Química

URI permanente desta comunidadehttps://locus.ufv.br/handle/123456789/11782

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Aggregation behavior of self-assembled nanoparticles made from carboxymethyl-hexanoyl chitosan and sodium dodecyl sulphate surfactant in water
(Journal of Molecular Liquids, 2019-03-15) Agudelo, Alvaro J. P.; Silva, Luis H. M. da; Rengifo, Andrés F. C.; Santos, Sandra C.; Lima, Vania R. de; Parize, Alexandre L.; Minatti, Edson
Biopolymers can be used to produce nano-objects in solution and they are generally of low cost and biocompatible. However, they commonly have low kinetic stability and form aggregates with a broad particle size distribution, characteristics that hinder their use in drug delivery systems. Herein, we report the thermodynamics and mechanisms underlying the formation of nanostructures through the self-assembly of carboxymethyl-hexanoyl chitosan (ONCHC) and the effect of the presence of the surfactant sodium dodecyl sulfate (SDS). The pre- and post-aggregation regimes were monitored using several techniques and indicated that self-assembly is thermodynamically favorable. The presence of SDS decreased the hydrodynamic radius and surface charge of the SDS-ONCHC nanoaggregates and increased the kinetic stability in aqueous solution over a period of 150 days. The SDS-ONCHC interaction is driven mainly by a hydrophobic effect and the addition of SDS increases the number and strength of the hydrophobic domains, where the integral enthalpy change for the aggregate formation is −2.11 kJ mol−1.
Aqueous two-phase systems of copolymer L64 + organic salt + water: Enthalpic L64–salt interaction and Othmer–Tobias, NRTL and UNIFAC thermodynamic modeling
(Chemical Engineering Journal, 2011-06-15) Andrade, Vivianne Molica de; Rodrigues, Guilherme Dias; Carvalho, Raquel Moreira Maduro de; Silva, Luis Henrique Mendes da; Silva, Maria C. Hespanhol da
Phase diagrams of two-phase systems (ATPS) composed by the triblock copolymer L64 + organic salt (sodium tartrate, sodium succinate, sodium citrate, or ammonium citrate) + water, at different temperatures (278, 288, and 298 K) are presented in this work. Contrary to behavior of ATPS formed by inorganic salts, the study of the temperature influence in the liquid–liquid equilibrium behavior of L64–organic salts ATPS showed an exothermic character for phase separation process. Microcalorimetric measurements showed that this phase separation energy is around −0.2 kJ mol−1 for all organic salts. The module of slope of tie line (STL) tends to increase with an increase in temperature. The cation nature effect showed that the salt Na3C6H5O7 was more effective in promoting phase separation than (NH4)3C6H5O7. The capacity of the different anions tested for inducing ATPS formation with L64 followed the order: C6H5O73− > C4H4O62− > C4H4O42−. Because the salt–L64 interaction energy to be very similar, the cation and anion effects on the phase separation could be attribute to a process driven by entropy. The interaction parameters of the NRTL and UNIFAC models were estimated through the experimental data of all ternary systems. The results of the NRTL (with 64 tie-lines) and UNIFAC (with 27 tie-lines) were considered excellent with global root mean square deviations, respectively, of the 1.04% and 0.87%. The consistencies of the all tie-line experimental compositions were improved by applying the Othmer–Tobias correlation.
Centrosymmetric resonance-assisted intermolecular hydrogen bonding chains in the enol form of β-diketone: Crystal structure and theoretical study
(Journal of Molecular Graphics and Modelling, 2016-07) Teixeira, Róbson R.; Pereira, Wagner L.; Ellena, Javier A.; Paixão, Drielly A.; Guilardi, Silvana; Franca, Eduardo F.
Isobenzofuran-1(3H)-ones (phtalides) are heterocycles that present a benzene ring fused to a γ-lactone functionality. This structural motif is found in several natural and synthetic compounds that present relevant biological activities. In the present investigation, the 3-(2-hydroxy-4,4-dimethyl-6-oxocyclohexen-1-yl)isobenzofuran-1(3H)-one was characterized by single-crystal X-ray analysis. In the crystal structure, there are two molecules per asymmetric unit. One of them exhibits resonance assisted hydrogen bonds (RAHBs). Semi-empirical and DFT calculations were performed to obtain electronic structure and π-delocalization parameters, in order to better understand the energy stabilization of RAHBs in the crystal packing of the studied molecule. The structural parameters showed good agreement between theoretical and experimental data. The theoretical investigation revealed that the RAHBs stabilization energy is directly related to the electronic delocalization of the enol form fragment. In addition, RAHBs significantly affected the HOMO and charge distribution around the conjugated system.
Characterization and evaluation of sorption potential of the iron mine waste after Samarco dam disaster in Doce River basin – Brazil
(Chemosphere, 2018-10) Almeida, Cristiane Aparecida; Oliveira, André Fernando de; Pacheco, Anderson Almeida; Lopes, Renata Pereira; Neves, Antônio Augusto; Queiroz, Maria Eliana Lopes Ribeiro de
The Fundão dam collapsed releasing 60 million tons of mining waste into the environment. The mining wastes should be better studied, since some of them are deposited on the alluvial plains soil and at the bottom of the rivers, like sediments, of the region affected. Thus, this work aims to perform the chemical, physical and adsorptive characterization of the samples colleted in region de Paracatu de Baixo. The mining waste has uneven surface, with sizes ranging from 2 to 200 μm, pHPCZ in 6.0. Are composed predominantly by kaolinite, goethite, hematite, gibbsite and quartz. It has been classified as non-hazardous residues. The adsorption studies showed the mining waste have a low Cationic Exchange Capacity. The sorption process was occurs by ion exchange and the kinetics follows the pseudo second order model (R2 > 0.78). The process is endothermic (ΔH in 29.33 kJ mol−1) and spontaneous (ΔG in −24.7 kJ mol−1 at 25 °C). The Langmuir model presented a better fit (R2 > 0.995) to the experimental data. Therefore, the methylene blue can be used as a cation model to predict the behavior of cationic species on the mining waste, with maximum adsorption capacity of 4.42 mg g−1 at 25 °C.
Chemical constituents of the bark of Gallesia gorazema
(Fitoterapia, 1999-04-01) Barbosa, Luiz CLaudio Almeida; Demuner, Antônio Jacinto; Teixeira, Robson; Madruga, M. S.
Chemical composition analysis of the essential oil from the bark of Gallesia gorazema was carried out by GC/MS. This analysis led to the identification of six non-sulfurated and 19 sulfurated compounds.
Early prediction of sugarcane genotypes susceptible and resistant to Diatraea saccharalis using spectroscopies and classification techniques
(Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2019-07-05) Porto, Nathália de A.; Roque, Jussara V.; Wartha, Cleiton A.; Cardoso, Wilson; Peternelli, Luiz A.; Barbosa, Márcio H. P.; Teófilo, Reinaldo F.
The aim of this work was to use spectroscopic methods and partial least squares discriminant analysis (PLS-DA) for the early prediction of genotype resistance or susceptibility to sugarcane borer. The sugarcane leaf +1 was directly analyzed with no sample preparation by ultraviolet-visible-near-infrared (UV-VIS-NIR), middle-infrared (MID), and near-infrared (NIR) spectroscopies. Also, laser-induced breakdown spectroscopy (LIBS) was used to analyze pellets of dried and ground leaves and stalks of sugarcane. Classification models were built using PLS-DA. The models built using UV-VIS-NIR, MID or NIR spectra exhibited ideal sensitivity, specificity, and classification errors, i.e., 1 for both sensitivity and specificity and 0 for classification errors. Regarding the models built using LIBS spectra, those using spectra of pellets made from dried and ground leaves also presented ideal sensitivity, specificity, and classification errors; on the other hand, models built using the spectra of pellets made of dried and ground stalks did not present ideal values for these parameters. Thus, the models built, except for the one using LIBS of pellets made of stalks, showed excellent predictive capacity, making them suitable for predicting the resistance or susceptibility of sugarcane genotypes in the early stages of a plant's life.
Hederagenin amide derivatives as potential antiproliferative agents
(European Journal of Medicinal Chemistry, 2019-04-15) Barbosa, Luiz C. A.; Demuner, Antonio J.; Rodríguez-Hernández, Diego; Martins, João Paulo Ataide; Csuk, René; Fischer (nee Heller), Lucie
In this study, a series of C-28 amides derivatives of hederagenin with or without the presence of an acetyl group at positions 3 and 23 in ring A, were synthetized aiming to develop potent cytotoxic agents. Their structures were confirmed by MS, IR, 1H NMR and 13C NMR spectroscopic analyses and their cytotoxic activities were screened in SRB assays using a panel of six human cancer cell lines. The majority of the amide derivatives were cytotoxic for a variety of human tumor cell lines. In general, the hydroxylated derivatives (1a-1d; EC50 in the range 1.2–22.5 μM) were less active than the acetylated derivatives (2a-2n; EC50 in the range 0.4–9.0 μM). Hydroxylated derivative bearing pyrrolidinyl substituent 1c, was the most active for HT29 human line cells (EC50 = 1.2 μM), however their acetylated derivative 2c was the most potent and selective against A2780, FaDu, SW1736 cells, showing EC50 values between 0.4 and 1.7 μM and SI between 5.6 and 24. Staining experiments combined with fluorescence microscopy indicate that the cell membrane became permeable, and finally a process of secondary necrosis was observed. In addition, the docking results showed that acetylated compounds display more affinity to HER2 than to USP7, indicating that HER2 is a most probable receptor, both proteins found in tumor cell line A2780.
Iron oxide/carbon nanotubes/chitosan magnetic composite film for chromium species removal
(Chemosphere, 2019-03) Marques Neto, José de Oliveira; Bellato, Carlos Roberto; Silva, Danilo de Castro
An adsorbent in the form of a CLCh/MWCNT/Fe film was prepared using multiple walled carbon nanotubes (MWCNT) doped with magnetic iron oxide and deposited in crosslinked chitosan (CLCh). The CLCh/MWCNT/Fe was characterized by Inductively Coupled Plasma Mass Spectrometry (ICP-MS), nitrogen (N2) adsorption/desorption, X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Spectrometry (EDS), Infrared Spectroscopy (IR) and Raman Spectroscopy. The CLCh/MWCNT/Fe film presented a maximum adsorption capacity for Cr(III) of 66.25 mg/g (150 min) and for Cr(VI) of 449.30 mg/g (60 min) at 25 °C. The CLCh/MWCNT/Fe can be easily removed from the aqueous solution by a mechanical separation or by magnetization due to its magnetic properties. In ten consecutive reutilization adsorption cycles the CLCh/MWCNT/Fe film presented efficiency losses of only 12% and 6% for the removal of Cr(III) and Cr(VI), respectively.
Is statistical lack of fit a reliable criterion for chemical complexity?
(Chemometrics and Intelligent Laboratory Systems, 1996-06) Reis, Cesar; Bruns, Roy E.; Andrade, João Carlos de; Nakai, Debora
Complexations of FeIII and CoII ions with thiocyanate in water-acetone-ethanol ternary mixtures are investigated using multivariate statistical techniques. Simplex lattice and hexagonal mixture designs lead to model equations resulting in similar conclusions. The FeII thiocyanate complex exhibits a very simple dependence (quadratic) on the ternary mixture composition. On the other hand this dependence is much more complex for the CoII thiocyanate complex since even a full cubic mixture model shows a significant lack of fit at the 95% confidence level. These results indicate that the different possible symmetries of the CoII complexes are more sensitive to the ternary mixture composition than are the multistep FeIII complex equilibria.
Low cost in situ digital image method, based on spot testing and smartphone images, for determination of ascorbic acid in Brazilian Amazon native and exotic fruits
(Food Chemistry, 2019-07-01) Suarez, Willian Toito; Santos, Vagner Bezerrados; Silva, Emelle K.N. da; Oliveira, Larissa M.A. de
In this work, we propose a method that employed a smartphone to capture images obtained from a colorimetric spot test to determine ascorbic acid (AA) in Brazilian Amazon native and exotic fruits. The spot test reaction was based on reduction of Fe(III) by AA and further complexation with 1,10-phenanthroline. After optimization, the limit of detection was 8.5 × 10−7 mol L−1. Brazilian Amazon native fruits such as bacuri, cupuaçu, muruci, yellow mombin, as well as others as cashew, mango, orange and passion fruit, were analyzed. In order to determine the accuracy of this method, iodometric titration was used; results were in close agreement with a confidence level of 95% (paired t-test). Moreover, recoveries ranged from 87.1 to 116%. The method is economic, environmentally friendly, and portable, and might useful for small producers and family agriculture businesses unable to afford specialized laboratory analysis in the north region of Brazilian Amazon.
n-Diamondynes: Expanding the family of carbon allotropes
(Carbon, 2018-09) Costa, Deyse G.; Capaz, Rodrigo B.; Henrique, Fábio J. F. S.; Oliveira, Felipe L.; Esteves, Pierre M.
A new family of carbon allotropes, called n-diamondynes, is proposed based on the insertion of acetylide units between the sp3-hybridized carbon atoms of diamond. We perform density-functional theory calculations in order to predict their structural, mechanical, vibrational and electronic properties. The variation of these properties with respect to the number of the acetylide moieties is systematically investigated. In addition, using grand-canonical Monte-Carlo simulations with classical force fields, we explore the potential of these porous materials for gas adsorption.
Nickel complexes with phosphines and N-R-sulfonyldithiocarbimates ligands: New antifungals for the control of Hemileia vastatrix and Phakopsora pachyrhizi
(Inorganica Chimica Acta, 2019-02-24) Vidigal, Antonio E. C.; Rubinger, Mayura M. M.; Queiroz, Luan F. de; Silva, Lucas F. da; Zambolim, Laércio; Guilardi, Silvana; Souza, Rafael A. C.; Ellena, Javier; Wetler, Emiliana B.; Oliveira, Marcelo R. L.
Nickel(II) complexes of general formula [Ni(RSO2N = CS2)(PPh3)2] (2a–h) or [Ni(RSO2N = CS2)dppe] (3a–h), where R = methyl (a), ethyl (b), butyl (c), octyl (d), phenyl (e), 4-isopropylphenyl (f), 4-tert-butylphenyl (g), 2-naphthyl (h), PPh3 = triphenylphosphine and dppe = 1,2-bis(diphenylphosphine)ethane were prepared, from which six are new substances (2f–h and 3f–h). The new compounds were characterized by elemental analysis of C, H, N and Ni, and by IR, UV–Vis and 1H, 13C and 31P NMR spectroscopies. The data were consistent with the formation of square planar nickel(II) complexes with mixed ligands, what was confirmed by single crystal X-ray diffraction studies on compounds 2f and 2h. These complexes present intramolecular NiHC anagostic interactions. All complexes inhibited the germination of Hemileia vastatrix and Phakopsora pachyrhizi, the causal agents of devastating diseases on soybean and coffee cultures. The most active compounds presented IC90 values as low as 405 µM against H. vastatrix, and 280 μM against P. pachyrhizi. Thus, the title compounds are target molecules for the development of new agrochemicals against the Asian soybean rust and Coffee leaf-rust diseases.
Preparation of calcined hydrotalcite/TiO2-Ag composite and enhanced photocatalytic properties
(Ceramics International, 2017-02-01) Almeida, Marciano F. de; Bellato, Carlos R.; Miranda, Liany D. L.; Milagres, Jaderson L.
A series of calcined hydrotalcite/TiO2-Ag (HTC/TiO2-Ag) composites with different silver (Ag) contents were successfully prepared and investigated as a catalyst for the photodegradation of phenol using UV–vis light (λ>300 nm). The Ag nanoparticles were deposited on the surface of TiO2 (TiO2-Ag) through photodeposition method. The TiO2-Ag nanoparticles were supported on hydrotalcite (HT) by the co-precipitation method at variable pH (HT/TiO2-Ag), and then calcined at 500 °C to obtain the HTC/TiO2-Ag composites. The composites were characterized by inductively coupled plasma mass spectrometry (ICP-MS), N2 adsorption/desorption (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), and diffuse reflectance spectra (DRS). Results show that there is an optimum silver ratio to obtain the highest photocatalytic performance in the HTC/TiO2-Ag photocatalyst which is 2 wt%, and is assigned as HTC/TiO2-Ag(2). The association of silver nanoparticles on TiO2 enhanced photocatalytic activity of the bare semiconductor composite. Only 56% of phenol was photodegraded when photodegradation was performed with HTC/TiO2, whereas ~100% was photodegraded using HTC/TiO2-Ag(2). The data gathered from the photocatalytic degradation of phenol were successfully fitted to Langmuir-Hinshelwood model, and can be described by pseudo-first order kinetics. The results showed the HTC/TiO2-Ag(2) as efficient photocatalyst, low cost, separable from solution by sedimentation, and reusable. The superior performance of HTC/TiO2-Ag(2) composite photocatalyst may be attributed to the synergic catalytic effect between silver and TiO2, dispersion of TiO2-Ag(2) nanoparticles supported on calcined hydrotalcite, and the calcined hydrotalcite like photocatalyst.
Quantum mechanical approach for structure elucidation of novel halogenated sesquiterpene lactones
(Journal of Molecular Structure, 2019-03-15) Alvarenga, Elson S.; Santos, Juliana O.; Moraes, Fernanda C.; Carneiro, Vânia M. T.
The stereochemistries of halogenated lumisantonin were rationalized by four distinct methods. In the first method the activation energies for the halonium ion intermediates and the reaction energies for all candidate structures were calculated. In the second approach the coupling constants were calculated and compared with the experimental values. The best matches for the calculated and experimental coupling constants were achieved by the modified procedure. In the third approach the computed 1H and 13C NMR chemical shifts were compared with the experimental values and the mean absolute errors (MAE) were measured. In the fourth method the adapted DP4 probabilities were evaluated and the determined stereochemistries for the sesquiterpene lactones (3a and 4a) were in agreement with the first three protocols.
Syntheses of epoxides, and structural analysis of (E)N-hexyl-3-(trans-3-methyloxiran-2-yl)prop-2-enamide by spectroscopic techniques and DFT calculations
(Journal of Molecular Structure, 2018-08-05) Aguiar, Alex R.; Alvarenga, Elson S.; Oliveira, Ramon P.; Carneiro, Vania Maria T.; Moura, Luciano G.
Pyrethroids are three membered ring compounds similar to the natural pyrethrins produced by the flowers of Chrysanthemum cinerariaefolium and C. coccineum. Pyrethroids are insecticides and may also have insect repellent properties and are generally harmless to humans. Due to our interest in compounds with insecticidal activity, we have synthesized seven epoxides (2a-g), which are structurally similar to pyrethroids. The epoxides were prepared by stereospecific and regioselective epoxidation of seven dienamides (1a-g) with meta-chloroperbenzoic acid. The energies for two attainable epoxides (2g and 2g′) at their respective equilibrium geometries were calculated, and we have shown that the title epoxide (2g) is more stable than the candidate epoxide (2g′) (trans)N-hexyl-3-((E)-prop-1-en-1-yl)oxirane-2-carboxamide by 13.37 kJ mol−1. Experimental and calculated nuclear magnetic resonance chemical shifts were compared for both candidate epoxides (2g and 2g′), and a better match was achieved for the title compound (2g). The complementarity of Raman and infrared (IR) spectroscopies is a feature that can be explored for the characterization of this class of compound. This is shown by the bands around 3092 cm−1 in the Raman and absent in the IR spectra. On the other hand a strong peak at 1625 cm−1 in the IR is tiny in the Raman. Therefore the title compound was completely identified by NMR, IR, and Raman spectroscopies, and this protocol can be extended to the herein prepared epoxide analogues.
Syntheses, crystal structure, spectroscopic characterization and antifungal activity of new N-R-sulfonyldithiocarbimate metal complexes
(Journal of Inorganic Biochemistry, 2009-07) Alves, Leandro C.; Rubinger, Mayura M. M.; Lindemann, Renata H.; Perpétuo, Genivaldo Júlio; Janczak, Jan; Miranda, Liany D. L.; Zambolim, Laércio; Oliveira, Marcelo R. L.
Five new compounds with the general formula of (Bu4N)2[M(RSO2NCS2)2], where Bu4N = tetrabutylammonium cation, (M = Ni, R = 4-FC6H4) (1), (M = Zn, R = 4-FC6H4, 4-ClC6H4, 4-BrC6H4, 4-IC6H4), (2), (3), (4) and (5), respectively, were obtained by the reaction of the appropriate potassium N-R-sulfonyldithiocarbimate (RSO2NCS2K2) with nickel(II) chloride hexahydrate or zinc(II) acetate dihydrate in metanol:water 1:1. The elemental analyses and the IR data are consistent with the formation of the expected bis(dithiocarbimato)metal(II) complexes. The 1H and 13C NMR spectra showed the signals for the tetrabutylammonium cation and the dithiocarbimate moieties. The compounds 1, 2 and 5 were also characterized by X-ray diffraction techniques. The nickel(II) is coordinated by two N-4-fluorophenylsulphonyldithiocarbimato(2-) ligands forming a planar coordination. The zinc(II) exhibits distorted tetrahedral configuration in compounds 2 and 5 due to the chelation effect of two sulfur atoms of the N-R-sulfonyldithiocarbimate ligands. The antifungal activities of the compounds were tested in vitro against Colletotrichum gloeosporioides, an important fungus that causes the plant disease known as anthracnose in fruit trees. All the complexes were active.
Synthesis and application of a new carboxylated cellulose derivative. Part I: Removal of Co2+, Cu2+ and Ni2+ from monocomponent spiked aqueous solution
(Journal of Colloid and Interface Science, 2016-12) Ferreira, Gabriel Max Dias; Silva, Luis Henrique Mendes da; Teodoro, Filipe Simões; Ramos, Stela Nhandeyara do Carmo; Elias, Megg Madonyk Cota; Mageste, Aparecida Barbosa; Gil, Laurent Frédéric; Gurgel, Leandro Vinícius Alves
A new carboxylated cellulose derivative (CTA) was prepared from the esterification of cellulose with 1,2,4-Benzenetricarboxylic anhydride. CTA was characterized by percent weight gain (pwg), amount of carboxylic acid groups (nCOOH), elemental analysis, FTIR, TGA, solid-state 13C NMR, X-ray diffraction (DRX), specific surface area, pore size distribution, SEM and EDX. The best CTA synthesis condition yielded a pwg and nCOOH of 94.5% and 6.81 mmol g−1, respectively. CTA was used as an adsorbent material to remove Co2+, Cu2+ and Ni2+ from monocomponent spiked aqueous solution. Adsorption studies were developed as a function of the solution pH, contact time and initial adsorbate concentration. Langmuir model better fitted the experimental adsorption data and the maximum adsorption capacities estimated by this model were 0.749, 1.487 and 1.001 mmol g−1 for Co2+, Cu2+ and Ni2+, respectively. The adsorption mechanism was investigated by using isothermal titration calorimetry. The values of ΔadsH° were in the range from 5.36 to 8.09 kJ mol−1, suggesting that the mechanism controlling the phenomenon is physisorption. Desorption and re-adsorption studies were also performed. Desorption and re-adsorption efficiencies were closer to 100%, allowing the recovery of both metal ions and CTA adsorbent.
Synthesis and application of sugarcane bagasse cellulose mixed esters. Part I: Removal of Co2+ and Ni2+ from single spiked aqueous solutions in batch mode using sugarcane bagasse cellulose succinate phthalate
(Journal of Colloid and Interface Science, 2019-01-01) Silva, Luis Henrique Mendes da; Elias, Megg Madonyk Cota; Ferreira, Gabriel Max Dias; Almeida, Francine Tatiane Rezende de; Rosa, Nathália Cristina Martins; Silva, Isabela Almeida; Filgueiras, Jefferson Gonçalves; Azevedo, Eduardo Ribeiro de; Melo, Tânia Márcia Sacramento; Gil, Laurent Frédéric; Gurgel, Leandro Vinícius Alves
Sugarcane bagasse cellulose mixed ester succinate phthalate (SBSPh) was synthesized by a novel one-pot reaction method. The effects of temperature, time and mole fraction of succinic anhydride (χSA) on the responses weight gain (wg), number of carboxylic acid groups (nT,COOH), and adsorption capacity (q) of Co2+ and Ni2+ were evaluated by a 23 experimental design. The chemical structure of the material was elucidated by Fourier transform infrared, 13C Multiple Cross-Polarization solid-state NMR spectroscopy and 1H NMR relaxometry. The best SBSPh synthesis condition (100 °C, 11 h, χSA of 0.2) yielded a wg of 59.1%, nT,COOH of 3.41 mmol g−1, and values of qCo2+ and qNi2+ of 0.348 and 0.346 mmol g−1, respectively. The Sips model fitted better the equilibrium data, and the maximum adsorption capacities (pH 5.75 and 25 °C) estimated by this model were 0.62 and 0.53 mmol g−1 for Co2+ and Ni2+, respectively. The ΔadsH° values estimated by isothermal titration calorimetry were 8.43 and 7.79 kJ mol−1 for Co2+ and Ni2+, respectively. Desorption and re-adsorption efficiencies were evaluated by a 22 experimental design, which showed that SBSPh adsorbent can be recovered and reused without significant loss of adsorption capacity.
Uncoupling and inhibition properties of 3,4-seco-friedelan-3-oic acid isolated from Maytenus imbricata
(Pesticide Biochemistry and Physiology, 2007-02) Barbosa, Luiz Claúdio de Almeida; Silva, Silvia Ribeiro de Souza e; Silva, Grácia Divina de Fátima; Duarte, Lucienir Pains; King-Diaz, Beatriz; Archundia-Camacho, Francisco; Lotina-Hennsen, Blas
3,4-Seco-friedelan-3-oic acid was isolated from Maytenus imbricata (Celastraceae). At low concentrations it inhibited non-cyclic electron transport and ATP synthesis in spinach chloroplasts, i.e., it behaved as a Hill reaction inhibitor, and at high concentrations it acts as an uncoupler by enhancing uncoupled electron transport and Mg2+–ATPase activity. 3,4-Seco-friedelan-3-oic acid did not inhibit PSII electron transport from DPC to DCPIPox and photosystem I activity, but it enhanced from TMQH2 to MV, corroborating its action as uncoupler. It inhibits electron flow through PSII from water to sodium silicomolybdate. The whole results indicate that the 3,4-seco-friedelan-3-oic acid target is at the OEC complex enzyme, the donor side of PSII. The fluorescence decay data shows the formation of the K-band, which match this result, acting as inhibitor at the donor side of PSII and it as an uncoupler.