Resumo em Inglês:

Multicomponent reactions (MCRs) are important transformations, which allow the attainment of structurally complex derivatives in a single step, starting from three or more compounds with relatively simple structures. These reactions are generally associated with the principles of green chemistry, allowing the incorporation of most (or all) atoms of the starting materials in the products (atom economy) and reducing purification steps (and, consequently, the need for solvents and waste production). For a long time, asymmetric methodologies (in special enantioselective protocols) for most multicomponent transformations remained a gap in the literature, limiting the use of these reactions to produce derivatives only as racemates or in low diastereoselectivities. Over the last two decades, a better comprehension of the mechanisms associated with these transformations allowed the development of efficient enantio- and diastereoselective procedures, attracting the interest of both academia and industry. In this review, selected examples of four important multicomponent reactions (Strecker, Mannich, Passerini and Ugi) will be discussed, presenting a general overview of the development of this field and pointing out possible advantages and limitations of the above mentioned methodologies. In some cases, discussions around mechanisms, proposed transition states and activation modes will be detailed disclosed.

Resumo em Inglês:

The genus Aristolochia stands out as the most representative of the Aristolochiaceae plant family, with approximately 550 species distributed around the world, many of which have little or no studies reported in the literature. Investigation of the acetone extract from leaves of Aristolochia warmingii Mast. resulted in the isolation and identification of twenty-three compounds, mostly lignans and neolignans, including the new furofuran lignans warminin A (1), warminin B (2) and warminin C (3). The structures of the compounds were established by comprehensive spectroscopic and spectrometric analyses. A large amount of (–)-epieudesmin (4) was isolated from the extract, which suggests that A. warmingii could be a potential source of this compound. The hexane, acetone, ethanol, and ethanol Soxhlet extracts, in addition to fourteen of the isolated compounds, were evaluated for their ability to inhibit the formation of advanced glycation end products (AGEs), but they did not show significant activities.

Resumo em Inglês:

5-Hydroxymethylfurfural (HMF) can be obtained from the dehydration of monosaccharides present in biomass, which helps add value to the raw material. The present work sought to study the relationship between the parameters of biomass characterization, including the content of reducing sugars, total soluble solids and the mid-infrared (MIR) and near-infrared (NIR) spectra, and the formation of HMF after synthesis. A thorough analysis was conducted in order to evaluate the residual agricultural biomass samples from sugarcane bagasse, corn stover, cassava branch, banana pseudostem and mango fruits after the drying (45 °C maximum) and ball mill grinding pre-processing procedure. HMF synthesis was performed using 0.50 mol L-1 HCl and n-butanol as extracting solvent. The analytical quantification of HMF and furfural (co-product of synthesis) was performed using high-performance liquid chromatography coupled to diode-array detector (HPLC-DAD). The highest efficiency of the synthesis of HMF was observed for the mango fruits (55.0 kg ton-1) and sugarcane bagasse biomass (47.5 kg ton-1) samples. The application of data fusion and principal component analysis (PCA) allowed us to identify the samples with greater potential for HMF synthesis.

Resumo em Inglês:

The use of extraction technique with disposable tips (DPX) was applied for the first time for the extraction and preconcentration of Yb in samples of liquid waste from the petrochemical industry and environmental water using bioabsorbent cork. The use of cork as an extracting phase in the determination of Yb by high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS) was evaluated. The pyrolysis and atomization temperatures were optimized at 1400 and 2400 °C, respectively. H2SO4, HNO3 and HCl acids were compared in the steps of cleaning the extraction phase and desorption of the analyte by DPX. The best extraction in the selected conditions was obtained with pH 8.0 and 5% v/v HCl. The recoveries were close to 100% for residual water and drinking water, 33 to 77% for produced water and 64 to 93% for river water. Tests with interfering ions in different concentrations were performed. The relative limit of quantification (LOQ) and limit of detection (LOD) were estimated at 0.03 and 0.01 µg L-1, respectively. The total time for the preparation of the samples by DPX was close to 1 min per sample. Extraction and pre-concentration were observed using DPX with a pre-enrichment factor of approximately 4 times.

Resumo em Inglês:

The water treatment sludge (WTS) is a residue composed of organic and inorganic matter in a solid, liquid, and gaseous state that has a variable composition concerning its physical, chemical, and biological characteristics. The irregular disposal of WTS can promote harmful changes to the environment, such as reduction of dissolved oxygen and increase in the concentration of aluminum and other metals in the receiving watercourses. To propose a suitable purpose for this residue, this work evaluated the physical and mechanical properties of the concrete and corrosion resistance of the reinforcement in a cementitious composite using WTS in replacement to the natural sand. A conventional concrete and a conventional mortar were used as a reference and a 3% WTS-content concrete, and a 3% WTS-content mortar were prepared to evaluate the WTS influence in mechanical properties and corrosion resistance. By electrochemical measurements, it was observed that the resistance of the cementitious matrix was not altered by WTS addition. Regarding steel resistance, the WTS may promote a higher susceptibility to frame corrosion, which can be correlated to the lower pH than reference medium (REF). The concrete reinforcement characterization indicates that concretes with WTS can be used as reinforced concrete structure in urban areas.

Resumo em Inglês:

The low-temperature electrochemical corrosion behavior of aircraft 2024 aluminum alloy was investigated in different concentrations of potassium-acetate-type fluid, and the results showed that the corrosion medium initially impacted some corrosiveness on the 2024 aluminum alloy. However, the corrosion rate of the alloy decreased with prolonged immersion in the corrosion medium, and this was attributed to the protective effect of the corrosion products layer, which impeded the attack by the aggressive solution. Time-domain analysis of electrochemical noise measurements at -5 °C revealed the occurrence of uniform corrosion on the alloy at the initial stages of immersion, general corrosion at the middle stages of immersion, and a pitting-dominated corrosion type from the middle to late stages of immersion.

Resumo em Inglês:

The efforts of contrasting the effects caused by the COVID-19 (coronavirus disease 2019) pandemic increased the disposal of active pharmaceutical ingredients. This paper reports the mechanisms and kinetics of the degradation in aqueous environments induced by •OH of two drugs, among those most widely probed at the outbreak of coronavirus, nitazoxanide and hydroxychloroquine. The investigation exploits quantum chemistry techniques and a reaction rate theory combined with diffusion-controlled processes and quantum mechanical tunneling. The reaction rate constants are obtained in an environmentally relevant temperature range. The results show that (i) the deacetylation of nitazoxanide with formation of tizoxanide is kinetically the most favorable channel, in agreement with experimental work; (ii) for hydroxychloroquine, the present theoretical calculations show that the most favorable channel is the addition of •OH at the aromatic ring. The half-life time degradation products are for both cases in the range between 12 to 138 days. Both drugs presented toxicities between harmful and toxic as obtained by computational toxicology calculations. The toxicity is also calculated for the degradation products: (i) in the nitazoxanide degradation process, tizoxanide was characterized as more toxic, while (ii) in the case of hydroxychloroquine, the major degradation product showed a decrease in the toxicity.

Resumo em Inglês:

This study describes the validation of a headspace gas chromatography with flame ionization (HS-GC-FID) method for the determination of propanal, pentanal, hexanal, octanal, and trans-2-nonenal originated by lipid oxidation from cat food samples, as well as the evaluation of the matrix effect in the results. This method was applied to the analysis of commercial cat food and proved to be suitable for the determination of these volatile compounds in different samples. Mean recoveries between 88 and 109% were obtained and repeatability expressed as relative standard deviation was always lower than 6.95%. The intra- and inter-assay precisions ranged from 0.44 to 20.88% and from 0.45 to 20.52%, respectively. In addition, the matrix effect of cat food samples was determined by comparing the slopes of the standard addition method, and the external calibration curve and its influences were verified. These results highlight the high potential of this method, which allows the determination of lipid oxidation products in cat food samples directly, without requiring prior sample preparation techniques.

Resumo em Inglês:

Penicillium meliponae, a recently described and rare species, was isolated as an endophytic fungus from the Amazonian plant Duguetia sthelechantha, and has been proven to be a pigment producer. Considering the high productivity of this species and the lack of data on its chemical composition, the present study aimed to characterize the chemical profile of P. meliponae and evaluate the influence of agitation and the use of different culture media. For this purpose, liquid chromatography coupled with mass spectrometry (LC-MS/MS) and molecular networking were used, allowing the identification of 17 azaphilone molecules with sclerotiorin-like skeletons, becoming the first chemical report of this species. In addition, the different production patterns in the tested culture media were indicative that this species is sensitive to changes in the composition of the carbon source and to the presence of agitation. Furthermore, this work contributes to the fragmentation mechanisms of the different possible structural arrangements for azaphilones of the sclerotiorin type and serves as a repository of information on the gas-phase behavior of this type of metabolite in mass spectrometry experiments and will assist future studies aimed at the discovery of azaphilones.

Resumo em Inglês:

The conversion of ethanol into hydrocarbons, particularly into light olefins, was studied over MCM-22 zeolite in their acid form (HMCM-22) and its derived forms obtained by dealumination with oxalic acid (HMCM-22(OA)) and delamination (HITQ-2). The treatment with oxalic acid did not affect zeolite textural properties but reduced the total density and strength of the acid sites. As to the delamination process, HITQ-2 zeolite presented the highest Brunauer, Emmett and Teller (BET) specific area, mesopore volume, and external area, but the microporosity was not affected. This sample showed a lower SiO2/Al2O3 ratio than the precursor HMCM-22, resulting in the highest acid site density but with the predominance of acid sites with weak and intermediate strength. Both dealumination and delamination led to an increase in the number of structural defects in the samples. The comparison of the catalytic performance at 500 ºC showed that despite the differences in the acidic and textural properties of the samples, they were active for ethanol conversion and highly selective for ethylene production. Ethanol conversion, followed by in situ diffuse reflectance spectroscopy (DRIFTS), was also investigated. It showed that, for both samples, the “coke band” intensity was already significant after 1 min of reaction, similar to what was detected for HMCM-22.

Resumo em Inglês:

Essential oils (EO) have diverse applications, such as antibacterial and antifungal activity. However, they are susceptible to oxidation in the presence of air, light, and moisture. In addition, they are thermally unstable. In this sense, it is necessary to develop techniques to increase the lifespan of EO. In this work, EO was obtained from cloves and characterized by different techniques. The major compounds found were eugenol (83%), eugenol acetate (9%), and β-caryophyllene (8%). The EO was encapsulated by extrusion using a microfluidic device. The sodium alginate was used as wall material, and the CaCl2 solution was used as a crosslinking agent. The microcapsule presented sizes of 164.7 ± 0.3 μm, with an encapsulation yield of 64 ± 14%. Functional characteristic groups of EO were observed in the microcapsule by infrared and Raman spectroscopies. The microcapsule increased the thermal decomposition of the EO from 162 to 230 °C. Release kinetics of the capsule was performed, with an equilibrium time of 72 h and release of 54% of the EO. Finally, the pure EO and encapsulated EO-microcapsules were applied in the Aedes aegypti larvae control, showing mean lethal concentration necessary to eliminate 50% (LC50) values of 74.4 and 96.9 μg mL-1 and lethal concentration necessary to eliminate 90% (LC90) of 106.2 and 133.3 μg mL-1 for pure EO and encapsulated EO, respectively. Therefore, it was concluded that these microcapsules have the potential for application in the Aedes aegypti larvae control.

Resumo em Inglês:

This work describes the route to prepare a novel core-shell catalyst based on 1,4-diazabicyclo[2,2,2]octane (DABCO) supported magnetic nanoparticles (MNPs). The morphology and composition of the obtained catalysts were characterized by Fourier-transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), X-ray powder diffraction (XRD), transmission electron microscopy (TEM), quantum design vibrating sample magnetometer (VSM) and scanning electron microscopy (SEM). These nanomaterials presented high performance as a basic catalyst for Knoevenagel condensation between malononitrile and aldehydes, leading to products with excellent yields (84-99%) and short reaction times (5-60 min). Furthermore, it was also efficient in the condensation of isatins with 4-phenylthiosemicarbazide, resulting in isatin-β-thiosemicarbazones with high yields (81-94%) and short times (60-180 min). It is worth mentioning that the catalyst was recovered and reused in these two kinds of reactions after six cycles without significant yield loss.

Resumo em Inglês:

Hematological problems are associated with Coronavirus disease 2019 (COVID-19). Respiratory impairment is the higher point studied, although without experimental studies related to the oxygen transport performed by erythrocytes. Therefore, we decided to investigate if erythrocytes from COVID-19 patients have their functionality changed. The case-control study included hospitalized patients with a positive real-time polymerase chain reaction (RT-PCR) result admitted to University Hospital. Volunteers (negative RT-PCR results) were recruited as a control group. Thus, we assessed different erythrocytes parameters, oxidative stress markers, and biophysical studies using whole blood and isolated hemoglobin. We found a decrease of 51% in oxygen uptake and reduced antioxidant enzyme activity in COVID-19 patients compared to controls. Raman spectrometry showed structural changes in the hemoglobin and lipids of the erythrocytes from COVID-19 patients; thus, these results were consolidated with an increase in Young’s modulus in erythrocytes followed by morphology changes. Besides, isolated hemoglobin from COVID-19 patients has a distinct interaction profile using a ligand model compared to the control. COVID-19 leads to structural, functional, and morphological damage to human erythrocytes. Our data showed structural and molecular changes and induction of oxidative stress in erythrocytes by COVID-19, a new perspective on the contribution of erythrocytes to a respiratory commitment in COVID-19.

Resumo em Inglês:

A hybrid molecular imprinted polymer (HMIP) obtained by the organic monomer 4-vinylpyridine (4-VP) and the inorganic precursor tetraethyl orthosilicate (TEOS) was synthesized for the selective extraction of urinary S-phenylmercapturic acid (u-SPMA), a biomarker of benzene exposure. The chemical and structural characterization of the synthetic adsorbent was performed by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and textural analysis employing N2 adsorption-desorption isotherms. Selective and adsorptive performance of the imprinted polymers were evaluated by kinetic, isothermal, thermodynamic, and selectivity studies. The kinetic data were well adjusted to pseudo-second order and intraparticle diffusion models, leading to selectivity coefficient (K) value of 0.03 g mg-1 min-1 for HMIP. In addition, the adsorption isotherms were better described by the Sip model achieving a maximum adsorption capacity of 284.81 μg g-1 (at 288.15 K).

Resumo em Inglês:

Losartan potassium and hydrochlorothiazide are often combined in pharmaceutical formulations for the treatment of hypertension. Therefore, the determination of these compounds in a single run is highly desirable for rapid quality control applications. The present study describes an ultra-fast (ca. 85 injections h-1) and environmentally friendly method based on capillary electrophoresis (CE) with capacitively coupled contactless conductivity detection for simultaneous quantification of potassium, losartan and hydrochlorothiazide. Cation (potassium) and anions (losartan and hydrochlorothiazide) were analyzed in a single run using a background electrolyte composed by 10.0 mmol L-1 boric acid (pH = 9.0, adjusted with sodium hydroxide). The limits of detection were 4.0, 3.0 and 10.0 μmol L-1 for potassium, losartan and hydrochlorothiazide, respectively. The proposed method is simple, fast, with minimal waste generation, and accurate (recovery values between 98 and 102%). The results obtained with the CE method were statistically similar (95% confidence level) to those obtained by high-performance liquid chromatography (losartan and hydrochlorothiazide) and flame photometry (potassium).