Resumo em Inglês:

Adulterants in biodiesel/diesel blends modifies its physical and chemical properties. In this work, Fourier Transform Mid-Infrared spectrometry (FT-MIR) and multivariate control charts based on Net Analyte Signal (NAS) were used to monitor the quality of Crambe methyl biodiesel in relation to the biodiesel content and the presence of adulterants. The calibration model was constructed from the decomposition of the instrumental signals of the calibration samples into three vectors: NAS, interference and residual. From these vectors, three control charts were built: (i) NAS chart to monitor the analyte of interest (Crambe methyl biodiesel); (ii) Interference chart to monitor the data matrix (all components in diesel without the analyte of interest); and (iii) Residual chart to monitor any non-systematic variations. To validate the calibration model, other groups of B10, BX and B10 samples adulterated by direct addition of soybean oil and used fry oil in the range of 4.85-30.13% (v/v) were used. All samples prepared in-quality specifics were correctly classified as “in-quality control” samples, and other samples were correctly classified as “out-of-quality control” samples. Therefore, the methodology developed proved to be efficient in monitoring the quality of this fuel and it can be used by supervisory and quality control agencies.

Resumo em Inglês:

The miniaturized extraction techniques use less aggressive methods to the environment, since they generate less waste and spend a minimum of organic solvents, besides having a good selectivity and specificity in the extractions. In this context, liquid-liquid dispersive microextraction (DLLME) has been highlighting. Thus, the present article describes an optimization of the DLLME using low environmental impact extractor solvent to determine the chlorpyrifos insecticide in water. The analytical curves presented values for the correlation coefficient (r) higher than 0.999. The limits of detection and quantification were 0.24 and 0.80 µg L-1, respectively. There were recoveries between 93 and 97 %, with relative standard deviation (RSD) varying between 1.00 and 3.61%. The developed methods presented accurate and reliable results, are simple and safe, characteristics important for the implementation of a methodology as a routine analysis, and were applied in the determination of chlorpyrifos in water samples from five points along the Rio Dourados, near the city of Fátima do Sul.

Resumo em Inglês:

In this study, a nanogel was developed from a natural polymer, chitosan, to be used in the Lippia origanoides essential oil encapsulation. The encapsulation process was used in order to improve the functional capacity of this essential oil as an antioxidant. To obtain the nanogel, the chitosan was modified with caffeic acid using EDC coupling agent. The obtained material was characterized by FTIR and TGA, revealing the formation of the chitosan-caffeic acid bond. The size, morphology and essential oil amount incorporated to the nanogel were investigated by DLS, SEM and gravimetric analysis, respectively. SEM and gravimetric analysis indicated that oil were efficiently trapped inside the CS-CA matrix, with encapsulation efficiency of 42 ± 2%. The EDL studies showed that the encapsulation of essential oil in the nanogel significantly affected your structure, with a average particle size of 417.26 ± 55.96. After essential oil incorporation into the CS-CA nanogel it was also observed a increase in its antioxidant capacity in terms of elimination of DPPH and ABTS radicals, and ferric reducing antioxidant power (FRAP). The successful development of this CS-CA nanogel loaded with L. origanoides essential oil will lead to a better applicability of this essential oil as an effective antioxidant.

Resumo em Inglês:

Cinnamyl alcohol (AC) and cinnamyl acetate (ACM) were used as substrates in olefin metathesis reactions catalyzed by RuCl2(PCy3)2(=CHPh), first-generation Grubbs catalyst-G1, and RuCl2(PCy3)(H2IMes)(= CHPh), second-generation Grubbs catalyst-G2. The reactions occurred in the same reaction conditions for both substrates, 50 °C, for 24 h, in the proportions Ru:substrate of 1:1 and 1:10 mol. At the end of each experiment, the reaction mixture was evaluated by GC-MS and NMR of 13C{1H}. The results revealed different products when G1 and G2 are applied in the metathesis of AC, 1,5-diphenyl-2-pentene and stilbene, respectively. When ACM is the substrate, no product is noted with G1 and stilbene was the compound obtained with G2 as catalyst. In this study, we have presented a discussion about the electronic and steric influence of the ancillary ligands in the yield and type of product formed in the catalytic process.

Resumo em Inglês:

The bioconversion of furfural to furfuryl alcohol using only carrot bits in water at room temperature and ambient pressure is presented. This reaction led to the bioreduction of furfural with 99% conversion and 99% selectivity to an alcohol. This simple and “fully” green process may represent an alternative to classic hydrogenation processes. Also, without work-up procedure, we demonstrate the aqueous solution can be submitted to microwave irradiation to obtain 4-hydroxy-2-cyclopentenone.

Resumo em Inglês:

Calystegines are nortropane alkaloids with three to five hydroxyl groups. These alkaloids are recognized as glycosidase inhibitors and thus may have therapeutic potential to be exploited. There are also reports of its possible toxic effects when they are present in foods. Commercial cultivars of human consumption in Brazil have been analyzed for calystegines content. Samples of Solanum tuberosum L. (potato), Ipomoea batatas L. (sweet potato), Solanum lycopersicum (tomato), Solanum melongena (eggplant) and Solanum aethiopicum L. (gilo) were obtained from local markets in Rio de Janeiro, RJ, Brazil. Qualitative analyzes were performed by gas chromatography coupled to mass spectrometry (GC/MS) and high performance liquid chromatography coupled to mass spectrometry (LC/MS). Gas chromatography with flame ionization detector (GC/FID) was used in quantitative analysis. Five calystegines (A3, B1, B2, B4 and C1) were detected in the whole sample set and the amounts of three of them were determined: A3 (1.94-15.88 mg kg-1); B2 (7.59-23.7 mg kg-1) and B4 (3.61-9.38 mg kg-1). This is the first report on the occurrence of these alkaloids in Solanum aethiopicum L.

Resumo em Inglês:

Three simple methods are described for the determination of amoxicillin (AMX) in bulk drug and dosage forms using iodate-iodide mixture reagent. These methods employed the well-known analytical reaction between iodate-iodide mixture in the presence of acid solution. The iodide oxidized by iodate to iodine in an amount equivalent to the -COOH group present in amoxicillin (AMX) and the liberated iodine determined by titrimetry and spectrophotometry. In the titrimetric method (method A), the liberated iodine was reacted with a measured excess of thiosulphate and the residual thiosulphate was determined by titration with a standard iodine solution using starch indicator, the method was applicable over 2 - 16 mg of AMX. In the second and third methods, the absorbance of the liberated iodine was measured at 370 nm (method B) and also iodine was reacted with starch and starch-iodine complex was measured at 570 nm (method C). In spectrophotometric methods (B and C), Beer’s law was obeyed over the concentration range of 5 - 50 and 5 - 60 µg mL-1 AMX with a molar absorptivity values of 5.55×103 L mol-1 cm-1 and 4.76×103 L mol-1 cm-1 for the method A and method B, respectively. The limits of detection (LOD) and quantification (LOQ) were calculated for method B and method C. The proposed methods were found to yield reliable results when applied to bulk drug and dosage forms analysis, and hence they can be applied in quality control laboratories.

Resumo em Inglês:

Leishmaniasis is endemic anthropozoonosis considered to be a severe public health problem. The treatment with pentavalent antimonials presents high toxicity motivating the search for effective and less toxic drugs. Hydrazones and N-acylhydrazones are functional groups that are prominent in Medicinal Chemistry, including as antiprotozoals. In this context, five hydrazones derived from the natural aldehydes were synthesized and the molecular structures were suitably determined to employ uni and bidimensional 1H and 13C NMR techniques. The antileishmanial activity of all hydrazones was determined against promastigote forms of Leishmania amazonensis, and the compounds HDZ-3, HDZ-4, and HDZ-5 showed the best results, with IC50 of 9.00, 38.10 and 26.30 µM, respectively. In the cytotoxic evaluation against RAW macrophages, HDZ-4 presented the least cytotoxic (CC50 = 222.24 µM) and the higher selectivity. Lipinski’s descriptors of the hydrazones were calculated, and the compounds HDZ-3 and HDZ-5 were more promising. These hydrazones are hybrids of natural aldehydes with drugs, the first is the result of the junction of the cinnamaldehyde with isoniazid, and the second of the vanillin with hydralazine. The results highlighted the Markush isonicotinoylhydrazone and phthalazinylhydrazone groups, molecular structures that are present in HDZ-3 and HDZ-5 and are therefore considered innovators in the development of antileishmanial drugs.

Resumo em Inglês:

A mathematical model describing the reduction of Hydrogen peroxide (H2O2) to water in a metal dispersed conducting polymer film is discussed. The model is based on a system of reaction-diffusion equations containing a non-linear term related to Michaelis-Menten kinetics of the enzymatic reaction. The approximate analytical expressions corresponding to the concentration of substrate and product for steady and non-steady state conditions have been obtained using a new approach to homotopy perturbation method (HPM). Approximate analytical expressions of the electrochemical oxidation current are also presented for steady and non-steady state conditions. The numerical simulation (Matlab program) response for concentration profiles was carried out and compared with the analytical results of this work and are found to be in good agreement. The influence of initial substrate concentration, the thickness of the film as well as the diffusion layer and kinetic parameters on the current response were investigated. A graphical procedure for estimating the kinetic parameters from the expression of the current response is also proposed.

Resumo em Inglês:

The baseline drift artifact (BDA), namely, the baseline bias between the Hadamard transform (HT) spectrum and the signal averaging (SA) spectrum was unfortunately found in the HT pulsed separation techniques, which makes the HT analytical chemistry face the challenge of non-stability and unreliability. In order to find out the origin and eliminate the BDA phenomenon, the multiplexing mechanism of Hadamard transform ion mobility spectrometry (HT-IMS) has been analyzed in this research. Through simulation and experimental comparisons, the non-ideal overlap defect in Hadamard multiplexing process was suggested as the cause for the BDA phenomenon. Eventually, with a correction method, the BDA phenomenon could be well addressed, which guarantees the reliability and stability of HT techniques without increasing the hardware complexity.

Resumo em Inglês:

Copaifera multijuga Hayne is the main species of the genus in the Amazon region, being exploited for copaiba oil production mainly because of its therapeutic properties. The plant parts (leaves, branches, and barks) are widely used in folk medicine. However, they are little explored in terms of chemical composition. In this study, the polar extracts of leaves, branches, and barks of the species were analysed by direct infusion in ESI-MS with the aid of reference standards and MS2 fragmentation experiments. Twenty-six substances (carboxylic acids, flavonoids, condensed tannins, a diterpene and fifteen isomers of galoylquinic acids) were detected. Metabolic profiles were similar between extracts of leaves and branches, especially with the detection of galloylquinic acids and carboxylic acids. In bark extract, condensed tannins epicatechin-(4β-8)-epiafzelechin (dimer) and epicatechin-(4β-8)-epiafzelechin-(4β-8)-epiafzelechin (trimer) were detected. The PCA showed differences and similarities in the chemical composition of the copaíba mari-mari extracts. Thus, galloylquinic acids and flavonoids kaempferol, 7-O-methyl-kaempferol, quercetin-3-O-L-pentoside, and quercetin-3-O-L-rhamnoside are described for the first time in C. multijuga. The phytotherapeutic properties of teas of the plant parts of the species may be associated with the suggested polyphenols.

Resumo em Inglês:

In Medicinal Chemistry, the knowledge, the study and the understanding of the intermolecular interactions inherent to the molecular recognition of a ligand by its target bioreceptor are essential. This is because understanding these interactions, which define the molecular complementarity between the two, is the key to analyze critically structure-activity relationship studies, allowing the optimization of the modulation of a target bioreceptor by a ligand. Thus, it is necessary the constant study and analysis of intermolecular interactions related to the ligand-bioreceptor complexes. In general, these interactions are all electrostatic in nature, being traditionally classified into two large groups, the electrostatic forces themselves (such as those present in ion-dipole or ion-ion interactions) and van der Waals forces. Despite being well known, theoretical and experimental studies have revealed an increasing number of interactions mediated by these forces. This work presents and discusses intermolecular interactions considering “classical interactions” and “new interactions” in the context of Medicinal Chemistry, taking into account their current definitions, some theoretical principles of each interaction and addressing examples in which these interactions were important for complementarity between a ligand and a biorreceptor.

Resumo em Inglês:

Cannabidiol (CBD) and tetrahydrocannabinol (THC) are the main active principles in the Cannabis extracts. Rich-CBD extracts are indicated to control seizures in epileptic patients, THC is indicated as antiemetic to patients in chemotherapy treatment and extracts with THC and CBD in proportions of approximately 1:1 are indicated to control spasticity in patients with multiple sclerosis. In Brazil epileptic pediatric patients are treated with imported Cannabis extracts registered as food supplement and with national not regulated Cannabis extracts. With the medical Cannabis sanitary regulation in Brazil, quality control methods will be required. A High Performance Liquid Chromatography (HPLC) method was developed and validated for five cannabinoids quantification in oily extracts and resins. The method was applied to 101 Cannabis extracts consumed by patients attended by a risk assessment program. Linearity, selectivity and precision met the validation criteria of national and international sanitary agencies. Cannabis imported oily extracts showed high CBD levels (72.53±60.63 mg mL-1) and low THC levels (1.21±1.32 mg mL-1), while national Cannabis extracts showed mainly two profiles, first composed by negative or cannabinoids traces and the second composed by THC rich extracts (9.81±13.49 mg mL-1). The HPLC method is useful to pharmaceutical production and risk assessment purposes.

Resumo em Inglês:

The identification of essential oils constituents has been made easier and faster by the use of automatic software search engines that compare the experimental mass spectra and calculate the retention indices with those in commercial databases. However, these search engines and databases are very expensive. Electronic sheets have been assembled in a set of linked sheets, so that after some data is inserted, linear retention indices, relative response factors, normalization, area correction and absolute quantitation are calculated automatically. The set has been applied to the analysis of essential oils and volatiles in laboratory routine and substantial reduction in time-consuming and error-prone repetitive work were observed. One specific example for the analysis of an essential oil is provided. The designed electronic sheets can be a costless alternative to commercial software for data handling and identification.

Resumo em Inglês:

The present study investigated the use of intermolecular interaction concepts by freshman chemistry students during general chemistry classes, explaining some of the solubility phenomenon. For this purpose, classes on the topic in question were monitored and two tests were asking for explanations for the difference in solubility of oxygen and carbon dioxide in water and in perfluorocarbons and oxygen in fresh or salt water. Students also made graphic representations showing the water - oxygen molecules interactions. An analysis of the data demonstrated that several students had difficulties in correctly identifying that intermolecular interactions are involved in these systems. The concept of polarizability, fundamental in these systems, was rarely used in their explanations. The answers also indicated extensive use of the “like dissolves like” rule to explain solubility rather than using a complete description of the interactive processes involved. Most of the students’ explanations suggest an understanding of the knowledge as data or fact reproducing information and ideas without an effective use and understanding of the chemical concepts.

Resumo em Inglês:

The paper presents a simple method of determining iteratively the progression curve asymptote for first and pseudo-first order reactions. For selected student exercises, thus obtained results were compared (see Supplementary Material) with those found by means of the method of determining asymptotes experimentally. A nonlinear fitting method was additionally employed to assess the accuracy.

Resumo em Inglês:

A one-pot diastereoselective synthesis of thiazolidine-ring fused systems derived from enantiomerically pure amino acids, L-cysteine or D-penicillamine, and achiral succindialdehyde is described as an experiment to be carried out by upper-division undergraduate students in a laboratory classroom. Reactions were performed under mild conditions, the products were isolated through simple experimental procedures and fully characterized. This study combines organic synthesis, determination of the purity of compounds (TLC analysis and melting point measurements), optical activity measurements as well as structural analysis (interpretation of 1D NMR and 2D NMR spectra). It offers a platform for the discussion of important organic chemistry concepts such as diastereoselectivity, kinetic control vs thermodynamic control and cyclization reactions via nucleophilic addition to imines/iminium cations.

Resumo em Inglês:

Spin crossover is a property found in some coordination compounds formed by the first series of transition metals with d4-d7 configuration. These complexes, when stimulated by an external factor (temperature, light, etc.), can be converted from their low spin states to high spin states, or vice versa. However, this issue is not addressed in the Inorganic Chemistry literature used in undergraduate courses. In this work, the Density Functional Theory is used to predict which complexes may present the Spin Cross Over property. In addition to establish a methodology to predict in which situations this process will occur, this computational tool can also be used in undergraduate or postgraduate classes to explore this property in the study of coordination compounds.