Layer-by-layer nanostructured hybrid films of polyaniline and vanadium oxide

Supramolecular structures of polyaniline (PANI) and vanadium oxide (V2O5) have been assembled via the electrostatic layer-by-layer (ELBL) technique. Strong ionic interactions and H-bonding impart unique features to the ELBL films, which are distinct from cast films obtained with the same materials. The interactions were manifested in UV-vis and Fourier transform infrared spectroscopy data. They are enhanced by the intimate contact between the components, as the films are molecularly thin, with 25 A per PANI/V2O5 bilayer.     

Energy‐Modulated Heterostructures Made with Conjugated Polymers for Directional Energy Transfer and Carrier Confinement

In this paper we demonstrate that multilayer structures with modulated bandgaps can be used for efficient energy transfer and carrier confinement inside a nanostructured film of a light‐emitting polymer. The films were produced with the layer‐by‐layer technique (LbL) with a poly(p‐phenylene vinylene) (PPV) precursor and a long chain dodecylbenzenesulfonate ion (DBS). DBS is incorporated selectively into the precursor chain, and with a rapid, low temperature conversion process (100 °C) superstructures with variable HOMO–LUMO gap could be formed along the deposition direction by changing the DBS concentration. Structures with different stair‐type energy modulations were produced, which are thermally stable and reproducible, as demonstrated by UV‐VIS. absorption measurements. Energy differences of up to 0.5 eV between the lowest and highest conjugated layers inside the stair structure could be achieved, which was sufficient to guide the excitation over long distances to the lower bandgap layer.     

Immobilization of liposomes in nanostructured layer-by-layer films containing dendrimers

Artificial vesicles or liposomes composed of lipid bilayers have been widely exploited as building blocks for artificial membranes, in attempts to mimic membrane interaction with drugs and proteins and to investigate drug delivery processes. In this study we report on the immobilization of liposomes of 1,2-dipalmitoyl-sn-Glycero-3-[Phospho-rac-(1-glycerol)] (Sodium Salt) (DPPG) in layer-by-layer (LbL) films, alternated with poly(amidoamine) G4 (PAMAM) dendrimer layers. The average size of the liposomes in solution was 120 nm as determined by dynamic light scattering, with their spherical shape being inferred from scanning electron microscopy (SEM) in cast films. LbL films containing up to 20 PAMAM/DPPG bilayers were assembled onto glass and/or silicon wafer substrates. The growth of the multilayers was achieved by alternately immersing the substrates into the PAMAM and DPPG solutions for 5 and 10 min, respectively. The formation of PAMAM/DPPG liposome multilayers and its ability to interact with BSA were confirmed by Fourier transform infrared spectroscopy (FTIR). The structural features and film thickness were obtained using X-ray diffraction and surface plasmon resonance (SPR).     

Phase transition in poly(vinylidene fluoride) investigated with micro-Raman spectroscopy

The phase transition from the non-polar alpha-phase to the polar beta-phase of poly(vinylidene fluoride) (PVDF) has been investigated using micro-Raman spectroscopy, which is advantageous because it is a nondestructive technique. Films of alpha-PVDF were subjected to stretching under controlled rates at 80 degrees C, while the transition to beta-PVDF was monitored by the decrease in the Raman band at 794 cm(-1) characteristic of the alpha-phase, along with the concomitant increase in the 839 cm(-1) band characteristic of the beta-phase. The alpha-->beta transition in our PVDF samples could be achieved even for the sample stretched to twice (2x-stretched) the initial length and it did not depend on the stretching rate in the range between 2.0 and 7.0 mm/min. These conclusions were corroborated by differential scanning calorimetry (DSC) and X-ray diffraction experiments for PVDF samples processed under the same conditions as in the Raman scattering measurements. Poling with negative corona discharge was found to affect the alpha-PVDF morphology, improving the Raman bands related to this crystalline phase. This effect is minimized for films stretched to higher ratios. Significantly, corona-induced effects could not be observed with the other experimental techniques, i.e., X-ray diffraction and infrared spectroscopy.     

Identification of α-parinaric acid in the seed oil ofSebastiana brasiliensis sprengel (Euphorbiaceae)

Besides some usual fatty acids, the seed oil ofSabastiana brasiliensis (Euphorbiaceae) contains up to 39% (estimated by ultraviolet spectroscopy) of α-parinaric acid (cis, trans, trans, cis-9, 11, 13, 15-octadecatetraenoic acid). The fatty acids were analyzed by gas chromatography and gas chromatography/mass spectrometry as their methyl esters. The structure of α-parinaric acid was proven by a combination of chemical and spectroscopic methods, conducted with the crude oil, the methyl ester mixture, and the isolated fatty acid methyl ester. Complete assignment of the¹H and¹³C nuclear magnetic resonance (NMR) shifts of α-parinaric acid was carried out by two-dimensional NMR experiments Presented in part at the 21st world Congress and Exhibition of the International Society for Fat Research (ISF), October 1–6, 1995, The Hague, The Netherlands.     

The effects of temperature on the molecular orientation of zinc phthalocyanine films

Phthalocyanine compounds have been widely investigated as candidate materials for technological applications, which is mainly due to their thermal stability and possibility of processing in the form of thin films. In most applications, the controlled growth of thin films with high crystalline quality is essential. In this study, zinc phthalocyanine (ZnPc) thin films were prepared by evaporation on glass and Au-coated glass substrates with subsequent annealing at different temperatures in ambient atmosphere. The morphological and structural features of 80 nm thick zinc phthalocyanine films were investigated, evidencing an α → β phase transformation after annealing the films at 200 °C, as indicated by UV–Vis spectroscopy and FTIR analyses. A better uniformity of the annealed films was also evidenced via AFM analysis, which may be of importance for applications where film homogeneity and excellent optical quality are required.     

Barrier and Mechanical Properties of Clay-Reinforced Polymeric Nanocomposites

In this work, clay-based nanocomposites films were prepared by addition of clay-Na⁺ natural montmorillonite in pectin and hydroxypropyl methylcellulose (HPMC) matrices. Mechanical (tensile strength, elastic modulus, and elongation) and barrier (Water Vapor Permeability (WVP), and Oxygen permeability (O₂P)) properties were investigated. From results, it was observed that the WVP and O₂P decreased when nanoclay was included into the HPMC and pectin matrix films. Additionally, the incorporation of nanoclay in the films significantly improved the mechanical properties because the reinforcing effect of clay from its high aspect ratio and its enormous surface area. These results are very important in packaging area.     

Immobilization of cholesterol oxidase in LbL films and detection of cholesterol using ac measurements

The preserved activity of immobilized biomolecules in layer-by-layer (LbL) films can be exploited in various applications, including biosensing. In this study, cholesterol oxidase (COX) layers were alternated with layers of poly(allylamine hydrochloride) (PAH) in LbL films whose morphology was investigated with atomic force microscopy (AFM). The adsorption kinetics of COX layers comprised two regimes, a fast, first-order kinetics process followed by a slow process fitted with a Johnson–Mehl–Avrami (JMA) function, with exponent ~ 2 characteristic of aggregates growing as disks. The concept based on the use of sensor arrays to increase sensitivity, widely employed in electronic tongues, was extended to biosensing with impedance spectroscopy measurements. Using three sensing units, made of LbL films of PAH/COX and PAH/PVS (polyvinyl sulfonic acid) and a bare gold interdigitated electrode, we were able to detect cholesterol in aqueous solutions down to the 10^? 6 M level. This high sensitivity is attributed to the molecular-recognition interaction between COX and cholesterol, and opens the way for clinical tests to be made with low cost, fast experimental procedures.     

Evaluation of the anti-inflammatory efficacy of Passiflora edulis

The aim of this study was to investigate the anti-inflammatory effect of the aqueous extract of Passiflora edulis forma flavicarpa Degenerer leaves in the air pouch inflammation model induced by carrageenan, histamine or substance P, in mice. An aqueous extract was prepared by infusion and lyophilized. Part of the extract was fractionated with n-butanol, resulting in the butanolic and aqueous residual fractions. The anti-inflammatory activities of the lyophilized extract and these two derived fractions were evaluated. In the inflammation induced by carrageenan, aqueous extract (100 mg/kg, i.p.), butanolic fraction (50 mg/kg, i.p.), aqueous residual fraction (100 mg/kg, i.p.) and dexamethasone (0.5 mg/kg, i.p.) inhibited the leukocyte, neutrophil, myeloperoxidase, nitric oxide, and interleukin-1 beta (IL-1β) levels (p < 0.05). The aqueous extract and butanolic and aqueous residual fractions, but not dexamethasone, decreased macrophage inflammatory protein-2 (MIP-2) levels (p < 0.05). Only dexamethasone inhibited mononuclear cells (p < 0.01). In the inflammation induced by histamine, the aqueous extract, butanolic and aqueous residual fractions, and dexamethasone inhibited total and differential leukocytes (p < 0.01). In the inflammation induced by substance P, the aqueous extract, butanolic and aqueous residual fractions, and dexamethasone also inhibited total leukocytes and mononuclears (p < 0.01). Neutrophils were only inhibited by aqueous extract, butanolic fraction, and dexamethasone (p < 0.05). In conclusion, the active principle(s) present in the P. edulis aqueous extract and its two fractions showed pronounced anti-inflammatory properties, inhibiting cell migration, proinflammatory cytokines, enzymes and mediators.