Scielo RSS <![CDATA[Journal of the Brazilian Chemical Society]]> vol. 27 num. 4 lang. en <![CDATA[SciELO Logo]]> <![CDATA[Current Approaches Against Alzheimer's Disease in Clinical Trials]]> Alzheimer's disease (AD) is a progressive degenerative brain disease which causes mental and physical decline, gradually resulting in death. Currently, this disease represents one of the uppermost human issues, both from the medical and economic point of view. Interest in the discovery of a drug for AD is enormous. However, despite the long-term and worldwide effort for a more effective therapy, the only available treatment is a symptomatic use of acetylcholinesterase inhibitors (AChEIs) and memantine. New therapeutic approaches as well as those based on cholinergic or amyloid theory have not brought the desired benefits yet. Thus, the question is whether an effective drug for this progressive disease will ever be developed or whether people will have to rely only on prevention and minimize risk factors of AD. <![CDATA[Comparison of Gold CD-R Types as Electrochemical Device and as Platform for Biosensors]]> The construction of gold electrodes using 3 kinds of gold recordable compact discs (CDtrodes) and characterization by electrochemical and spectroscopic techniques are herein reported. Following a surface pretreatment in 0.5 mol L-1 sulfuric acid (H2SO4), the electrochemical experiments were performed in the presence of redox couple ferro/ferricyanide [Fe(CN)6]3-/4-. The immobilization of an oligopeptide bio-inspired by acetylcholinesterase onto the CDtrode was also evaluated. Surface characterization was done by cyclic voltammetry, electrochemical impedance spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy and atomic force microscopy. CDtrodes are known to be of low cost, fast and simple construction. They are suitable for immobilizing biological molecules and could be used as disposable transducer for the construction of biosensors. <![CDATA[Cascade Synthesis of Thieno[2,3-<em>b</em>]pyridines by Using Intramolecular Cyclization Reactions of 3-Cyano-2-(organylmethylthio)pyridines]]> 2-Amino-4-aryl-6-mercaptopyridine-3,5-dicarbonitriles as starting materials have been prepared by reducing of 2-amino-4-aryl-6-(phenylthio)pyridine-3,5-dicarbonitrile derivatives which were synthesized on stepwise one-pot three component reaction of malononitrile, aldehydes and thiophenol in the presence of base catalysts such as triethylamine, high surface area (HSA) MgO or nanocrystalline magnesium oxide. Alkylation of 2-amino-4-aryl-6-mercaptopyridine-3,5-dicarbonitriles with α-halogen compounds in presence of sodium alkoxide as base catalyst followed with cyclization afforded the thieno[2,3-b]pyridine derivatives in excellent yields and in a short reaction time. <![CDATA[Agarose Based Magnetic Solid-Phase Extraction-Magnetic Field Agitation for Determination of Trace Amounts of Molybdenum in Beans]]> A magnetic solid-phase extraction method based on agarose coated magnetic nanoparticles (ACMNPs) coupled to a magnetic field agitation (MFA) device was developed and used for the preconcentration and graphite furnace atomic absorption spectrometric determination of trace amounts of MoVI in beans. The formation of the nanoparticles and their encapsulation in agarose micro-flakes was conducted in a single step. The nanomagnetic agarose particles were activated by an epichlorohydrin method, functionalized by phenylephrine and used for selective preconcentration of MoVI. The influence of different analytical parameters such as pH, extraction time, type and volume of eluent and amount of adsorbent on the preconcentration of MoVI were investigated. No important interferences were observed for the determination of the analyte in presence of several other metal ions. The capacity of the adsorbent for MoVI at pH 4.0, was 13.2 µg per mL of its packed volume. Eight replicated analyses at the optimized conditions resulted in a recovery of 95.3% with a relative standard deviation of 4.9%. The detection limit of the method (3σ) for MoVI was 49 ng L-1. The method was successfully applied to the determination of MoVI in beans samples. <![CDATA[Voltammetric Determination of Ethionamide in Pharmaceutical Formulations and Human Urine using a Boron-Doped Diamond Electrode]]> This work reports a simple and low cost voltammetric approach comprising a boron-doped diamond electrode (BDDE) to determine the antibiotic ethionamide (ETO). Cyclic voltammetry studies revealed that ETO exhibits an irreversible reduction peak at -0.95 V and an irreversible oxidation peak at +1.4 V onto BDDE (vs. saturated Ag/AgCl reference electrode) in Britton-Robinson buffer solution (pH 5.0, 0.1 mol L-1). Different voltammetric scan rates (from 10 to 150 mV s-1) suggested that the reduction of ETO on the BDDE surface is a diffusion-controlled process. Square wave voltammetry (SWV) optimized conditions showed a linear response to ETO from 1.00 to 80.0 µmol L-1 (R2 = 0.998) with a limit of detection of 0.294 µmol L-1 and limit of quantification of 0.980 µmol L-1. The developed square wave voltammetric method was successfully used in the determination of ETO in human urine and pharmaceutical formulation. The ETO quantification results in pharmaceutical tablets obtained by SWV-BDDE were comparable to those found by official analytical protocols. <![CDATA[Acid Decomposition of Yerba Mate (<em>Ilex paraguariensis</em>) Using a Reflux System for the Evaluation of Al, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Na, Pb and Zn Contents by Atomic Spectrometric Techniques]]> In the first part of this paper, two acid decomposition procedures for the determination of Al, Ca, Fe, Mg, Mn and Zn contents in yerba mate samples by inductively coupled plasma optical emission spectrometry (ICP OES) were compared. Using a reflux system, the samples were treated with a mixture of HNO3 and H2O2 for 3 hours at 220 °C in the digester block. The results from five commercial yerba mate samples were compared with the results obtained from microwave digestion. Good agreement between the procedures at a 95% confidence level was obtained with relative standard deviation (RSD) values lower than 10.0%. The accuracy was evaluated using addition and recovery experiments (80.5 to 112.8%). In the second part, Ca, Cd, Cr, Cu, Fe, K, Mg, Na, Pb and Zn concentrations were evaluated in the yerba mate infusion. The results showed that elements such as Na, K, Mg and Zn are easily transferred to the hot water used for the infusion. For Pb and Cd, the concentrations found in the analyzed samples were lower than the values established by Brazilian legislation. <![CDATA[Functionalized Multi Walled Carbon Nanotubes as a Carrier for Doxorubicin: Drug Adsorption Study and Statistical Optimization of Drug Loading by Factorial Design Methodology]]> Multi walled carbon nanotubes (MWNTs) have been identified as an efficient drug carrier. Here a controlled drug delivery system based on modified MWNTs with polyethylene glycol (PEG) was developed (MWNTs-PEG). Then doxorubicin (DOX) as an anticancer drug loaded to nanocarrier. All the parameters affecting the DOX adsorption such as: dose of adsorbent, pH, initial DOX concentration and contact time were studied for the first time by factorial design methodology to evaluate and optimize the adsorption conditions. The adsorption isotherm and other properties including kinetics and thermodynamics were studied. The adsorption isotherm was well described by the Freundlich model and adsorption kinetics followed a pseudo-second order model. The thermodynamic studies showed that the adsorption of DOX on nanocarrier is spontaneous and exothermic in nature. The cumulative release of DOX from MWNTs-PEG was pH dependent and the release rate was much higher at pH 5.5 than that at pH 7.4. <![CDATA[A New Steroidal Saponin from the Tubers of <em>Ophiopogon japonicus</em> and Its Protective Effect Against Cisplatin-Induced Renal Cell Toxicity]]> A new furostanol saponin, ophiopogonin T, was isolated from the tubers of Ophiopogon japonicus. Its structure was established by extensive spectroscopic techniques including 1D (1H and 13C) and 2D nuclear magnetic resonance (NMR) experiments (correlation spectroscopy (COSY), heteronuclear single quantum coherence (HSQC), heteronuclear multiple bond correlation (HMBC) and nuclear Overhauser effect spectroscopy (NOESY)), high-resolution electrospray ionization mass spectrometry (ESIMS), and chemical methods. Using cell-based assays, this compound was evaluated for its cytotoxic effect on cancer cell lines and its protective effect against anticancer drug-induced nephrotoxicity. Cisplatin-induced cytotoxicity in porcine kidney (LLC-PK1) cells was significantly reduced upon treatment with ophiopogonin T, without affecting human hepatoma (HepG2) cancer cell proliferation or tube formation in human umbilical vein endothelial cells (HUVECs). These results collectively reflect the beneficial effect of ophiopogonin T on the side effects of cisplatin. <![CDATA[Feasibility of Using AAS for the Characterization of a Tuna Fish Candidate Reference Material for Total Hg and Methyl-Hg Measurement]]> This work describes the evaluation of several parameters for preparing a tuna fish candidate reference material (RM) in order to measure its total Hg and methyl-Hg mass fractions by cold vapor atomic absorption spectrometry (CV-AAS) and solid sampling graphite furnace atomic absorption spectrometry (SS-GF AAS). Best results were acquired after extraction with toluene and L-cysteine for 15 min at 80 °C. The parameters investigated were stability of chemical composition during production, homogeneity and analyte segregation. No analyte segregation was observed and the material was shown to be stable even when stored at 50 °C for 10 months. Total Hg mass fraction was 3.03 ± 0.22 µg g-1 by CV AAS, 2.99 ± 0.43 µg g-1 by SS-GF AAS and 2.95 ± 0.15 µg g-1 by direct mercury analyser (DMA). Methyl-Hg mass fraction was 2.49 ± 0.13 µg g-1 by CV AAS and 2.44 ± 0.46 µg g-1 by SS-GF AAS. <![CDATA[Chemical Profiling of Street Cocaine from Different Brazilian Regions]]> This work describes results of chemical profiling by gas chromatography with flame ionization detector (GC-FID) of the main components (purity, oxidation level, and cutting agents) in 642 street cocaine samples seized in five different Brazilian States between 2011 and 2014. The analysis revealed the presence of cocaine with mean content of 49.8%. Freebase samples showed cocaine average content of 66.0%, whereas hydrochloride and not determined (n.d.) present cocaine content of 44.5% and 11.8%, respectively. Cocaine base samples show moderately (16%) to not oxidized (81%) levels, whereas cocaine hydrochloride samples exhibit moderate (37%) to high (22%) oxidation degrees. Approximately 34% of all the analyzed samples did not have any adulterant identified. Base cocaine samples are even less adulterated (42% uncut) with phenacetin being present in 53% (average content of 15%). Caffeine and lidocaine were mostly found in hydrochloride samples, while the n.d. samples show a combination of either phenacetin or a caffeine/lidocaine mixture. A mass balance approach is presented and seizures information can be combined to deliver intelligence and statistical analysis that might contribute to the understanding of street cocaine composition scenario. A total of 269 samples were characterized as crack cocaine showing phenacetin as the main adulterant and presenting an average cocaine content of 68.3%. <![CDATA[Hybrid Self-Assembled Materials Constituted by Ferromagnetic Nanoparticles and Tannic Acid: a Theoretical and Experimental Investigation]]> Hybrid magnetite materials are interesting for both biomedical and catalytic applications due to their well-known biocompatibility, as well as their magnetic and electric properties. In this work we prepared Fe3O4 nanoparticles (NPs) coated with tannic acid (TA), a natural polyphenol, through two different synthetic routes, aiming to understand the influence of TA in the synthesis step and contribute to the development of water-dispersible magnetic materials. The coating process was verified by information obtained from transmission electron microscopy (TEM), zeta-potential and Fourier transform infrared (FTIR) spectroscopy. The incorporation of TA after Fe3O4 NPs production generated spherical NPs smaller than 10 nm, suggesting that TA plays a fundamental role in the nucleation and organization of Fe3O4 NPs. Data from both density functional theory (DFT) and FTIR allowed us to infer that Fe3O4 interacts mainly with the carbonyl groups of TA. Hybrid materials having improved water-dispersibility are very attractive for biomedical applications. <![CDATA[Preliminary Study about the Origin of Trace Elements in the Atmospheric Deposition in Two Brazilian Subtropical Estuaries]]> The atmospheric deposition of dissolved trace elements was investigated in two subtropical estuarine systems, located on the coast of Paraná, Southeast Brazil. The samples (n = 91) were collected in three periods, from May to September 2010, in four different areas. Trace elements concentrations (Al, Fe, Zn, Mn, Ba, Ca, Mo, V, As, Cu, Co, Ni, Cr and Pb) were determined for dissolved fraction using inductively coupled plasma-mass spectrometry (ICP-MS). pH measurements revealed the occurrence of a slightly acidic precipitation in the investigated points. Among the trace elements, Zn was the most abundant, followed by Al, Fe, Mn, Cu, Ba and V. The analysis of the enrichment factors enabled the identification of the different sources of the analysed elements. The origin of the Al and Fe elements were entirely continental, whereas Zn was primarily associated with human activities. Thus, the atmospheric deposition may be a primary route of exposure to anthropogenic Zn for estuarine biota. <![CDATA[Multivariate Optimization of a Simultaneous Cloud Point Extraction Procedure of Cd, Cu and Ni from Sediments Samples and Determination by ICP OES]]> A simultaneous preconcentration method for cadmium, copper and nickel in samples of sediments and determination by inductively coupled plasma optical emission spectrometry was developed. The method is based on the extraction of the metals as complexes formed with 2-(5-bromo-2-pyridylazo)-5-(diethylamino)-phenol (5-Br-PADAP) at cloud point of the nonionic surfactant polyethylene glycol tert-octylphenyl ether (triton X-114). Optimization was performed using a Doehlert design and constrained mixture design. Desirability function was used to provide a simultaneous optimization of the evaluated responses. The developed method presented limits of quantification of 0.066, 0.149 and 0.191 µg g-1 and an enrichment factor of 18.4, 16.8 and 18.2 fold for cadmium, copper and nickel, respectively. The proposed method was applied in sediment samples collected in the urban stretch of the Contas River (Jequié, BA, Brazil). Adequate accuracy was found by analysis of two certified reference materials (NIST 1646a estuarine sediments and NIST 2702 marine sediment). <![CDATA[Ixorine, a New Cyclopeptide Alkaloid from the Branches of <em>Ixora brevifolia</em>]]> The isolation and structure determination of new cyclic peptide alkaloid ixorine, along with five known constituents frangulanine, syringaresinol, cinnamtannin B-1, daucosterol and mannitol from the branches of Ixora brevifolia are described. The cyclic peptide frangulanine is being described for the first time in the Rubiaceae family. The structures were elucidated on their spectral data basis, mainly one- (1H, 13C, DEPT) and two-dimensional (COSY, NOESY, HSQC and HMBC) nuclear magnetic resonance (NMR) and by comparison with data from the literature. The mixture of two cyclopeptide alkaloids showed weak activity against Leishmania amazonensis. <![CDATA[A Multicomponent Synthesis of 2-Amino-3-cyanopyridine Derivatives Catalyzed by Heterogeneous and Recyclable Copper Nanoparticles on Charcoal]]> An efficient and convenient method was developed for synthesis of 2-amino-3-cyanopyridine derivatives via the four-component coupling reaction between ketone, aldehyde, malononitrile, and ammonium acetate in the presence of 2 mol% copper nanoparticles on charcoal (Cu/C) catalyst. A variety of ketones and aldehydes was used to afford the corresponding products in good to excellent yields. The method is applicable to large-scale operation without any problem. The catalyst could be quantitatively recovered from the reaction mixture by simple filtration and reused at least eight times with almost consistent activity. <![CDATA[Cytotoxicity and Leishmanicidal Activity of Isoniazid-Derived Hydrazones and 2-Pyrazineformamide Thiosemicarbazones]]> The isoniazid-derived hydrazones 2-pyridinecarbaldehyde- (HPCIH), 2-acetylpyridine- (HAPIH), 2-benzoylpyridine- (HBPIH), 2-pyridineformamide- (HPAmIH) and 2-pyrazineformamide- (HPzAmIH) isonicotinoyl hydrazones, as well as the pyrazinamide-derived thiosemicarbazones 2-pyrazineformamide- (HPzAm4DH), N(4)-methyl-2-pyrazineformamide- (HPzAm4M), N(4)-ethyl-2-pyrazineformamide- (HPzAm4E) and N(4)-phenyl-2-pyrazineformamide- (HPzAm4Ph) thiosemicarbazones, were assayed for their action against intracellular amastigote form of Leishmania (Viannia) braziliensis strains and the glioblastoma multiforme (SF-295), colon adenocarcinoma (HCT-116), ovarian cancer (OVCAR-8) and acute myeloid leukemia (HL-60) human tumor cell lines. All compounds exhibited leishmanicidal effects, with concentrations at which 50% of parasites were inhibited (IC50) in the 10.70-18.84 µM range. Moreover, the compounds were up to 30-fold less toxic to macrophages than to the parasites. Pyrazinamide-derived thiosemicarbazones proved to have poor activity against the tumor cell lines at 5 µg mL-1, whereas, in general the isoniazid-derived hydrazones presented good activity, being HAPIH and HBPIH the most potent compounds (IC50 = 0.42-1.5 µM). <![CDATA[Determination of CO<sub>2</sub>, CH<sub>4</sub> and N<sub>2</sub>O: a Case Study for the City of Rio de Janeiro Using a New Sampling Method]]> A new sampling method using polypropylene syringes and chemical analysis by gas chromatography was proposed and applied to determine CO2, CH4 and N2O. The samples' stability was evaluated and compared with the stability of the samples in stainless steel canisters and Tedlar® bags. This methodology was applied to a case study in the urban area of the city of Rio de Janeiro, Brazil. In 2012, annual averages of 507.6 ± 13.2 µmol mol-1 for CO2, 1.95 ± 0.06 µmol mol-1 for CH4 and 325.3 ± 3.4 nmol mol-1 for N2O were obtained. The results for CO2 and CH4 showed peak values in the warmer months and lower values in winter. This CO2 behavior is the opposite of that observed in studies performed in many other cities around the world and may be climate-related. CH4 and N2O inputs are probably due to the evaporation of liquid and solid waste both from landfill sites located within the city boundaries and from polluted rivers and canals. Additionally, other anthropogenic sources may be considered, such as the release of CH4 by the gas fuel network of the urban area and the emissions due to the use of compressed natural gas by light vehicles. <![CDATA[PdCl<sub>2</sub> Immobilized in Polyacrylamide: a Low Cost and Eco-Friendly Catalyst for Suzuki-Miyaura Reactions]]> PdCl2 immobilized in polyacrylamide (PAM), named Pd/PAM, produced at an extremely low cost, was found to be an efficient catalyst for Suzuki-Miyaura cross-coupling reactions. Iodo- and bromoarenes may couple with phenylboronic acid under eco-friendly conditions (i.e., phosphine-free and with ethanol as the solvent) to give excellent product yields. Aryl chlorides, in contrast, were found to be unsuitable reagents in this context, yielding modest results. The recyclability of Pd/PAM is limited because of PdII leaching, which leaves only the base polymer on the surface after six runs. The Pd/PAM catalyst was initially prepared via the formation of a PAM hydrogel using an aqueous PdCl2 solution. After drying, the solid Pd/PAM was characterized by scanning electron microscopy (SEM), electron-dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), and inductively coupled plasma optical emission spectrometry (ICP OES). <![CDATA[Exploring the Versatility of an Atomic Absorption Spectrometer: Application to Direct Molecular Determination of Caffeine and Propranolol]]> A simple strategy using an atomic absorption spectrometer (AAS) for the direct determination of molecular compounds is proposed. The determination of caffeine and propranolol employing atomic absorption instrumentation was conducted, monitoring the emission lines of Fe (271.9 nm) and Mg (285.2 nm), respectively, using a quartz cuvette (1.0 cm) positioned in the burner head. Samples or standards were inserted into the cuvette in order to obtain the absorbance measurements. The parameters of merit were evaluated and the limits of detection were 0.46 and 0.56 mg L-1 for caffeine and propranolol, respectively, with a coefficient of determination R2 &gt; 0.999. The methods developed were applied to the determination of caffeine and propranolol in real samples of beverages and pharmaceutical formulations, respectively. To evaluate the accuracy of the proposed methodologies the results obtained by atomic absorption spectrometer were compared with those obtained by molecular absorption spectrophotometry (UV-Vis) and high performance liquid chromatography (HPLC) or capillary electrophoresis (CE). <![CDATA[Simultaneous Determination of Thorium and Uranium in Mineral Fertilizers by Inductively Coupled Plasma Optical Emission Spectrometry]]> The simultaneous determination of thorium and uranium in mineral fertilizers by inductively coupled plasma optical emission spectrometry (ICP OES) was optimized. The three-level factorial design was applied to optimize the operating conditions of radiofrequency power and nebulizer gas flow rate. The analytical method was specific and selective for both elements.