Scielo RSS <![CDATA[Journal of the Brazilian Chemical Society]]> vol. 29 num. 5 lang. en <![CDATA[SciELO Logo]]> <![CDATA[Sustainability & Diversity through Chemistry: Together, We Made that Happen]]> <![CDATA[Determination of Enantioselectivities by Means of Chiral Stationary Phase HPLC in Order to Identify Effective Proline-Derived Organocatalysts]]> The pyrrolidine fragment is a privileged scaffold within chiral ligands employed in coordination complexes exhibiting catalytic activity in asymmetric reactions and, more recently, as enantioselective organocatalysts per se. Likewise, the employment of (S)-proline as starting material constitutes the most direct form to synthesize those chiral derivatives. Afterwards, a preliminary evaluation of the catalytic performance of proline-derived compounds consists of screening many prochiral substrates in well standardized model reactions such as Michael additions and Mannich reactions, with the aim of identifying “broad spectrum” catalysts for more complex synthetic applications. Therefore, a central part of this process involves the fast and direct measurement of enantioselectivities of optically active adducts. The growing development of chiral stationary phases and thus, the wide commercial availability of chiral columns have consolidated high performance liquid chromatography (HPLC) as the preferred technique to identify the most effective catalysts. <![CDATA[Advances of Submarine Groundwater Discharge Studies in South America]]> Submarine groundwater discharge (SGD) is the hidden portion of water that discharges into the ocean across the ocean-land interface, and it is considered one of the hydrological cycle's major components. Two decades ago, SGD in South America was undocumented, and significant advances on this field has occurred since then. This paper presents the results of SGD investigations, a compilation of the SGD estimations, and the areas lacking of data in South America. The compilation of observed SGD in South America shows that groundwater seepage from the land to the ocean occurs in many environments along the coast. Considering only the few regions for which the total SGD flux was estimated, the SGD flux (ca. 1.2 × 108 m3 day-1) is equivalent in volume to almost 70% of Amazon River discharge. Although the study of SGD in South America has greatly advanced, many uninvestigated sites and key questions remain. <![CDATA[Ditryptophan Cross-Links as Novel Products of Protein Oxidation]]> Protein oxidation is an unavoidable consequence of aerobic metabolism. The oxidation of most proteins residues is non-repairable and may affect protein structure and function. In particular, protein cross-links arising from oxidative modifications are presumably toxic to cells because they may accumulate and induce protein aggregation. However, most of these irreversible protein cross-links remain partially characterized. Up to very recently, ditryptophan cross-links (Trp-Trp), in particular, have been largely disregarded in the literature. Here, we briefly review studies showing that Trp-Trp cross-links can be formed in proteins exposed to a variety of oxidants. The challenges to fully characterize Trp-Trp cross-links are discussed as well as their potential roles in protein dysfunction and aggregation. <![CDATA[Electrochemical Systems for Renewable Energy Conversion from Salinity and Proton Gradients]]> Ever-rising energy demand, fossil fuel dependence, and climate issues have harmful consequences to the society. Exploring clean and renewable energy to diversify the world energy matrix has become an urgent matter. Less explored or unexplored renewable energy sources like the salinity and proton gradient energy are an attractive alternative with great energy potential. This paper discusses important electrochemical systems for energy conversion from natural and artificial concentration gradients, namely capacitive mixing (CapMix), mixing entropy batteries (MEB), and neutralization batteries (NB); the working principle and thermodynamic formalism of these systems; and the materials employed in the assembly of these systems. <![CDATA[Green Processing of Strategic Elements Based on Magnetic Nanohydrometallurgy]]> Magnetic nanohydrometallurgy (NHM) is a new process based on engineered superparamagnetic nanoparticles capable of performing as complexing agents for extracting and recovering strategic metals from mineral sources and urban wastes, as well as for removing hazardous elements from contaminated water. Its principles and application are reviewed in this paper. Typical examples involving copper, silver and mercury processing are here discussed, including the exploitation of a novel nanotechnological strategy for capturing and fractionating rare earth elements. <![CDATA[Fundamental Consideration for Electrochemical Engineering of Supercapattery]]> Supercapattery is the generic name for various electrochemical energy storage (EES) devices combining the merits of battery (high energy density) and supercapacitor (high power density and long cycling life). In this article, the principle and applications of EES devices are selectively reviewed as the background for supercapattery development. The focus is on the engineering aspects for fabrication of two types of supercapattery: (i) by coupling a battery electrode with a supercapacitor electrode, or (ii) from materials that possess both the Nernstian and capacitive charge storage capacities. Fundamental rationales are discussed in relation with the designs, such as why the device is always asymmetrical, and what materials are suitable for making supercapattery. Whilst the key is how to optimize device performance in terms of energy capacity, power capability and cycle life, cost is also discussed on resource rich materials such as nanostructured composites and redox electrolytes. <![CDATA[Nanopharmaceuticals and Their Applications in Bladder Cancer Therapy: a Mini Review]]> The primary treatment for high-grade non-muscle invasive bladder cancer (NMIBC) is based on surgery by transurethral resection of bladder tumor (TURBT), followed by intravesical immunotherapy with Bacillus Calmette-Guerin (BCG) to prevent recurrence and to reduce the tumor progression. However, BCG therapy shows several undesirable effects. The current treatment on NMIBC is doxorubicin (DOX), but with high toxicity. Our nanotechnology strategy was done through scaffolds for the NMIBC treatment: graphene oxide (GO) and a nanostructured lipid carrier (NLC). A GO hybrid for administration of DOX and small interfering RNA (siRNA) was developed. This hybrids administered in vivo against NMIBC in rats gave absence of lesions. NLC was prepared by using a mixture of two lipids stabilized by a surfactant and DOX by high homogenization pressure technique. In this case showed a 20% of the animals exhibited benign lesions (papillary hyperplasia), however, in the presence of siRNA reached 40% of rats with benignant lesions. These two scaffolds are potential new drugs for DOX for bladder cancer treatment without any cardiotoxicity problems. <![CDATA[Development of Web and Mobile Applications for Chemical Toxicity Prediction]]> Computational tools are recognized to provide high-quality predictions for the assessment of chemical toxicity. In the recent years, mobile devices have become ubiquitous, allowing for the development of innovative and useful models implemented as chemical software applications. Here, we will briefly discuss this recent uptick in the development of web-based and mobile applications for chemical problems, focusing on best practices, development, usage and interpretation. As an example, we also describe two innovative apps (Pred-hERG and Pred-Skin) for chemical toxicity prediction developed in our laboratory. These applications are based on predictive quantitative structure-activity relationships (QSAR) models developed using the largest publicly available datasets of structurally diverse compounds. The developed tools ensure both highly accurate predictions and easy interpretation of the models, allowing users to discriminate potential toxicants and to purpose structural modifications to design safer chemicals. <![CDATA[Grafting of Quinones on Carbons as Active Electrode Materials in Electrochemical Capacitors]]> The electrochemical performance of electrochemical capacitors can be improved with electroactive quinone molecules. Systems based on redox active electrolyte as well as physisorbed and chemically grafted molecules have been investigated. In all these cases, carbon materials were used as substrate and electrode material. This short review will mainly describe work related to these systems and materials from the authors' laboratories. Nonetheless, some important studies from other research groups will be discussed. <![CDATA[Natural Products from Marine Invertebrates and Microorganisms in Brazil between 2004 and 2017: Still the Challenges, More Rewards]]> The Brazilian marine biodiversity represents a unique, yet underexplored resource of biologically active compounds. This review provides an analysis of the development of marine natural products chemistry in Brazil within the period comprised between 2004 and 2017. Emphasis is directed towards marine invertebrate and marine microorganisms metabolites, including isolation, structure analysis, biosynthesis, bioactivities and total synthesis. An overview of the research on marine natural products by Brazilian researchers is also discussed, as well as perspectives for the development of the chemistry of marine natural products in Brazil. <![CDATA[Flow Analysis: Looking Back and Forward]]> Flow analysis changed significantly the way of performing chemical analysis by (i) mechanization of analytical procedures in a continuous flowing stream with minimal sample intercontamination; (ii) analytical measurements without attaining chemical equilibria, thus increasing the applicability of kinetic methods and allowing the exploitation of non-quantitative processes; (iii) exploitation of concentration gradients and (iv) use of unstable reagents or measurement of unstable products. Flow-based procedures are generally characterized by high sample throughput, improved precision, minimized waste generation, and often better selectivity. The performance of detection systems is usually improved because of the in-line sample conditioning and measurements under reproductive dynamic conditions and timing. However, after achieving several innovations, perspectives for further developments have been questioned mainly because of the recent decrease in the number of publications on flow analysis. The aim of this review is then to discuss the impact of flow-based methods on chemical analysis, emphasizing recent applications and developments, including miniaturization, bioanalysis, microextractions, green analytical chemistry and synergic hyphenation with other techniques and processes. The author's personal view about research perspectives in the field is also presented. <![CDATA[Computer-Guided Total Synthesis of Natural Products. Recent Examples and Future Perspectives]]> Quantum chemical calculations of nuclear magnetic resonance (NMR) shifts and coupling constants have been extensively employed in recent years mainly to facilitate structural elucidation of organic molecules. When the results of such calculations are used to determine the most likely structure of a natural product in advance, guiding the subsequent synthetic work, the term “computer-guided synthesis” could be coined. This review article describes the most relevant examples from recent literature, highlighting the scope and limitations of this merged computational/experimental approach as well. <![CDATA[Functionalization of P3HT with Various Mono- and Multidentate Anchor Groups]]> Due to its favorable optoelectronic properties and the accessibility via Grignard metathesis (GRIM) polymerization, poly(3-hexylthiophene) (P3HT) is one of the most applied conjugated polymers. The ‘living' nature of GRIM polymerization enables the modification of the polymer and the installation of desired properties. In the present study, two versatile approaches for the synthesis of anchor group-modified P3HT have been developed, which enable the functionalization of various inorganic nanoparticles. Depending on the polymerization conditions, mono- and bifunctional ethynyl-terminated P3HT or solely monofunctionalized aldehyde-terminated P3HT was synthesized. Afterwards, the quantitative introduction of amine, mono- and multidentate disulfide and catechol anchor groups was performed by copper-catalyzed 1,3-dipolar cycloaddition or via imine formation reactions. The influence of the polymeric ligand structure on the functionalization of nanoparticles was then investigated for CdSe@ZnS quantum dots and TiO2 nanorods by transmission electron microscopy (TEM) and infrared (IR) spectroscopy. <![CDATA[In situ Determination of K, Ca, S and Si in Fresh Sugar Cane Leaves by Handheld Energy Dispersive X-Ray Fluorescence Spectrometry]]> A portable energy dispersive X-ray fluorescence spectrometer was evaluated in the in situ analysis of fresh sugar cane leaves for real time plant nutrition diagnosis. Fresh leaf fragments (n = 10 sugar cane varieties; 20 fragments per leaf; 2 measurement sites per fragment) were irradiated and the averaged data from X-ray characteristic emission lines intensities (for K, Ca, S and Si Kα lines) were in close agreement with mass fraction data obtained by a validated comparative method. The linear correlation coefficients (r) ranged from 0.9575 for Ca to 0.9851 for Si. The obtained limits of detection were at least two-fold lower than the critical nutrient levels. Manganese can also be properly determined, but validation still requires more robust calibration models. The proposed method is a straightforward approach towards the fast evaluation of the nutritional profile of plants avoiding time-consuming steps, which involve drying, grinding, weighing, and acid digestion. <![CDATA[CO Tolerance and Stability of Proton Exchange Membrane Fuel Cells with Nafion<sup>®</sup> and Aquivion<sup>®</sup> Membranes and Mo-Based Anode Electrocatalysts]]> This work presents a CO tolerance study of PtMo/C (70:30, Pt:Mo) and Pt/MoO2-C anode catalysts on proton exchange membrane fuel cells (PEMFC) with Nafion® and Aquivion® ionomer membranes. Results denote improved activity for the hydrogen oxidation reaction (HOR) in the presence of CO on both anode catalysts at 85 ºC. Experiments of identical location transmission electron microscopy evidenced very good stability of the Pt particles along an accelerate stress test (AST) applied to the Mo-based anode catalysts. However, a crossover of degradation Mo products originated in the anode and going to the cathode takes place along this anode AST, causing a PEMFC performance decay. A very little effect of the nature of the membrane, Nafion® or Aquivion®, is observed over these crossover phenomena. Results also denote that when operating at appropriate high temperatures (105 ºC for Nafion® and 125 ºC for Aquivion®), there is no need of incorporating unstable oxophilic transition metals on Pt to achieve improved CO tolerance on PEMFCs, when the CO level in the hydrogen fed is of the order of 100 ppm. <![CDATA[Biosynthetic Insights into p-Hydroxybenzoic Acid-Derived Benzopyrans in Piper gaudichaudianum]]> Piper gaudichaudianum Kunth (Piperaceae) accumulates gaudichaudianic acid, a prenylated benzopyran, as its major component. Interestingly, this trypanocidal compound occurs as a racemic mixture. Herein, transcriptomic investigations of Piper gaudichaudianum using the RNA-seq approach are reported, and from the analysis of the transcripts expressed it was possible to propose a complete biosynthetic pathway for the production of gaudichaudianic acid, including the steps that originate its precursor, p-hydroxybenzoic acid. Peperomia obtusifolia (L.) A. Dietr. (Piperaceae) also accumulates racemic benzopyrans, however, its chromanes originate from the polyketide pathway, while the chromenes from Piper derives from the shikimate pathway. Recent transcriptomic and proteomic studies of the former species did not identify polyketide synthases involved in the production of the benzopyran moiety, but revealed the expression of tocopherol cyclase, which may be responsible for the cyclization of the 3,4-dihydro-2H-pyran ring. The analysis of the enzymes involved in the secondary metabolism of Piper gaudichaudianum and the comparison with the data previously obtained from Peperomia obtusifolia can provide valuable information on how these compounds are biosynthesized. <![CDATA[Production of Furan Compounds from Sugarcane Bagasse Using a Catalytic System Containing ZnCl<sub>2</sub>/HCl or AlCl<sub>3</sub>/HCl in a Biphasic System]]> In this work, two catalytic systems combining Lewis and Brønsted acids (ZnCl2/HCl and AlCl3/HCl) were applied in a tetrahydrofuran (THF)/NaClaq biphasic system to produce furan compounds from plant polysaccharides. The following cellulosic matrices were applied for this purpose: α-cellulose, microcrystalline cellulose and both native and steam-exploded sugarcane bagasse. The AlCl3/HCl catalytic system afforded the best yields for α-cellulose conversion to furan compounds (hydrolysis followed by dehydration). The highest yields of 5-(hydroxymethyl)-furfural (HMF) and furfural were 44.0 and 92.2% for AlCl3/HCl and 36.5 and 81.4% for ZnCl2/HCl, respectively. Cellulosic materials with lower crystallinity indexes afforded the best performance in hydrolysis followed by dehydration, giving relatively high yields of HMF and furfural. The HMF yields were similar for both native and steam-exploded sugarcane bagasse and the presence of lignin had a negative effect on HMF production. The highest furfural yield from native sugarcane bagasse was 60.6% with AlCl3/HCl catalytic system. <![CDATA[An Environmentally Friendly Procedure to Obtain Flavonoids from Brazilian Citrus Waste]]> Currently, most food waste is used as animal feed and this process does not take advantage of the available chemical composition. A Brazilian example is the citrus fruit processing wastes (CFPW), which have begun to draw attention due to their biological importance. In order to access the main compounds of this matrix, an efficient and environmentally friendly procedure was tested. From this extract, flavonoids as naringenin, hesperitin, chrysoeriol, sinensetin, 3,5,6,7,3',4'-hexamethoxyflavone, nobiletin, 5-methoxysalvigenin, 3,5,6,7,8,3',4'-heptamethoxyflavone, 3,5,6,7,4'-pentamethoxyflavone and isosakuranetin were identified by high performance liquid chromatography (HPLC-UV), liquid chromatography-mass spectrometry (LC-MS) and liquid chromatography-nuclear magnetic resonance (LC-NMR). This study describes the potential use of citrus waste as a source of biologically active compounds. The extraction method proposed for this work was not expensive and the flavonoids were obtained in large amounts, thus, this extraction method is being developed using pilot plant scale-up techniques and will soon be available to the industry at a low cost. <![CDATA[Electrodeposition of Prussian Blue/Carbon Nanotube Composites at a Liquid-Liquid Interface]]> The iron complex hexacyanoferrate (Fe4[Fe(CN)6]3), known as Prussian Blue (PB), was electrodeposited over a free-standing carbon nanotube (CNT) film assembled at the interface between two immiscible liquids, water and 1,2-dichlorobenzene. Polarization of the interface achieved through a fixed potential or under potential variation enabled iron present inside CNTs to generate a stable CNT/PB composite. We report herein on the observation that the deposition of PB is dependent on both the pH and applied potential. It was found that aqueous phases containing K3[Fe(CN)6] can decompose under an applied potential, while those containing K4[Fe(CN)6] presented more stable behavior making it a suitable precursor for PB synthesis. The electrodeposition and modification of the interface was followed by in situ spectroelectrochemical Raman spectroscopy, which indicated that an increase in signal due to PB formation was acompanied by changes in the CNT bands due to modification of the CNT walls by decoration with PB, forming a composite structure. <![CDATA[Determination of Target Pesticide Residues in Tropical Fruits Employing Matrix Solid-Phase Dispersion (MSPD) Extraction Followed by High Resolution Gas Chromatography]]> A simple method based on matrix solid-phase dispersion (MSPD) extraction and gas chromatography with electron-capture detection (GC-ECD) is employed to determine pesticide residues in the following tropical fruits: banana, mango, melon, papaya and pineapple. In the MSPD proposed method, C18, silica gel and ethyl acetate presented the best results in the extraction, clean-up and elution steps, respectively. Spiked blank samples were used to minimize the matrix effect in the chromatographic determination. The validation process was conducted at three different concentration levels of spiked samples (0.50-2.50 µg g-1) in within-a-day and in among days assays. The limits of detection for the pesticides ranged from 4.0 to 23 µg kg-1. The method showed acceptable selectivity, coefficients of correlation higher than 0.997, and recovery between 76-105%. The within-a-day precision was assessed through the relative standard deviation (2.8-19%) for the different levels of spiked samples tested. <![CDATA[Simultaneous Multienzymatic Screening with Fluorogenic Probes]]> The simultaneous screening of multiple enzyme activities in a single assay has numerous advantages over the traditional format, since it decreases sampling errors, allows savings in reagents and consumables and reduces the time and labor required to conduct the assays. In the present study, a direct and sensitive assay for the simultaneous detection of epoxide hydrolase and esterase (or lipase) activities was developed. Signal overlap is avoided by synthesizing fluorogenic probes with enzyme-specific alkyl linkers, connected to different fluorophores (resorfurin and umbelliferone), which exhibit emission spectra at different wavelengths. The simultaneous assays were conducted in microplate format with the fluorogenic probes monitored in the same well that uses microorganisms as enzyme source. Our results show that the fluorescent signal from each of the probes used here can be discriminated, allowing multiple enzyme activity detection and quantitation. <![CDATA[Total Synthesis of Altissimacoumarin D, a Small Molecule Sirtuin1 Activator]]> The total synthesis of the plant natural product altissimacoumarin D was achieved by the Mitsunobu alkylation of isofraxidin by geraniol. Isofraxidin was prepared from 2,4-dihydroxybenzaldehyde in five steps. The key reaction was the Knoevenagel condensation of an ortho-hydroxybenzaldehyde with Meldrum's acid under neutral conditions in water and one-pot acid catalyzed cyclization to the coumarin. <![CDATA[Mass Spectrometry Analysis of Protonated Marine Natural Product Seriniquinone]]> Seriniquinone is a natural quinone isolated from a rare marine bacterium of the genus Serinicoccus. This secondary metabolite has been shown to have anticancer properties, which has raised attention of the scientific community. In this short report, we present the first investigation of the gas-phase chemistry fragmentation reactions of seriniquinone in electrospray ionization tandem mass spectrometry (ESI-MS/MS), to be further applied in pharmacokinetics and metabolism studies. All the proposals herein were supported by computational chemistry.