Studies on the interaction between humic substances and conducting polymers for sensor application

The interaction between humic substances and poly(o-ethoxyaniline) (POEA), a conducting polymer, was investigated for both solution and self-assembled films. The results have shown that the humic substances induce a doping of POEA by protonation, as indicated by UV-Vis and Raman spectroscopies. The atomic force microscopy (AFM) studies on the self-assembled films have shown that the average roughness of the polymer film has increased after exposing it to humic substances (fulvic and humic acids), consistent with the interaction between POEA and humic substances. However, this change in morphology is reversible by washing the films with water in agreement with the electrical data allowing using this system in sensor applications. Here, the sensor formed by an array of different sensing units was able to detect and distinguish humic substances in aqueous solution, as shown by multivariate analysis (principal component analysis). The motivation to detect humic substance comes due to its importance in terms of quality control of water or soil. ©2005 Sociedade Brasileira de Química.

Effect of controlled conductivity on thermal sensing property of 0-3 pyroelectric composite

Composite films made of lead zirconate titanate ceramic particles coated with polyaniline and poly(vinylidene fluoride) - PZT-PAni/PVDF were produced by hot pressing the powder mixtures in the desired ceramic volume fraction. The ceramic particles were coated during the polyaniline synthesis and the conductivity of the conductor polymer was controlled by different degrees of protonation. Composites were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), ac and dc electrical measurements, the longitudinal d33 piezo coefficient and the photopyroelectric response. Results showed that the presence of PAni increased the dielectric permittivity of the composite and allowed better efficiency in the poling process, which increased the piezo- and pyroelectric activities of the composite film and reduced both the poling time and the poling electric field. The thermal sensing of the material was also analyzed, showing that this composite can be used as pyroelectric sensor. © 2013 IOP Publishing Ltd.

Fast assembly of non-thiolated DNA on gold surface at lower pH

In a typical protocol for attaching DNA to a gold electrode, thiolated DNA is incubated with the electrode at neutral pH overnight. Here we report fast adsorption of non-thiolated DNA oligomers on gold electrodes at acidic pH (i.e., pH ~3.0). The peak-to-peak potential difference and the redox peak currents in typical cyclic voltammetry of [Fe(CN)6]3- are investigated to monitor the attachment. Compared with incubation at neutral pH, the lower pH can significantly promote the adsorption processes, enabling efficient adsorption even in 30min. The adsorption rate is DNA concentration-dependent, while the ionic strength shows no influence. Moreover, the adsorption is base-discriminative, with a preferred order of A>C≫G, T, which is attributed to the protonation of A and C at low pH and their higher binding affinity to gold surface. The immobilized DNA is functional and can hybridize with its complementary DNA but not a random DNA. This work is promising to provide a useful time-saving strategy for DNA assembly on gold electrodes, allowing fast fabrication of DNA-based biosensors and devices. © 2013 Elsevier Inc.

Otimização do processamento para obtenção de compósitos polímero/cerâmica com propriedades piezo e piroelétricas

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Caracterização e estudo do comportamento térmico dos adutos flunixina-meglumina e diclofenaco-meglumina

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Planejamento de novos derivados da Edaravona

Um estudo teórico detalhado da edaravona foi realizado usando o método TFD (Teoria do Funcional da Densidade) com o conjunto de base B3LYP/6-31G*, com o objetivo de esclarecer o mecanismo sequestraste de radical e a influência do tautomerismo da edaravona em condições ácidas, importantes para auxiliar na elucidação do mecanismo de sequestro de radical pela edaravona no processo isquêmico. Em estudos teóricos anteriores, a tautomerização, o efeito do solvente e a abstração do elétron não foram considerados. Em nosso estudo, a estabilidade e reatividade foram determinadas através de parâmetros geométricos e energéticos. Os cálculos foram realizados em fase gasosa e o método PCM em fase aquosa e metanólica. As condições ácidas ou básicas foram consideradas pelas energias de dissociação e protonação, com consequente formação das formas aniônicas e catiônicas, respectivamente. As propriedades antioxidantes foram calculadas com base nos valores de HOMO, potencial de ionização (PI) e energia de dissociação da ligação (EDL). Os valores de HOMO e PI mostraram que o tautomero N-H é melhor antioxidante pela saída do elétron e os valores de EDL mostraram que o tautomero O-H é melhor antioxidante pela saída de hidrogênio. A protonação é mais favorecida termodinamicamente que a desprotonação. Além disso, a energia de protonação explica, teoricamente, a baixa diferença entre a protonação do N e O. O efeito do solvente diminuiu as barreiras de energias para a isomerização nos tautomeros O-H ou N-H. Adicionalmente, foram avaliados três derivados de pirazolonas com suas capacidades antioxidantes comparadas com a edaravona, em um esforço para identificar o farmacóforo antioxidante. A capacidade antioxidante da antipirina, dipirona, fenilbutazona e edaravona foram determinadas pela inibição de dois radicais estáveis DPPH e ABTS. A edaravona e fenilbutazona foram as mais potente para a inibição de radical DPPH e ABTS que a dipirona, enquanto que a antipirina não mostrou atividade em todas as concentrações analisadas. Simultaneamente, o método TFD previu o valor do potencial antioxidante in silico para explicar a relação de estrutura-atividade (REA). Além disso, foram calculados seus valores de HOMO, EDL X-H, e energia de estabilização (DEiso). Todos os cálculos foram executados usando o programa Gaussian 03, Hyperchem 7.5, e ChemOffice 2005. Os resultados mostraram que o derivado com C-H na posição C-4 aumentou a abstração do elétron ou de hidrogênio. Finalmente, a estratégia geral empregada para planejar os novos derivados se baseou nos estudos de dezoito derivados da edaravona descritos na literatura. Os estudos de REA classificaram os compostos em três grupos, como mais ativo, ativo e menos ativo. Nove derivados foram planejados a partir do composto mais ativo selecionado pelo estudo teórico.

Theoretical insight into the mechanism for the inhibition of the cysteine protease cathepsin B by 1,2,4-thiadiazole derivatives

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Estudo de estirilpironas de Cryptocarya mandioccana por espectrometria de massas e análise configuracional por ressonância magnética nuclear e dicroísmo circular

Pós-graduação em Química - IQ

Combining Experimental Evidence and Molecular Dynamic Simulations To Understand the Mechanism of Action of the Antimicrobial Octapeptide Jelleine-I

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Oligomeric state and structural stability of two hyperthermophilic beta-glucosidases from Thermotoga petrophila

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Complexation of some trivalent lanthanides, scandium(III) and thorium(IV) by benzylidenepyruvates and cinnamylidenepyruvate in aqueous solution

The protonation constants of benzylidenepyruvate, 2-chloro-, 4-chlorobenzylidinepyruvate and cinnamylidenepyruvate as well as the stability constants of their binary 1:1 complexes with Cu(II), La(III), Pr(III), Sm(III), Lu(III), Sc(III) and Th(IV) have been determined spectrophotometrically in an aqueous medium at 25 °C and ionic strength 0.500 M, held with sodium perchlorate. Coordination centres in the aforementioned ligands are suggested. © 1995.

Estudos computacionais de esfingomielinases D: docking, dinâmica molecular e métodos híbridos QM/MM

Pós-graduação em Biofísica Molecular - IBILCE

Estudos computacionais de esfingomielinases D: docking, dinâmica molecular e métodos híbridos QM/MM

Pós-graduação em Biofísica Molecular - IBILCE

Interaction of cationic water-soluble meso-tetrakis(4-N-methylpyridiniumyl)porphyrin (TMPyP) with ionic and nonionic micelles: aggregation and binding

The equilibrium of meso-tetrakis(4-N-methylpyridiniumyl)porphyrin (TMPyP) in aqueous solution in the presence of surfactants was studied by optical spectroscopic techniques and SAXS (small angle X-ray scattering). Anionic SDS (sodium dodecyl sulfate), zwitterionic HPS (N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate) and nonionic TRITON X-100 (t-octyl-phenoxypolyethoxyethanol), surfactants were used. TMPyP is characterized by a protonation equilibrium with a pK(a) around 1.0, associated with the diacid-free base transition, and a second pK(a) around 12.0 related with the transition between the free base and the monoanion form. Three independent species were observed for TMPyP at pH 6.0 as a function of SDS concentration: free TMPyP, TMPyP-SDS aggregates and porphyrin monomer bound to micelles. For HPS and TRITON X-100, the equilibrium of TMPyP as a function of pH is quite similar to that obtained in pure aqueous solution: no aggregation was observed, suggesting that electrostatic contribution is the major factor in the interaction between TMPyP and surfactants. SAXS data analysis demonstrated a prolate ellipsoidal shape for SDS micelles; no significant changes in shape and size were observed for SDS-TMPyP co-micelles. Moreover, the ionization coefficient, alpha, decreases with the increase of the porphyrin concentration, suggesting the ""screening"" of the anionic charge of SDS by the cationic porphyrin. These results are consistent with optical absorption, fluorescence and RLS (resonance light scattering) spectroscopies data, allowing to conclude that neutral surfactants present a smaller interaction with the cationic porphyrin as compared with an ionic surfactant. Therefore, the interaction of TMPyP with the ionic and nonionic surfactants is predominantly due to the electrostatic contribution. Copyright (c) 2008 Society of Porphyrins & Phthalocyanines.

Gas-phase reactivity of protonated 2-oxazoline derivatives: mass spectrometry and computational studies

RATIONALE: Oxazolines have attracted the attention of researchers worldwide due to their versatility as carboxylic acid protecting groups, chiral auxiliaries, and ligands for asymmetric catalysis. Electrospray ionization tandem mass spectrometric (ESI-MS/MS) analysis of five 2-oxazoline derivatives has been conducted, in order to understand the influence of the side chain on the gas-phase dissociation of these protonated compounds under collision-induced dissociation (CID) conditions. METHODS: Mass spectrometric analyses were conducted in a quadrupole time-of-flight (Q-TOF) spectrometer fitted with electrospray ionization source. Protonation sites have been proposed on the basis of the gas-phase basicity, proton affinity, atomic charges, and a molecular electrostatic potential map obtained on the basis of the quantum chemistry calculations at the B3LYP/6-31 + G(d, p) and G2(MP2) levels. RESULTS: Analysis of the atomic charges, gas-phase basicity and proton affinities values indicates that the nitrogen atom is a possible proton acceptor site. On the basis of these results, two main fragmentation processes have been suggested: one taking place via neutral elimination of the oxazoline moiety (99 u) and another occurring by sequential elimination of neutral fragments with 72 u and 27 u. These processes should lead to formation of R+. CONCLUSIONS: The ESI-MS/MS experiments have shown that the side chain could affect the dissociation mechanism of protonated 2-oxazoline derivatives. For the compound that exhibits a hydroxyl at the lateral chain, water loss has been suggested to happen through an E2-type elimination, in an exothermic step. Copyright (C) 2012 John Wiley & Sons, Ltd.