Resumo em Inglês:

The synthetic versatility and the potential applications of porphyrins and analogues in different fields have aroused special interest in their study, especially to mimic biological systems, such as cytochrome P-450. The ability of the porphyrin tetrapyrrolic core to accommodate metal ions of varying charges can modulate the type of application of these compounds. As a contribution, in this special number in honor to the Brazilian women who have devoted their lives to the growth and dissemination of chemistry knowledge, we report the advances in porphyrin research in Brazil for catalytic purposes and other applications, beginning at the Universidade de São Paulo (USP) at Ribeirão Preto. We also discuss some works that have resulted from joint research effort between Brazilian researchers and Portuguese colleagues from the Universidade de Aveiro, Portugal, working in the porphyrin field.

Resumo em Inglês:

Quantum dots (QDs) are semiconductor nanocrystals, which present unique photophysical properties, enabling their application as new fluorescent platforms for biomedical sciences. Colloidal QDs are end-capped with organic or inorganic compounds, not only to prevent their agglomeration but also to provide reaction sites for the attachment of targeting (bio)molecules, nanoparticles or other interfaces, for specific biological purposes. The (bio)conjugation can involve non-covalent or covalent interactions, which can be accomplished through different strategies. The final assembly needs to maintain its chemical and optical stability and biochemical functionality. Although a relative good comprehension of the experimental procedures has been established, the bioconjugation process is still a challenge. The present manuscript aims to review the main (bio)conjugation strategies successfully applied to QDs, describing the steps necessary to prepare stable targeting fluorescent nanoplatforms, as well as some usual methods used to evaluate and optimize this process.

Resumo em Inglês:

A new tetraglycosylated flavonoid derivative of kaempferol was isolated from the butanol extract of leaves of Platycyamus regnellii (Fabaceae) using high-speed countercurrent chromatography (HSCCC). The butanol extract (960.5 mg) was initially fractionated with the solvent system EtOAC-BuOH-H2O 2:8:10 (v/v/v) (elution in normal phase mode). The fractions containing the major tetraglycosylated flavonoid were further purified with the same solvent system by modifying the ratios to 3:7:10 (v/v/v) and alternating the elution to reversed phase mode. The structure of the isolated flavonoid (48.1 mg, 99.7% purity by ultra-high performance liquid chromatography with diode array detector (UHPLC-DAD)) was characterized by spectrometric and spectroscopic methods and identified as kaempferol 3-O-β-D-glucopiranosyl-(1®2)-α-L-rhamnopiranoside-(1®6)-α-L-rhamnopiranoside-7-O-α-L-rhamnopiranoside. Other minor flavonoids were also detected and tentatively identified using ultra-high performance liquid chromatography with diode array detector coupled to mass spectrometry using the electrospray ionization interface (UHPLC-DAD-ESI-MS/MS). By using the latter technique, a second tetraglycosylated flavonol with an O-methyl substituent (either rhamnetin, 3-O-methyl-quercetin or isorhamnetin) was detected, together with a triglycosylated kaempferol and diglycosylated flavonoids (either rhamnetin, 3-O-methyl-quercetin or isorhamnetin).

Resumo em Inglês:

The main objective of the present work is the investigation of a new method for starch hydrolysis. For this, we proposed the acid hydrolysis under the action of an external electric field, able to develop a faster reaction than the conventional one. Corn starch with 18% amylose was subjected to a fixed voltage, varying the external electric field application time and the number of cycles. Morphology, crystallinity, and thermal stability of the starches were investigated by optical and scanning electron microscopy (SEM), X-ray diffraction (XRD), and small-angle X-ray scattering (SAXS). The results showed that the acid hydrolysis coupled with an external electric field allows a significant reduction in hydrolysis time, due to the orientation of the electrolyte ions. Cavities were observed at the surface of hydrolyzed starches after treatment. However, the principal feature is related to the increase of the granule crystallinity with increasing hydrolysis time. The results suggest that the starches treated by this new method are interesting candidates for application in the food industry if greater gelatinization resistance is required.

Resumo em Inglês:

The multi-energy calibration (MEC) was evaluated for the determination of Ca, Cu, Fe, K, Mg, Na, P, S, and Zn in meat samples by inductively coupled plasma optical spectrometry (ICP OES). This calibration method consists of using only two calibration standards and several atomic and ionic emission wavelengths with different sensitivities to determine the analyte concentration in the sample. Both calibration mixtures are prepared using the same amount of sample, which contributes to minimize matrix effects. The accuracy was evaluated using two certified reference materials, bovine liver (SRM 1577c) and bovine muscle (SRM 8414), with recoveries within 87-107% range. The method was applied for the determination of the analytes in meats of chicken, sheep loin, sheep carcass and bovine, and prove to be usable in samples with different characteristics.

Resumo em Inglês:

This study aims at identifying and discriminating gunshot residue (GSR) from conventional ammunition of six different calibers by total reflection X-ray fluorescence (TXRF) and pattern recognition by principal component analysis (PCA). GSR samples were collected from hands of volunteer shooters with swabs moistened with deionized water and were extracted with 5% v v-1 nitric acid. Aliquots were deposited on quartz disks for further determination by TXRF of the elements Al, S, Ca, K, Mn, Fe, Ni, Cu, Zn, Br, Sr, Sb, Ba and Pb, whose concentrations were imported into the MATLAB® software for PCA execution. The method proved to be adequate for identification of one- and three-shot residue inorganic components from .40, 9 mm, .380, .38 and .308 calibers, and of three-shot residues from .32 caliber, as well as for sample discrimination as a function of the conventional ammunition calibers studied.

Resumo em Inglês:

Hybrid monolithic columns present characteristics of both silica and organic monoliths, such as good mechanical properties, wide pH tolerance, high permeability and stability and little swelling or shrinkage. A common way to prepare this type of material is by using alkoxysilanes and organic monomers via the sol-gel process and click chemistry reactions. In this paper, a co-condensation organic-silica hybrid monolith was prepared based on tetramethoxysilane (TMOS) and vinyltrimethoxysilane (VTMS) as precursors for the sol-gel process. The hybrid monolithic matrix was modified with dodecanethiol through the thiol-ene click chemistry reaction and the resulting material was compared with a dodecanesilane bonded phase column, in order to evaluate the differences in the chromatographic performance of a stationary phase prepared by a classic reaction or by a thiol-ene click reaction. Additionally, the stability of the thiol-ene column over time was evaluated. The effects of different synthetic proportions were investigated in detail by scanning electron microscopy (SEM), scanning capacitively coupled contactless conductivity detection (sC4D), Fourier-transform infrared spectroscopy (FTIR) and retention behavior in capillary liquid chromatography (cLC). The hybrid monolithic column prepared with dodecanethiol was the best one for the separation of alkylbenzenes and polycyclic aromatic hydrocarbons by cLC-UV.

Resumo em Inglês:

The present work evaluated the effect on charge transfer in functionalized TiO2 nanostructured systems using different binders. We highlight the conditions required to form self-assembled systems by varying the number of layers, as well as by substituting them for an organic binder, cysteine. Additionally, we study the pH effect of the precursor solution (HAuCl4) on gold nanoparticles (AuNPs) formation. The morphological characterization allowed us to determine the percentage of Au atoms on the surface of the synthesized nanoparticles. Inductively coupled plasma mass spectrometry (ICP-MS) analysis determined the amount of gold deposited on the TiO2 surface, which ranged from 4.56 to 253.00 ng mm-2 depending on the system used. Based on Fourier-transform infrared spectroscopy (FTIR) and Raman analysis, it was possible to propose a photolysis mechanism for AuNP formation in accordance with the change in the binders. The different systems were subjected to hydrogen photogeneration by a water splitting process, resulting in 2.02 µmol cm-2 of hydrogen production for cysteine binder [Cys+HAuCl4-2.7]. There proved to be an excellent synergy between the morphological aspects, crystallinity, and stability of this arrangement.

Resumo em Inglês:

São Simão’s Brazilian kaolinite has been treated with titanium(IV) isopropoxide and cobalt(II) tetracarboxymetallophthalocyanine under different conditions (acidic or basic), leading, after drying at 100 ºC, to new titania-doped cobalt(II)-metallophthalocyanine/kaolinite solids. These solids were characterized by chemical analysis, powder X-ray diffraction, Fourier transform infrared spectroscopy, thermal analyses and nitrogen adsorption. No significant changes were observed by diffractometry, but the specific surface area depended of the synthetic route followed. The ability of these solids for photodegradation of trimethoprim, caffeine and prometryn was evaluated. The photodegradation was followed via mass spectrometry and UV-Vis absorption spectroscopy. The presence of photodegradation by-products was verified in all cases. All the photocatalysts showed high photodegradation rate against prometryn, trimethoprim and caffeine, the degradation efficiencies were 54, 30 and 90%, respectively, when using the heterogeneous photocatalysts. Comparison with commercial TiO2 (Degusa®) proved that the synthesized photocatalyst based on kaolinite present higher degradation rate than isolated titanium dioxide.

Resumo em Inglês:

Materials science has observed a continuous increase in the use of metal nanoparticles in a wide range of studies, from fundamental physics to technological applications such as photocatalysis and optical communication devices. This broad scope has the same fundamental origin, the localized surface plasmons, whose excitation leads to strong light confinement, especially in the vicinity of closely spaced nanoparticles, the hot spots. The field amplification may be used to amplify the Raman scattering of adsorbed molecules, which is known as surface-enhanced Raman scattering (SERS). A crucial and limiting characteristic of SERS hot spots is their very localized nature, that influences the SERS intensity reproducibility as well as the probabilities of observation of single-molecule SERS signals. In this paper we discuss the correlation between SERS performance and gold nanorod cluster structures using transmission electron microscopy, SERS spectra and numerical simulations. The experimental data showed interesting behavior for the combination of end-to-end and side-by-side interactions, revealing the possibility of creating strong hot spots with a more extended spatial distribution. The results give insights into the development of high-performance SERS substrates.

Resumo em Inglês:

Aedes aegypti is the main vector of three neglected tropical diseases: dengue, zika and chikungunya. Dengue is under surveillance by health organizations worldwide due to the risk of epidemics. Since there is no specific treatment for dengue, most studies have focused on preventing the reproduction and/or development of the mosquitoes. We studied the larvicidal activity of five phosphates and phosphorothioates derived from cardol, one of the four main components of cashew nut shell liquid (Anacardium occidentale L.), at different concentrations. The organophosphorothioate derivatives were tested for their in vitro inhibitory potential against acetylcholinesterase (AChE). One compound, Cdl.i-dPS (median lethal concentration (LC50) = 0.8 ppm), was four times more efficient compared to an important commercial larvicide, Temephos (LC50 = 3.2 ppm), and showed greater AChE inhibition than its monosubstituted analogue and Temephos.

Resumo em Inglês:

Silver (AgNPs) and gold (AuNPs) nanoparticles in aqueous solution were generated and stabilized using the 10-oxo-10H-dibenzene thiopyran-3-4-dicarboximide chitosan (TXICh) macrophotoinitiator. The photoinitiator and the nanoparticles in aqueous solution were characterized by UV-Vis spectroscopy and transmission electron microscopy (TEM). Pure TXICh in aqueous solution forms self-assembled particles with diameter around 30 nm. AgNPs were prepared using TXICh in the presence and absence of triethanolamine (TEOH). During irradiation, a broad band in the range of 410-415 nm was observed, corresponding to the plasmon absorption, indicating the AgNPs formation. TEM images revealed that the AgNPs had spherical shape in the absence and presence of TEOH. The synthesis of AgNPs in the presence of TEOH occurred rapidly (maximum conversion reached after 15 min), whereas in its absence 4 hours were required. The AgNPs prepared with TXICh/TEOH presented smaller and more uniform nanoparticles size. AuNPs were also prepared using TXICh as photoinitiator/stabilizer system. These nanoparticles showed an intense surface plasmon band at 530 nm and the TEM images revealed spherical particles of around 4 nm. These studies indicate that TXICh can act not only as a photoinitiator, but also as a stabilizer in the AgNPs and AuNPs formation.

Resumo em Inglês:

Currently, there is great interest in the study of water-soluble metal compounds capable of releasing carbon monoxide, due to their potential therapeutic use. This paper reports the synthesis, spectroscopic characteristics and CO release properties of three water-soluble manganese(I) carbonyl compounds [Mn(aaz)(CO)3]Br (1; where aaz = 6-amino-6-methylperhydro-1,4-diazepine), [Mn(Me2aaz)(CO)3]Br (2; where Me2aaz = 6-amino-1,4,6-trimethyl-1,4-diazacycloheptane) and [Mn(tacn)(CO)3]Br (3; where tacn = 1,4,7-triazacyclononane), that can act as photoCORMs (where CORM is carbon monoxide-releasing molecule). The main aim was to propose a mechanism for the CO release. Compounds 1-3 are capable of releasing carbon monoxide when exposed to light (λ385 and λ410) and thus, act as photoCORMs. The formation of a biscarbonyl intermediate was identified during the photo-release process at λ385 and the quantum yields and rates of CO release were determined. The proposed CO release mechanisms involve two steps, where photo and redox processes take place, and compounds 1 and 2 exhibit a slightly different mechanism from compound 3. A good understanding of the CO photo-release mechanism is very important with regard to the development of more efficient compounds, particularly those intended for medical applications.

Resumo em Inglês:

A mesoporous, high surface area and conductive silica/titania graphite composite modified with chitosan and functionalized with tyrosinase was prepared. The composite was obtained by the sol-gel method and the surface of the resultant material was modified with chitosan solutions containing 5, 10 and 15% by mass. The textural characterization showed that even after modification with chitosan, the composite maintains a pore volume near 0.70 cm3 g-1 and pore diameter between 10 and 50 nm, adequate for enzyme immobilization. The tyrosinase was immobilized on the composite that was modified with 5% chitosan solution. A carbon ceramic electrode was manufactured with this material and was used as an electrochemical biosensor for phenolic compounds, showing low detection limits in the linear range from 40 to 350 µmol L-1 and good sensitivity of 0.284, 0.141 and 0.165 µA µmol-1 L for catechol, dopamine and pyrogallol, respectively. In this composite the enzyme showed to be operative and stable after several months.

Resumo em Inglês:

The antibiotic streptazolin (1), its E-isomer (2), along with the stereoisomers strepchazolin A (3) and strepchazolin B (4) and the inorganic compound cyclooctasulfur (5) were produced in solid culture by Streptomyces chartreusis ICBG377, which was isolated from the fungal garden of the leaf-cutter ant Acromyrmex subterraneus brunneus. This is the first time compound 2 is reported as a natural product. Compound 5, which showed antagonist activity against the specialized pathogenic fungus Escovopsis sp., was also produced by Streptomyces chartreusis ICBG323, isolated from the exoskeleton of winged male of Mycocepurus goeldii. The absolute configurations of 3 and 4 were confirmed by the combination of vibrational circular dichroism (VCD) spectroscopy and density functional theory (DFT) calculations. These results clearly demostrate the power of VCD to tell apart epimeric natural products. Compounds 1, 3 and 4 were produced by geographically distant but phylogenetically close strains, S. chartreusis ICBG 377 isolated in Brazil, and S. chartreusis NA02069, a marine sediment strain isolated in China.

Resumo em Inglês:

This paper presents a comparative study about the oxygen reduction reaction (ORR) catalyzed by nanoparticles of Fe2O3 and Co3O4 applied on the surface of glassy carbon electrodes (GCE). The nanoparticles were synthesized using the modified polymeric precursor method (Pechini). These two nanomaterials were characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) techniques. The estimated average particle sizes were 21 and 31 nm for Fe2O3 and Co3O4, respectively. Electrochemical impedance spectroscopy (EIS) showed that Fe2O3/GCE has lower charge transfer resistance than Co3O4/GCE. The surface electrochemistry of both Fe2O3/GCE and Co3O4/GCE was studied in the solution free of O2, and their corresponding reaction mechanisms were analyzed. The electrocatalytic ORR activities of these two catalysts were studied by cyclic voltammetry (CV) and rotating disk electrode (RDE) in acidic solution. The results obtained by RDE indicated that both Fe2O3/GCE and Co3O4/GCE can catalyze the ORR with a dominating 2-electron transfer process to produce H2O2, using a potential of -0.8 V. These kinetic results indicate that Fe2O3/GCE is more efficient than Co3O4/GCE in terms of ORR. Considering the low cost of these two non-noble metal catalysts, they may be used as viable alternatives for ORR electrocatalysts.

Resumo em Inglês:

Piper glabratum is a plant native from South America, which has been little studied, despite its use in folk medicine. In this study, chemical composition, antioxidant and antifungal activities of essential oils (EOs) from leaves of P. glabratum were investigated. The influence of seasonality on its chemical composition was also evaluated. The chemical characterization was performed by two-dimensional gas chromatography coupled with quadrupole mass spectrometry (GC×GC/qMS). Altogether, 199 compounds were identified in the EOs and their composition varied during the seasonal cycle. The main compounds found were sesquiterpenes and their oxygenated analogues. EOs showed antioxidant activity, measured by 2,2-diphenyl-1-picrylhydrazyl-DPPH (from 28.1 to 33.4 µg mL-1) and β-carotene assays (from 57.4 to 66.4%), and inhibitory action against C. albicans. The oils provided expressive properties; however, the yield of EO from winter was not enough for activities assays, remarking the influence of the seasonality on the biological activities of this plant.

Resumo em Inglês:

Films of a poly(fluorene-bisthiophene) derivative, named PFBT, were electrodeposited onto indium tin oxide (ITO) electrodes and their electrochromic and fluorescence properties were investigated. Such films displayed color variation from yellow, in the neutral state, to green, in the oxidized state, as shown by tracking of the CIE (Commission Internationale de l’Eclairage) 1931 xy chromaticity coordinates. PFBT films are fluorescent in the neutral state (E = 0.0 V vs. Ag/Ag+) with emission at 532 nm; however, upon oxidation at 0.85 V the photoluminescence intensity is significantly decreased. A solid-state electrochromic device was assembled using PFBT and poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT-PSS) films and a polymer electrolyte. The device presented color variation from transmissive greenish-yellow to blue and reversible fluorescent properties upon switching between -1.5 to 1.5 V vs. PEDOT. Thus, the high contrast and stability both in electrochromism and electrofluorescence of the PFBT film and its device make them suitable for application in multifunctional optical devices.

Resumo em Inglês:

The use of bioprocess to convert low valued biomass or agroindustrial byproducts into high-value chemicals is an emerging area. However, laboratories usually use outdated analytical techniques to identify bioproducts, losing valuable information, such as the identification of unexpected compounds. In this work, we presented a successful systematic and modern analytical approach based on direct infusion mass spectrometry (DIMS) for an automated high-throughput screening of untargeted compounds from glycerin bioconversion process. We describe advantages of DIMS and its combined application with chemometrics towards an untargeted metabolomics approach to analyze several samples in a short time (11 samples per h). Three batches with 34 samples from the bioconversion of glycerin using several filamentous fungi strains were analyzed. Batch 347 was selected as promising, since high value chemicals, such as amide, phenolic and acid compounds, were identified. The platform presented was fast, robust, and versatile, then it could be applied to different bioprocesses.

Resumo em Inglês:

The bioaccessibility of Zn during in vitro gastrointestinal digestion from yogurt was investigated. In addition, the methodologies of sample preparation (dry and wet digestion, and slurry sampling) for the determination of total concentration of Zn in yogurt by flame atomic absorption spectrometry were also compared in this work. In comparison with digestion procedures, the proposed slurry sampling is simple and less time-consuming procedure. The limit of quantification determined was 1.3 µg g-1. The concentrations of Zn in the Brazilian yogurt ranged from 3.40 to 5.62 µg g-1. The percentage of the bioaccessible fraction of Zn from the samples ranged from 10 to 26%. This corresponds to an average daily intake of less than 2% of the metal for adults and children, suggesting that the Brazilian yogurt contributes with a low amount of Zn for the human diet.