Scielo RSS <![CDATA[Journal of the Brazilian Chemical Society]]> vol. 29 num. 4 lang. pt <![CDATA[SciELO Logo]]> <![CDATA[Development of a Novel and Simple Electroanalytical Procedure for the Determination of Copper in Biofuel Employing a Sensor Based on Vulcan Functionalized with Carbazone]]> A novel and simple electroanalytical method for the determination of Cu2+ in biodiesel samples by stripping voltammetric analysis was developed. The method employs a carbon paste electrode (CPE) modified with Vulcan carbon, previouly functionalized with carbazone (CBZ). The CPE/Vulcan-CBZ sensor promoted a significant increase in the analytical signal obtained from copper as compared to unmodified CPE, and the CPE modified with Vulcan carbon (CPE/ Vulcan). Vulcan-CBZ, Vulcan and CBZ materials were characterized by Fourier transform infrared spectroscopy (FTIR) technique. The electrochemical behavior of the sensor was evaluated using cyclic voltammetry (CV) and square-wave anodic stripping voltammetric (SWASV) techniques. The CPE/Vulcan-CBZ modified electrode showed excellent response and was able to detect Cu2+ at nanomolar levels. The electrochemical method is based on preconcentration of Cu2+ ions on the CPE/Vulcan-CBZ at 0.35 V vs. Ag/AgCl(sat) in 0.2 mol L-1 ammonium sulfate solution ((NH4)2SO4), pH 3.5, during 120 s, followed by subsequent chemical stripping. The analytical signal showed a linear response for Cu2+ concentrations in the range from 6 to 190 nmol L-1 (r = 0.998), with a detection limit of 1.2 nmol L-1. The sensor was successfully applied for the determination of Cu2+ in biodiesel and the average recovery varied between 97.0 and 102.8% for the soybean biodiesel samples and between 109.6 and 111.0% for the babassu biodiesel samples showing a good accuracy for the proposed method. <![CDATA[Qualitative and Quantitative Chemical Investigation of Orthopedic Alloys by Combining Wet Digestion, Spectroanalytical Methods and Direct Solid Analysis]]> In this study, two laser-based techniques, laser-induced breakdown spectroscopy (LIBS) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) were used for analytical signal evaluation of Ti, Al, and V and investigation of possible harmful elements eventually present as minor elements in Ti alloys. Due to the lack of certified reference materials, samples were also analyzed by wavelength dispersive X-ray fluorescence (WDXRF) and inductively coupled plasma optical emission spectrometry (ICP OES) after microwave-assisted digestion. To maximize the efficiency of LIBS and LA-ICP-MS, operational conditions were adjusted aiming to find optimal analytical performance. LIBS showed several Ti emission lines and few signals for Al and V. LA-ICP-MS was able to detect all three major constituents. For quantitative analysis, the correlation of intensity signals from LIBS analysis with reference values obtained by ICP OES was not successful, showing that there are still difficulties for quantification using solid samples. Measurements using ICP OES showed that additionally to major constituents, only Fe was present in concentrations around 0.2%. Analysis by WDXRF confirmed the presence of Fe. Results using both methods, i.e., ICP OES and WDXRF, were in good agreement. <![CDATA[Electrocatalytic Oxidation Removal of Phenol from Aqueous Solution with Metal Oxides Doped Carbon Aerogel]]> Metal oxides (manganese oxide, MnO, manganese dioxide, MnO2, copper oxide, CuO, zinc oxide, ZnO and nickel oxide, NiO) doped carbon aerogel (CA) were prepared and used as catalysts in heterogeneous oxidation of phenol from aqueous solution in a three-dimensional (3D) electrode reactor. Textural characterization of metal oxides doped CA showed that the metal oxide nanoparticles are dispersed separately throughout the carbon matrix. The experimental results showed that phenol was degraded mainly by hydroxyl (•OH) radicals. The presence of metal oxides accelerated •OH radical generation. The •OH radical quantity depends on the type of metal oxide. The n-type semiconductor was more active than p-type semiconductor for •OH radical generation. Furthermore, acceleration effect of •OH radical generation catalyzed by metal oxides doped CA was investigated and demonstrated. <![CDATA[A New Method for the Determination of Creatinine in Urine Samples Based on Disposable Pipette Extraction]]> A method based on disposable pipette extraction (DPX) was successfully applied to creatinine determination in urine samples analysis using liquid chromatography with ultraviolet spectrophotometric detection (DPX/LC-UV). DPX variables, number of draw/eject cycles, sample pH, and type of the desorption solvent, were employed in a factorial experimental design to optimize the sorption equilibrium and time analysis. Among the evaluated DPX variables, the highest extraction efficiency was obtained with 500 µL of urine sample mixed with 1 mL of borate solution (pH 9) with one draw/eject cycle followed by liquid desorption of 1 mL of methanol in seven draw/eject cycles. The developed DPX/LC-UV method showed a linear response from the limit of quantification of 0.317 to 3.390 g L-1 with r2 = 0.996 and inter-day precision with a coefficient of variation below 8.8%. Based on these results, the proposed method can be a useful tool for determining the creatinine levels in urine samples. <![CDATA[Synthesis and Antibacterial Evaluation of 2-Ethyl-1-(4-substituted)phenyl-1 <em>H</em>-imidazole Derivatives as Open-Chain Analogues of 7-Alkoxyl-4,5-dihydro-imidazo[1,2-<em>a</em>]quinolines]]> A novel series of 2-ethyl-1-(4-substituted)phenyl-1H-imidazole derivatives was designed, synthesized, and tested for its antibacterial activity against various bacterial strains. Most of the synthesized compounds showed potent inhibition of several Gram-positive and Gram-negative bacterial strains with minimum inhibitory concentration (MIC) values in the range of 4-256 nmol mL-1 in vitro. The compound [2-ethyl-1-(4-pentoxy)phenyl-1H-imidazole] exhibited the most potent inhibitory activity. The MIC of this compound against S. aureus was found to be 8 nmol mL-1, smaller than that of the reference agents, ciprofloxacin and amoxicillin. Furthermore, the compound exhibited modest activity against several bacterial strains in a dose range of 8-256 nmol mL-1. <![CDATA[HR-MAS NMR Allied to Chemometric on <em>Hancornia speciosa</em> Varieties Differentiation]]> This work describes the potential of chemometric analyses applied to 1H high-resolution magic angle spinning nuclear magnetic resonance (1H HR-MAS NMR) data for the chemotaxonomic investigation of Hancornia speciosa (Apocynaceae) varieties. This plant, popularly known as mangaba, has a complex morphological differentiation and thus chemical analyses can be used for their taxonomic classification. In comparison to traditional techniques, 1H HR-MAS NMR allied with chemometrics provided a simple and low cost method for chemotaxonomy. Leaves of four varieties of H. speciosa from a common garden experiment was studied and demonstrated that H. speciosa var. speciosa differs from others due to its specific metabolic profile, and var. pubescens was discriminated based on its high phenolic compound content. The distinction between the latter variety and gardineri is important once it allows for the selection of samples with greater commercial value, once they produce the largest and heaviest fruits. <![CDATA[Design, Synthesis, Biological Evaluation and Molecular Modeling Studies of Novel Eugenol Esters as Leishmanicidal Agents]]> Leishmaniasis is a neglected pathology with a high incidence worldwide, and is a governmental health issue due to the increased morbidity and mortality associated with the disease and a scarce therapeutic arsenal. Cysteine proteases have been investigated as targets for new drugs because they are essential in the infectivity of the parasite during its interaction with the host and in its nutrition. This study aimed to identify compounds with leishmanicidal activity, by synthesis of compounds, in vitro evaluation of their biological activity and using molecular modeling and bioinformatics tools. The study of biological activity demonstrated that one compound showed inhibitory activity against the enzyme rCPB 2.8 at a concentration of 100 µmol L-1. Activation of the enzyme rCPB 2.8 by other 4 compounds was also verified, which may be related to the interaction of these compounds with an allosteric site on the enzyme. <![CDATA[Development and Validation of a Rapid and Reliable RP-HPLC-PDA Method for the Quantification of Six Diterpenes in <em>Copaifera duckei</em>, <em>Copaifera reticulata</em> and <em>Copaifera multijuga</em> Oleoresins]]> Oleoresins from Copaifera species are extensively used in folk medicine in Brazil, which are employed mainly in the production of cosmetic formulations in Brazil, North America and Europe. Considering the lack of validated analytical methods for the analyses of diterpenes in Copaifera oleoresins, it was developed a validated and reliable reversed-phase high-performance liquid chromatography with photodiode array detection (RP-HPLC-PDA) method for the analysis of six diterpenes, including: (-)-polyalthic acid; (13E)-ent-labda-7,13-dien-15-oic acid; ent-8(17)-labden-15,18-dioic acid; (-)-copalic acid; (-)-3β-acetoxycopalic acid and (-)-3β-hydroxycopalic acid. These compounds were isolated from C. duckei, C. reticulata and C. multijuga oleoresins by chromatographic means. The analytical curves were linear with regression coefficients (r2) between 0.9903 and 0.9999. The limits of detection (LOD) and quantification (LOQ) values were 0.35 to 3.09 µg mL-1 and 1.05 to 9.36 µg mL-1, respectively. The method also displayed good precision and accuracy. The developed analytical method is reliable and a useful tool for the analysis of Copaifera oleoresin and its products. <![CDATA[Two Novel Donepezil-Lipoic Acid Hybrids: Synthesis, Anticholinesterase and Antioxidant Activities and Theoretical Studies]]> Alzheimer disease (AD) is a complex disease related to multiple pathogenic mechanisms. A strategy to develop effective drugs is based on the so-called multi-target directed ligands (MTDL) by using hybrid compounds. So, in the present study, we have designed and synthesized two hybrids, containing the indanone-piperidine moiety of donepezil, a drug approved for the treatment of AD, and the lipoic acid scaffold, an antioxidant compound endowed with neuroprotective effects. One hybrid was synthesized in four steps with 42% global yield, and the other hybrid in six steps with 19% global yield. The latter hybrid displayed moderate inhibitory activity against human acetylcholinesterase (hAChE) and greater activity against human butyrylcholinesterases (hBuChE). The selectivity for hBuChE was further rationalized by theoretical study. Importantly, the second hybrid showed a good antioxidant activity, exhibiting better ability in scavenging 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals than lipoic acid. <![CDATA[Microemulsion as Sample Preparation for Direct Flame Atomic Absorption Spectrometry (FAAS) Determination of Total Iron in Crude and Refined Vegetable Oils]]> This work proposed a novel, relatively low-cost and rapid analytical method using microemulsion as sample preparation to determine iron (Fe) in vegetable oils by flame atomic absorption spectrometry technique (FAAS). The vegetable oil microemulsions were obtained by mixing appropriate proportions of the crude and refined vegetable oil, Triton® X-100, 1-propanol and nitric acid 50% (v v-1). Moreover, an external calibration method was established using aqueous Fe standards instead of expensive and unstable organometallic standards. The limits of detection and quantification were 0.40 and 1.3 mg kg-1 of oil, respectively. The accuracy was checked by recovery studies (with recoveries ranging 84-105%) and by Fe determination in digested vegetable oil samples by inductively coupled plasma optical emission spectrometry (ICP OES) as comparative procedure. The proposed analytical method was efficient to determine Fe in crude and refined vegetable oils from various vegetable sources, besides being suitable for routine analyses due to its simplicity. <![CDATA[Magnetic Solid-Phase Extraction Combined with Dispersive Liquid-Liquid Microextraction Followed by HPLC for Determination of Four Aromatic Amines Released from Azo Dyes in Paper Samples]]> A novel extraction technique combining dispersive liquid-liquid microextraction (DLLME) with magnetic solid-phase extraction (MSPE) is presented for pre-concentration of four primary aromatic amines (PAAs) released from azo dyes in paper samples prior to high performance liquid chromatography (HPLC). n-Octanol was used as the extractant and hydrophobic oleic acid modified Fe3O4 nanoparticles (Fe3O4@OA NPs) as an efficient adsorbent was applied to retrieve the PAAs-containing n-octanol in the DLLME step. Because of the rapid mass transfer associated with the DLLME and MSPE steps, fast extraction could be achieved. The main parameters affecting the efficiency of MSPE-DLLME procedure of PAAs were investigated and optimized. Under optimum conditions, the recoveries ranged from 79.6 to 88.5% and the limits of detection (LODs) were in the range of 0.21-1.16 ng mL-1 (S / N = 3). The intra-day precision (relative standard deviation (RSD)) was below 7.8% and inter-day RSD was less than 11%. <![CDATA[Antimicrobial Activity of <em>Paepalanthus planifolius</em> and its Major Components against Selected Human Pathogens]]> The chemical investigation of ethyl acetate extract from Paepalanthus planifolius capitula resulted in the identification of 1H-naphtho[2,3-c]pyran-1-one,9-[(6-O-β-D-glucopyranosyl-β-D-glucopyranosyl)oxy]-3,4-dihydro-10-hydroxy-7-methoxy-3-methyl, semi-vioxanthin 9-O-β-D-glucopyranoside, toralactone-9-O-β-D-glucopyranoside, paepalantine-9-O-β-D-glucopyranoside, semi-vioxanthin, 1H-naphtho[2,3-c]pyran-1-one,3,4-dihydro-9,10-dihydroxy-5,7-dimethoxy-3-methyl, vioxanthin and paepalantine dimer, and also the isolation and identification of a new naphthopyranone dimer named planifoliusin A. The chemical structures of two compounds were elucidated by performing spectroscopic 1D and 2D nuclear magnetic resonance (NMR) experiments and spectrometric HRMS (high-resolution mass spectrometry) analysis. Other six naphthopyranone dimers were proposed by MS fragmentation patterns. The minimum inhibitory concentration (MIC) values for vioxanthin (7.8 µg mL-1), planifoliusin A (15.6 µg mL-1) and the ethyl acetate extract (31.2 µg mL-1) showed antimicrobial activity against Staphylococcus aureus (ATCC 25923). <![CDATA[Targeted-Analysis of β-Carboline Alkaloids in Passionfruit (“Maracujá”) by SBSE(PDMS)-LC/Flu and UHPLC-MS]]> Samples of pulp and seeds of sour (P. edulis) and sweet (P. alata) passionfruit were subjected to targeted analysis to identify β-carboline alkaloids, using combined UHPLC-MS (ultrahigh performance liquid chromatography-mass spectrometry) and SBSE(PDMS) (stir bar sorption extraction using polydimethylsiloxane as stationary phase) for sample preconcentration. All the samples contained harmane and harmine; harmaline was found only in P. alata seeds and in P. edulis pulp, while harmalol was found only in P. alata seeds. An analysis of sweet passionfruit by SBSE(PDMS) combined with LC/Flu (liquid chromatography/fluorescence detection) indicated 1.03 × 10-1 ± 3.05 × 10-3 µg harmane L-1 pulp and 7.44 × 10-5 ± 2.55 × 10-6 µg harmane g-1 seeds, but harmine was not detectable by the quantitative method. Our findings underscore the need for further studies about passionfruit food safety, in view of the potential toxicity of β-carboline alkaloids.