Henrique E. Toma

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

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Publications (308)801.81 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Four different types of modern glass were exposed to the open atmosphere for 5 months in São Paulo city. The effect of TiO2 (self-cleaning glass) and a silver nanoparticle polymeric coating on biofilm formation was evaluated under these conditions. Examination by various types of microscopy, standard microbiological sampling and culture methods, and estimation of transparency to light by measuring the current induced in an underlying photovoltaic cell showed that the self-cleaning glass did reduce biofilm formation very significantly as compared to other glass samples. The presence of the polymeric nanosilver coating on the glass surface increased the adhesion of microorganisms, except for self-cleaning glass. Both plating and direct microscope examination showed that the major colonizers were fungi, with few phototrophs (principally Chlorella) being detected. Approximately 80% of the fungi growing on plates were yeast-like, although substantial cover by fungal filaments was seen by direct microscopy of non-TiO2-coated glass. The results suggest that the TiO2 coating inhibits the formation of fungal filaments, hence reducing overall biofilm cover. Silver nanoparticles in a plastic film were not effective in reducing sub-aerial biofilm formation on non-TiO2-coated glass.
    No preview · Article · Mar 2016 · International Biodeterioration & Biodegradation
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    ABSTRACT: Glutamate dehydrogenase (GDH) is a well known homohexameric enzyme and its performance in immobilized form was systematically investigated in this work, in order to provide a better understanding of the multimeric enzyme immobilization effects in relation to the monomeric ones. For this purpose, GDH was immobilized on four different magnetic supports and the outcome from such immobilization was characterized in terms of their stabilization and activity. Immobilization procedures involving amine coupling via glutaraldehyde cross-linking yielded the least stable ones, even lower than free GDH, showing no recoverability. However, the immobilization procedures using larger aldehyde cross-linkers presented higher thermal stabilities than free GDH and could be recycled at least 10 times, with a nearly constant activity. Such differences in stability and activities were thoroughly evaluated in terms of the enzymatic structure, which has guided the reasoning behind the intriguing allosteric behavior of the immobilized GDH. The atypical allosteric response exhibited by MagNP-APTS/GDH, MagNP@SiO2-APTS/GDH and MagNP-APTS/Glyoxyl-Agarose/GDH led us to invoke the intrinsic disorder theory to explain the results. This theory has proved an excellent tool to guide researches on immobilized enzymes and understand its effects.
    No preview · Article · Jan 2016 · RSC Advances
  • Sabrina da N. Almeida · Henrique E. Toma
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    ABSTRACT: A successful nanohydrometallurgical separation of neodymium and lanthanum ions has been demonstrated by using superparamagnetic nanoparticles functionalized with ethylenediaminepropylsilane/diethylenetriaminepentaacetic acid, as complexing agents. Neodymium is preferentially captured in relation to lanthanum, reflecting the trends of the stability constants dictated by the lanthanide contraction. A high separation efficiency (> 99%) has been achieved after three successive complexation and releasing stages. The overall process can be performed under green and sustainable conditions, e.g., at room temperature, in aqueous solution and mild pHs, allowing the nanoparticles recycling, and dispensing the use of more time/energy consuming physical separation processes.
    No preview · Article · Jan 2016 · Hydrometallurgy
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    ABSTRACT: Alcohol dehydrogenase (ADH) from Saccharomyces cerevisiae was covalently attached, via glutaraldehyde, to magnetite nanoparticles (MagNP) previously coated with aminopropyltriethoxysilane (MagNP/APTS), or with a silica shell followed by the APTS coating (MagNP@SiO2/APTS). In both cases, a great improvement of enzymatic activity has been observed for the ethanol-acetaldehyde conversion. The MagNP@SiO2/APTS-ADH system exhibited the best stability with respect to pH and temperature. Its residual activity after 10 successive recovery cycles and 24 h storage, was maintained around 80% in comparison with 20% for the MagNP/APTS system, and a null activity for free ADH. Luminescence measurements for the immobilized enzyme indicated the occurrence of conformational changes on ADH, contributing for its improved catalytic performance.
    No preview · Article · Dec 2015 · Journal of Nanoscience and Nanotechnology
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    ABSTRACT: The synergic effect, observed in dye sensitized solar cells assembled with mesoporous electrodes made of mixtures of anatase and rutile nanoparticles, was revealed to depend on a delicate balance of competing contributions from chemical capacitance and resistance to electron diffusion instead of a longer electron lifetime in TiO2 conduction band, as consequence of a slower electron recombination rate at the electrode/electrolyte interface. The parameters influencing the charge diffusion in actually running dye-sensitized solar cells (DSCs) were carefully evaluated by impedance spectra simulation and correlated with the percentage of rutile and anatase in the respective mesoporous electrode. Cells were assembled with mesoporous titanium dioxide (TiO2) electrodes fabricated with sixteen different anatase/rutile mixtures, ranging from pure anatase to pure rutile. All measurements were carried out in triplicate in order to give statistically validated results. The enhanced charge diffusion at 15% of rutile in the mixed film cells was found to be associated with the presence of isolated rutile islands embedded in a more conducting anatase phase, as confirmed by confocal Raman microscopy.
    Full-text · Article · Dec 2015
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    ABSTRACT: Surface enhanced Raman spectroelectrochemistry (SERS) spectroelectrochemistry provides a very sensitive technique to investigate the vibrational characteristics of coordination compounds and their particular behavior under the influence of plasmonic surfaces, concomitant with the exploitation of their redox properties and electronic spectra. The results, however, depend upon the mechanisms involved in the intensification of Raman spectra associated with the electromagnetic, resonance Raman and charge-transfer excitation at the Fermi levels. By probing the model complex [(Ru3O)(CH3COO)6(4,4'-bipy)3](n) (n = 1, 0, -1) adsorbed onto rough gold electrode surfaces, contrasting SERS profiles were obtained at several successive redox potentials and oxidation states, which enables a critical discussion on the role of the complex interaction with the gold surface, and the influence of the specific electronic bands in the triruthenium acetate cluster. Density functional theory (DFT) and time-dependent DFT calculations were carried out for the complex bound to an Au20 cluster to show the participation of active lowest unoccupied molecular orbital levels centered on the gold atoms. The corresponding charge-transfer band was predicted around 1200 nm, which supports a charge-transfer interpretation for the SERS response observed at λexc = 1064 nm. The selective enhancement of the vibrational modes was discussed based on the Raman theoretical calculations.
    No preview · Article · Sep 2015 · Inorganic Chemistry
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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.
    No preview · Article · Mar 2015 · New Journal of Chemistry
  • Henrique E. Toma
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    ABSTRACT: Magnetic nanohydrometallurgy (MNHM), although yet in a very incipient stage, is opening new exciting perspectives in the conventional hydrometallurgy, aggregating nanotechnology to the mineral area. MNHM is based on the same principles of coordination chemistry successfully employed in modern extractive hydrometallurgy processes; however it uses specially designed superparamagnetic nanoparticles for capturing, transporting, confining and processing metal ions, with the aid of an external magnet. The working nanoparticles are completely recovered after the electrodeposition process, sustaining a cyclic process which can be automated, without using organic solvents and intensive chemical processing, as is the case of the current extractive hydrometallurgy and electrowinning technology. At the laboratory scale, the entire procedure can be performed in the same reactor, fulfilling, in addition to the processing and recovery facilities, the most important requisites of Green Chemistry.
    No preview · Article · Feb 2015 · Green Chemistry
  • Sergio H. Toma · Jonnatan J. Santos · Koiti Araki · Henrique E. Toma
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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.
    No preview · Article · Jan 2015 · Analytica Chimica Acta
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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.
    No preview · Article · Oct 2014 · Journal of Coordination Chemistry
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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.
    No preview · Article · Oct 2014 · Canadian Journal of Chemistry
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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.
    Full-text · Article · Sep 2014 · Journal of Raman Spectroscopy
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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.
    No preview · Article · Aug 2014 · Hydrometallurgy
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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.
    No preview · Article · Mar 2014 · Berichte der deutschen chemischen Gesellschaft
  • 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.
    No preview · Article · Jan 2014 · Química Nova
  • 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.
    No preview · Article · Dec 2013 · European Journal of Inorganic Chemistry
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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.
    No preview · Article · Oct 2013 · Inorganic Chemistry Communications
  • Bernardo A. Iglesias · Henrique E. Toma · Koiti Araki

    No preview · Conference Paper · Sep 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.
    Full-text · Article · Aug 2013 · Inorganica Chimica Acta
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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.
    Full-text · Article · Aug 2013 · Journal of Biomedical Nanotechnology

Publication Stats

5k Citations
801.81 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