Fabricação e caracterização elétrica de filmes nanoestruturados de derivados do politiofeno

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

How does spacer length of imidazolium gemini surfactants control the fabrication of 2D-Langmuir films of silver-nanoparticles at the air-water interface?

A series of gemini surfactants based on cationic imidazolium ring as polar headgroup, abbreviated as lm-n-lm], 2Br(-) (n = 2, 5, 6 and 12), was synthesized. Their ability to stabilize silver nanoparticles in aqueous media was investigated. The resulting suspensions were characterized by UV-Vis spectroscopy and transmission electron microscopy (TEM). They exhibit specific morphologies by adopting different supramolecular assemblies in aqueous media depending on the internal packing arrangements and on the number of spacer methylene units -(CH2)(n)-]. Individual colloids were extracted from the aqueous to chloroform layer and spread at the air/water interface to allow the formation of well-defined Langmuir films. By analysis of the surface pressure-area isotherms, the details about the packing behavior and orientation of the imidazolium gemini surfactant capped silver nanoparticles were obtained. Morphological features of the dynamic process of monolayer compression at the air-water interface were elucidated using Brewster angle microscopy (BAM). These monolayers were further transferred on mica sheets by the Langmuir-Blodgett technique at their associated collapse pressure and the morphology of these monolayers was investigated by atomic force microscopy (AFM). The number of spacer methylene units -(CH2)(n)-] of the gemini surfactants exerted critical influence in modulating the characteristics of the resulting Langmuir films. (C) 2014 Elsevier Inc. All rights reserved.

How does spacer length of imidazolium gemini surfactants control the fabrication of 2D-Langmuir films of silver-nanoparticles at the air-water interface?

A series of gemini surfactants based on cationic imidazolium ring as polar headgroup, abbreviated as Im-n-Im], 2Br(-) (n = 2, 5,6 and 12), was synthesized. Their ability to stabilize silver nanoparticles in aqueous media was investigated. The resulting suspensions were characterized by UV-Vis spectroscopy and transmission electron microscopy (TEM). They exhibit specific morphologies by adopting different supramolecular assemblies in aqueous media depending on the internal packing arrangements and on the number of spacer methylene units -(CH2)(n)-]. Individual colloids were extracted from the aqueous to chloroform layer and spread at the air/water interface to allow the formation of well-defined Langmuir films. By analysis of the surface pressure-area isotherms, the details about the packing behavior and orientation of the imidazolium gemini surfactant capped silver nanoparticles were obtained. Morphological features of the dynamic process of monolayer compression at the air-water interface were elucidated using Brewster angle microscopy (BAM). These monolayers were further transferred on mica sheets by the Langmuir-Blodgett technique at their associated collapse pressure and the morphology of these monolayers was investigated by atomic force microscopy (AFM). The number of spacer methylene units (CH2)(n)-] of the gemini surfactants exerted critical influence in modulating the characteristics of the resulting Langmuir films. (C) 2014 Elsevier Inc. All rights reserved.

Surface pressure-area isotherms for Langmuir monolayers and a docking molecular orientation of perylene tetracarboxylic derivatives on a water surface

The surface pressure-molecular area (pi-A) isotherms for Langmuir monolayers of four perylenetetracarboxylic (PTCD) derivatives, measured with varying subphase temperatures and compression speeds, are reported. The behavior of these PTCD derivatives at the water-air interface is modeled using the rigid docking method. This approach is the first attempt to model the molecular orientation of PTCD on the water surface to be compared with experimental Langmuir isotherms. Through this methodology, it would be possible to anticipate aggregation and determine if favorable spatial orientations of perylenes are generated on the water surface. The pi-A isotherm experiments show that these molecules can support high surface pressures, indicating strong packing on the water surface and that the isotherms are compression speed independent but temperature dependent. The molecular orientation and stacking was further examined in Langmuir-Blodgett (LB) monolayers deposited onto glass and glass coated with Ag island films using UV-visible absorption and surface-enhanced fluorescence (SEF) measurements.

Desenvolvimento e seleção de sensores para avaliação de refrigerantes em língua eletrônica

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Sistemas bioinspirados aplicados no estudo de interação e sensoriamento de derivados xantênicos

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

Formation of thin luminescent Eu3+-LB films by in situ coordination with 2,3,5,6-tetra(2 '-pyridyl)pyrazine and 1-octadecanol in pure and mixed Langmuir monolayers

The in situ complexation between 2,3,5,6-tetra(2-pyridyl)pyrazine (tppz) molecules and europium ions at the air-liquid interface by means of mixed 1-octadecanol Langmuir films is reported. These films were transferred to solid supports by means of the Langmuir-Blodgett (LB) technique. The EDS maps attested the homogeneity of the LB films as well as the presence of the europium ions. The mixed alcohol/tppz LB film contained a larger amount of europium ions as compared to the pure octadecanol LB film. This work reports the production of a thin luminescent Eu3+ film containing europium ions using only alcohol molecules as ligands an unexpected result, since it is well known that there is an occurrence of non-radiative deactivation of excited europium by hydroxyl groups. Europium ion multiple binding sites were detected from lifetime decay measurements of these films in the presence of tppz molecules. (C) 2012 Elsevier B.V. All rights reserved.

Langmuir films containing ibuprofen and phospholipids

This study shows the incorporation of ibuprofen, an anti-inflammatory drug, in Langmuir monolayers as cell membrane models. Significant effects were observed for dipalmitoyl phosphatidyl choline (DPPC) monolayers with relevant changes in the elasticity of the monolayer. Dipalmitoyl phosphatidyl glycerol (DPPG) monolayers were affected by small concentrations of ibuprofen, from 1 to 5 mol%. For both types of monolayer, ibuprofen could penetrate into the hydrophobic part of the monolayer, which was confirmed with polarization-modulated infrared reflection–absorption spectroscopy (PM-IRRAS). Brewster angle microscopy (BAM) images showed that ibuprofen prevents the formation of large domains of DPPC. The pharmacological action should occur primarily with penetration of ibuprofen via electrically neutral phospholipid headgroups of the membrane.

Formation of one-dimensional capped ZnO nanoparticle assemblies at the air/water interface

The self-assembling behavior and microscopic structure of zinc oxide nanoparticle Langmuir-Blodgett monolayer films were investigated for the case of zinc oxide nanoparticles coated with a hydrophobic layer of dodecanethiol. Evolution of nanoparticle film structure as a function of surface pressure (π) at the air-water interface was monitored in situ using Brewster’s angle microscopy, where it was determined that π=16 mN/m produced near-defect-free monolayer films. Transmission electron micrographs of drop-cast and Langmuir-Schaefer deposited films of the dodecanethiol-coated zinc oxide nanoparticles revealed that the nanoparticle preparation method yielded a microscopic structure that consisted of one-dimensional rodlike assemblies of nanoparticles with typical dimensions of 25 x 400 nm, encased in the organic dodecanethiol layer. These nanoparticle-containing rodlike micelles were aligned into ordered arrangements of parallel rods using the Langmuir-Blodgett technique.

Zinc oxide quantum dot nanostructures

Zinc oxide (ZnO) is one of the most intensely studied wide band gap semiconductors due to its many desirable properties. This project established new techniques for investigating the hydrodynamic properties of ZnO nanoparticles, their assembly into useful photonic structures, and their multiphoton absorption coefficients for excitation with visible or infrared light rather than ultraviolet light. The methods developed are also applicable to a wide range of nanoparticle samples.

Polymer Protected Gold Nanoparticles

Polymer protected gold nanoparticles have successfully been synthesized by both "grafting-from" and "grafting-to" techniques. The synthesis methods of the gold particles were systematically studied. Two chemically different homopolymers were used to protect gold particles: thermo-responsive poly(N-isopropylacrylamide), PNIPAM, and polystyrene, PS. Both polymers were synthesized by using a controlled/living radical polymerization process, reversible addition-fragmentation chain transfer (RAFT) polymerization, to obtain monodisperse polymers of various molar masses and carrying dithiobenzoate end groups. Hence, particles protected either with PNIPAM, PNIPAM-AuNPs, or with a mixture of two polymers, PNIPAM/PS-AuNPs (i.e., amphiphilic gold nanoparticles), were prepared. The particles contain monodisperse polymer shells, though the cores are somewhat polydisperse. Aqueous PNIPAM-AuNPs prepared using a "grafting-from" technique, show thermo-responsive properties derived from the tethered PNIPAM chains. For PNIPAM-AuNPs prepared using a "grafting-to" technique, two-phase transitions of PNIPAM were observed in the microcalorimetric studies of the aqueous solutions. The first transition with a sharp and narrow endothermic peak occurs at lower temperature, and the second one with a broader peak at higher temperature. In the first transition PNIPAM segments show much higher cooperativity than in the second one. The observations are tentatively rationalized by assuming that the PNIPAM brush can be subdivided into two zones, an inner and an outer one. In the inner zone, the PNIPAM segments are close to the gold surface, densely packed, less hydrated, and undergo the first transition. In the outer zone, on the other hand, the PNIPAM segments are looser and more hydrated, adopt a restricted random coil conformation, and show a phase transition, which is dependent on both particle concentration and the chemical nature of the end groups of the PNIPAM chains. Monolayers of the amphiphilic gold nanoparticles at the air-water interface show several characteristic regions upon compression in a Langmuir trough at room temperature. These can be attributed to the polymer conformational transitions from a pancake to a brush. Also, the compression isotherms show temperature dependence due to the thermo-responsive properties of the tethered PNIPAM chains. The films were successfully deposited on substrates by Langmuir-Blodgett technique. The sessile drop contact angle measurements conducted on both sides of the monolayer deposited at room temperature reveal two slightly different contact angles, that may indicate phase separation between the tethered PNIPAM and PS chains on the gold core. The optical properties of amphiphilic gold nanoparticles were studied both in situ at the air-water interface and on the deposited films. The in situ SPR band of the monolayer shows a blue shift with compression, while a red shift with the deposition cycle occurs in the deposited films. The blue shift is compression-induced and closely related to the conformational change of the tethered PNIPAM chains, which may cause a decrease in the polarity of the local environment of the gold cores. The red shift in the deposited films is due to a weak interparticle coupling between adjacent particles. Temperature effects on the SPR band in both cases were also investigated. In the in situ case, at a constant surface pressure, an increase in temperature leads to a red shift in the SPR, likely due to the shrinking of the tethered PNIPAM chains, as well as to a slight decrease of the distance between the adjacent particles resulting in an increase in the interparticle coupling. However, in the case of the deposited films, the SPR band red-shifts with the deposition cycles more at a high temperature than at a low temperature. This is because the compressibility of the polymer coated gold nanoparticles at a high temperature leads to a smaller interparticle distance, resulting in an increase of the interparticle coupling in the deposited multilayers.

Exciton Plasmon Coupling in Hybrid Semiconductor - Metal Nanoparticle Monolayers

Hybrid semiconductor-metal nanoparticles monolayer of Cadmium Sclenide and gold nanoparticles has been prepared, using Langmuir – Blodgett technique. The near field photoluminescence spectra from such monolayer films, shows red shift similar to 75 meV with respect to CdSe QDs monolayer film and splitting similar to 57 meV. The composite spectra are much broader similar to 330 meV compared to the corresponding emission spectra of CdSe monolayer similar to 165 meV. The possible explanation for the observed features are provided in terms of exciton - Plasmon interaction.

Sequence Specific Interaction between Promoter DNA and Escherichia coli RNA Polymerase: Comparative Thermodynamic Analysis with One Immobilized Partner

Sequence specific interaction between DNA and protein molecules has been a subject of active investigation for decades now. Here, we have chosen single promoter containing bacteriophage Delta D-III T7 DNA and Escherichia coli RNA polymerase and followed their recognition at the air-water interface by using the surface plasmon resonance (SPR) technique, where the movement of one of the reacting species is restricted by way of arraying them on an immobilized support. For the Langmuir monolayer studies, we used a RNA polymerase with a histidine tag attached to one of its subunits, thus making it an xcellent substrate for Ni(II) ions, while the SPR Studies were done using biotin-labeled DNA immobilized on a streptavidin-coated chip. Detailed analysis of the thermodynamic parameters as a function of concentration and temperature revealed that the interaction of RNA polymerase with T7 DNA is largely entropy driven (83 (+/- 12) kcal mol(-1)) with a positive enthalpy of 13.6 (+/- 3.6) kcal mol(-1), The free energy of reaction determined by SPR and Langmuir-Blodgett technique was -11 (+/- 2) and -15.6 kcal mol(-1), respectively. The ability of these methods to retain the specificity of the recognition process was also established.

Nonspecific Interaction between DNA and Protein allows for Cooperativity: A Case Study with Mycobacterium DNA Binding Protein

Different DNA-binding proteins have different interaction modes with DNA. Sequence-specific DNA protein interaction has been mostly associated with regulatory processes inside a cell, and as such extensive studies have been made. Adequate data is also available on nonspecific DNA protein interaction, as an intermediate to protein's search for its cognate partner. Multidomain nonspecific DNA protein interaction involving physical sequestering of DNA has often been implicated to regulate gene expression indirectly. However, data available on this type of interaction is limited. One such interaction is the binding of DNA with mycobacterium DNA binding proteins. We have used the Langmuir-Blodgett technique to evaluate for the first time the kinetics and thermodynamics of Mycobacterium smegmatis Dps 1 binding to DNA. By immobilizing one of the interacting partners, we have shown that, when a kinetic bottleneck is applied, the binding mechanism showed cooperative binding (n = 2.72) at lower temperatures, but the degree of cooperativity gradually reduces (n = 1.38) as the temperature was increased We have also compared the kinetics and thermodynamics of sequence-specific and nonspecific DNA protein interactions under the same set of conditions.

稀土配合物分子组装及其性质研究

分子组装技术是一种在分子水平上进行的有序薄膜组装技术,包括Langmuir-Blodgett(LB)膜技术及自组装技术.该论文中,对稀土配合物及稀土杂多化合物的分子组装进行了系统的研究,取得了一些令人感兴趣的研究结果:合成了Na<,9>EuW<,10>O<,36>,Na<,9>DyW<,10>O<,36>,Na<,9>SmW<,10>O<,36>,K<,13>Eu(SiW<,11>O<,39>)<,2>,K<,13>Eu(GeW<,11>O<,39>)<,2>,K<,15>Eu(BW<,11>O<,39>)<,2>等稀土多金属氧酸盐,用LB膜技术将其组装入双十八烷基二甲基溴化铵(DODA)和十八胺(ODA)分子中,得到稀土杂多化合物LB膜.以稀土离子为亚相,制备了邻十六酰基苯甲酸-稀土(铽和铕)和对十六烷氧基苯甲酸铽LB膜.以1,2-二羟基苯-3,5-二磺酸铽(Tiron-Tb)为亚相,制备了DODA/Tiron-TbLB膜.以3-氨丙基三乙氧基硅烷为前驱体,制备了Na<,9>EuW<,10>O<,36>,Na<,9>DyW<,10>O<,36>的自组装膜.荧光光谱研究表明,在自组装膜中配体能将能量有效地传递给稀土离子.