Showing papers by "João Costa Pessoa published in 2011"
TL;DR: In the search for new therapeutic tools against diseases produced by kinetoplastid parasites five vanadyl complexes, [V(IV)O(L-2H)(phen)], including 1,10-phenanthroline (phen) and tridentate salicylaldehyde semicarbazone derivatives as ligands have been synthesized and characterized in the solid state and in solution by using different techniques.
112 citations
TL;DR: A partially new model for HSA–VIVO interactions is introduced, in which the two binding sites compete not only with each other, but also with hydrolysis of the metal ion.
98 citations
TL;DR: Speciation of the systems and plausible intermediates involved in the catalytic oxidation processes are established by UV-Vis, EPR, (51)V NMR and DFT studies, and the radical pathway was found to be even more favorable than the Sharpless mechanism.
Abstract: The reaction between [VIVO(acac)2] and the ONN donor Schiff base obtained by the condensation of pyridoxal and 2-aminoethylbenzimidazole (Hpydx-aebmz, I) or 2-aminomethylbenzimidazole (Hpydx-ambmz, II) in equimolar amounts results in the formation of [VIVO(acac)(pydx-aebmz)] 1 and [VIVO(acac)(pydx-ambmz)] 2, respectively The aerobic oxidation of the methanolic solution of 1 yielded [VVO2(pydx-aebmz)] 3 and its reaction with aqueous H2O2 gave the oxidoperoxidovanadium(V) complex, [VVO(O2)(pydx-aebmz)] 4 The formation of 4 in solution is also established by titrations of methanolic solutions of 1 with H2O2 By titrating solutions of 3 and of 4 with aqueous H2O2 several distinct VV-pydx-aebmz species also containing the peroxido ligand are detected The full geometry optimization of all species envisaged was done using DFT methods for suitable model complexes The 51V NMR chemical shifts (δV) have also been calculated, the theoretical data being used to support assignments of the experimental chemical shifts The 51V hyperfine coupling constants are calculated for 1, the obtained values being in good agreement with the experimental EPR data Reaction between the VIVO2+ exchanged zeolite-Y and Hpydx-aebmz and Hpydx-ambmz in refluxing methanol, followed by aerial oxidation results in the formation of the encapsulated VVO2-complexes, abbreviated herein as [VVO2(pydx-aebmz)]-Y 5 and [VVO2(pydx-ambmz)]-Y 6 The molecular structure of 1, determined by single crystal X-ray diffraction, confirms its distorted octahedral geometry with the ONN binding mode of the tridentate ligand, with one acetylacetonato group remaining bound to the VIVO-centre Oxidation of styrene is investigated using some of these complexes as catalyst precursors with H2O2 as oxidant Under optimised reaction conditions for the conversion of styrene in acetonitrile, a maximum of 68% conversion of styrene (with [VVO2(pydx-aebmz)]-Y) and 65% (with [VVO2(pydx-ambmz)]-Y) is achieved in 6 h of reaction time The selectivity of the various products is similar for both catalysts and follows the order: benzaldehyde (ca 55%) > 1-phenylethane-1,2-diol > benzoic acid > styrene oxide > phenyl acetaldehyde Speciation of the systems and plausible intermediates involved in the catalytic oxidation processes are established by UV-Vis, EPR, 51V NMR and DFT studies Both non-radical (Sharpless) and radical mechanisms of the olefin oxidations were theoretically studied, and the radical pathway was found to be even more favorable than the Sharpless mechanism
72 citations
TL;DR: It has been found that the introduction of halogen substituents in the phenolate rings of the chelators enhanced the cytotoxicity of the respective Cu(II) complexes.
70 citations
TL;DR: A new Schiff base, [H(4)pydmedpt](2+)·2Cl(-), derived from one of the forms of vitamin B(6) has been synthesized by condensation of pyridoxal hydrochloride with N,N-bis[3-aminopropyl]-methylamine (medpt) and characterized by analytical and spectroscopic methods.
Abstract: A new Schiff base, [H4pydmedpt]2+·2Cl–, derived from one of the forms of vitamin B6 has been synthesized by condensation of pyridoxal hydrochloride with N,N-bis[3-aminopropyl]-methylamine (medpt) and characterized by analytical and spectroscopic methods. The molecular structure is calculated by density functional theory (DFT) procedures, and the donor properties of each individual donor atom are evaluated by calculation of the Fukui function. One pot reaction of pyridoxal and medpt with vanadyl acetylacetonate yields the brown complex [VIVO(H2pydmedpt)]2+·2Cl–1, which upon recrystallization from water crystallizes as [VIVO(pydmedpt)]·5H2O 2. The compounds are characterized by analytical and spectroscopic methods, 2 being also characterized by single crystal X-ray diffraction. It displays a slightly distorted octahedral geometry around the vanadium atom involving the coordination of Namine, two Nimine, and Ophenolato donors of the ligand. One of the phenolato oxygen donors is positioned trans to the termin...
66 citations
TL;DR: In this paper, the reaction of oxidovanadium(IV)-exchanged zeolite-Y with N,N′-ethylenebis(pyridoxyliminato) (H2pydx-en, I), N, N′-propylenebis(polypropylene) (Pyridoxylinato, II) and H2pYDx-1,2-pn (III) in methanol heated at reflux leads to the formation of the corresponding complexes, abbreviated herein as [VIVO(p
Abstract: The reaction of oxidovanadium(IV)-exchanged zeolite-Y with N,N′-ethylenebis(pyridoxyliminato) (H2pydx-en, I), N,N′-propylenebis(pyridoxyliminato) (H2pydx-1,3-pn, II) and H2pydx-1,2-pn (III) in methanol heated at reflux leads to the formation of the corresponding complexes, abbreviated herein as [VIVO(pydx-en)]-Y (4), [VIVO(pydx-1,3-pn)]-Y (5) and [VIVO(pydx-1,2-pn)]-Y (6) in the supercages of zeolite-Y. The neat complexes [VIVO(pydx-en)] (1), [VIVO(pydx-1,3-pn)] (2) and [VIVO(pydx-1,2-pn)] (3) were also prepared. Spectroscopic studies (IR, UV/Vis and EPR), elemental analyses, thermal studies, field-emission scanning electron micrographs (FESEM) and X-ray diffraction patterns were used to characterize these complexes. Oxidations of styrene, cyclohexene and methyl phenyl sulfide were investigated using these complexes as catalyst precursors in the presence of H2O2 as oxidant. Under the optimized reaction conditions, a maximum of 85.5 % conversion of styrene was obtained with 4, 84.6 % conversion with 5 and 82.9 % conversion with 6 in 6 h of reaction time. The selectivity of the various products was similar for the catalyst precursors 4–6 and followed the order: benzaldehyde > 1-phenylethane-1,2-diol > benzoic acid > phenyl acetaldehyde. With cyclohexene, a maximum conversion of 95.9 % was achieved with 4, 94.5 % with 5 and 94.2 % conversion with 6, also in 6 h of reaction time. The selectivity of the various products was similar for the three catalysts: 2-cyclohexen-1-one > 2-cyclohexen-1-ol > cyclohexane-1,2-diol. The oxidation of methyl phenyl sulfide was achieved with 4, 5 and 6 in 2.5 h of reaction time with 85.5, 82.1 and 80 % conversion, with higher selectivity towards sulfoxide. Overall, the encapsulated catalysts were significantly more active than their neat counterparts and have the further advantage of being recyclable. No relevant difference in activity was found due to a change in the diamine in the Schiff base ligands I–III. UV/Vis and 51V NMR spectroscopic experiments with 1 confirmed the plausible formation of VVO(O2)L as intermediates in the catalytic oxidations.
39 citations
TL;DR: In this paper, an account of the preparation of polystyrene anchored complexes and their use as catalysts in functionalization of alkenes is presented, and the main advantages of the use of the prepared supported catalyst are specified, namely their recyclability and their higher activity.
36 citations
TL;DR: In this article, neutral and cationic titanium and zirconium diamine bis(phenolate) complexes supported by chiral ligands L-1 and L-2 are described.
Abstract: Neutral and cationic titanium and zirconium diamine bis(phenolate) complexes supported by chiral ligands L-1 and L-2 are described [L-1 = (R)-6,6'-{1-(dimethylamino)propan-2-ylazanediyl}bis(methylene)-bis(2,4-di-tert-butylphenolate); L-2 = (S)-6,6'-{(1-ethylpyrrolidin-2-yl)methylazanediyl}bis-(methylene)- bis(2,4-di-tert-butylphenolate)]. Complexes [TiL(OiPr)(2)] [L = L-1 (1), L-2 (2)], [(TiLX)-X-2(OiPr)] [X = Cl (3), CH2Ph (4)], [TiL1(CH2Ph)(2)] (5), [ZrLCl2] [L = L-1 (6), L-2 (7)] and [ZrL(CH2Ph)(2)] [L = L-1 (8), L-2 (9)] are C-1-symmetric species readily prepared in moderate to high yields. Cationic compounds were obtained from complexes 5, 8 and 9 through reactions with B(C6F5)(3). The monocationic species reveal the eta(2)-binding character of the benzyl groups and noncoordinated [B(C6F5)(3)(CH2Ph)](-). Complexes 5-9 were tested in the polymerization of ethylene and propylene upon activation with modified methylaluminoxane (MMAO), B(C6F5)(3) or [NHMe2Ph](+) as cocatalysts. The [(ZrLCl2)-Cl-1]/MMAO and [ZrL1(CH2Ph)(2)]/B(C6F5)(3) systems revealed high activities in the polymerization of propylene (2.1 x 10(3) and 1.5 x 10(3) gpolmmol(cat)(-1)h(-1), respectively), leading to atatic polypropylene, whereas the titanium complexes showed no activity.
26 citations
TL;DR: In this article, an experimental and numerical investigation of the first order and slowly varying wave exciting forces on a body of simple geometry which is restrained from moving is presented, where both monochromatic waves and three sets of bi-chromatic waves corresponding to three difference frequencies were tested.
19 citations
TL;DR: The reduced Schiff bases of salicylaldehyde and pyridoxal (and o-vaniline) with L-tyrosine (Tyr) and D,L-o-tyrousine (o-Tyr), designated as sal-tyr (1), sal-o-, tyr-t, pyr-T, t, t, t, o-Vaniline (O-T), as well as the oxidovanadium(IV) complex VO(sal-o-) (6) have been prepared in the solid state and in
Abstract: The reduced Schiff bases of salicylaldehyde and pyridoxal (and o-vaniline) with L-tyrosine (Tyr) and D,L-o-tyrosine (o-Tyr), designated as sal-Tyr (1), sal-o-Tyr (2), pyr-Tyr (3), pyr-o-Tyr (4), and o-van-L-Tyr (5), as well as the oxidovanadium(IV) complex VO(sal-o-Tyr) (6) have been prepared. The compounds have been characterized in the solid state and in solution. The structure of 3 has been determined by X-ray diffraction. Complexation of these ligands with vanadium in aqueous solution has been studied by pH potentiometry, UV/Vis, and circular dichroism (for the L-Tyr derivatives), as well as by EPR for the VIVO systems and 51V NMR for the VVO2 systems. Stoichiometries and complex formation constants have been determined by pH potentiometry (25 °C, I = 0.2 M KCl) 1:1 complexes are formed in most systems with variable protonation states VOLH2 (only with 3 and 4), VOLH, VOL, and VOLH–1. Dinuclear species (VOL)2H and (VOL)2 were identified only in the case of 3. Spectroscopic data provided information about the most probable binding modes for each stoichiometry. The VIVO complexes formed with the o-Tyr-derived ligands are more stable than those with L-Tyr, the more adequate coordination position of the phenolate in the o-Tyr ligands shows a more significant stabilizing effect compared with 3 and 4.
14 citations
31 Oct 2011
TL;DR: In this paper, the first order and second order wave exciting forces acting on a body of simple geometry subjected to long crested irregular waves are investigated, where the body is axis-symmetric about the vertical axis, like a vertical cylinder with a rounded bottom.
Abstract: The paper presents an experimental investigation of the first order and second order wave exciting forces acting on a body of simple geometry subjected to long crested irregular waves. The body is axis-symmetric about the vertical axis, like a vertical cylinder with a rounded bottom, and it is restrained from moving. Second order spectral analysis is applied to obtain the linear spectra, coherence spectra and cross bi-spectra of both the incident wave elevation and of the horizontal and vertical wave exciting forces. Then the linear and quadratic transfer functions (QTF) of the exciting forces are obtained. The QTF obtained from the analysis of irregular wave measurements are compared with results from experiments in bi-chromatic waves and with numerical predictions from a second order potential flow code.Copyright © 2011 by ASME