Gilson DeFreitas-Silva

Federal University of Minas Gerais, Cidade de Minas, Minas Gerais, Brazil

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Publications (9)22.68 Total impact

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    ABSTRACT: Supramolecular assemblies are a field of main stream investigation due to its technological and scientific importance. Porphyrins and single-walled carbon nanotubes supramolecular assemblies have drawn special attention because of the ease of assemblage and electronic and photonic interactions. Here we summarize the various applications on nanoscience and nanotechnology of porphyrin/single-walled carbon nanotube molecular assemblies. Stemming from basic physics toward medical applications we show that the molecular pair is a merry combination.
    Synthetic Metals 07/2014; 193:64–70. · 2.11 Impact Factor
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    ABSTRACT: This work describes the synthesis and characterization of the novel catalyst 5-(3-bromo,4-amino)phenyl-10,15,20-trisphenyl-2,3,7,8,12,13,17,18-octabromoporphyrinmanganese(III) chloride (MnIIIBr9APTPPCl). This compound, MnIIIAPTPPCl and MnIIITPPCl were employed as catalysts in cyclohexane oxidation using PhIO or PhI(OAc)2 as oxidants. In the reactions with PhIO and PhI(OAc)2, MnIIIBr9APTPPCl led to higher yields of products compared to the other catalysts. Furthermore, for the first time it was observed a recovery of the third generation (β-octabrominated) catalyst in reactions using PhI(OAc)2 as oxidant. Reactions were performed with the addition of imidazole or water as additives. The reactions with imidazole showed higher yields for cyclohexanol in all systems studied. For systems using PhIO it was also observed a decrease of catalysts oxidative destruction. All the systems using PhIO and water led to an increase in product yield. However, the recovery of catalyst was low for almost all these systems. Nevertheless, this is the first work to show the role of water as an effective additive in the oxidation of cyclohexane catalyzed by manganese porphyrins.
    Applied Catalysis A General 01/2014; 469:124–131. · 3.41 Impact Factor
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    ABSTRACT: Photoluminescence (PL) measurements of porphyrin-doped single-walled carbon nanotubes (SWCNTs) were performed in sodium dodecylbenzenesulfonate (NaDDBS) aqueous dispersions. PL spectra were used to draw PL maps in which maxima correspond to absorption–emission excitonic processes related to (E11, E22) first Van Hove singularities of the SWCNT electronic structure. The influence of the net charge of the porphyrin is a determining factor in the energy map maximum shifts (EMMS) relative to that of a pristine NaDDBS/SWCNT dispersion. A non-interacting porphyrin is used as a reference to discard the influence of the dielectric constant of the medium in the EMMS.
    Carbon. 01/2010;
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    ABSTRACT: Mn(III) N-alkylpyridylporphyrins are among the most potent known SOD mimics and catalytic peroxynitrite scavengers and modulators of redox-based cellular transcriptional activity. In addition to their intrinsic antioxidant capacity, bioavailability plays a major role in their in vivo efficacy. Although of identical antioxidant capacity, lipophilic MnTnHex-2-PyP is up to 120-fold more efficient in reducing oxidative stress injuries than hydrophilic MnTE-2-PyP. Owing to limitations of an analytical nature, porphyrin lipophilicity has been often estimated by the thin-layer chromatographic Rf parameter, instead of the standard n-octanol/water partition coefficient, POW. Herein we used a new methodological approach to finally describe the MnP lipophilicity, using the conventional log POW means, for a series of biologically active ortho and meta isomers of Mn(III) N-alkylpyridylporphyrins. Three new porphyrins (MnTnBu-3-PyP, MnTnHex-3-PyP, and MnTnHep-2-PyP) were synthesized to strengthen the conclusions. The log POW was linearly related to Rf and to the number of carbons in the alkyl chain (nC) for both isomer series, the meta isomers being 10-fold more lipophilic than the analogous ortho porphyrins. Increasing the length of the alkyl chain by one carbon atom increases the log POW value ∼1 log unit with both isomers. Dramatic ∼4 and ∼5 orders of magnitude increases in the lipophilicity of the ortho isomers, by extending the pyridyl alkyl chains from two (MnTE-2-PyP, log POW = − 6.89) to six (MnTnHex-2-PyP, log POW = − 2.76) and eight carbon atoms (MnTnOct-2-PyP, log POW = − 1.24), parallels the increased efficacy in several oxidative-stress injury models, particularly those of the central nervous system, in which transport across the blood–brain barrier is critical. Although meta isomers are only slightly less potent SOD mimics and antioxidants than their ortho analogues, their higher lipophilicity and smaller bulkiness may lead to a higher cellular uptake and overall similar effectiveness in vivo.
    Free Radical Biology and Medicine 01/2009; · 5.27 Impact Factor
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    ABSTRACT: A homologous series of beta-brominated porphyrins derived from meso-tetrakis(4-carbomethoxyphenyl)porphyrinatomanganese(III) chloride, i.e., Mn(III)(Br(x)TCMPP)Cl (x=0,2,4,6, and 8), was prepared and investigated as cytochrome P450 models. Hydroxylations of cyclohexane by iodosylbenzene (PhIO) and iodobenzene diacetate (PhI(OAc)(2)) in the presence or absence of water were carried out as P450 model reactions. The influence of the degree of beta-bromination of the macrocycle on the UV-vis spectra, the Mn(III)/Mn(II) reduction potential, and the catalytic properties of the Mn(III)(Br(x)TCMPP)Cl (x=0,2,4,6, and 8) series were examined. The catalytic efficiency does not correlate with the Mn(III)/Mn(II) reduction potential and shows a bell-shaped behavior, where the best results are achieved with the hexabrominated complex. Better hydroxylation yields were achieved by using PhI(OAc)(2) as oxygen donor, but at expenses of catalyst recovery; addition of water to this system resulted in a increase in the reaction rate. Recycling of the more oxidatively robust complexes Mn(III)(Br(6)TCMPP)Cl and Mn(III)(Br(8)TCMPP)Cl is feasible when using PhIO as oxygen donor. Selectivity and UV-vis data suggested that hydroxylation by both PhIO and PhI(OAc)(2) share closely related active species and mechanism. We also show that the Mn(III)/Mn(II) reduction potentials are inappropriate predictors of P450-type activity of Mn porphyrin-catalyzed oxidations.
    Journal of inorganic biochemistry 11/2008; 102(10):1932-41. · 3.25 Impact Factor
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    ABSTRACT: Photoluminescence (PL) measurements of porphyrin-doped single wall carbon nanotubes (SWNT) were studied in sodium dodecylbenzenesulfonate (NaDDBS) aqueous dispersions. The PL spectra were used to draw PL maps were the maxima corresponds to absorption-emission excitonic processes related to (E11, E22) first Van Hove singularities of the SWNT electronic structure. The influence of the net charge of the porphyrin was a determinant factor in the energy map maximum shifts (EMMS) compared to the energy map of a pristine NaDDBS/SWNT dispersion. A non-interacting porphyrin is used as a reference to discard the influence of the dielectric constant of the medium in the EMMS.
    10/2008;
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    ABSTRACT: Understanding the factors that determine the ability of Mn porphyrins to scavenge reactive species is essential for tuning their in vivo efficacy. We present herein the revised structure-activity relationships accounting for the critical importance of electrostatics in the Mn porphyrin-based redox modulation systems and show that the design of effective SOD mimics (per se) based on anionic porphyrins is greatly hindered by inappropriate electrostatics. A new strategy for the beta-octabromination of the prototypical anionic Mn porphyrins Mn(III) meso-tetrakis(p-carboxylatophenyl)porphyrin ([Mn(III)TCPP](3-) or MnTBAP(3-)) and Mn(III) meso-tetrakis(p-sulfonatophenyl)porphyrin ([Mn(III)TSPP](3-)), to yield the corresponding anionic analogues [Mn(III)Br(8)TCPP](3-) and [Mn(III)Br(8)TSPP](3-), respectively, is described along with characterization data, stability studies, and their ability to substitute for SOD in SOD-deficient Escherichia coli. Despite the Mn(III)/Mn(II) reduction potential of [Mn(III)Br(8)TCPP](3-) and [Mn(III)Br(8)TSPP](3-) being close to the SOD-enzyme optimum and nearly identical to that of the cationic Mn(III) meso-tetrakis(N-methylpyridinium-2-yl)porphyrin (Mn(III)TM-2-PyP(5+)), the SOD activity of both anionic brominated porphyrins ([Mn(III)Br(8)TCPP](3-), E(1/2)=+213 mV vs NHE, log k(cat)=5.07; [Mn(III)Br(8)TSPP](3-), E(1/2)=+209 mV, log k(cat)=5.56) is considerably lower than that of Mn(III)TM-2-PyP(5+) (E(1/2)=+220 mV, log k(cat)=7.79). This illustrates the impact of electrostatic guidance of O(2)(-) toward the metal center of the mimic. With low k(cat), the [Mn(III)TCPP](3-), [Mn(III)TSPP](3-), and [Mn(III)Br(8)TCPP](3-) did not rescue SOD-deficient E. coli. The striking ability of [Mn(III)Br(8)TSPP](3-) to substitute for the SOD enzymes in the E. coli model does not correlate with its log k(cat). In fact, the protectiveness of [Mn(III)Br(8)TSPP](3-) is comparable to or better than that of the potent SOD mimic Mn(III)TM-2-PyP(5+), even though the dismutation rate constant of the anionic complex is 170-fold smaller. Analyses of the medium and E. coli cell extract revealed that the major species in the [Mn(III)Br(8)TSPP](3-) system is not the Mn complex, but the free-base porphyrin [H(2)Br(8)TSPP](4-) instead. Control experiments with extracellular MnCl(2) showed the lack of E. coli protection, indicating that "free" Mn(2+) cannot enter the cell to a significant extent. We proposed herein the alternative mechanism where a labile Mn porphyrin [Mn(III)Br(8)TSPP](3-) is not an SOD mimic per se but carries Mn into the E. coli cell.
    Free Radical Biology and Medicine 08/2008; 45(2):201-10. · 5.27 Impact Factor
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    ABSTRACT: Mn porphyrins are among the most efficient SOD mimics with potency approaching that of SOD enzymes. The most potent ones, Mn(III) N-alkylpyridylporphyrins bear positive charges in a close proximity to the metal site, affording thermodynamic and kinetic facilitation for the reaction with negatively charged superoxide. The addition of electron-withdrawing bromines onto beta-pyrrolic positions dramatically improves thermodynamic facilitation for the O2*- dismutation. We have previously characterized the para isomer, Mn(II)Br(8)TM-4-PyP(4+) [Mn(II) beta-octabromo-meso-tetrakis(N-methylpyridinium-4-yl)porphyrin]. Herein we fully characterized its meta analogue, Mn(II)Br(8)TM-3-PyP(4+) with respect to UV/vis spectroscopy, electron spray mass spectrometry, electrochemistry, O2*- dismutation, metal-ligand stability, and the ability to protect SOD-deficient Escherichia coli in comparison with its para analogue. The increased electron-deficiency of the metal center stabilizes Mn in its +2 oxidation state. The metal-centered Mn(III)/Mn(II) reduction potential, E((1/2))=+468 mV vs NHE, is increased by 416 mV with respect to non-brominated analogue, Mn(III)TM-3-PyP(5+) and is only 12 mV less positive than for para isomer. Yet, the complex is significantly more stable towards the loss of metal than its para analogue. As expected, based on the structure-activity relationships, an increase in E((1/2)) results in a higher catalytic rate constant for the O2*- dismutation, log k(cat)> or =8.85; 1.5-fold increase with respect to the para isomer. The IC(50) was calculated to be < or =3.7 nM. Manipulation of the electron-deficiency of a cationic porphyrin resulted, therefore, in the highest k(cat) ever reported for a metalloporphyrin, being essentially identical to the k(cat) of superoxide dismutases (log k(cat)=8.84-9.30). The positive kinetic salt effect points to the unexpected, unique and first time recorded behavior of Mn beta-octabrominated porphyrins when compared to other Mn porphyrins studied thus far. When species of opposing charges react, the increase in ionic strength invariably results in the decreased rate constant; with brominated porphyrins the opposite was found to be true. The effect is 3.5-fold greater with meta than with para isomer, which is discussed with respect to the closer proximity of the quaternary nitrogens of the meta isomer to the metal center than that of the para isomer. The potency of Mn(II)Br(8)TM-3-PyP(4+) was corroborated by in vivo studies, where 500 nM allows SOD-deficient E. coli to grow >60% of the growth of wild type; at concentrations > or =5 microM it exhibits toxicity. Our work shows that exceptionally high k(cat) for the O2*- disproportionation can be achieved not only with an N(5)-type coordination motif, as rationalized previously for aza crown ether (cyclic polyamines) complexes, but also with a N(4)-type motif as in the Mn porphyrin case; both motifs sharing "up-down-up-down" steric arrangement.
    Archives of Biochemistry and Biophysics 04/2008; 477(1):105-12. · 3.37 Impact Factor
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    ABSTRACT: In this paper we report the immobilization of different cationic and neutral metalloporphyrins (MPs) on silica-coated Fe3O4 nanoparticles, obtained by basic hydrolytic sol–gel process. We characterized the MP-immobilized materials by UV–vis spectroscopy (UV–vis), X-ray diffraction (XRD), infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). We achieved 100% and 2% immobilization of cationic and neutral MPs, respectively. The strong electrostatic interactions between the hydroxylated surface of the silica and the positive charges of the cationic MPs favored immobilization of the charged MPs; the neutral MP probably established a weak bond with the silica and easily leached from the support. We investigated the catalytic activity of the immobilized MPs in the oxidation of cyclooctene, cyclohexene, and cyclohexane using iodosylbenzene as oxygen donor. We used the immobilized MPs in at least five successive cyclooctene oxidation reactions – the yields did not decrease, confirming that the catalyst can be reused. The synthesized catalysts displayed magnetic properties, which allowed their fast separation from the reaction medium using a simple magnet.
    Applied Catalysis A: General. 459:121–130.

Publication Stats

84 Citations
22.68 Total Impact Points

Institutions

  • 2008–2014
    • Federal University of Minas Gerais
      • Departamento de Química
      Cidade de Minas, Minas Gerais, Brazil
  • 2009
    • Saint Louis University
      • Department of Internal Medicine
      Saint Louis, MI, United States
  • 2008–2009
    • Duke University Medical Center
      • Department of Radiation Oncology
      Durham, North Carolina, United States