of acetone and acetonitrile as disperser solvent and a mixture of chloroform and monochlorobenzene as extractor solvent, it is possible to employ the traditional DLLME with chlorinated solvents to extract the multiclass pesticides from the water samples. <![CDATA[<em>p</em>-Cymenesulphonyl Chloride: A Bio-Based Activating Group and Protecting Group for Greener Organic Synthesis]]> A bio-derived protecting/activating group has been synthesized by introducing a sulphonyl chloride group to the aromatic ring of p-cymene derived from citrus peel waste. The resulting p-cymenesulphonyl chloride was evaluated as an activating group by reacting with 1-octanol, 2-octanol, phenol and piperidine, and further reactions of the activated alcohols. The comparison to tosyl chloride demonstrates that the bio-based alternative can be effectively utilized as a direct replacement for the current fossil derived equivalent. <![CDATA[Instrumental and Experimental Conditions for the Application of Fourier Transform Infrared Analysis on Soil and Humic Acid Samples, Combined with Chemometrics Tools and Scanning Electron Microscopy]]> The investigation of the chemical properties of soil organic matter (OM), by the use of some spectroscopic techniques, requires the removal of the mineral impurities of the samples. Therefore, the objective of this study was to evaluate the influence of the pretreatment of samples and, also, the influence of instrumental conditions on the qualitative and quantitative results obtained by Fourier transform infrared (FTIR) spectroscopy to soil and humic acid (HA) samples. The obtained results showed that: the mass of potassium bromide (KBr) used on the background pellet influenced the characteristics of samples spectra; the baseline correction changes the intensity of the absorptions; both the extraction of HA as the hydrofluoric acid (HF) treatment were not efficient in removing the mineral impurities of the samples. The scanning electron microscopy (SEM) analysis showed differences due to the extraction, but not due to the HF treatment. The present study shows the importance of the use of adequate treatments, before, during and after the spectroscopic study of soil OM, providing valuable information for future works. <![CDATA[Volatilization of Ammonia Originating from Urea Treated with Oxidized Charcoal]]> Loss of N through volatilization of ammonia is the main limitation for agricultural use of urea. The aim of this study was to evaluate the volatilization of NH3 from urea granulated (Ug) or urea coated (Ur) with two oxidized charcoals produced by the oxidation of eucalyptus charcoal with 4.0 mol L-1 HNO3, followed by the post-treatment with NaOH (CHox) or without post-treatment with NaOH (CHox-OH). Ug and Ur were produced with 5, 10, 15 and 20% (m/m) of CHox or CHox-OH. The volatilization of NH3 was evaluated as 100 mg of N in the form of Ug or Ur applied to samples of a Hapludalf placed in a system with continuous and controlled air flow. The Ug with CHox-OH or with CHox was more effective in reducing the volatilization of NH3 than the Ur. It was estimated that the Ug with 16% of CHox or CHox-OH, with 39% N, reduced the volatilization by 40% in relation to urea without the additives. Results show that charcoal oxidized is an effective additive for reducing ammonia volatilization of urea. <![CDATA[ALK-5 Inhibition: A Molecular Interpretation of the Main Physicochemical Properties Related to Bioactive Ligands]]> Activin-like kinase 5 (ALK-5) receptor represents an attractive object to treat cancer. Analyses on the quantitative structure-activity relationship were performed to explore the relationship between the molecular structure of 1,5-naphthyridine, pyrazole and quinazoline derivatives and the inhibition of the activin-like kinase 5. From a data set containing 59 compounds, various electronic descriptors were calculated using density functional theory (DFT) method; stereochemical descriptors (as molecular volume and area), polar surface area (PSA), log P and dragon descriptors were also calculated. The ordered predictor selection (OPS) algorithm, weighted principal component analysis (PCA) and Fisher's weights (FW), combined with sequential forward selection, were employed to select the most relevant descriptors to be employed in all partial least square regressions. Using this procedure, we selected the most informative descriptors and significant correlation coefficients were achieved (r2 = 0.74, q2= 0.83). Additional validation tests were carried out, indicating that the obtained model is robust and reliable and, consequently, it can be used to predict the biological activity of new compounds. <![CDATA[Synthesis of Poly(Vinylferrocene) Perchlorate/Poly(3,3’-Diaminobenzidine) Modified Electrode in Dichloromethane for Electroanalysis of Hydroquinone]]> Poly(vinylferrocenium) perchlorate-poly(3,3’-diaminobenzidine) (PVF+ClO4–-PDAB) composite film was synthesized electrochemically for the first time on Pt disc electrode in a dichloromethane solution containing poly(vinylferrocene) (PVF) polymer, 3,3’-diaminobenzidine (DAB) monomer and tetrabutylammonium perchlorate as supporting electrolyte. This modified electrode was characterized using cyclic voltammetry, Fourier transform infrared spectroscopy (FTIR), UV-Vis spectrophotometry, atomic absorption spectroscopy (AAS), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) methods and it was used for amperometric determination of hydroquinone (HQ) at potential ranges of 0.40 and 0.60 V. The best analytical results for HQ was obtained at 0.45 V in NaHSO4/Na2SO4 solution (pH 2.0) and limit of detection, limit of quantification and linear response range were found as 7.469 × 10-5, 2.489 × 10-4 and 2.489 × 10-4-65.0 mmol L-1 (R2 = 0.996), respectively. These results were compared to poly(3,3’-diaminobenzidine) (PDAB) coated and uncoated Pt electrodes. The best analytical results were obtained with composite film because of behavior as electron transfer mediator of PVF. <![CDATA[Coupling DLLME-CE for the Stereoselective Analysis of Venlafaxine and Its Main Metabolites after Biotransformation by Fungi]]> Fungal biotransformations have become very important in the study of chiral drugs because the reactions performed by these microorganisms may be enantioselective. However, analyses of analytes present in liquid culture medium have proved to be very difficult due to the complexity of this matrix. The aim of this work was to couple dispersive liquid-liquid microextraction (DLLME) with capillary electrophoresis to evaluate the biotransformation of the antidepressant drug venlafaxine (Vx) into its chiral metabolites, N-desmethylvenlafaxine (NDV) and O-desmethylvenlafaxine (ODV) by fungi. The chiral separation was carried out in 50 mmol L-1 sodium phosphate buffer pH 2.0 containing 8 mmol L-1 α-cyclodextrin and 1.0% (m/v) carboxymethyl-β-cyclodextrin. The temperature of the capillary was set at 20 °C. A voltage of +20 kV was applied during analysis. The DLLME was accomplished using 300 µL of isopropanol (disperser solvent) and 200 µL of chloroform (extraction solvent). The method was completely validated and showed to be linear over the concentration range of 75-938 ng μL-1 for ODV and NDV enantiomers and of 500-15000 ng μL-1for venlafaxine enantiomers with a correlation coefficient higher than 0.99. The selectivity of the method was evaluated and no interference peaks were detected in the migration time of the analytes. The limit of quantification was 75 ng μL-1 for metabolite enantiomers and 500 ng μL-1 for venlafaxine enantiomers. The study showed a stereoselective biotransformation of venlafaxine into (+)-(S)-N-desmethylvenlafaxine by the fungus Cunninghamella elegans ATCC 10028B with an enantiomeric excess of 100%.