Henrique E. Toma

University of São Paulo, San Paulo, São Paulo, Brazil

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Publications (278)467.58 Total impact

  • Hydrometallurgy 01/2014; · 2.17 Impact Factor
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    ABSTRACT: The most challenging and wanted development in photodynamic therapy is the control of photosensitizer (PS) cytolocalization and the mechanism of cell death. 5,10,15-triphenyl-20-(3-N-methylpyridinium-yl)porphyrin (3MMe) administered to HeLa cells as DMSO solution accumulates in the cytoplasmic membrane (CM) where it causes severe photodamage and cell necrosis. In contrast, when incorporated in marine atelocollagen/xantham gum polymeric nanocapsules, the PS is shuttled through CM allowing its gradual release and accumulation in mitochondria and lysosomes. Little photodamage was caused to cells in this case, but compelling evidences are presented showing that encapsulation changes the cytolocalization and shifts the cell death mechanism from necrosis to apoptosis. In conclusion, both of those challenges can be overcome by encapsulation of typical PSs such as 3MMe by using the new concept of photodynamic treatment with minimal cell damage by targeting specifically some key organelles. We are confident that these findings are important for the development of more efficient photosensitizers tailored to induce apoptosis while minimizing undesirable side effects such as over-inflammation.
    Journal of Biomedical Nanotechnology 08/2013; 9(8):1307-17. · 5.26 Impact Factor
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    ABSTRACT: We have studied the effect of positive and negative back gate voltage on the Schottky barrier of few layer graphene transistors (devices) in the presence of Air, Nitrogen and different ethanol vapor concentrations. The presence of the Schottky barrier in these devices is attributed to unintentional doping of the different areas of the graphene flake and is modulated by applying a positive gate voltage, increasing the source-drain current.
    Journal of Physics Conference Series 03/2013; 421(1):2005-.
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    ABSTRACT: A hybrid material with excellent mechanical and biological properties is produced by electrospinning a co-solution of PET and collagen. The fibers are mapped using SEM, confocal Raman microscopy and collagenase digestion assays. Fibers of different compositions and morphologies are intermingled within the same membrane, resulting in a heterogeneous scaffold. The collagen distribution and exposure are found to depend on the PET/collagen ratio. The materials are chemically and mechanically characterized and biologically tested with fibroblasts (3T3-L1) and a HUVEC culture in vitro. All of the hybrid scaffolds show better cell attachment and proliferation than PET. These materials are potential candidates to be used as vascular grafts.
    Macromolecular Bioscience 10/2012; · 3.74 Impact Factor
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    ABSTRACT: The relative amounts of amorphous and crystalline γ- and α-phases in polyamide-6 nanocomposites, estimated from the deconvolution of X-ray diffraction peaks using Gaussian functions, correlates with their mechanical, thermomechanical, and barrier properties. The incorporation of organoclay platelets (Cloisite 15A and 30B) induced the crystallization of the polymer in the γ form at expense of the amorphous phase, such that 1–2 wt % of Cloisite is enough to enhance the mechanical and the thermomechanical properties. However, higher nanofiller loads were necessary to achieve good barrier effects, because this property is mainly dependent on the tortuous path permeation mechanism of the gas molecules through the nanocomposite films.
    Journal of Applied Polymer Science 08/2012; 125(4):3239. · 1.40 Impact Factor
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    ABSTRACT: The photochemical cis-trans isomerization of the 4-{4-[2-(pyridin-4-yl)ethenyl]phenyl}-2,2':6',2''-terpyridine ligand (vpytpy) was investigated by UV-vis, NMR and TWIM-MS. Ion mobility mass spectrometry was performed pursuing the quantification of the isomeric composition during photolysis, however an in-source trans-to-cis isomerization process was observed. In order to overcome this inherent phenomenon, the isomerization of the vpytpy species was suppressed by complexation, reacting with iron(II) ions, and forming the [Fe(vpytpy)(2)](2+) complex. The strategy of "freezing" the cis-trans isomerizable ligand at a given geometric conformation was effective, preventing further isomerization, thus allowing the distinction of each one of the isomers in the photolysed mixture. In addition, the experimental drift times were related to the calculated surface areas of the three possible cis-cis, cis-trans and trans-trans iron(II) complex isomers. The stabilization of the ligand in a given conformation also allows us to obtain the cis-cis and cis-trans complexes exhibiting the ligand in the metastable cis-conformation, as well as in the thermodynamically stable trans-conformation.
    The Analyst 07/2012; 137(17):4045-51. · 4.23 Impact Factor
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    ABSTRACT: Sevenfold enhancement of photoconversion efficiency was achieved by incorporation of peripheral ruthenium complexes to a porphyrin dye, generating supramolecular effects capable of playing several key roles (e.g., transferring energy to, inhibiting aggregation, and accepting the hole generated in the porphyrin center after electron injection), providing new insights for the design of better DSSC photosensitizers.
    Chemical Communications 06/2012; 48(55):6939-41. · 6.38 Impact Factor
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    ABSTRACT: Travelling wave ion mobility mass spectrometry (TWIM-MS) with post-TWIM and pre-TWIM collision-induced dissociation (CID) experiments were used to form, separate and characterize protomers sampled directly from solutions or generated in the gas phase via CID. When in solution equilibria, these species were transferred to the gas phase via electrospray ionization, and then separated by TWIM-MS. CID performed after TWIM separation (post-TWIM) allowed the characterization of both protomers via structurally diagnostic fragments. Protonated aniline (1) sampled from solution was found to be constituted of a ca. 5:1 mixture of two gaseous protomers, that is, the N-protonated (1a) and ring protonated (1b) molecules, respectively. When dissociated, 1a nearly exclusively loses NH(3) , whereas 1b displays a much diverse set of fragments. When formed via CID, varying populations of 1a and 1b were detected. Two co-existing protomers of two isomeric porphyrins were also separated and characterized via post-TWIM CID. A deprotonated porphyrin sampled from a basic methanolic solution was found to be constituted predominantly of the protomer arising from deprotonation at the carboxyl group, which dissociates promptly by CO(2) loss, but a CID-resistant protomer arising from deprotonation at a porphyrinic ring NH was also detected and characterized. The doubly deprotonated porphyrin was found to be constituted predominantly of a single protomer arising from deprotonation of two carboxyl groups.
    Biological Mass Spectrometry 06/2012; 47(6):712-9. · 3.41 Impact Factor
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    ABSTRACT: The new triazene-porphyrin dye 5-(1-(4-phenyl)-3-(4-nitrophenyl)triazene)-10,15,20-triphenylporphyrin, encompassing a reactive protonated triazene moiety, was prepared starting from meso-tetraphenylporphyrin (H2TPP), first converting it to the 5-(4-nitrophenyl)-10,15,20-triphenylporphyrin, then reducing to the 5-(4-aminophenyl)-10,15,20-tri(phenyl)porphyrin intermediate, and reacting with the diazonium salt of 4-nitroaniline; and characterized by spectroscopic and electrochemical methods. The absorption spectrum of the neutral species resembled the sum of H2TPP and of 1,3-bis(4-nitrophenyl)triazene spectrum, but the deprotonated anionic species showed more delocalized frontier orbitals, behaving as a push-pull system exhibiting triazenide-to-porphyrin charge-transfer transitions.
    Journal of Porphyrins and Phthalocyanines 05/2012; 16(02). · 1.43 Impact Factor
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    ABSTRACT: The photodynamic properties of eight hydrophobic monocationic methyl and ruthenium polypyridine complex derivatives of free-base and zinc(II) meso-triphenyl-monopyridylporphyrin series were evaluated and compared using HeLa cells as model. The cream-like polymeric nanocapsule formulations of marine atelocollagen/xanthan gum, prepared by the coacervation method, exhibited high phototoxicity but negligible cytotoxicity in the dark. Interestingly, the formulations of a given series presented similar photodynamic activities but the methylated free-base derivatives were significantly more phototoxic than the respective ruthenated photosensitizers, reflecting the higher photoinduced singlet oxygen quantum yields of those monocationic porphyrin dyes.
    Journal of Porphyrins and Phthalocyanines 04/2012; 16(01). · 1.43 Impact Factor
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    ABSTRACT: A new modified tetrapyridylporphyrin symmetrically coordinated to four [Ru(phen)2Cl]+ groups has been synthesized and its structural and electrochemical properties have been investigated by means of 1H and COSY NMR, UV-vis and luminescence spectroscopy, cyclic voltammetry and spectroelectrochemistry. The presence of the phenanthroline ligands has improved the stability of the molecular films generated on the surface of conventional solid electrodes in comparison with the analogous bipyridine derivative. The performance of the modified electrodes has been evaluated for the detection of dopamine, with excellent results.
    Journal of Porphyrins and Phthalocyanines 04/2012; 02(06). · 1.43 Impact Factor
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    ABSTRACT: The acid protection effect promoted by traces of PdCl(2) in [Ni(dmgH)(2)] spot tests was elucidated from confocal Raman microscopy imaging, which revealed the formation of protecting layers of [Pd(dmgH)(2)] closing the extremities of the [Ni(dmgH)(2)] filaments.
    Analytical Chemistry 03/2012; 84(7):3067-9. · 5.70 Impact Factor
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    ABSTRACT: The ability of travelling wave ion mobility mass spectrometry (TWIM-MS) to resolve cationic meta/para and cis/trans isomers of mono-, di-, tri- and tetra-ruthenated supramolecular porphyrins was investigated. All meta isomers were found to be more compact than the para isomers and therefore mixtures of all isomeric pairs could be properly resolved with baseline or close to baseline peak-to-peak resolution (R(p-p)). Di-substituted cis/trans isomers were found, however, to present very similar drift times and could not be resolved. N(2) and CO(2) were tested as the drift gas, and similar α but considerably better values of R(p) and R(p-p) were always observed for CO(2).
    Rapid Communications in Mass Spectrometry 02/2012; 26(3):263-8. · 2.51 Impact Factor
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    ABSTRACT: A new concept for in vitro visual evaluation of sun protection factor (SPF) of cosmetic formulations based on a supramolecular ultraviolet (UV) dosimeter was clearly demonstrated. The method closely parallels the method validated for in vivo evaluation and relies on the determination of the slightest perceptible bleaching of an iron-complex dye/nanocrystalline-titanium dioxide interface (UV dosimeter) in combination with an artificial skin substrate simulating the actual human skin in the presence and absence of a cosmetic formulation. The successful evaluation of SPF was ensured by the similarity of the erythema response of our dosimeter and human skin to UV light irradiation. A good linear correlation of in vitro and in vivo data up to SPF 40 confirmed the effectiveness of such a simple, cheap, and fast method. In short, here we unravel a convenient and accessible visual FPS evaluation method that can help improving the control on cosmetic products contributing to the reduction of skin cancer, one of the critical public health issues nowadays.
    Journal of Pharmaceutical Sciences 02/2012; 101(2):726-32. · 3.13 Impact Factor
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    ABSTRACT: Doubly N-confused dioxohexaphyrins were characterized by cyclic voltammetry and spectroelectrochemistry in the -2.5 to +2.0 V vsAg|Ag+ (0.10 M, in CH3CN) range. Six reversible monoelectronic processes were found suggesting that the rich electrochemistry of porphyrin systems was preserved in that expanded macrocycle. However, the electronic and electrochemical properties of the free-base, Cu(II) and Ni(II) species were shown to be sensitive to the coordinated transition metal ions and solvent revealing a quite complex behavior, probably reflecting the higher flexibility and strong conformational effects on the energy levels and stability of those complexes.
    Journal of Porphyrins and Phthalocyanines 01/2012; 09(12). · 1.43 Impact Factor
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    ABSTRACT: A series of meso-phenylpyridylporphyrins and their respective supermolecular species obtained by the coordination of [Ru(bipy)2Cl]+ groups to the pyridyl substituents was synthesized and characterized. Their spectroscopic and electrochemical behavior were similar to that observed for the meso-tetra(4-pyridyl)porphyrin derivative, but the redox potential of the Ru(III/II) redox pair was about 70 mV more negative. The porphyrin centered fluorescence quantum yield exhibited a linear decrease as a function of the number of pyridyl substituents on the porphyrin ring. Efficient intramolecular energy transfer processes from the 3MLCT state of the ruthenium complexes to the porphyrin center were observed at 77K in ethanol glass.
    Journal of Porphyrins and Phthalocyanines 01/2012; 06(01). · 1.43 Impact Factor
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    ABSTRACT: Gold nanoparticles (Au-NPs) were deposited on single layer graphene (SLG) and few layers graphene (FLG) by applying the gas aggregation technique, previously adapted to a 4-gun commercial magnetron sputtering system. The samples were supported on SiO2 (280 nm)/Si substrates, and the influence of the applied DC power and deposition times on the nanoparticle–graphene system was investigated by Confocal Raman Microscopy. Analysis of the G and 2D bands of the Raman spectra shows that the integrated intensity ratio (I2D/IG) was higher for SLG than for FLG. For the samples produced using a sputtering power of 30 W, the intensity (peak height) of the G and 2D bands increased with the deposition time, whereas for those produced applying 60 W the peak heights of the G and 2D bands decreased with the deposition time. This behaviour was ascribed to the formation of larger Au-NPs aggregates in the last case. A significant increase of the Full Width Half Maximum (FWHM) of the G band for SLG and FLG was also observed as a function of the DC power and deposition time. Surprisingly, the fine details of the Raman spectra revealed an unintentional doping of SLG and FLG accompanying the increase of size and aggregation of the Au-NPs.
    Diamond and Related Materials 01/2012; 23:18-22. · 1.71 Impact Factor
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    ABSTRACT: Titanium dioxide has been extensively used in photocatalysis and dye-sensitized solar cells, where control of the anatase-to-rutile phase transformation may allow the realization of more efficient devices exploiting the synergic effects at anatase/rutile interfaces. Thus, a systematic study showing the proof of concept of a dye-induced morphological transition and an anatase-to-rutile transition based on visible laser (532 nm) and nano/micro patterning of mesoporous anatase (Degussa P25 TiO(2)) films is described for the first time using a confocal Raman microscope. At low laser intensities, only the bleaching of the adsorbed N3 dye was observed. However, high enough temperatures to promote melting/densification processes and create a deep hole at the focus and an extensive phase transformation in the surrounding material were achieved using 1s laser pulses of 25-41 mW/cm(2), in resonance with the MLCT band. The dye was shown to play a key role, being responsible for the absorption and efficient conversion of the laser light into heat. As a matter of fact, the dye is photothermally decomposed to amorphous carbon or to gaseous species (CO(x), NO(x), and H(2)O) under a N(2) or O(2) atmosphere, respectively.
    Langmuir 06/2011; 27(15):9094-9. · 4.19 Impact Factor
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    ABSTRACT: Nickel hydroxide can provide an outstanding cathode material in alkaline secondary batteries, however the progressive decrease of the charge capacity as a function of the number of oxidation/reduction cycles is a challenging problem to be solved. New improvements on the electrochemical properties of electrode materials can be achieved by exploiting the much better performance of alpha-nickel hydroxide. Such materials were obtained in a stable form by sol-gel method and characterized by thermogravimetric analyses, UV-Vis spectroscopy, X-ray diffractometry, scanning and transmission electron microscopy, cyclic voltammetry and electrochemical quartz crystal microbalance techniques. The results revealed not only the formation of the alpha-Ni(OH)2 phase, but also a much better electrochemical reversibility and stability as compared with similar materials obtained by electrochemical precipitation method.
    Journal of Nanoscience and Nanotechnology 05/2011; 11(5):3985-96. · 1.15 Impact Factor
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    Izilda A. Bagatin, Koiti Araki, Henrique E. Toma
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    ABSTRACT: The interaction of a calix[4]arene-based species containing two 8-oxyquinoline chromophore pendants with hazardous metal ions has been investigated using optical absorption and fluorimetric techniques. In the presence of Hg2+, Cd2+, and Pb2+ ions, there is only a small decrease of the calixarene absorption band at 283 nm. The main changes are associated with the absorption band of the 8-oxyquinoline group at 315 nm, undergoing a systematic bathochromic shift to above 350 nm. In addition, a systematic decrease of the oxyquinoline emission at λem = 392 nm (λexc = 315 nm) has been observed. These observations are consistent with the coordination of the metal ions to the quinoline groups attached to the calixarene ligand, providing a useful fluoroinophore species for analytical purposes.
    Canadian Journal of Chemistry 04/2011; 89(5):562-567. · 0.96 Impact Factor

Publication Stats

832 Citations
467.58 Total Impact Points


  • 1978–2014
    • University of São Paulo
      • • Institute of Chemistry (IQ)
      • • Departamento de Química Fundamental (IQ) (São Paulo)
      San Paulo, São Paulo, Brazil
  • 2004–2012
    • University of Campinas
      • Instituto de Química (IQ)
      Campinas, Estado de Sao Paulo, Brazil
  • 2009
    • Johns Hopkins University
      Baltimore, Maryland, United States
  • 2008
    • Universidade Estadual de Maringá
      • Departamento de Química
      Maringá, Estado do Parana, Brazil
  • 1989–2005
    • Universidade Federal do Paraná
      • Departamento de Química
      Curitiba, Estado do Parana, Brazil
    • Universidade Federal de São Paulo
      San Paulo, São Paulo, Brazil
  • 1987
    • Instituto de Química
      San Paulo, São Paulo, Brazil