cometadata/datacite-titles-descriptions-related-identifiers huggingface dataset:
DOI: 10.6084/m9.figshare.6832793.v1
title: AVOCADO, SPENT COFFEE GROUNDS, LICURI AND COCONUT MILK FOR OIL EXTRACTION, BIODIESEL PRODUCTION, AND SPECTRAL ANALYSIS

description: An undergraduate organic chemistry experiment for oil extraction and biodiesel production using alternative biomass was developed, whereby oils of avocado, coconut and spent coffee grounds were obtained and submitted to transesterification reaction with CH3OH under NaOH catalysis. Avocado and coffee oils were obtained by typical extraction and coconut oil was obtained through water evaporation of coconut milk in a domestic microwave oven. The commercial oil of licuri (Syagrus coronate), a Brazilian native biomass, was also converted to biodiesel. All four oils and four biodiesels were characterized by 1H-NMR and FTIR, and a comparative study of these spectra reveled that FTIR analyses alone provides enough information to discriminate between oil and biodiesel and confirm transesterification reaction. Besides, the unsaturation degree of all oils was determined by 1H-NMR. A mechanistic proposal concerning the role of NaOH catalysis is presented, excluding the sodium methoxide formation.
DOI: 10.6084/m9.figshare.6944162
title: POLYBROMINATED DIPHENYL ETHERS (PBDE) AS PERSISTENT CONTAMINANTS: ORIGIN, BEHAVIOR IN THE ENVIRONMENT AND ANALYTICAL STRATEGIES

description: Flame retardants are substances mixed with numerous materials to inhibit the combustion process, reducing risks and damages caused by fires. Among these substances, polybrominated diphenyl ethers (PBDEs) have been widely used for decades due to their low cost and high efficiency. However, since they are mixed and not chemically bonded to the materials, PBDEs can be released over time being transported through numerous pathways until they reach soils and aquatic systems, where they can accumulate in sediments and biota. Due to their high chemical stability, an essential feature for flame retardants, they are considered persistent contaminants. Several studies report the presence of PBDEs in atmospheric and aquatic particulate matter, sediments, soils and biological matrices such as marine animals, tissues and human fluids. In Brazil, little is known about the use and commercialization of PBDEs, as well as their levels in different environmental compartments. Thus, this review provides an overview of the origin of PBDEs in the environment as well as information inherent to the understanding of the behavior and presence of this contaminants of recent interest in different environmental compartments. Finally, the manuscript also brings state-of-the-art analytical approaches used for environmental sampling, preservation, preparation and sample analysis.
DOI: 10.6084/m9.figshare.6944162.v1
title: POLYBROMINATED DIPHENYL ETHERS (PBDE) AS PERSISTENT CONTAMINANTS: ORIGIN, BEHAVIOR IN THE ENVIRONMENT AND ANALYTICAL STRATEGIES

description: Flame retardants are substances mixed with numerous materials to inhibit the combustion process, reducing risks and damages caused by fires. Among these substances, polybrominated diphenyl ethers (PBDEs) have been widely used for decades due to their low cost and high efficiency. However, since they are mixed and not chemically bonded to the materials, PBDEs can be released over time being transported through numerous pathways until they reach soils and aquatic systems, where they can accumulate in sediments and biota. Due to their high chemical stability, an essential feature for flame retardants, they are considered persistent contaminants. Several studies report the presence of PBDEs in atmospheric and aquatic particulate matter, sediments, soils and biological matrices such as marine animals, tissues and human fluids. In Brazil, little is known about the use and commercialization of PBDEs, as well as their levels in different environmental compartments. Thus, this review provides an overview of the origin of PBDEs in the environment as well as information inherent to the understanding of the behavior and presence of this contaminants of recent interest in different environmental compartments. Finally, the manuscript also brings state-of-the-art analytical approaches used for environmental sampling, preservation, preparation and sample analysis.
DOI: 10.6084/m9.figshare.6832802.v1
title: UNIFIED TOPOLOGY OF FRONTIER MOLECULAR ORBITALS TO EXPLAIN PERICYCLIC REACTIONS

description: In this work is proposed a didactic alternative vision to teach pericyclic reactions. To this end, they were classified according to the connectivity of reactants systems, as connected atom reactions (CAR) and the other possibility, as not connected atom reactions (NOCAR). Electrocyclic reactions and sigmatropic rearrangements are examples of CAR categorization, and the cycloadditions being NOCAR. With these two categories, a pedagogical alternative description is proposed to the orbital topology in reactants to explain the pericyclic reactions. According to this classification, the HOMO's topology is adequate to all CAR, while the traditional HOMO-LUMO's topology is adequate to NOCAR. All issues typically deduced by the traditional treatment, such as allowed and forbidden reactions, and stereochemical aspects are also explained by the alternative approach.
DOI: 10.6084/m9.figshare.6832802
title: UNIFIED TOPOLOGY OF FRONTIER MOLECULAR ORBITALS TO EXPLAIN PERICYCLIC REACTIONS

description: In this work is proposed a didactic alternative vision to teach pericyclic reactions. To this end, they were classified according to the connectivity of reactants systems, as connected atom reactions (CAR) and the other possibility, as not connected atom reactions (NOCAR). Electrocyclic reactions and sigmatropic rearrangements are examples of CAR categorization, and the cycloadditions being NOCAR. With these two categories, a pedagogical alternative description is proposed to the orbital topology in reactants to explain the pericyclic reactions. According to this classification, the HOMO's topology is adequate to all CAR, while the traditional HOMO-LUMO's topology is adequate to NOCAR. All issues typically deduced by the traditional treatment, such as allowed and forbidden reactions, and stereochemical aspects are also explained by the alternative approach.
DOI: 10.6084/m9.figshare.7186322
title: CHARACTERIZATION OF CEO2 DOPED MGAL2O4 PREPARED BY THE CHELATING AGENTS-ASSISTED IMPREGNATION METHOD

description: MgAl2O4 spinel employed as support of reforming catalysts was doped by CeO2. The samples were prepared by wet impregnation from aqueous solutions of cerium nitrate, with and without chelating agents. The chelating agents used were ethylenediamine-tetraacetic acid (EDTA), nitrilotriacetic acid (NTA) and citric acid (CA) at different pH of impregnation. The solids were characterized by TG, XRD, SBET, TPR, SEM-EDX and CO2-TPD. Nanoparticles of CeO2 between 5 and 6.8 nm were obtained by the thermal decomposition in air at 600 °C. The surface cerium reduction occurred in a wide temperature range of 450° to 670 °C. The use of citric acid at pH= 8 led to the lowest crystallite size of CeO2 and the lowest interaction with the spinel. The H2 consumption and extent of CeO2-support interaction did not show a clear dependence with the CeO2 crystallite sizes. The use of chelating agents in the impregnation step did not modify the total basicity. Slight changes in the strength of weak basic sites were observed.
DOI: 10.6084/m9.figshare.7186322.v1
title: CHARACTERIZATION OF CEO2 DOPED MGAL2O4 PREPARED BY THE CHELATING AGENTS-ASSISTED IMPREGNATION METHOD

description: MgAl2O4 spinel employed as support of reforming catalysts was doped by CeO2. The samples were prepared by wet impregnation from aqueous solutions of cerium nitrate, with and without chelating agents. The chelating agents used were ethylenediamine-tetraacetic acid (EDTA), nitrilotriacetic acid (NTA) and citric acid (CA) at different pH of impregnation. The solids were characterized by TG, XRD, SBET, TPR, SEM-EDX and CO2-TPD. Nanoparticles of CeO2 between 5 and 6.8 nm were obtained by the thermal decomposition in air at 600 °C. The surface cerium reduction occurred in a wide temperature range of 450° to 670 °C. The use of citric acid at pH= 8 led to the lowest crystallite size of CeO2 and the lowest interaction with the spinel. The H2 consumption and extent of CeO2-support interaction did not show a clear dependence with the CeO2 crystallite sizes. The use of chelating agents in the impregnation step did not modify the total basicity. Slight changes in the strength of weak basic sites were observed.
DOI: 10.6084/m9.figshare.7773902
title: METHODOLOGY TO PROMOTE THE QUALITATIVE DETECTION OF ORGANIC COMPOUNDS IN PETROLEUM/WATER INTERFACES

description: The possibility of detecting some organic compounds directly in a petroleum/water interface was described. Aqueous phase was composed by 1 x 10-3 mol L-1 NaCl solution and the oil phase was carried out using crude oil forming an oil/water interface. Carbon based screen-printed electrodes was used in conjunction with square-wave voltammetry technique, constituting the main tools of this technical note. Petroleum was contaminated with phenol, naphthalene and cyclohexane. The oxidation potentials for these three molecules were 0,72, 0,81 and 0,87 V vs. Ag, respectively. Phenol was chosen to study the stability of currents during the process. After 15 minutes, the currents of this process were stable. Although the formation of a passivation film, the qualitative detection of the molecules was possible. Finally, the main advantage of this methodology is the possibility of detecting contaminants in oil without the necessity of complicated pre-treatment steps.
DOI: 10.6084/m9.figshare.7773623
title: ARTIFACTS IN THE ANALYSIS AND ASSESSMENT OF LOW-COST CONTAINERS FOR SAMPLING AND STORING GREENHOUSE GASES

description: The objectives of this study were twofold: to assess two chromatographic methods for the analysis of greenhouse gases (GHG) and carbon monoxide, and to propose and evaluate a low-cost and reusable alternative system for their sampling and storage, using 10 different container configurations (flasks and bags). To that end, standard samples containing the gases of interest (CO2, CH4 and CO) and different types of real samples were tested. Finally, procedures for the sampling, storage and analysis of CO2 and CH4 were evaluated and optimized. Two chromatographic methods were applied, using different analysis conditions and columns. Gas chromatography analysis of sample stability and container reusability demonstrated that borosilicate flasks with butyl rubber and PTFE/silicone septa are ideal for storing samples, allowing up to 5 successive sampling cycles with no significant loss of recovery. For larger volume samples, multilayer foil bags are the most stable for the compounds analyzed. The tests conducted with real and synthetic gas samples under optimized chromatography conditions using both methods indicated satisfactory performance for CO2 and CH4 quantification. However, CO analysis in the column with a polystyrene-divinylbenzene stationary phase (Method 1) produced an artifact due to the presence of oxygen in the samples, restricting its quantification.
DOI: 10.6084/m9.figshare.7773623.v1
title: ARTIFACTS IN THE ANALYSIS AND ASSESSMENT OF LOW-COST CONTAINERS FOR SAMPLING AND STORING GREENHOUSE GASES

description: The objectives of this study were twofold: to assess two chromatographic methods for the analysis of greenhouse gases (GHG) and carbon monoxide, and to propose and evaluate a low-cost and reusable alternative system for their sampling and storage, using 10 different container configurations (flasks and bags). To that end, standard samples containing the gases of interest (CO2, CH4 and CO) and different types of real samples were tested. Finally, procedures for the sampling, storage and analysis of CO2 and CH4 were evaluated and optimized. Two chromatographic methods were applied, using different analysis conditions and columns. Gas chromatography analysis of sample stability and container reusability demonstrated that borosilicate flasks with butyl rubber and PTFE/silicone septa are ideal for storing samples, allowing up to 5 successive sampling cycles with no significant loss of recovery. For larger volume samples, multilayer foil bags are the most stable for the compounds analyzed. The tests conducted with real and synthetic gas samples under optimized chromatography conditions using both methods indicated satisfactory performance for CO2 and CH4 quantification. However, CO analysis in the column with a polystyrene-divinylbenzene stationary phase (Method 1) produced an artifact due to the presence of oxygen in the samples, restricting its quantification.
DOI: 10.6084/m9.figshare.7773902.v1
title: METHODOLOGY TO PROMOTE THE QUALITATIVE DETECTION OF ORGANIC COMPOUNDS IN PETROLEUM/WATER INTERFACES

description: The possibility of detecting some organic compounds directly in a petroleum/water interface was described. Aqueous phase was composed by 1 x 10-3 mol L-1 NaCl solution and the oil phase was carried out using crude oil forming an oil/water interface. Carbon based screen-printed electrodes was used in conjunction with square-wave voltammetry technique, constituting the main tools of this technical note. Petroleum was contaminated with phenol, naphthalene and cyclohexane. The oxidation potentials for these three molecules were 0,72, 0,81 and 0,87 V vs. Ag, respectively. Phenol was chosen to study the stability of currents during the process. After 15 minutes, the currents of this process were stable. Although the formation of a passivation film, the qualitative detection of the molecules was possible. Finally, the main advantage of this methodology is the possibility of detecting contaminants in oil without the necessity of complicated pre-treatment steps.
DOI: 10.6084/m9.figshare.7773893
title: VALIDATION OF A SPECTROPHOTOMETRIC METHOD FOR QUANTIFICATION OF ACETYLSALICYLIC ACID in PHARMACEUTICAL FORMULATIONS: A PROPOSAL OF EXPERIMENTAL ACTIVITY FOR INSTRUMENTAL ANALYSIS

description: In the present article it is described the validation of a simple, precise, accurate, rapid and low-cost UV spectrophotometric method for the quantification of acetylsalicylic acid in pharmaceutical formulations. The method was validated by linearity, specificity, range, accuracy, precision, robustness, and limits of detection and quantification. The method was linear in the range between 24 – 36 µg mL-1, presenting a good correlation coefficient (r = 0.9994) and adequate limits of quantification (6.57 µg mL-1) and detection (1.99 µg mL-1). Precision analysis showed low coefficient of variation (&lt; 2.0%) and a good average recovery percentual (99.42% - reference and 95.94% - generic). The results and the statistical treated proved that the method may be considered a precise, accurate and low cost analytical alternative for laboratory routine and experimental activity. The method was applied for acetylsalicylic acid determination in two different pharmaceuticals formulations. The results of these analyzes are in accordance with the values declared by the manufacturer, at a 95% confidence level. This experimental activity is a simple and might be used as an practice activities on teaching laboratories improve the student learning.
DOI: 10.6084/m9.figshare.7773893.v1
title: VALIDATION OF A SPECTROPHOTOMETRIC METHOD FOR QUANTIFICATION OF ACETYLSALICYLIC ACID in PHARMACEUTICAL FORMULATIONS: A PROPOSAL OF EXPERIMENTAL ACTIVITY FOR INSTRUMENTAL ANALYSIS

description: In the present article it is described the validation of a simple, precise, accurate, rapid and low-cost UV spectrophotometric method for the quantification of acetylsalicylic acid in pharmaceutical formulations. The method was validated by linearity, specificity, range, accuracy, precision, robustness, and limits of detection and quantification. The method was linear in the range between 24 – 36 µg mL-1, presenting a good correlation coefficient (r = 0.9994) and adequate limits of quantification (6.57 µg mL-1) and detection (1.99 µg mL-1). Precision analysis showed low coefficient of variation (&lt; 2.0%) and a good average recovery percentual (99.42% - reference and 95.94% - generic). The results and the statistical treated proved that the method may be considered a precise, accurate and low cost analytical alternative for laboratory routine and experimental activity. The method was applied for acetylsalicylic acid determination in two different pharmaceuticals formulations. The results of these analyzes are in accordance with the values declared by the manufacturer, at a 95% confidence level. This experimental activity is a simple and might be used as an practice activities on teaching laboratories improve the student learning.
DOI: 10.6084/m9.figshare.7941485
title: ELUCIDATION OF THE INDUCED CHIRALITY OF DANSYLGLYCINE BY ITS INTERACTION WITH HUMAN SERUM ALBUMIN

description: Human serum albumin (HSA) plays an important role in the transport of a wide variety of substances, including compounds with pharmacological properties. The dansylglycine (DanG) is a fluorescent amino acid derivative specific for the site II of HSA. This work aimed to elucidate the induction of chirality in the DanG due to its bonding to the HSA. Theoretical electronic circular dichroism spectra (ECDs) were simulated using the Density Functional Theory (DFT) and the implicit Solvation Model based on Density (SMD). The DanG-HSA complexation resulted in the appearance of a positive ECD spectrum centered at 346 nm. Focusing on the dihedral angles between the -N(CH3)2 group bounded to the naphthalene ring, the potential energy surface (PES) of the DanG was obtained. Analysis of the various conformations obtained revealed that the calculated dihedral angle (150º) is in agreed with the experimental ECD spectrum. In addition, we observed that the nitrogen atom of the -N(CH3)2 group presented the greatest contribution to the HOMO-LUMO transition that gives rise to the n→π* electronic transition involved in the generation of the ECD signal. Molecular docking analysis of the complexation between DanG and HSA revealed a conformation with a dihedral angle similar to that obtained by DFT.
DOI: 10.6084/m9.figshare.7941485.v1
title: ELUCIDATION OF THE INDUCED CHIRALITY OF DANSYLGLYCINE BY ITS INTERACTION WITH HUMAN SERUM ALBUMIN

description: Human serum albumin (HSA) plays an important role in the transport of a wide variety of substances, including compounds with pharmacological properties. The dansylglycine (DanG) is a fluorescent amino acid derivative specific for the site II of HSA. This work aimed to elucidate the induction of chirality in the DanG due to its bonding to the HSA. Theoretical electronic circular dichroism spectra (ECDs) were simulated using the Density Functional Theory (DFT) and the implicit Solvation Model based on Density (SMD). The DanG-HSA complexation resulted in the appearance of a positive ECD spectrum centered at 346 nm. Focusing on the dihedral angles between the -N(CH3)2 group bounded to the naphthalene ring, the potential energy surface (PES) of the DanG was obtained. Analysis of the various conformations obtained revealed that the calculated dihedral angle (150º) is in agreed with the experimental ECD spectrum. In addition, we observed that the nitrogen atom of the -N(CH3)2 group presented the greatest contribution to the HOMO-LUMO transition that gives rise to the n→π* electronic transition involved in the generation of the ECD signal. Molecular docking analysis of the complexation between DanG and HSA revealed a conformation with a dihedral angle similar to that obtained by DFT.
DOI: 10.6084/m9.figshare.7942127
title: MOLECULE DESIGN AND PROPERTIES OF CYCLIC ENERGETIC MATERIALS BASED ON NITROGUANIDINE AND 1,1-DIAMINO-2,2-DINITROETHENE

description: A series of cyclic energetic derivatives based on nitroguanidine and 1,1-diamino-2,2-dinitroethene were theoretically designed. The spatial structures, infrared spectrometry, heats of formation, electronic structures, detonation properties, and thermal stabilities of these designed compounds were fully investigated by density functional theory. It is found that all the designed compounds have moderate stabilities (bond dissociation energies range from 11.3 to 99.0 kJ mol-1), high crystal densities (from 1.9589 to 2.00188 g cm-3), high positive heats of formation (from 649.6 to 1060.8 kJ mol-1) and high positive heats of detonation (from 1074.77 to 1332.06 cal g-1) which lead to the excellent detonation properties (detonation velocities range from 8.71 to 9.05 km s-1 while detonation pressures range from 35.47 to 38.55 GPa). Electronic structures such as electrostatic potentials on the surface, electronic densities, highest occupied molecular orbitals, lowest unoccupied molecular orbitals and their energy gaps were also simulated to give a better understanding of chemical and physical properties of these compounds. All the data may shine lights on the explosive searching and synthesis.
DOI: 10.6084/m9.figshare.7942127.v1
title: MOLECULE DESIGN AND PROPERTIES OF CYCLIC ENERGETIC MATERIALS BASED ON NITROGUANIDINE AND 1,1-DIAMINO-2,2-DINITROETHENE

description: A series of cyclic energetic derivatives based on nitroguanidine and 1,1-diamino-2,2-dinitroethene were theoretically designed. The spatial structures, infrared spectrometry, heats of formation, electronic structures, detonation properties, and thermal stabilities of these designed compounds were fully investigated by density functional theory. It is found that all the designed compounds have moderate stabilities (bond dissociation energies range from 11.3 to 99.0 kJ mol-1), high crystal densities (from 1.9589 to 2.00188 g cm-3), high positive heats of formation (from 649.6 to 1060.8 kJ mol-1) and high positive heats of detonation (from 1074.77 to 1332.06 cal g-1) which lead to the excellent detonation properties (detonation velocities range from 8.71 to 9.05 km s-1 while detonation pressures range from 35.47 to 38.55 GPa). Electronic structures such as electrostatic potentials on the surface, electronic densities, highest occupied molecular orbitals, lowest unoccupied molecular orbitals and their energy gaps were also simulated to give a better understanding of chemical and physical properties of these compounds. All the data may shine lights on the explosive searching and synthesis.
DOI: 10.6084/m9.figshare.7942505
title: COMPARISON BETWEEN SOXHLET AND MICROWAVE EXTRACTION TECHNIQUES FOR POLYCYLIC AROMATIC HYDROCARBONS IN LIVER AND ADIPOSE TISSUES OF MARINE TETRAPODS AND EVALUATION OF THE HETEROGENEITY OF TISSUES

description: For the evaluation of PAH extraction techniques in adipose and liver tissues of marine tetrapod, samples of some species (Pontoporia blainvillei, Chelonia mydas, Thalassarche melanophris, and Balaenoptera brydei) were spiked with PAH standards and extracted using soxhlet system and microwave oven. The results of both extraction techniques for the two different tissues of the four species of tetrapod were within the quality assurance and quality control criteria, that means both extraction techniques produced acceptable recoveries for surrogate and spiked compounds added to the sample tissues. Although both techniques of extraction met quality criteria and were considered suitable for extraction of marine tetrapod tissues, the soxhlet system produced a higher recovery of the spiked compounds and a lower standard deviation between the replicates than the microwave extraction; therefore the soxhlet system was considered the more efficient extraction method for PAH. The evaluation of liver and adipose tissue PAH accumulation, as well as the influence of tissue heterogeneity, was impaired as the concentrations of PAHs in almost all samples were lower than the detection limits of the analytical method.