Resumo em Inglês:

The incorporation of Cerrado fruits in food products such as ice cream has many advantages because it represents a source of nutrients and bioactive compounds. Given the demand for less laborious methods to analyze food, the paper spray ionization mass spectrometry technique was applied for the first time for a rapid characterization of the chemical components found cagaita ice cream. PS-MS in positive and negative ionization modes were used. The profile of volatile compounds was determined by headspace solid-phase microextraction combined with gas chromatography-mass spectrometry. Fingerprints obtained through PS-MS identified various classes of compounds, such as flavones, anthocyanins, sugars, organic acids, hydroxybenzoic acids, fatty acids, hydroxycinnamic acids, lignin, and phenylpropanoid. The use of both fibers enabled the extraction and identification of 18 volatile compounds in cagaita, and 16 of them were also identified in cagaita ice cream. The most common volatile compound found in both cagaita and ice cream was 3-carene monoterpene. Considering the effect of processing on cagaita constituents, 89% of the volatile compounds remained in the ice cream. Also, 78% of the fruit chemical compounds analyzed by PS-MS were found in the product. Thus, the results indicate that most of the fruit compounds remained in the ice cream after processing.

Resumo em Inglês:

Previous researches showed that fatty acids analysis might be a useful tool to support the taxonomic investigation. In this approach the fatty acids content of ten Malvoideae species was analyzed and its chemotaxonomic significance has been investigated. The aerial parts of the species were collected in the Northeast of Brazil and their fatty acid methyl esters were analyzed by gas chromatography with flame ionization detector. The chemometric analysis consisted of principal component analysis (PCA) and hierarchical clustering analysis (HCA) with the euclidean distance between the samples given by the Ward.D2 algorithm. This is the first report of fatty acids from Wissadula peripocifolia, Herissantia crispa, Bakeridesia pickelii, Sidastrum micranthum, Pavonia cancellata and Pavonia malacophylla. The results showed the predominance of palmitic (C16:0), oleic (C18:1) and linoleic (C18:2) acids in the studied species. By the PCA and HCA analysis, the fatty acid composition was able to distinguish the species Herissantia crispa and Pavonia malacophylla. Our findings showed a chemotaxonomic proximity among species from different genera reflecting the taxonomic and phylogenetic closeness previously demonstrated by molecular investigations on Malvoidae species. Furthermore, our results demonstrated that the fatty acid analysis may be an interesting tool to support the taxonomic investigations on Malvoideae species.

Resumo em Inglês:

The difluoroamino derivatives of prismane were designed and calculated at the B3LYP/6-311G** level. The detonation performances, as well as the band gap, were investigated to look for high energy density compounds. Our calculations showed that difluoroamino group is an effective substitute group for increasing density and heats of formation. All compounds have large heats of formation, and there is a linear relationship between the heats of formation (HOFs) and the substituent numbers. Bond dissociation energies of trigger bonds are all over 200kJ/mol, which indicated that these prismane derivatives have good stability. More than three substituted groups made the detonation performances meet the requirement of energetic materials. Our calculations provided basic information for the further syntheses of title molecules.

Resumo em Inglês:

Nitrate is an abundant ion that is present in many industrialized products and the environment. Various analytical methods have been described using the Griess-Ilosvay reagent for the determination of nitrate in different matrices after its reduction to nitrite, in most cases with metallic cadmium as the reducer. This work proposes a new method using aluminum spheres coated with a copper film for this reduction. To optimize the method, it was important to evaluate the conditions for the deposition of the copper film on the aluminum spheres, using a Doehlert matrix. The optimized method provided an analytical range from 2.0 to 100 µmol L-1, with a coefficient of determination of 0.9996 and a standard deviation of residuals (sres) of 7.59 x 10-4. The Limits of Detection and Quantification were 0.59 and 2.0 µmol L-1 respectively. The method was applied using mineral water samples and was shown to provide repeatability less than 6.98% and accuracy obtained through recovery essays between 81.1 and 104.6% for the determination of nitrate in this type of sample.

Resumo em Inglês:

We have incorporated rhodamine into polyamide membranes by additive manufacture selective laser sintering technology. Incorporation into 0.5 cm2 membranes was conducted at different pH values and constant temperature of 25 oC. The amounts of incorporated dye were determined by a calibration curve, and analyses showed rhodamine incorporation in the order of 10-6 mol L-1. The absorption spectra of the solutions and membranes after rhodamine incorporation showed maximum absorption at 553 nm and a shoulder at 522 nm, which indicated that a dimer was formed. Photoluminescence presented maximum emission at 575 nm for the sample incorporated with rhodamine in acid pH. The membranes that were treated with acid presented shorter adsorption time and demanded 180 min to reach equilibrium, whereas the non-treated membrane and the membranes that were treated with base required 1440 min to reach equilibrium. Polyamide membrane has proven to be an excellent material for the incorporation of dyes and compounds for application as luminescent sensors.

Resumo em Inglês:

Selecting a method to compute partial atomic charges is not trivial because different methods usually provide different charge values and there is no consensus on the most useful approach. In this work, Mulliken, MBS, Chelp, Chelpg, MK, Hirshfeld, NPA, DMA and AIM methods were selected to compute atomic charges and electric dipole moment vector of N-{N-(Pterin-7-yl)carbonylglycyl}-L-tyrosine molecule, a ricin inhibitor which has different types of bonds and chemical environments. While MBS and DMA methods provided the most chemically consistent charges according to atomic electronegativity and electron resonance effects criteria, Chelp, Chelpg and MK had the worst performances. Atomic charges and dipole moment calculated by the Hirshfeld method had the smallest magnitudes, a well-known behavior. Despite the differences among atomic charges predicted by all methods, the direction of the dipole moment vector was essentially the same. Further charge calculations using different basis sets and quantum methods indicated that the dependency on this aspect was the highest for Mulliken and Chelp and the lowest for MBS, Hirshfeld and DMA methods. Thus, results point to MBS and DMA as the most suitable methods for computing chemically consistent atomic charges and dipole moment vectors of similar systems for different applications; e.g., molecular dynamics.

Resumo em Inglês:

Chlordecone (CLD) has been used as a pesticide for a long time to control the proliferation of various insects in tropical countries like the French West Indies. CLD was included in 2009 in the list of persistent organic pollutants (POPs) by the Stockholm Convention, prohibiting its production and use worldwide. Thus, its removal from water and soils is a sanitary emergency. With the purpose of limiting impregnation of the population by chlordecone in Martinique and Guadeloupe, since 1999 production and drinking water purification installations have been equipped with activated carbon filters without much knowledge on the adsorption mechanism of these pollutants on activated carbons (AC) surface. This article reviews the available information about how functionalized activated carbons can be used for improving the decontamination of polluted with CLD waters. The recent computational investigations about the CLD interactions with functionalized AC by molecular modeling are well-reviewed, considering geometrical and energetic features with the purpose of better understand the adsorption process. Finally, some aspects, trends, and perspectives on using computational tools for understanding the adsorption of CLD on AC and designing more efficient AC are also discussed.

Resumo em Inglês:

Coumarins are natural products characterized as 2H-chromen-2-one, according to IUPAC nomenclature, largely distributed in plants, as well as, in species of fungi and bacteria. Nowadays, many synthetic procedures allow the discovery of coumarins with expanded chemical space. The ability to exert non-covalent interactions with many enzymes and receptors in living organisms lead the coumarins to exhibit a wide range of biological activities and applications. Then, this manuscript provides an overview of the use of coumarin compounds in medicinal chemistry in treating many diseases. Important examples of the last years have been selected concerning the activities of coumarins as anticoagulant, anticancer, antioxidant, antiviral, anti-diabetics, anti-inflammatory, antibacterial, antifungal, and anti-neurodegenerative agents. Thus, this work aims at contributing to the development of new rational research projects searching for new treatments and bioactive compounds for many pathologies using coumarin derivatives.

Resumo em Inglês:

Phosphorus (P) is an important chemical marker of the past human presence, because, besides indicates the localization of possible archaeological sites, also, contributes to clarify doubts regarding to origin, duration and to specific functions that were developed in them. The present study aimed to obtain a simple, accurate, fast and non-destructible analytical method to determine phosphorus in sediment samples of the Toca da Baixa dos Caboclos archaeological site, an enclave of the Serra da Capivara National Park, Piauí, Brazil. For the proposed method, a portable energy dispersive X-ray fluorescence (p-ED-XRF) equipment and cross calibration to sample direct analysis were used. The results show that the concentrations obtained by the proposed method, cross calibration with use of p-ED-XRF, and by the spectrophotometric method were considered statistically equal, when compared by the paired t test (p=0.05). By its turn, the intermediate accuracy and recovery tests showed values in the range of 2.41−3.56% and 85.10-102.66%, respectively.

Resumo em Inglês:

In this work the feasibility of sequential multi-element determination of Zn, Fe, Mg, Cu, Na, K, Cr, Al and Ca in biodiesel samples by high-resolution continuum source flame atomic absorption spectrometry (HR-CS FAAS) was investigated. Biodiesel samples obtained from different sources and different chemical processes were analysed. The samples were diluted with n-propanol and water (1.4 mol L-1 HNO3) to form a microemulsion (ME) before its introduction in the HR-CS FAAS using a flow injection mode. The sample B-01 (obtained from soybean oil) was used for optimisation of the instrumental parameters. The accuracy of the proposed method was checked by analysis of certified reference material (CRM) Conostan BDM2A (for K and Na) and BDM2B (for Ca and Mg) and by comparison with acid digestion and recovery tests (for Zn, Fe, Cu, Cr and Al). The obtained results for CRM analysis showed good agreement with certified values within 95% of confidence (Student’s t-test). Recovery tests values ranged from 87-114%. The method developed for the analysis of biodiesel samples is accurate, simple, fast, and suitable for routine application.

Resumo em Inglês:

Gamma-hydroxybutyrate (GHB) is a depressant of the central nervous system able to promote disinhibition, anterograde amnesia and its use is related to Drug-Facilitated Crimes (DFC). Urine is the biological matrix of choice for toxicological analysis in victims of rape and/or theft in suspected victims of DFC. The aim of this work was the development of a simple and ultra-fast methodology for GHB determination in urine samples using GC-MS. Briefly, 250 µL of urine was pipetted in a vial and fortified with 10 µL (250 µg mL-1) of internal standard GHB-d6. Then, the sample was acidified and submitted to extraction with ethyl acetate. After stirring, the material was taken to a microcentrifuge (1 minute at 5000 rpm). Then the dried residue was derivatized with BSTFA + 1% TCMS for 10 min at 70 ºC before injection. This method was successfully validated according UNODC and EMEA guidelines on bioanalytical method validation with limit of detection and limit of quantification were 0.25 and 0.50 µg mL-1, respectively. Considering all steps for GHB determination, this analytical procedure allows the fastest detection of GHB in urine samples when compared to literature allowing the analysis of DFC suspect cases or clinical when endogenous GHB requires to be measured.

Resumo em Inglês:

This paper proposes the development of a simple experiment with easily accessible and low cost materials, enabling its practice with or without laboratory infrastructure, with feasibility for computational theoretical study. On the other hand, the objective of the work is to develop a chemical experiment that demonstrates that the chromophore curcumin (natural indicator) is responsible for indicating the acidity or basicity of a given solution. The experiment has different applicability, being useful in the approach of different chemical contents, showing potential for multi and interdisciplinary approaches. Subjects such as tautomeric equilibrium, chromophoric compounds, hydrogen potential, UV-Vis electron absorption spectra analysis and molecular modeling are explored.

Resumo em Inglês:

In Part I of a three-part series, we present an objective survey of the technical literature discussing the inclusion of orbitals in high-school and post-secondary general chemistry. We start with the definition of orbitals. The presentation of orbitals in secondary (high) school is presented with arguments for and against. The content of orbitals in the curriculum of general chemistry is presented and summarized in terms of 1) electron configuration, 2) periodic table, 3) molecular structure and 4) reactivity. Previous discussion in favor of and against each theme is presented. Recent research in chemical education is also reviewed.

Resumo em Inglês:

The present work demonstrates how neural networks are used to do non-linear regressions. The technique is presented in a simple and didactic manner and applied to fit potential energy surfaces for the FeC molecule and for the reaction H + H2. It shows how to do the fitting for single- and multi-variable system providing examples and code that can be easily extended to many problems in chemistry. All the code used to perform the fitting and generate the results is available as a Jupyter Notebook, which can be used without neither installation nor configuration

Resumo em Inglês:

The death of professor Rolf Huisgen (1920-2020) was announced on March 26th 2020, in the midst of the COVID-19 pandemic. Professor Huisgen was professor emeritus at the University of Munich in Germany, and studied in detail the mechanism of the 1,3-dipolar cycloaddition reaction, significantly expanding its scope. Even though he did not discover this reaction, it was through his studies that it became important in organic synthesis. Indeed, in honor of his work, the reaction became known as Huisgen’s cycloaddition and it has been consolidated as a useful method for the preparation of five-membered heterocyclic compounds. Considering these facts, in this review we provide an overview on the applications of 1,3-dipolar cycloaddition reactions, starting with the seminal examples in the field and further discussing the most recent applications.

Resumo em Inglês:

The Baltic German chemist Wilhelm Ostwald (1853-1932) had his scientific prestige eclipsed in the history of chemistry due to his rejection to atomic theory, which suggests the permanence of the whig interpretation on history of chemistry in the narratives about him. In this paper, we intend to present elements on Ostwald’s biography far from his role in the atomic controversy from the 19th century, as for example his efforts for the popularization of physical chemistry; his role as a teacher and a textbook writer, and his role as a chemical researcher, being responsible for relevant studies on chemical affinity and catalysis, for example. Finally, we conclude this paper defending that Ostwald’s trajectory cannot be neglected for those interested in history of science.