Influence of the Substrate and Precursor on the Magnetic and Magneto-transport Properties in Magnetite Films

We have investigated the magnetic and transport properties of nanoscaled Fe3O4 films obtained from Chemical Vapor Deposition (CVD) technique using [(FeFe2III)-Fe-II(OBut)(8)] and [Fe-2(III)(OBut)(6)] precursors. Samples were deposited on different substrates (i.e., MgO (001), MgAl2O4 (001) and Al2O3 (0001)) with thicknesses varying from 50 to 350 nm. Atomic Force Microscopy analysis indicated a granular nature of the samples, irrespective of the synthesis conditions (precursor and deposition temperature, T-pre) and substrate. Despite the similar morphology of the films, magnetic and transport properties were found to depend on the precursor used for deposition. Using [(FeFe2III)-Fe-II(OBut)(8)] as precursor resulted in lower resistivity, higher M-S and a sharper magnetization decrease at the Verwey transition (T-V). The temperature dependence of resistivity was found to depend on the precursor and T-pre. We found that the transport is dominated by the density of antiferromagnetic antiphase boundaries (AF-APB's) when [(FeFe2III)-Fe-II(OBut)(8)] precursor and T-pre = 363 K are used. On the other hand, grain boundary-scattering seems to be the main mechanism when [Fe-2(III)(OBut)(6)] is used. The Magnetoresistance (MR(H)) displayed an approximate linear behavior in the high field regime (H > 796 kA/m), with a maximum value at room-temperature of similar to 2-3 % for H = 1592 kA/m, irrespective from the transport mechanism.

The migration of Mn2+ ions in Cd1-xMnxS nanocrystals: Thermal annealing control

This work reports evidence of the induced migration of Mn2+ ions in Cd(1-x)MnxS nanocrystals (NCs) by selecting a specific thermal treatment for each sample. The growth and characterization of these magnetic dots were investigated by atomic force microscopy (AFM), optical absorption (OA), and electronic paramagnetic resonance (EPR) techniques. The comparison of experimental and simulated EPR spectra confirms the incorporation of Mn2+ ions both in the core and at the dot surface regions. The thermal treatment of a magnetic sample, via selected annealing temperature and/or time, affects the fine and hyperfine interaction constants which modify the shape and the intensity of the EPR transition spectrum. The identification of these changes has allowed tracing the magnetic ion migration from core to surface regions of a dot as well as inferring the local density of the magnetic impurity ions. (C) 2011 Elsevier Ltd. All rights reserved.

Natural rubber latex LbL films: Characterization and growth of fibroblasts

The recent biomedical applications of natural rubber (NR) latex, mostly in dry membranes, have motivated research into novel, more noble uses of this low-cost biomaterial. In this article, we provide the first report on the fabrication of layer-by-layer (LbL) films of NR alternated with the polyelectrolytes polyethylenimine (PEI) and polyallylamine hydrochloride (PAH). Stable (PAH/NR)n and (PEI/NR)n LbL films displayed similar physicochemical properties, but differed in terms of film morphology according to atomic force microscopy (AFM) and scanning electron microscopy (SEM) data. Most significantly, (PEI/NR)5 LbL films were made of smaller and flattened particles, which were not efficient for the growth and proliferation of normal human fibroblasts (NHF). In contrast, efficient NHF proliferation could be obtained with (PAH/NR)n LbL films, with the fibroblasts exhibiting the expected elongated morphology. Furthermore, cell growth did not occur for cast films of NR, thus demonstrating the suitability of the LbL method for this biologically related application. The differences between the two polyelectrolytes illustrate the importance of the film architecture and morphology, which open the way for exploiting the molecular control inherent in the LbL technique for further applications of NR-containing films. (c) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

The Role of Nanometer-Scaled Ligand Patterns in Polyvalent Binding by Large Mannan-Binding Lectin Oligomers

Mannan-binding lectin (MBL) is an important protein of the innate immune system and protects the body against infection through opsonization and activation of the complement system on surfaces with an appropriate presentation of carbohydrate ligands. The quaternary structure of human MBL is built from oligomerization of structural units into polydisperse complexes typically with three to eight structural units, each containing three lectin domains. Insight into the connection between the structure and ligand-binding properties of these oligomers has been lacking. In this article, we present an analysis of the binding to neoglycoprotein-coated surfaces by size-fractionated human MBL oligomers studied with small-angle x-ray scattering and surface plasmon resonance spectroscopy. The MBL oligomers bound to these surfaces mainly in two modes, with dissociation constants in the micro to nanomolar order. The binding kinetics were markedly influenced by both the density of ligands and the number of ligand-binding domains in the oligomers. These findings demonstrated that the MBL-binding kinetics are critically dependent on structural characteristics on the nanometer scale, both with regard to the dimensions of the oligomer, as well as the ligand presentation on surfaces. Therefore, our work suggested that the surface binding of MBL involves recognition of patterns with dimensions on the order of 10-20 nm. The recent understanding that the surfaces of many microbes are organized with structural features on the nanometer scale suggests that these properties of MBL ligand recognition potentially constitute an important part of the pattern-recognition ability of these polyvalent oligomers. The Journal of Immunology, 2012, 188: 1292-1306.

Structural aspects of polyanion and hydrophobically modified polycation multilayers on hydrophilic or hydrophobic surfaces

Multilayer films of carboxymethylcellulose (CMC), a polyanion, and bromide salts of poly(4-vinylpyridine) quaternized with linear aliphatic chains of 2 (ethyl) and 5 (pentyl) carbon atoms, coded as QPVP-C2 and QPVP-C5, respectively, were fabricated by layer-by-layer (LbL) self-assembly onto Si/SiO2 wafers (hydrophilic substrate) or polystyrene, PS, films (hydrophobic substrate). The films were characterized by means of ex situ and in situ ellipsometry, atomic force microscopy (AFM), contact angle measurements and sum frequency generation vibrational spectroscopy (SFG). Antimicrobial tests were used to assess the exposure of pyridinium moieties to the aqueous medium. In situ ellipsometry indicated that for Si/SiO2 the chains were more expanded than the PS films and both substrates systems composed of QPVP-C5 were thicker than those with QPVP-C2. For dried layers, the alkyl side group size had a small effect on the thickness evolution, regardless of the substrate. At pH 2 the multilayers showed high resistance, evidencing that the build-up is driven not only by cooperative polymer-polymer ion pairing, but also by hydrophobic interactions between the alkyl side chains. The LbL films became irregular as the number of depositions increased. After the last deposition, the wettability of QPVP-C2 or QPVP-C5 terminated systems on the Si/SiO2 wafers and PS films were similar, except for QPVP-C2 on Si/SiO2 wafers. Unlike the morphology observed for LbL films on Si/SiO2 wafers, PS induced the formation of porous structures. SFG showed that in air the molecular orientation of pyridinium groups in multilayers with QPVP-C5 was stronger than in those containing QPVP-C2. The exposure of pyridinium moieties to the aqueous medium was more pronounced when the LbL were assembled on Si/SiO2 wafers.

Development of a recombinant fusion protein based on the dynein light chain LC8 for non-viral gene delivery

The low efficiency of gene transfer is a recurrent problem in DNA vaccine development and gene therapy studies using non-viral vectors such as plasmid DNA (pDNA). This is mainly due to the fact that during their traffic to the target cell's nuclei, plasmid vectors must overcome a series of physical, enzymatic and diffusional barriers. The main objective of this work is the development of recombinant proteins specifically designed for pDNA delivery, which take advantage of molecular motors like dynein, for the transport of cargos from the periphery to the centrosome of mammalian cells. A DNA binding sequence was fused to the N-terminus of the recombinant human dynein light chain LC8. Expression studies indicated that the fusion protein was correctly expressed in soluble form using E. coli BL21(DE3) strain. As expected, gel permeation assays found the purified protein mainly present as dimers, the functional oligomeric state of LC8. Gel retardation assays and atomic force microscopy proved the ability of the fusion protein to interact and condense pDNA. Zeta potential measurements indicated that LC8 with DNA binding domain (LD4) has an enhanced capacity to interact and condense pDNA, generating positively charged complexes. Transfection of cultured HeLa cells confirmed the ability of the LD4 to facilitate pDNA uptake and indicate the involvement of the retrograde transport in the intracellular trafficking of pDNA: LD4 complexes. Finally, cytotoxicity studies demonstrated a very low toxicity of the fusion protein vector, indicating the potential for in vivo applications. The study presented here is part of an effort to develop new modular shuttle proteins able to take advantage of strategies used by viruses to infect mammalian cells, aiming to provide new tools for gene therapy and DNA vaccination studies. (C) 2012 Elsevier B.V. All rights reserved.

Galactomannan thin films as supports for the immobilization of Concanavalin A and/or dengue viruses

The immobilization of the glucose/mannose-binding lectin from Concanavalia ensiformis seeds (ConA) onto a monolayer made of a galactomannan extracted from Leucaena leucocephala seeds (GML), which was adsorbed onto - amino-terminated surfaces, was investigated by means of ellipsometry and atomic force microscopy. The mean thickness of GML monolayer, which polysaccharide consists of linear 1 -> 4-linked beta-D-mannopyranosil units partially substituted at C-6 by alpha-D-galactopyranosyl units, amounted to (1.5 +/- 0.2) nm. ConA molecules adsorbed onto GML surfaces forming (2.0 +/- 0.5) nm thick layers. However, in the presence of mannose the adsorption failed, indicating that ConA binding sites were blocked by mannose and were no longer available for mannose units present in the GML backbone. The GML film was also used as support for the adsorption of three serotypes of dengue virus particles (DENV-1, DENV-2 and DENV-3), where DENV-2 formed the thickest film (4 +/- 2) nm. The adsorbed layer of DENV-2 onto ConA-covered GML surfaces presented mean thickness values similar to that determined for DENV-2 onto bare GML surfaces. The addition of free mannose units prevented DENV-2 adsorption onto ConA-covered GML films by similar to 50%, suggesting competition between virus and mannose for ConA binding sites. This finding suggests that if ConA is also adsorbed to GML surface and its binding site is blocked by free mannose, virus particles are able to recognized GML mannose unities substituted by galactose. interactions between polysaccharides thin films, proteins, and viruses are of great relevance since they can provide basis for the development of biotechnological devices. These results indicate that GML is a potential polysaccharide for biomaterials development, as those could involve interactions between ConA in immune system and viruses. (C) 2011 Elsevier B.V. All rights reserved.

Photo-induced electron transfer in supramolecular materials of titania nanostructures and cytochrome c

In the present paper, we report on the molecular interaction and photochemistry of TiO2 nanoparticles (NPs) and cytochrome c systems for understanding the effects of supramolecular organization and electron transfer by using two TiO2 structures: P25 TiO2 NPs and titanate nanotubes. The adsorption and reduction of cytochrome c heme iron promoted by photo-excited TiO2, arranged as P25 TiO2 NPs and as nanotubes, were characterized using electronic absorption spectroscopy, thermogravimetric analysis, and atomic force microscopy. In an aqueous buffered suspension (pH 8.0), the mass of cytochrome c adsorbed on the P25 TiO2 NP surface was 2.3 fold lower (0.75 mu g m(-2)) than that adsorbed on the titanate nanotubes (1.75 mu g m(-2)). Probably due to the high coverage of titanate nanotubes by adsorbed cytochrome c, the low amount of soluble remaining protein was not as efficiently photo-reduced by this nanostructure as it was by the P25 TiO2 NPs. Cytochrome c, which desorbed from both titanium materials, did not exhibit changes in its redox properties. In the presence of the TiO2 NPs, the photo-induced electron transfer from water to soluble cytochrome c heme iron was corroborated by the following findings: (i) identification by EPR of the hydroxyl radical production during the irradiation of an aqueous suspension of TiO2 NPs, (ii) impairment of a cytochrome c reduction by photo-excited TiO2 in the presence of dioxane, which affects the dielectric constant of the water, and (iii) change in the rate of TiO2-promoted cytochrome c reduction when water was replaced with D2O. The TiO2-promoted photo-reduction of cytochrome c was reverted by peroxides. Cytochrome c incorporated in the titanate nanotubes was also reversibly reduced under irradiation, as confirmed by EPR and UV-visible spectroscopy.

Self-Assembly of Poly(4-vynil-N-alkylpyridinium) Bromide onto Silica: Effect of Side-Chain Length on Structural Aspects at a Molecular Level

Self-assembly of poly(4-vynil-N-alkyl)pyridinium bromide with alkyl side chains of 2, 5, 7, 10, or 16 carbons from ethanolic solutions onto flat silica surfaces was studied by means of ellipsometry, atomic force microscopy (AFM), contact angle measurements, and sum-frequency generation (SFG) vibrational spectroscopy in the CH3 and CH2 stretch region. Ab initio quantum-chemical calculations on the N-alkylpyridinium side-group with restricted Hartree-Fock (RHF) method and 6-311G (d,p) basis set were C one to estimate the charge distribution along the pyridinium ring and the alkyl side-chain. SFG results showed that longer side chains promote the disorientation of the alkyl groups at the surface, corroborating with the contact angle values. AFM images revealed film homogeneity, regardless the alkyl side group. However, after 24 h contact with water, ringlike structures appeared on the film surfaces, when the polycation alkyl side chain had 7 or less carbons, and as the alkyl chain increased to 10 or 16 carbons, the films dewetted because the hydrophobic interactions prevailed over the electrostatic interactions between the pyridinium charged groups and the negatively charged SiO2 surface. Under acid conditions (HCl 0.1 mol.L-1), the film mean thickness values decreased up to 50% of original values when the alkyl side chains were ethyl or pentyl groups due to ion-pair disruption, but for longer groups they remained unchanged. Quantum-chemical optimization and Mulliken electron population showed that (i) from C2 to C15 the positive charge at the headgroup (HG) decreased 0.025, while the charge at combined HG + alpha-CH2 increased 0.037; and (ii) for C6 or longer, the alkyl side group presents a tilt in the geometry, moving away from the plane. Such effects summed up over the whole polymer chain give support to suggest that when the side chains are longer than 7 carbons, the hydrophobic interaction decreases film stability and increases acid resistance.

Adsorption of Sodium Dodecyl Sulfate on Ge Substrate: The Effect of a Low-Polarity Solvent

This paper describes the adsorption of sodium dodecyl sulfate (SDS) molecules in a low polar solvent on Ge substrate by using Fourier transform infrared-attenuated total reflection (FTIR-ATR) spectroscopy and atomic force microscopy (AFM). The maximum SDS amount adsorbed is (5.0 +/- 0.3) x 10(14) molecules cm(-2) in CHCl3, while with the use of CCl4 as subphase the ability of SDS adsorbed is 48% lower. AFM images show that depositions are highly disordered over the interface, and it was possible to establish that the size of the SDS deposition is around 30-40 nm over the Ge surface. A complete description of the infrared spectroscopic bands for the head and tail groups in the SDS molecule is also provided.

Transparent UV-absorbers thin films of zinc oxide: Ceria system synthesized via sol-gel process

Transparent nanostructure ZnO:CeO2 and ZnO thin films to use as solar protector were prepared by non-alkoxide sol-gel process and deposited on boronsilicate glass substrate by dip-coating technique and then heated at 300-500 degrees C. The films were characterized structurally, morphologically and optically by X-ray diffraction (XRD), atomic force microscopy (AFM), field emission gun-scanning electron microscopy (FEG-SEM), scanning electron microscopy (SEM) and UV-Vis transmittance spectroscopy. The coatings presented high transparency in the visible region and excellent absorption in the UV. The band gap of the deposited films was estimated between 3.10 and 3.18 eV. Absorption of the films in the UV was increased by presence of cerium. The results suggest that the materials are promising candidates to use as coating solar protective. (C) 2012 Elsevier B.V. All rights reserved.

Biochemical, physicochemical and molecular characterization of a genuine 2-Cys-peroxiredoxin purified from cowpea [Vigna unguiculata (L.) Walpers] leaves

Background: Peroxiredoxins have diverse functions in cellular defense-signaling pathways. 2-Cys-peroxiredoxins (2-Cys-Prx) reduce H2O2 and alkyl-hydroperoxide. This study describes the purification and characterization of a genuine 2-Cys-Prx from Vigna unguiculata (Vu-2-Cys-Prx). Methods: Vu-2-Cys-Prx was purified from leaves by ammonium sulfate fractionation, chitin affinity and ion exchange chromatography. Results: Vu-2-Cys-Prx reduces H2O2 using NADPH and DTT. Vu-2-Cys-Prx is a 44 kDa (SDS-PAGE)/46 kDa (exclusion chromatography) protein that appears as a 22 kDa molecule under reducing conditions, indicating that it is a homodimer linked intermolecularly by disulfide bonds and has a pI range of 4.56-4.72; its NH2-terminal sequence was similar to 2-Cys-Prx from Phaseolus vulgaris (96%) and Populus tricocarpa (96%). Analysis by ESI-Q-TOF MS/MS showed a molecular mass/pI of 28.622 kDa/5.18. Vu-2-Cys-Prx has 8% alpha-helix, 39% beta-sheet, 22% of turns and 31% of unordered forms. Vu-2-Cys-Prx was heat stable, has optimal activity at pH 7.0, and prevented plasmid DNA degradation. Atomic force microscopy shows that Vu-2-Cys-Prx oligomerized in decamers which might be associated with its molecular chaperone activity that prevented denaturation of insulin and citrate synthase. Its cDNA analysis showed that the redox-active Cys(52) residue and the amino acids Pro(45), Thr(49) and Arg(128) are conserved as in other 2-Cys-Prx. General significance: The biochemical and molecular features of Vu-2-Cys-Prx are similar to other members of 2-Cys-Prx family. To date, only one publication reported on the purification of native 2-Cys-Prx from leaves and the subsequent analysis by N-terminal Edman sequencing, which is crucial for construction of stromal recombinant 2-Cys-Prx proteins. (C) 2012 Elsevier B.V. All rights reserved.

Ultra-structural mapping of sugarcane bagasse after oxalic acid fiber expansion (OAFEX) and ethanol production by Candida shehatae and Saccharomyces cerevisiae

Background Diminishing supplies of fossil fuels and oil spills are rousing to explore the alternative sources of energy that can be produced from non-food/feed-based substrates. Due to its abundance, sugarcane bagasse (SB) could be a model substrate for the second-generation biofuel cellulosic ethanol. However, the efficient bioconversion of SB remains a challenge for the commercial production of cellulosic ethanol. We hypothesized that oxalic-acid-mediated thermochemical pretreatment (OAFEX) would overcome the native recalcitrance of SB by enhancing the cellulase amenability toward the embedded cellulosic microfibrils. Results OAFEX treatment revealed the solubilization of hemicellulose releasing sugars (12.56 g/l xylose and 1.85 g/l glucose), leaving cellulignin in an accessible form for enzymatic hydrolysis. The highest hydrolytic efficiency (66.51%) of cellulignin was achieved by enzymatic hydrolysis (Celluclast 1.5 L and Novozym 188). The ultrastructure characterization of SB using scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy, Fourier transform–near infrared spectroscopy (FT-NIR), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) revealed structural differences before and after OAFEX treatment with enzymatic hydrolysis. Furthermore, fermentation mediated by C. shehatae UFMG HM52.2 and S. cerevisiae 174 showed fuel ethanol production from detoxified acid (3.2 g/l, yield 0.353 g/g; 0.52 g/l, yield, 0.246 g/g) and enzymatic hydrolysates (4.83 g/l, yield, 0.28 g/g; 6.6 g/l, yield 0.46 g/g). Conclusions OAFEX treatment revealed marked hemicellulose degradation, improving the cellulases’ ability to access the cellulignin and release fermentable sugars from the pretreated substrate. The ultrastructure of SB after OAFEX and enzymatic hydrolysis of cellulignin established thorough insights at the molecular level.

Morphology, microstructure and electrocatalytic properties of activated copper surfaces

Morphologic changes on copper surfaces upon applying an established potential protocol were examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results showed a good correlation between the time employed in the electrode activation and the resulting microstructure and electrochemical activity.

XRD, AFM, IR and TGA study of nanostructured hydroxyapatite

In this work, the synthetic hydroxyapatite (HAP) was studied using different preparation routes to decrease the crystal size and to study the temperature effect on the HAP nano-sized hydroxyapatite crystallization. X-ray diffraction (XRD) analysis indicated that all samples were composed by crystalline and amorphous phases . The sample with greater quantity of amorphous phase (40% of total mass) was studied. The nano-sized hydroxyapatite powder was heated and studied at 300, 500, 700, 900 and 1150 °C. All samples were characterized by XRD and their XRD patterns refined using the Rietveld method. The crystallites presented an anisotropic form, being larger in the [001] direction. It was observed that the crystallite size increased continuously with the heating temperature and the eccentricity of the ellipsoidal shape changed from 2.75 at 300 °C to 1.94, 1.43, 1.04 and 1.00 respectively at 500, 700, 900 and 1150 °C. In order to better characterize the morphology of the HAP the samples were also examined using atomic force microscopy (AFM), infrared spectrometry (IR) and thermogravimetric analysis (TGA).