Química

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Applications of micelle and microemulsion systems containing aminated surfactants synthesized from ricinoleic acid as carbon-steel corrosion inhibitors
(Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2009-05-15) Gurgel, Alexandre; Moura, Everlane Ferreira; Wanderley Neto, Alcides de Oliveira; Dantas, Tereza Neuma de Castro; Scatena Júnior, Hélio
The high affinity of surfactant molecules to adsorb onto interfaces is responsible for their applications in several interfacial systems. For this reason, surfactants can be used as good corrosion inhibitors in metallic surfaces. The main objective of this work was to examine the anticorrosion ability of three novel surfactant molecules synthesized from ricinoleic acid, a castor oil derivative. The surfactants are: sodium 12-N,N-diethylamino-9-octadecenoate (AR1S), sodium 12-N,N-diethylamino-9,10-dihydroxy-octadecanoate (AE2S) and sodium 12-N,N-diethylamino-9-octadecanoate (AE1S). Their ability to inhibit corrosion in AISI 1010 carbon-steel has been investigated by preparing specific micellar solutions and microemulsion systems. Adsorption phenomena have been electrochemically studied with the Frumkin model, indicating that the surfactant solutions tested can inhibit corrosion with levels as high as 95%. On the other hand, the microemulsion systems, although featuring relatively lower performance, are advantageous in that they are able to dissolve more active matter. These results are useful as a basis to propose and study particular applications such as the transport of oil in petrochemical industries.
Aqueous two-phase systems: a new approach for the determination of p-aminophenol
(Journal of Hazardous Materials, 2011-08-15) Rodrigues, Guilherme Dias; Lemos, Leandro Rodrigues de; Patrício, Pamela da Rocha; Silva, Luis Henrique Mendes da; Silva, Maria do Carmo Hespanhol da
A new method has been developed for the spectrophotometric determination of p-aminophenol (PAP) in water, paracetamol formulations and human urine samples with a recovery rate between 94.9 and 101%. This method exploits an aqueous two-phase system (ATPS) liquid–liquid extraction technique with the reaction of PAP, sodium nitroprusside and hydroxylamine hydrochloride in pH 12.0, which produces the [Fe2(CN)10]^10− anion complex that spontaneously concentrates in the top phase of the ATPS (). The ATPS does not require an organic solvent, which is a safer and cleaner liquid–liquid extraction technique for the determination of PAP. The linear range of detection was from 5.00 to 500 μg kg^−1 (R ≥ 0.9990; n = 8) with a coefficient of variation of 2.11% (n = 5). The method exhibited a detection limit of 2.40 μg kg^−1 and a quantification limit of 8.00 μg kg^−1. The ATPS method showed a recovery that ranged between 96.4 and 103% for the determination of PAP in natural water and wastewater samples, which was in excellent agreement with the results of the standard 4-aminoantipyrine method that was performed on the same samples.
Aqueous two-phase systems: An efficient, environmentally safe and economically viable method for purification of natural dye carmine
(Tecnologia de Alimentos, 2009-11-09) Mageste, Aparecida Barbosa; Lemos, Leandro Rodrigues de; Ferreira, Guilherme Max Dias; Silva, Maria do Carmo Hespanhol da; Silva, Luis Henrique Mendes da; Bonomo, Renata Cristina Ferreira; Minim, Luis Antonio
Partition of the natural dye carmine has been studied in aqueous two-phase systems prepared by mixing aqueous solutions of polymer or copolymer with aqueous salt solutions (Na2SO4 and Li2SO4). The carmine dye partition coefficient was investigated as a function of system pH, polymer molar mass, hydrophobicity, system tie-line length and nature of the electrolyte. It has been observed that the carmine partition coefficient is highly dependent on the electrolyte nature and pH of the system, reaching values as high as 300, indicating the high potential of the two-phase extraction with ATPS in the purification of carmine dye. The partition relative order was Li2SO4 ≫ Na2SO4. Carmine molecules were concentrated in the polymer-rich phase, indicating an enthalpic specific interaction between carmine and the pseudopolycation, which is formed by cation adsorption along the macromolecule chain. When the enthalpic carmine–pseudopolycation interaction decreases, entropic forces dominate the natural dye-transfer process, and the carmine partitioning coefficient decreases. The optimization of the extraction process was obtained by a central composite face-centered (CCF) design. The CCF design was used to evaluate the influence of Li2SO4 and PEO 1500 concentration and of the pH on the partition coefficient of carmine. The conditions that maximize the partition of carmine into the top phase were determined to be high concentrations of PEO and Li2SO4 and low pH values within the ranges studied.
Assignment of the relative and absolute stereochemistry of two novel epoxides using NMR and DFT-GIAO calculations
(Journal of Molecular Structure, 2018-07-15) Moraes, F. C.; Alvarenga, E. S.; Demuner, A. J.; Viana, V. M.
Considering the potential biological application of isobenzofuranones, especially as agrochemical defensives, two novel epoxides, (1aR,2R,2aR,5S,5aS,6S,6aS)- 5-(hydroxymethyl)hexahydro-2,6-methanooxireno[2,3-f]isobenzofuran-3(1aH)-one (9), and (1aS,2S,2aR,5S,5aS,6R,6aR)-5-(hydroxymethyl)hexahydro-2,6-methanooxireno[2,3-f]isobenzofuran-3(1aH)-one (10), were synthesized from the readily available D-mannitol in six steps. The multiplicities of the hydrogens located at the bridge of the bicycle are distinct for epoxides 9 and 10 due to W coupling, and this feature was employed to confirm the assignment of these nuclei. Besides analyses of the 2D NMR spectra, the assignments of the nuclei at the epoxide ring were also inferred from information obtained by theoretical calculations. The calculated 1H and 13C NMR chemical shifts for eight candidate structures were compared with the experimental chemical shifts of 9 and 10 by measuring the mean absolute errors (MAE) and by the DP4 statistical analysis. The structures and relative configurations of 9, and 10 were determined via NMR spectroscopy assisted with theoretical calculations. As consequence of the enantioselective syntheses starting from a natural polyol, the absolute configurations of the epoxides 9 and 10 were also defined.
A comparative study on the crystal structure of bicycle analogues to the natural phytotoxin helminthosporins
(Journal of Molecular Structure, 2016-02-05) Barbosa, Luiz Cláudio de Almeida; Teixeira, Robson Ricardo; Nogueira, Leonardo Brandão; Maltha, Celia Regina Alvares; Doriguetto, Antônio Carlos; Martins, Felipe Terra
Herein we described structural insights of a series of analogues to helminthosporin phytotoxins. The key reaction used to prepare the compounds corresponded to the [3 + 4] cycloaddition between the oxyallyl cation generated from 2,4-dibromopentan-3-one and different furans. Their structures were confirmed upon IR, NMR and X-ray diffraction analyses. While bicycles 7, 8 and 9 crystallize in the centrosymmetric monoclinic space group P21/c, compound 10 was solved in the noncentrosymmetric orthorhombic space group P212121. The solid materials obtained were shown to be racemic crystals (7, 8, 9) or racemic conglomerate (10). In all compounds, there is formation of a bicycle featured by fused tetrahydropyranone and 2,5-dihydrofuran rings. They adopt chair and envelope conformations, respectively. Crystal packing of all compounds is stabilized through C–H•••O contacts. Conformational aspects as well as similarities and differences among the crystal structures of the synthesized analogues are discussed.
Conformational analysis of 8-oxabicyclo[3.2.1]oct-6-en-3-one derivatives by NMR and theoretical calculations
(Journal of Molecular Structure, 2006-06-19) Maltha, Célia R. A.; Alcântara, Antônio Flávio C.; Piló-Veloso, Dorila; Almeida, Wagner B. de; Barbosa, Luiz Cláudio A.
This work describes the conformational analysis of alcohols 2α,4α-dimethyl-6,7-exo-isopropylidenedioxy-8-oxabicyclo[3.2.1]octan-3α-ol (5) and –3β-ol (6) and of alcohols 1,2α,4α,5-tetramethyl-6,7-exo-isopropylidenedioxy-8-oxabicyclo[3.2.1]octan-3α-ol (7) and -3β-ol (8). Based on NMR data and AM1, HF/6-31G* and DFT/B3LYP/6-31G* geometry optimization, the pyran ring of compounds (5) to (7) is found to have a chair conformation. In the case of (8), NMR data indicate the presence of a boat conformer (8boat). However, the chair conformer (8chair) is predicted to have smaller relative energy as given by calculations employing different basis sets for either calculations on isolated molecules or including the solvent used in the NMR analyses (CDCl3). In contradistinction to thermodynamic results, DFT/B3LYP/6-31G* calculations of hydrogen (δH) and carbon (δC) chemical shifts of (8boat) were concordant with NMR experimental data of (8). Therefore, the chemical shift calculations agree better with the experimental results than does the quantum chemical calculations leading to the conformational analysis of (8).
Conformerism, enantiomorphism and double catemer motifs in para-substituted nostoclide analogues
(Journal of Molecular Structure, 2016-02-15) Teixeira, Róbson Ricardo; Barbosa, Luiz Claudio Almeida; Antolinez, Isabel Valero; Corrêa, Rodrigo de Souza; Martins, Felipe Terra; Doriguetto, Antônio Carlos
We have here elucidated the crystal structures of five nostoclide analogues. A common feature in all compounds is a substituent at the para-position of the benzylidene group. Compounds with either bromine (3) or hydroxyl (4) as para-substituent crystallizes with Z’ = 2 as result of conformerism. It was also observed that Z' > 1 in the compound with a para-dimethylamino substituent (1). However, its four crystallographically independent molecules are conformationally similar. They are not related by crystallographic symmetry due to the offset packing of their C–H … OC nonclassical hydrogen bonded double chains. This compound (1) has also crystallized in a chiral space group (P21) despite the lack of a stereocenter. Such enantiomorphism phenomenon is related to the presence of only one of the two mirror benzyl conformations with phenyl ring at the equatorial position opposite the lactone oxygen atom. The molecular mean plane of nostoclide analogues has been featured by high level of planarity, except in the brominated compound where two twisted conformations occurred due to rotations on the single bond axis into benzylidene group. The benzyl conformation has been the greatest difference between the two crystallographically independent molecules of the para-hydroxylated compound (4). The crystal packing of the compounds is marked by double catemer motif assembled through C–H … OC non-classical hydrogen bonds, although C–H … π interactions do play an important role in stabilizing the crystal packing of some compounds of the series.
Corymbia spp. and Eucalyptus spp. essential oils have insecticidal activity against Plutella xylostella
(Industrial Crops and Products, 2017-12-15) Filomeno, Claudinei Andrade; Barbosa, Luiz Claudio Almeida; Teixeira, Robson Ricardo; Pinheiro, Antônio Lelis; Farias, Elizeu de Sá; Silva, Eliete Meire de Paula; Picanço, Marcelo Coutinho
Plutella xylostella (L.) is the main brassica pest worldwide and is difficult to control even with commercial insecticides. In this study, assessments were made of the contact toxicity of essential oils (EOs) from ten Myrtaceae species. For this, the leaves of four Corymbia species (C. citriodora, C. intermedia, C. maculata, and C. ptychocarpa) and six Eucalyptus species (E. andrewsii, E. crebra, E. punctata, E. pyrocarpa, E. siderophloia, and E. sphaerocarpa) were collected during the Brazilian dry season and subjected to hydrodistillation for extraction of EOs. For C. citriodora, another sample was also collected during the rainy season. The essential oil (EO) content of all samples ranged from 0.07% w/w to 3.3% w/w and GC–MS analyses allowed the identification of 52 compounds. For E. andrewsii, E. pyrocarpa, and C. ptychocarpa there was no previous report on EO chemical composition. For C. citriodora, a higher EO content for the samples collected during the dry season was found (2.72% versus 1.53% for the rainy season). The insecticidal activity of all eleven EOs was evaluated via topical application on the second-instar larvae of P. xylostella. The most active EOs were produced by C. citriodora collected during the dry season, with citronellal (86.8%) and isopulegol (4.7%) being the main constituents. At 30 μg/mg of insect, these EOs caused 80% P. xylostella mortality, being more active than neem oil used as positive control. These EOs presented low toxicity for Solenopsis saevissima, a natural predator of P. xylostella. Bioassays also demonstrated a synergistic effect between citronellal and (-)-isopulegol at all tested proportions. The results described here suggest that C. citriodora EOs can be an environmentally friendly alternative method to control P. xylostella.
A digital image method of spot tests for determination of copper in sugar cane spirits
(Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2017-10-05) Pessoa, Kenia Dias; Suarez, Willian Toito; Reis, Marina Ferreira dos; Franco, Mathews de Oliveira Krambeck; Moreira, Renata Pereira Lopes; Santos, Vagner Bezerra dos
In this work the development and validation of analytical methodology for determination of copper in sugarcane spirit samples is carried out. The digital image based (DIB) method was applied along with spot test from the colorimetric reaction employing the RGB color model. For the determination of copper concentration, it was used the cuprizone - a bidentate organic reagent - which forms with copper a blue chelate in an alkaline medium. A linear calibration curve over the concentration range from 0.75 to 5.00 mg L^−1 (r2 = 0.9988) was obtained and limits of detection and quantification of 0.078 mg L^−1 and 0.26 mg L^−1 were acquired, respectively. For the accuracy studies, recovery per- centages ranged from 98 to 104% were obtained. The comparison of cooper concentration results in sugar cane spirits using the DIB method and Flame Atomic Absorption Spectrometry as reference method showed no significant differ- ences between both methods, which were performed using the paired t-test in 95% of confidence level. Thus, the spot test method associated with DIB allows the use of devices as digital cameras and smartphones to evaluate colorimetric reaction with low waste generation, practicality, quickness, accuracy, precision, high portability and low-cost.
Experimental and theoretical NMR determination of isoniazid and sodium p-sulfonatocalix[n]arenes inclusion complexes
(European Journal of Pharmaceutical Sciences, 2012-10-09) Teixeira, Milena G.; Assis, João V. de; Soares, Cássia G. P.; Lopes, Juliana F.; Carvalho, Guilherme S. L.; Lourenço, Maria C. S.; Almeida, Mauro V. de; Almeida, Wagner B. de; Fernandes, Sergio A.
In this work the inclusion complex formation of isoniazid with sodium p-sulfonatocalix[n]arenes is reported aiming to improve the physicochemical and biopharmaceutical properties of isoniazid a first line antibuberculosis drug. The architectures of the complexes were proposed according to NMR data Job plot indicating details on the insertion of the isoniazid in the calix[n]arenes cavities. DFT theoretical NMR calculations were also performed for sodium p-sulfonatocalix[4]arene complex with isoniazid, with various modes of complexation being considered, to provide support for the experimental proposal. A comparison between experimental and theoretical 1H NMR chemical shifts profiles allowed for the inclusion complex characterization confirming the isoniazid inclusion mode which is preferentially through the hydrazide moiety. The remarkable agreement between experimental and theoretical NMR profiles adds support to their use in the structural characterization of inclusion compounds. Antibacterial activity was evaluated and the results indicated the inclusion complexes as a potential strategy for tuberculosis treatment.
Experimental and theoretical studies on the characterization of monocrotaline by infrared and Raman spectroscopies
(Journal of Molecular Structure, 2017-05-05) Oliveira, Ramon Prata; Demuner, Antonio Jacinto; Alvarenga, Elson Santiago; Parma, Monica Cropo; Barbosa, Luiz Claudio Almeida; Guimarães, Luciano de Moura; Aguiar, Alex Ramos
The use of plants in folk medicine has a long and ancient history in the treatment of various diseases. Currently, a large proportion of commercial drugs are based on natural products or are synthetic compounds inspired on such natural substances. Therefore, in this communication to aid that research, structural and spectroscopic analysis of the natural pyrrolizidine alkaloid called monocrotaline was carried out. Pyrrolizidine alkaloids that are commonly found in the Boraginaceae and Asteraceae families are among the great diversity of secondary metabolites which are produced by plants to act as a defense mechanism against herbivores and microbes. In the present study, the natural product, monocrotaline, an alkaloid isolated from the leaves of Crotalaria paulina, with potential application in medicine, was characterized by infrared (IR) and Raman spectroscopy with the support of Density Functional Theory (DFT) calculations. IR and Raman spectra of monocrotaline were recorded at room temperature ranging from 4000 to 400 cm 1 . DFT calculations with the hybrid functional B3LYP and the basis set 6-31 þ G(d,p) were performed with the purpose of obtaining information on the structural and vibrational properties of this structure. A perfect fit between the experimentally measured frequencies of the IR and Raman spectra and the calculated values were observed, and we have performed the complete identification of monocrotaline by these techniques.
Extracts from the leaves of Piper piscatorum (Trel. Yunc.) obtained by supercritical extraction of with CO2, employing ethanol and methanol as co-solvents
(Industrial Crops and Products, 2013-05) Pimentel, Flávio A.; Cardoso, Maria das G.; Guimarães, Luiz G.L.; Queiroz, Fabiana; Barbosa, Luiz C.A.; Morais, Augusto R.; Nelson, David L.; Andrade, Milene A.; Zacaroni, Lidiany M.; Pimentel, Sônia Maria N.P.
The efficiency of the extraction of fresh and dried leaves of Piper piscatorum was evaluated employing supercritical CO2 and co-solvents (10% ethanol and 10% methanol) at 40 °C and 70 °C and a pressure of 400 bar. The extracts were characterized chemically by GC–MS and GC–FID. The major components of the extracts were piperovatine, followed by palmitic acid, pentadecane and pipercallosidine. Drying of the leaves caused modifications in their composition, mainly reducing the concentration of the amides, which have activity as anesthetics. The highest yields of the piperovatine (0.93%, w/w) and pipercallosidine (0.24%, w/w) were obtained from the fresh leaves extracted with CO2 modified with 10% ethanol at 40 °C.
Fuel properties of Brassica juncea oil methyl esters blended with ultra-low sulfur diesel fuel
(Renewable Energy, 2015-06) Jham, Gulab Newandram; Evangelista, Roque L.; Moser, Bryan R.
Brassica juncea is a drought-tolerant member of the Brassicaceae plant family with high oil content and a short growing season that is tolerant of low quality soils. It was investigated as a feedstock for production of biodiesel along with evaluation of subsequent fuel properties, both neat and in blends with petroleum diesel fuel. These results were compared against relevant fuel standards such as ASTM D6751, EN 14214, ASTM D975, EN 590, and ASTM D7467. Crude B. juncea oil was extracted from unconditioned seeds utilizing a continuous tubular radial expeller. The oil was then chemically refined via degumming, neutralization and bleaching to render it amenable to direct homogeneous sodium methoxide-catalyzed transesterification. The principal fatty acid detected in B. juncea oil was erucic acid (44.1%). The resulting biodiesel yielded fuel properties compliant with the biodiesel standards with the exception of oxidative stability and kinematic viscosity in the case of EN 14214. Addition of tert-butylhydroquinone and blending with soybean oil-derived biodiesel ameliorated these deficiencies. The fuel properties of B5 and B20 blends of B. juncea oil methyl esters (BJME) in ultra-low sulfur (<15 ppm S) diesel (ULSD) fuel were within the ranges specified in the petrodiesel standards ASTM D975, EN 590 and ASTM D7467 with the exception of derived cetane number in the case of EN 590. This deficiency was attributed to the inherently low cetane number of the certification-grade ULSD, as it did not contain performance-enhancing additives. In summary, this study reports new fuel property data for BJME along with properties of B5 and B20 blends in ULSD. Such results will be useful for the development of B. juncea as an alternative source of biodiesel fuel.
A green and sensitive method to determine phenols in water and wastewater samples using an aqueous two-phase system
(Talanta, 2009-09-04) Rodrigues, Guilherme Dias; Lemos, Leandro Rodrigues de; Silva, Luis Henrique Mendes da; Silva, Maria do Carmo Hespanhol da; Minim, Luis Antonio; Coimbra, Jane Sélia dos Reis
A greener and more sensitive spectrophotometric procedure has been developed for the determination of phenol and o-cresol that exploits an aqueous two-phase system (ATPS) using a liquid–liquid extraction technique. An ATPS is formed mostly by water and does not require organic solvent. Other ATPS components used in this study were the polymer, polyethylene oxide, and some salts (i.e., Li2SO4, Na2SO4 or K2HPO4 + KOH). The method is based on the reaction between phenol, sodium nitroprusside (NPS) and hydroxylamine hydrochloride (HL) in an alkaline medium (pH 12.0), producing the complex anion [Fe2(CN)10]^10− that spontaneously concentrates in the top phase of the system. The linear range was 1.50–500 μg kg^−1 (R ≥ 0.9997; n = 8) with coefficients of variation equal to 0.38% for phenol and 0.30% for o-cresol (n = 5). The method yielded limits of detection (LODs) of 1.27 and 1.88 μg kg^−1 and limits of quantification (LOQs) of 4.22 and 6.28 μg kg^−1 for phenol and o-cresol, respectively. Recoveries between 95.7% and 107% were obtained for the determination of phenol in natural water and wastewater samples. In addition, excellent agreement was observed between this new ATPS method and the standard 4-aminoantipyrine (4-AAP) method.
Green recovery of mercury from domestic and industrial waste
(Journal of Hazardous Materials, 2015-11-10) Cunha, Roselaine C. da; Patrício, Pamela R.; Vargas, Silvia J. Rodriguez; Silva, Luis Henrique Mendes da; Silva, Maria C. Hespanhol da
Recovery of mercury from effluents is fundamental for environmental preservation. A new, green method was developed for separation of mercury from effluent containing different metals. The extraction/separation of Hg(II) was studied using aqueous two-phase system (ATPS) comprising by polyethylene oxide (PEO1500) or triblock copolymers (L64 or L35), electrolyte (sodium citrate or sodium sulfate) and water in the presence or absence of chloride ions. The extraction behavior of the Hg(II) for the macromolecule-rich phase is affected by the following parameters: amount of added extractant, pH, and the nature of the electrolyte and macromolecule of the ATPS. The APTS of PEO1500 + sodium citrate + H2O (pH 1.00 and 0.225 mol kg−1 KCl) produced the highest Hg(II) %E = (92.3 ± 5.2)%. Under the same conditions, excellent separation factors (1.54 × 102 − 3.21 × 1010) for recovery of mercury in the presence of co-existing metals were obtained. Efficient and selective extraction of Hg(II) from domestic and industrial synthetic effluents was achieved using this ATPS.
Headspace solid phase microextraction-gas chromatography for the determination of trihalomethanes in fish
(Microchemical Journal, 2017-07) Delvaux Júnior, Nelson A.; Queiroz, Maria E.L.R. de; Neves, Antônio A.; Oliveira, André F.; Silva, Marcos R. F. da; Faroni, Lêda R. A.; Heleno, Fernanda F.
The aim of this work is to develop a method for determining trihalomethanes (THMs) in fish samples. The proposed method uses solid phase microextraction and gas chromatography with an electron capture detector. Factors such as temperature, extraction time and type of fiber were assessed to maximize the performance of the extraction technique. The performance of the method was evaluated using selectivity, linearity, precision, accuracy and limits of detection (LOD) and quantification (LOQ). The new method allows analysis of THMs with appropriate selectivity and linearity, with coefficient of correlation > 0.98. The LOD and LOQ of the analytes of interest are from 0.11 to 0.35 μg kg− 1 and 0.35 to 1.18 μg kg− 1, respectively. In addition, the relative standard deviation (RSD) was between 1.6 and 8%, and the relative recovery was between 76 and 113%. The optimized and validated method was applied to fish samples purchased from the Viçosa (MG) local market. At least three of the THMs of interest were detected in most of the analyzed fish samples with maximum values for the concentration of chloroform, bromodichloromethane and bromoform at 8.33, 0.42 and 2.41 μg kg− 1, respectively.
Liquid–liquid equilibrium of aqueous two-phase systems composed of poly(ethylene oxide) 1500 and different electrolytes ((NH4 )2SO4 , ZnSO4 and K2HPO4 ): experimental and correlation
(Fluid Phase Equilibria, 2011-06-15) Lemos, Leandro Rodrigues de; Patrício, Pamela da Rocha; Rodrigues, Guilherme Dias; Carvalho, Raquel Moreira Maduro de; Silva, Maria C. Hespanhol da; Silva, Luis Henrique Mendes da
Phase diagrams of aqueous two-phase systems composed of PEO1500 + salt (di-potassium phosphate + potassium hydroxide or ammonium sulfate or zinc sulfate) + water were determined at (283.15, 298.15, and 313.15) K. All systems produce a large two-phase region; however the influence of temperature on the binodal position seems to be very small. By analyzing the effects of ammonium sulfate or zinc sulfate, it was observed that zinc was more effective in promoting phase separation than ammonium. The consistency of the tie-line data was ascertained by applying the Othmer–Tobias correlation. In this paper, aqueous two-phase systems data for nine ternary systems are correlated by using the NRTL model and UNIFAC for the activity coefficient. The results are very satisfactory, with root mean square deviations between experimental and calculated compositions as low as 0.99 and 1.21%, respectively. However the NRTL model better represents the systems in study, when compared with UNIFAC.
Low-temperature clean-up method for the determination of pyrethroids in milk using gas chromatography with electron capture detection
(Talanta, 2008-02-08) Goulart, Simone Machado; Queiroz, Maria Eliana L.R. de; Neves, Antônio Augusto; Queiroz, José Humberto de
This paper describes a new gas-chrormatography with electron capture detection (GC-ECD) method for determination of some pyrethroids in milk samples. The extraction of the pyrethroids was carried out by liquid–liquid extraction with clean-up by precipitation at low temperature, without additional stages for removal of fat interferences. The method was efficient with recoveries of 93.0 ± 0.1% for cipermethrin and 84.0 ± 0.3% for deltamethrin. The quantification limits were 0.75 μg L−1 for both pyrethroids. The method was simple, of easy execution, and used only small quantities of organic solvent. After optimization and validation, the method was used for the determination of residues of the pyrethroids cipermethrin and deltamethrin in milk and in lactea drink commercialized in Viçosa (MG, Brazil). Some samples presented contamination with deltamethrin at levels below the maximum contamination limits established by the FAO.
New rubrolide analogues as inhibitors of photosynthesis light reactions
(Journal of Photochemistry and Photobiology B:, 2015-03-01) Varejão, Jodieh O.S.; Barbosa, Luiz C.A.; Ramos, Gabriela Álvarez; Varejão, Eduardo V.V.; King-Díaz, Beatriz; Lotina-Hennsen, Blas
Natural products called rubrolides have been investigated as a model for the development of new herbi- cides that act on the photosynthesis apparatus. This study comprises a comprehensive analysis of the photosynthesis inhibitory ability of 27 new structurally diverse rubrolide analogues. In general, the results revealed that the compounds exhibited efficient inhibition of the photosynthetic process, but in some cases low water solubility may be a limiting factor. To elucidate their mode of action, the effects of the compounds on PSII and PSI, as well as their partial reaction on chloroplasts and the chlorophyll a fluorescence transients were measured. Our results showed that some of the most active rubrolide ana- logues act as a Hill reaction inhibitors at the QB level by interacting with the D1 protein at the reducing side of PSII. All of the active analogues follow Tice’s rule of 5, which indicates that these compounds pre- sent physicochemical properties suitable for herbicides.
A new spectrophotometric method for determination of EDTA in water using its complex with Mn(III)
(Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2016-06-06) Andrade, Carlos Eduardo O.; Oliveira, André F.; Neves, Antônio A.; Queiroz, Maria Eliana L.R.
EDTA is an important ligand used in many industrial products as well as in agriculture, where it is employed to assist in phytoextraction procedures and the absorption of nutrients by plants. Due to its intensive use and recalcitrance, it is now considered an emerging pollutant in water, so there is great interest in techniques suitable for its monitoring. This work proposes a method based on formation of the Mn(III)-EDTA complex after oxidation of the Mn(II)-EDTA complex by PbO2 immobilized on cyanoacrylate spheres. A design of experiments (DOE) based on the Doehlert matrix was used to determine the optimum conditions of the method, and the influence of the variables was evaluated using a multiple linear regression (MLR) model. The optimized method presented a linear response in the range from 0.77 to 100.0 μmol L− 1, with analytical sensitivity of 7.7 × 103 L mol− 1, a coefficient of determination of 0.999, and a limit of detection of 0.23 μmol L− 1. The method was applied using samples fortified at different concentration levels, and the recoveries achieved were between 97.0 and 104.9%.