Hállen D. R. Calado
Universidade Federal de Minas Gerais
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Publication
Featured researches published by Hállen D. R. Calado.
Journal of Coordination Chemistry | 2005
Ricardo F. F. da Costa; Anayive P. Rebolledo; Tulio Matencio; Hállen D. R. Calado; José D. Ardisson; Maria E. Cortés; Bernardo L. Rodrigues; Heloisa Beraldo
Complexes of 2-benzoylpyridine thiosemicarbazone (H2Bz4DH) as well as of its N(4)-methyl (H2Bz4Me) and N(4)-phenyl (H2Bz4Ph) analogues with iron(II), nickel(II) and zinc(II) were characterized by a variety of spectroscopic techniques. Electrochemical studies revealed that the iron(II) complexes undergo oxidation giving the iron(III) analogues, which could be reduced back by cellular thiols such as thioredoxine, suggesting that this process could occur in biological media. The thiosemicarbazones have antifungal activity against Candida albicans that significantly decreases on coordination. The crystal structure 2-benzoylpyridine-N(4)-methyl thiosemicarbazone (H2Bz4Me) was determined.
Journal of the Brazilian Chemical Society | 2006
Gustavo Catão Alves; Luiz O. Ladeira; Ariete Righi; Klaus Krambrock; Hállen D. R. Calado; Rossimiriam Pereira de Freitas Gil; M. V. B. Pinheiro
In this work we report on an alternative synthesis of water-soluble fullerenes known as fullerols, aiming for biomedical applications. The synthesis is based on a process in which polyethylene glycol (PEG400) is used as phase-transfer catalyst between fullerene/benzene and aqueous NaOH solutions. The polyhydroxylation of the fullerenes occurs in the NaOH solution under a continuous flow of O2 to enhance the reaction yield. The resulting compound was characterized with infrared spectroscopy, nuclear magnetic resonance, thermo-gravimetric analysis and optical absorption. The formation of C60(OH)18-20 in high yields was confirmed.
Journal of the Brazilian Chemical Society | 2011
Marcos Roberto de Abreu Alves; Hállen D. R. Calado; Claudio Luis Donnici; Tulio Matencio
This work reports the synthesis of three polymers and two new copolymers based on 3-substituted polythiophene derivatives, all of them demonstrated photoluminescent properties. All polymers synthesized, i.e., poly(3-methoxythiophene) (PMOT), poly(3-thiopheneethanol) (PTE), poly(3-thiophenemethanol) (PTM), poly(3-methoxythiophene-co-3-thiopheneethanol) (PMOT-co-TE) and poly(3-methoxythiophene-co-3-thiophenemethanol) (PMOT-co-TM), were characterized by FT IR, UV-Vis, photoluminescence (PL), thermal analysis (TG and DSC) and X-ray diffraction (XRD). All materials emitted light in the orange region of the visible spectrum. Spectrometric analysis in the infrared region demonstrated the successful synthesis of polymers and copolymers by the presence of characteristic bands. Thermal analysis showed that the obtained materials had good thermal stability.
Química Nova | 2010
Rodrigo L. Lavall; Juliana Aparecida Sales; Raquel S. Borges; Hállen D. R. Calado; J.C. Machado; D. Windmöller; Glaura G. Silva; Rodrigo G. Lacerda; Luiz O. Ladeira
Polyurethane/multi-walled carbon nanotube (MWCNT) nanocomposites have been prepared with nanotube concentrations between 0.01 wt% and 1 wt%. MWCNT as-synthesized samples with ~74 nm diameter and ~7 μm length were introduced by solution processing in the polyurethane matrix. Scanning electron microscopy (SEM) images demonstrated good dispersion and adhesion of the CNTs to the polymeric matrix. The C=O stretching band showed evidence of perturbation of the hydrogen interaction between urethanic moieties in the nanocomposites as compared to pure TPU. Differential scanning calorimetry and positron anihilation lifetime spectroscopy measurements allowed the detection of glass transition displacement with carbon nanotube addition. Furthermore, the electrical conductivity of the nanocomposites was significantly increased with the addition of CNT.
Sensors | 2013
Carla Patrícia Lacerda Rubinger; Hállen D. R. Calado; Rero Marques Rubinger; Henrique S. Oliveira; Claudio Luis Donnici
In this work; resistive moisture sensors were obtained by dip coating sulfonated polycarbonate (SPC) onto silver interdigitated electrodes. Commercial polycarbonate was sulfonated with acetyl sulphate at two different sulfonation degrees corresponding to 9.0 and 18.0 mole %. Impedance spectroscopy was used to investigate the humidity sensing properties at controlled relative humidity (RH%) environments generated from standard saline solutions in the range of 11–90 RH%. For the highest sulfonated sample; in the RH% range investigated (11 to 90%); the sensor impedance changed from 4.7 MΩ to 18 kΩ. Humidity sensors made from sulfonated polycarbonate showed exponential decay behavior of the impedance at constant frequency with the environmental relative humidity. Sample 9SPC presented dielectric relaxation response for environmental humidity between 58 and 90 RH% while sample 18SPC presented dielectric relaxation response for the entire measured range between 11 and 90 RH%. Sulfonated polycarbonate could be a promising material for the fabrication of simple and cheap humidity-sensing sensors for the assessment of relative humidity of the surrounding environment, as suggested by experimental results.
Journal of Applied Physics | 2008
M. Valadares; I. Silvestre; Hállen D. R. Calado; Bernardo R. A. Neves; P. S. S. Guimarães; L. A. Cury
Photoluminescence (PL) and electroluminescence (EL) emission from blended films composed by poly[2-(2′,5′-bis(2′-ethyl-hexyloxy)phenyl)-1,4-phenylenevinylene] (BEHP-PPV) and poly(3- hexylthiophene) (P3HT) conjugated polymers with different relative concentrations are investigated. The main changes observed on the PL spectra of the blended films with temperature and excitation power are associated to an increase of the emission efficiency of the P3HT constituent. The EL spectrum of a light emission device (LED) fabricated with the BEHP-PPV:P3HT blend presents a similar broad emission as in the PL measurement but shifted to higher wavelengths. The blended LEDs show a significantly higher emission efficiency than the LEDs made with the pure constituents. The apparent color of the blended LED shifts to a purer red as the applied voltage is increased. This tuning capacity was interpreted as due to a change in the effective gap of the blend caused by the redistribution of injected carriers in the BEHP-PPV:P3HT ...
international conference on nanoscience and nanotechnology | 2006
Glaura G. Silva; Hállen D. R. Calado; Anthony W. Musumeci; Wayde N. Martens; Eric R. Waclawik; Ray L. Frost; Graeme A. George
Single walled carbon nanotubes (SWNTs) were incorporated in polymer nanocomposites based on poly(3-octylthiophene) (P3OT), thermoplastic polyurethane (TPU) or a blend of them. Thermogravimetry demonstrated the success of the purification procedure employed in the chemical treatment of SWNTs prior to composite preparation. Stable dispersions of SWNTs in chloroform were obtained by non-covalent interactions with the dissolved polymers. Composites exhibited glass transitions, melting temperatures and heat of fusion which changed in relation to pure polymers. This behavior is discussed as associated to interactions between nanotubes and polymers. The conductivity at room temperature of the blend (TPU-P3OT) with SWNT is higher than the P3OT/SWNT composite.
Química Nova | 2010
Marcos Roberto de Abreu Alves; Hállen D. R. Calado; Tulio Matencio; Claudio Luis Donnici
In this review we summarize recent synthetic investigations about the preparation of oligothiophenes and polythiophenes, the most important π-conjugated organic materials for applications in electrochromic and electroluminescent devices. It is showed that many interesting and novel functionalized oligothiophenes have been synthesized by convenient coupling strategies (Heck, Kumada, Negishi, Suzuki, Stille and Ullmann) and oxidative coupling methods. Synthesis of polythiophenes are also presented and described according to chemical and electrochemical polymerization methodologies. The description of these noteworthy synthetic methods illustrates how important and promising are the interdisciplinary approaches in the obtaining of oligothiophenes and polythiophenes.
MRS Proceedings | 2008
Hállen D. R. Calado; Marcelo Valadares; Anthony W. Musumeci; Eric R. Waclawik; L. A. Cury; Glaura G. Silva
Carbon nanotubes (CNT) / conjugated polymer composites have been used for the preparation of thin film-modified electrodes. Thin, short, multi-walled CNT (MWNT) (purity higher than 95%) was completely coated by regioregular poly(3-hexylthiophene) (P3HT) through precipitation of a mixture of both in the non-solvent methanol. This work reports the electrochemical and optical characterization of P3HT and composites after dissolution in xylene and spin casting of films with thickness
Journal of Solid State Electrochemistry | 2016
Marcus Henrique de Araujo; Tulio Matencio; Claudio Luis Donnici; Hállen D. R. Calado
The present work reports the synthesis of four electron-acceptor beta-substituted thiophenes that were studied as monomers for electrochemical polymerization with 3,4-ethylenedioxythiophene (EDOT), an electron-donating monomer, aiming the combination of electron-acceptor and donor monomer thiophene to a simpler and convenient build up of novel donor–acceptor copolymeric materials via electrochemical polymerization. Four novel copolymers poly(EDOT-co-3-thiophene phenylacetate), (PEDOT-co-PPhTAc-2a), poly(EDOT-co-3-thiophene(4-nitrophenyl)acetate) (PEDOT-co-PPhTAc-2b), poly(EDOT-co-3-thiophenephenylcarboxylate) (PEDOT-co-PPhTCb), and poly(EDOT-co-3-(phenoxymethyl)thiophene) (PEDOT-co-PPhOMT) were electrochemically polymerized. The monomers were characterized by spectrometric techniques (FTIR, 1H NMR, and 13C NMR), and the copolymers were identified by electrochemical analyses and FT-IR. Although the corresponding homopolymers could not be obtained, in the presence of EDOT, the copolymers were formed in a quasi-reversible electrochemical kinetics. The infrared spectra of the copolymers as well the electrochemical profile corroborates their obtaining. The mass variation during the electrosynthesis was analyzed using a quartz crystal microbalance. The film’s morphologies were investigated by SEM. Interestingly, the combination of electron-rich monomer thiophene (EDOT) and these electron-deficient carboxy-substituted thiophenes might be a convenient building block couple to increase the performance control of physic-chemical properties of mixed polythiophenes with innovative applications and they also showed a possible applicability as charge storage device.