Henrique E. Toma

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

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Publications (313)827.7 Total impact

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    ABSTRACT: The structure of poly-tetraruthenated nickel porphyrin was unveiled for the first time, by electrochemistry, Raman spectroelectrochemistry and hydroxyl radical trapping assay. The electrocatalytic active material, precipitated on the electrode surface after successive cycling of [NiTPyP{Ru(bipy)2Cl}4]4+ species in strong aqueous alkaline solution (pH=13), was found to be a peroxo bridged coordination polymer. The electropolymerization process involves hydroxyl radicals (as confirmed by the characteristic set of DMPO/•OH adduct EPR peaks) as reaction intermediates, electrocatalytically generated in the 0.80-1.10 V range, that induce the formation of Ni-O-O-Ni coordination polymers, as evidenced by Raman spectroelectrochemistry and molecular modeling studies. The film growth is halted above 1.10 V due to the formation of oxygen gas bubbles.
    Langmuir 03/2015; 31(14). DOI:10.1021/acs.langmuir.5b00250 · 4.46 Impact Factor
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    ABSTRACT: The association of formaldehyde dehydrogenase from Pseudomonas putida (FalDH) with two different magnetic nanoparticles led to distinct enzyme responses depending upon the chemical modification process applied. The magnetite nanoparticles coated with aminopropyltriethoxysilane (MagNP-APTS) exhibited a lower activity and stability, while magnetite coated with a silica shell and APTS (MagNP@SiO2APTS) afforded excellent results, improving the stability and performance of FalDH in relation to the free enzyme. Such differences were ascribed to unfavorable conformational changes in the MagNP-APTS–FalDH system, as indicated by the kinetics and Raman spectroscopy data, not discarding the possible interference from the exposed Fe(II)/(III) ions. The MagNP@SiO2APTS–FalDH catalyst could be successfully recycled by using an external magnet, keeping its highest performance close to 100%, during the first four cycles, and decaying slightly up to 70% after the 10th cycle.
    New Journal of Chemistry 03/2015; 39(3). DOI:10.1039/C4NJ01716A · 3.16 Impact Factor
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    ABSTRACT: A simple and accessible method for molecular analyses down to the picomolar range was realized using self-assembled hybrid superparamagnetic nanostructured materials, instead of complicated SERS substrates such as core–shell, surface nanostructured, or matrix embedded gold nanoparticles. Good signal-to-noise ratio has been achieved in a reproducible way even at concentrations down to 5 × 10−11 M using methylene blue (MB) and phenanthroline (phen) as model species, exploiting the plasmonic properties of conventional citrate protected gold nanoparticles and alkylamine functionalized magnetite nanoparticles. The hot spots were generated by salt induced aggregation of gold nanoparticles (AuNP) in the presence of those analytes. Then, the aggregates of AuNP/analyte were decorated with small magnetite nanoparticles by electrostatic self-assembly forming MagSERS hybrid nanostructured materials. SERS peaks were enhanced up to 100 times after magnetic concentration in a circular spot using a magnet in comparison with the respective dispersion of the nanostructured material.
    Analytica Chimica Acta 01/2015; 855. DOI:10.1016/j.aca.2014.12.005 · 4.52 Impact Factor
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    ABSTRACT: The study of non-innocent redox behavior of ligands is important for the development of new catalysts and to comprehend the function of bioinorganic molecules in biochemical processes. In this work, we present a description of the non-innocent behavior of 1-(2′-pyridylazo)-2-naphtholate (pan) coordinated to ruthenium complexes. The synthesis and characterization of a series of [Ru(pan)(PPh3)(L)]PF6 complexes [where L = 2,2′-bipyridine (bpy), 4,4′-dimethyl-2,2′-bipyridine (dmbpy), and 1,10-phenanthroline (phen)] are presented. UV–vis analyses of the studied ruthenium complexes show intense absorptions from intraligand π–π* and metal-to-ligand charge-transfer transitions bands in the visible region. This observation shows a significant contribution of the pan ligand in all electronic transitions and is the indicative of non-innocent behavior. Theoretical calculations were carried out to support the UV–vis spectral assignments. Non-innocent behavior of pan was observed and confirmed using the electrochemical parameter E L(L) and by electrochemical studies. The pan ligand is non-innocent and can be modulated by donor and acceptor character of the other ligands present in the coordination sphere of the complex.
    Journal of Coordination Chemistry 10/2014; 67(20). DOI:10.1080/00958972.2014.963064 · 2.22 Impact Factor
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    ABSTRACT: The bis(4-thienylterpyridine)iron(II) complex was employed, in comparison with the 4-phenylterpyridine analogue, as a molecular probe for monitoring the surface plasmon interactions with gold nanoparticles. The two complexes exhibited distinct SERS responses, confirming the binding of the thienyl group to the gold nanoparticles. Their inclusion into beta-cyclodextrin anchored on TiO2 surfaces provided a useful system for applications in UV dosimetry, based on the gradual bleaching of the violet-blue color under sunlight and air.
    Canadian Journal of Chemistry 10/2014; 92(10):918-924. DOI:10.1139/cjc-2014-0025 · 1.01 Impact Factor
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    ABSTRACT: Magnetic graphite materials (GMag) were prepared by adsorbing oleate coated magnetite nanoparticles (MagNP) on the exposed surfaces of graphite, in the powder form. The materials were characterized by SEM (scanning electron microscopy) and EDX (energy dispersive X-ray fluorescence), and their magnetic properties were probed with a SQUID (superconducting quantum interference device) magnetometer. By incorporating MagNP, the modified graphite became responsive to magnetic fields, either as a powder or liquid suspension, allowing to reflect white light and lasers, and to control the light beam transmission, simulating smart windows and optical displays.
    Carbon 10/2014; 77:600-606. DOI:10.1016/j.carbon.2014.05.064 · 6.16 Impact Factor
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    ABSTRACT: A dicarboxybipyridine-trimercaptotriazine ruthenium complex, primarily designed for dye solar cells, has been successfully employed for generating electrostatically stabilized gold colloids, because of its high negative charge and capability of binding to gold nanoparticles via the sulfur groups. Surprisingly, a strong SERS enhancement has been observed for the isolated nanoparticles, exceeding those recorded after inducing agglomeration. Such unusual response has been ascribed to the predominant contribution of the charge-transfer and resonance Raman mechanisms, more than compensating for the lack of the local hot spots, in relation to the agglomerated systems.
    Journal of Raman Spectroscopy 09/2014; DOI:10.1002/jrs.4562 · 2.52 Impact Factor
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    ABSTRACT: The electrochemical recovery of silver by employing recyclable superparamagnetic carbon materials (Cmag) is reported. The proposed strategy explores the adsorption properties and the large surface area of carbon, in conjunction with the superparamagnetic properties of magnetite nanoparticles, in order to collect Ag+ ions from the solution and to promove their rapid confinement at the working electrode surface, using an external magnet. Efficient electrodeposition can be performed in this way, facilitated by the preconcentration effect at the electrode. The adsorption process at the magnetic carbon particles proceeds according to the Langmuir model, exhibiting an adsorption capability of 61.5 mg of silver per gram of Cmag. As a proof of concept, an automated system was specially designed for performing successive batch cycles, encompassing the capture, transport, confinement, electrodepositon of silver, and recycling of the magnetite coated carbon particles from the electrode. The recovery process was successfully demonstrated in this work, by processing discarded X-ray photographic films.
    Hydrometallurgy 08/2014; 147. DOI:10.1016/j.hydromet.2014.06.001 · 2.22 Impact Factor
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    ABSTRACT: We synthesized a long-chain phenylazopyridine ligand and used it to obtain three new amphiphilic trinuclear ruthenium acetate clusters. The amphiphilicity and anisometric form of the long-chain ligand allowed the complexes to self-assemble at the liquid–air interface and enabled their deposition by the Langmuir–Blodgett technique. We obtained the linear complex [Ru3O(C2H3O2)6(py)2L]+ [L = 4-(4-dodecyloxyphenylazo)pyridine, py = pyridine], which was more stable than the triangular [Ru3O(C2H3O2)6L3]+ and more suitable for application in electrochromic switching devices, as attested by its fast switching and optical changes in the near-IR region. Indeed, our electrochromic device remained stable for hundreds of switching cycles.
    Berichte der deutschen chemischen Gesellschaft 03/2014; 2014(7). DOI:10.1002/ejic.201301442
  • Henrique E. Toma
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    ABSTRACT: The centenary of Alfred Werner's Nobel Prize in Chemistry has prompted this retrospect on his important contributions for the development of stereochemistry and for the understanding of the nature of the coordination compounds. His genealogy has been described, including a discussion on the famous Jorgensen-Werner controversy. As an extension, it has also been reported the German biography of Heinrich Rheinboldt, the founder of the Chemistry School at the University of Sao Paulo, and his relation with Werner's scientific heritage.
    Química Nova 01/2014; 37(3). DOI:10.5935/0100-4042.20140093 · 0.66 Impact Factor
  • Caterina G. C. M. Netto, Henrique E. Toma
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    ABSTRACT: A binuclear cobalt complex, [Co2BPP], derived from the (R,R)-Trost-bis-ProPhenol (BPP) ligand, has been investigated as a catalyst for CO2 uptake and its electrochemical reduction. The complex exhibits labile acetate ligands that can be readily exchanged with CO2, leading to pronounced changes in its vibrational spectra, with νC=O peaks observed at 1700 and 1596 cm–1. The electrochemical reduction of the CoIII centers at –0.5 V was significantly enhanced in the presence of CO2, evidencing a chemical reaction coupled to an electrode process. Instead of yielding CO or HCOOH as observed in most artificial systems, formaldehyde was identified as the major product below –1.0 V, showing that CO2 can undergo four-electron reduction by the [Co2BPP] electrocatalyst.
    European Journal of Inorganic Chemistry 12/2013; 2013(34):5826-5830. DOI:10.1002/ejic.201301158 · 2.97 Impact Factor
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    ABSTRACT: A terpyridine ligand encompassing a terminal 4-carboxyphenyl group (cptpy), was employed in a new Ru(II) black dye, in the presence of 8-quinolinolate (Q) and SCN- as ancillary ligands. Such compound, here referred as [Ru(cptpy) (Q) (NCS)], was designed aiming its inclusion into carboxymethyl-beta-cyclodextrin, anchored on TiO2. This host-guest strategy was employed to prevent the formation of aggregates and protect the photoinjecting moiety against parallel deactivation events. Such expectation has indeed been fulfilled by the system. On the other hand, 8-quinolinolate as a strong electron donor ligand, effectively enhanced the light harvesting behavior of the dye, shifting and spreading the IPCE peaks over the entire visible region. Unfortunately, the red shift of visible charge-transfer bands was compensated by a decrease of the Ru(III)/(II) potentials, slowing down the electron transfer kinetics with the I-3/I- redox mediator. Therefore, the observed counterbalance between charge transfer energies and redox potentials imposes a critical limit in the design of better mononuclear ruthenium-polypyridine dyes.
    Inorganic Chemistry Communications 10/2013; 36:35-38. DOI:10.1016/j.inoche.2013.08.007 · 2.06 Impact Factor
  • Bernardo A. Iglesias, Henrique E. Toma, Koiti Araki
    14th Brazilian Meeting on Organic Synthesis; 09/2013
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    ABSTRACT: The light-to-electricity conversion efficiencies of the new (Bu4N)3[Ru(dcbpy)2(tmtH2)], (Bu4N)4[Ru(dcbpy)2(tmtH)] and (Bu4N)5[Ru(dcbpy)2(tmt)] complexes, where dcbpy = 2,2′-bipyridyl-4,4′-dicarboxylate and tmt = 2,4,6-trimercapto-1,3,5-triazine, were comparable with those obtained with the N719 dye. Furthermore, the contribution of two MLCT and a LMCT charge-transfer band to the energy conversion process was revealed by deconvolution of the photoaction spectra, indicating that they are the first ruthenium dyes presenting long distance photo-injection from a ligand-to-metal charge-transfer excited state.
    Inorganica Chimica Acta 08/2013; 404:23–28. DOI:10.1016/j.ica.2013.04.016 · 2.04 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. DOI:10.1166/jbn.2013.1614 · 7.58 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-. DOI:10.1088/1742-6596/421/1/012005
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    ABSTRACT: Enzymes are highly efficient catalysts extensively employed in biotechnology. Among the many challenging aspects in this area, enzymes are yet difficult to obtain and purify, which makes them extremely expensive. Therefore, the industrial use of such expensive biocatalysts suffers from a critical point, which is the lack of efficient recovery processes.As a very promising strategy, superparamagnetic nanoparticles based on magnetite (Fe3O4) and maghemite (γ-Fe2O3) have been recently employed as supporting materials for enzymes, exhibiting striking characteristics, such as large surface area, mobility and high mass transference. More than that, they can be easily recovered by applying an external magnetic field. In addition to their excellent environmental compatibility, the use of such superparamagnetic nanoparticles represents an effective green chemistry approach, since it prolongs, through the successive recovery cycles, the useful lifetime of the biocatalyst.Several enzymes and biomolecules, including antibodies, albumin, α-chymotrypsin, aminopeptidase, acetylcholine esterase, amylase, amyloglucosidase, celullase, epoxide hydrolases, esterase, lipase, lysozyme, pectinases, phosphatase, pyruvate phosphate dikinase, trypsin, subtilisin, urease, chitosanase, haloalkane dehalogenase, RNA polymerase, lactate dehydrogenase, alcohol dehydrogenase, galactosidase, catalase, cholesterol oxidase, d-amino acid oxidase, cathecol dioxygenase, fructosyl amino acid oxidase, l-lactate dehydrogenase, xanthine oxidase, glucose oxidase, glucosidase, laccase, peroxidases, tyrosinase and so on, have been successfully immobilized onto magnetic nanoparticles, and the recent progress in this area is focused on this review.
    Journal of Molecular Catalysis B Enzymatic 01/2013; 85-86:71-92. DOI:10.1016/j.molcatb.2012.08.010 · 2.75 Impact Factor
  • Henrique E. Toma
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    ABSTRACT: Nanotechnology and green chemistry can have much in common from the point of view of processes, considering the possibilities of improving efficiency and quality, achieving a better economy of atoms and energy, promoting catalysis under mild and sustainable conditions, and facilitating online monitoring of production lines and environment. Some of these aspects are dealt with in this paper, focusing on selected examples of application of functionalized nanoparticles and -materials in chemistry and industry.
    Pure and Applied Chemistry 01/2013; 85(8). DOI:10.1351/PAC-CON-12-12-02 · 3.11 Impact Factor
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    ABSTRACT: The exceptional stability of FTO electrodes modified with Ni1-xCox(OH)(2) in the alpha polymorphic phase was assigned to Co(II) substitution in the Ni(II) reticule, decreasing the basal plane distances and the average grain size, as confirmed by careful analyses of their X-ray diffractograms and thermal behavior as a function of the cobalt content. That phenomenon can be assigned to thermodynamic rather than kinetic factors, reflected by much higher dehydration/dehydroxilation temperatures, as expected for the stabilization of the mixed alpha-phase hydroxides in detriment of the oxides, opening real perspectives for application of alpha-Ni1-xCox(OH)(2) in high efficiency batteries and devices.
    RSC Advances 01/2013; 3(43):20261. DOI:10.1039/c3ra42417k · 3.84 Impact Factor
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    ABSTRACT: Formate dehydrogenase from Candida boidinii (FDH) was immobilized on three different magnetic supports: one composed by magnetite nanoparticles directly silanized with APTS (aminopropyltriethoxysilane), i.e. MagNP-APTS; the second one containing a silica gel coated magnetite core which was further silanized with APTS (MagNP@SiO2-APTS), and the third one consisting of magnetite-APTS coated with Glyoxyl-Agarose (MagNP-Glyoxyl-Agarose). The catalytic activity of the three FDH systems was investigated as a function of pH and temperature. The silica gel coated nanoparticles provided the highest conversion rates; however, in terms of recycling, magnetite without the silica shell led to the most stable system. By using the enzyme tryptophan residues as internal fluorescence probes, the structure-activity behavior was investigated in the presence of the formate and NAD+ substrates, revealing a rather contrasting behavior in the three cases. Because of its peculiar behavior, a direct interaction of the magnetic nanoparticles with the catalytic sites seems to be implicated in the case of MagNP-APTS.
    Journal of Molecular Catalysis B Enzymatic 12/2012; 84:136–143. DOI:10.1016/j.molcatb.2012.03.021 · 2.75 Impact Factor

Publication Stats

4k Citations
827.70 Total Impact Points

Institutions

  • 1973–2015
    • University of São Paulo
      • • Institute of Chemistry (IQ)
      • • Departamento de Química Fundamental (IQ) (São Paulo)
      San Paulo, São Paulo, Brazil
  • 1994–2011
    • CEP America
      Емеривил, California, United States
  • 2001
    • Instituto de Química
      San Paulo, São Paulo, Brazil
  • 1987
    • São Paulo State University
      San Paulo, São Paulo, Brazil
  • 1982
    • Pasadena City College
      Pasadena, Texas, United States
  • 1975
    • Universität Stuttgart
      • Institute of Inorganic Chemistry
      Stuttgart, Baden-Wuerttemberg, Germany