Low-temperature structural effects in the (TMTSF)2PF6 and AsF6 Bechgaard salts

We present a detailed low-temperature investigation of the statics and dynamics of the anions and methyl groups in the organic conductors (TMTSF) 2PF6 and (TMTSF)2AsF6 (TMTSF: tetramethyl-tetraselenafulvalene). The 4 K neutron-scattering structure refinement of the fully deuterated (TMTSF)2PF6-D12 salt allows locating precisely the methyl groups at 4 K. This structure is compared to the one of the fully hydrogenated (TMTSF)2PF6-H12 salt previously determined at the same temperature. Surprisingly, it is found that deuteration corresponds to the application of a negative pressure of 5×102 MPa to the H12 salt. Accurate measurements of the Bragg intensity show anomalous thermal variations at low temperature both in the deuterated PF 6 and AsF6 salts. Two different thermal behaviors have been distinguished. Small Bragg-angle measurements reflect the presence of low-frequency modes at characteristic energies θE = 8.3 K and θE = 6.7 K for the PF6-D12 and AsF6-D12 salts, respectively. These modes correspond to the low-temperature methyl group motion. Large Bragg-angle measurements evidence an unexpected structural change around 55 K, which probably corresponds to the linkage of the anions to the methyl groups via the formation of F...D-CD2 bonds observed in the 4 K structural refinement. Finally we show that the thermal expansion coefficient of (TMTSF)2PF6 is dominated by the librational motion of the PF6 units. We quantitatively analyze the low-temperature variation of the lattice expansion via the contribution of Einstein oscillators, which allows us to determine for the first time the characteristic frequency of the PF6 librations: θE ≈ 50 K and θE = 76 K for the PF6-D12 and PF6-H12 salts, respectively. © 2013 American Physical Society.

Charge-ordering transition in (TMTTF)2X explored via dilatometry

Charge-ordering phenomena have been highly topical over the past few years. A phase transition towards a charge-ordered state has been observed experimentally in several classes of materials. Among them, many studies have been devoted to the family of quasi-one-dimensional organic charge-transfer salts (TMTTF)2X, where (TMTTF) stands for tetramethyltetrathiafulvalene and X for a monovalent anion (X = PF6, AsF6 and SbF6). However, the relationship between the electron localization phenomena and the role of the lattice distortion in stabilizing the charge-ordering pattern is poorly documented in the literature. Here we present a brief overview of selected literature results, with emphasis placed on recent thermal expansion experiments probing the charge-ordering transition of these salts. © 2013 IOP Publishing Ltd.

Development and application of an electronic tongue for detection and monitoring of nitrate, nitrite and ammonium levels in waters

This work presents the first study and development of an electronic tongue analysis system for the monitoring of nitrogen stable species: nitrate, nitrite and ammonium in water. The electronic tongue was composed of an array of 15 potentiometric poly(vinyl chloride) membrane sensors sensitive to cations and anions plus an artificial neural network (ANN) response model. The building of the ANN model was performed in a medium containing sodium, potassium, and chloride as interfering ions, thus simulating real environmental samples. The correlation coefficient in the cross-validation of nitrate, nitrite and ammonium was satisfactory in the three cases with values higher than 0.92. Finally, the utility of the proposed system is shown in the monitoring of the photoelectrocatalytic treatment of nitrate. © 2013 Elsevier B.V.

Caracterização da interação de inositol hexafosfato e cloreto com hemoglobina humana: aspectos energéticos e estruturais

Pós-graduação em Biofísica Molecular - IBILCE

Preparação e caracterização de óxido de zinco nanoestruturado

Pós-graduação em Ciência e Tecnologia de Materiais - FC

Peperomia blanda (Piperaceae): avaliação das atividades antibacteriana e antioxidante

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Análise de especiação redox de arsênio in situ usando a técnica de difusão de filmes finos por gradiente de concentração

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Avaliação da taxa de remoção de material dissolvido devido ao intemperismo químico da formação Serra Geral na bacia do Ribeirão Preto

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Utilização de bacteriófagos em associação com Lactobacillus no controle de Salmonella enterica subs. enterica sorotipo typhimurium antibiótico-resitente em frangos de corte (Gallus gallus domesticus - Linnaes, 1758)

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

Estudo da dopagem no óxido de manganês tipo espinélio nanoestruturado no desempenho de um sensor potenciométrico para íons lítio

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Estudo e caracterização da eletropolimerização de moléculas nanoestruturadas a Base de Schiff

Pós-graduação em Química - IBILCE

Determinação de conservantes e contaminantes em alimentos e bebidas por Eletroforese capilar

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Níquel (II) e moléculas orgânicas multidentadas como building blocks na construção de sólidos de coordenação porosos

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Complexos de rutênio (II) contendo ligantes nitrogenados como fotossensibilizadores em células solares

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Hidrogeoquímica do aquífero Bauru na área urbana do município de Marília (SP)

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)