Complementary study on the electrical and structural properties of poly(3-alkylthiophene) and its copolymers synthesized on ITO by electrochemical impedance and Raman spectroscopy

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

NIR luminescent Er3+/Yb3+ co-doped SiO2-ZrO2 nanostructured planar and channel waveguides: Optical and structural properties

Optical and structural properties of planar and channel waveguides based on sol gel Er3+ and Yb3+ co-doped SiO2-ZrO2 are reported. Microstructured channels with high homogeneous surface profile were written onto the surface of multilayered densified films deposited on SiO2/Si substrates by a femtosecond laser etching technique. The densification of the planar waveguides was evaluated from changes in the refractive index and thickness, with full densification being achieved at 900 degrees C after annealing from 23 up to 500 min, depending on the ZrO2 content Crystal nucleation and growth took place together with densification, thereby producing transparent glass ceramic planar waveguides containing rare earth-doped ZrO2 nanocrystals dispersed in a silica-based glassy host Low roughness and crack-free surface as well as high confinement coefficient were achieved for all the compositions. Enhanced NIR luminescence of the Er3+ ions was observed for the Yb3+- codoped planar waveguides, denoting an efficient energy transfer from the Yb3+ to the Er3+ ion. (C) 2012 Elsevier B.V. All rights reserved.

Correlation of the Physicochemical and Structural Properties of pDNA/Cationic Liposome Complexes with Their in Vitro Transfection

In this study, we characterized the conventional physicochemical properties of the complexes formed by plasmid DNA (pDNA) and cationic liposomes (CL) composed of egg phosphatidylcholine (EPC), 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), and 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) (50/25/25% molar ratio). We found that these properties are nearly unaffected at the studied ranges when the molar charge ratio (R-+/-) between the positive charge from the CL and negative charge from pDNA is not close to the isoneutrality region (R-+/- = 1). However, the results from in vitro transfection of HeLa cells showed important differences when R-+/- is varied, indicating that the relationships between the physicochemical and biological characteristics were not completely elucidated. To obtain information regarding possible liposome structural modifications, small-angle X-ray scattering (SAXS) experiments were performed as a function of R-+/- to obtain correlations between structural, physicochemical, and transfection properties. The SAXS results revealed that pDNA/CL complexes can be described as being composed of single bilayers, double bilayers, and multiple bilayers, depending on the R-+/- value. Interestingly, for R-+/- = 9, 6, and 3, the system is composed of single and double bilayers, and the fraction of the latter increases with the amount of DNA (or a decreasing R-+/-) in the system. This information is used to explain the transfection differences observed at an R-+/- = 9 as compared to R-+/- = 3 and 6. Close to the isoneutrality region (R-+/- = 1.8), there was an excess of pDNA, which induced the formation of a fraction of aggregates with multiple bilayers. These aggregates likely provide additional resistance against the release of pDNA during the transfection phenomenon, reflected as a decrease in the transfection level. The obtained results permitted proper correlation of the physicochemical and structural properties of pDNA/CL complexes with the in vitro transfection of HeLa cells by these complexes, contributing to a better understanding of the gene delivery process.

Structural properties and energetics of diffuse Rb-87 clusters in three-dimension

A correlated two-body basis function is used to describe the three-dimensional bosonic clusters interacting via two-body van der Waals potential. We calculate the ground state and the zero orbital angular momentum excited states for Rb-N clusters with up to N = 40. We solve the many-particle Schrodinger equation by potential harmonics expansion method, which keeps all possible two-body correlations in the calculation and determines the lowest effective many-body potential. We study energetics and structural properties for such diffuse clusters both at dimer and tuned scattering length. The motivation of the present study is to investigate the possibility of formation of N-body clusters interacting through the van der Waals interaction. We also compare the system with the well studied He, Ne, and Ar clusters. We also calculate correlation properties and observe the generalised Tjon line for large cluster. We test the validity of the shape-independent potential in the calculation of the ground state energy of such diffuse cluster. These are the first such calculations reported for Rb clusters. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4730972]

Theoretical and experimental studies on the electronic, optical, and structural properties of poly-pyrrole-2-carboxylic acid films

A theoretical approach is used here to explain experimental results obtained from the electrosynthesis of polypyrrole-2-carboxylic acid (PPY-2-COOH) films in nonaqueous medium. An analysis of the Fukui function (reactivity index) indicates that the monomer (pyrrole-2-carboxylic acid, PY-2-COOH), and dimers and trimers are oxidized in the C4 or C5 positions of the heterocyclic ring of the PY-2-COOH structure. After calculating the heat of formation using semiempirical Austin Model 1 post-Hartree-Fock parameterization for dimer species, both C4 and C5 positions adjacent to the aromatic rings of PPY-2-COOH were considered the most susceptible ones to oxidative coupling reactions. The ZINDO-S/CI semiempirical method was used to simulate the electronic transitions typically seen in the UV-VIS-NIR range in monomer and oligomers with different conjugation lengths. The use of an electrochemical quartz crystal microbalance provides sufficient information to propose a polymerization mechanism of PY-2-COOH based on molecular modeling and experimental results.

Design-based stereology to quantify structural properties of artificial and natural snow using thin sections

The quantification of the structural properties of snow is traditionally based on model-based stereology. Model-based stereology requires assumptions about the shape of the investigated structure. Here, we show how the density, specific surface area, and grain boundary area can be measured using a design-based method, where no assumptions about structural properties are necessary. The stereological results were also compared to X-ray tomography to control the accuracy of the method. The specific surface area calculated with the stereological method was 19.8 ± 12.3% smaller than with X-ray tomography. For the density, the stereological method gave results that were 11.7 ± 12.1% larger than X-ray tomography. The statistical analysis of the estimates confirmed that the stereological method and the sampling used are accurate. This stereological method was successfully tested on artificially produced ice beads but also on several snow types. Combining stereology and polarisation microscopy provides a good estimate of grain boundary areas in ice beads and in natural snow, with some limitatio

Multi-scale study of hydrogen isotopes structural properties in solid phase in the context of inertial fusion target manufacturing

Designing the ignition and high-gain targets for inertial confinement fusion (ICF) requires a condensed uniform layer of the hydrogen fuel on the inner surface of a spherical polymer shell. The fuel layers have to be highly uniform in thickness and roughness.

Structural properties of InAlN single layers nearly latice-matched to GaN grown by plasma assisted molecular beal epitaxy

The high lattice mismatch between III-nitride binaries (InN, GaN and AlN) remains a key problem to grow high quality III-nitride heterostructures. Recent interest has been focused on the growth of high-quality InAlN layers, with approximately 18% of indium incorporation, in-plane lattice-matched (LM) to GaN. While a lot of work has been done by metal-organic vapour phase epitaxy (MOVPE) by Carlin and co-workers, its growth by molecular beam epitaxy (MBE) is still in infancy

Optical and structural properties of InAlN/GaN Bragg reflectors examined by transmission electron microscopy and electron energy loss spectroscopy

Molecular beam epitaxy growth of ten-period lattice-matched InAlN/GaN distributed Bragg reflectors (DBRs) with peak reflectivity centered around 400nm is reported including optical and transmission electron microscopy (TEM) measurements [1]. Good periodicity heterostructures with crack-free surfaces were confirmed, but, also a significant residual optical absorption below the bandgap was measured. The TEM characterization ascribes the origin of this problem to polymorfism and planar defects in the GaN layers and to the existence of an In-rich layer at the InAlN/GaN interfaces. In this work, several TEM based techniques have been combined.

Chrysanthemum chlorotic mottle viroid: Unusual structural properties of a subgroup of self-cleaving viroids with hammerhead ribozymes

The causal agent of chrysanthemum chlorotic mottle (CChM) disease has been identified, cloned, and sequenced. It is a viroid RNA (CChMVd) of 398–399 nucleotides. In vitro transcripts with the complete CChMVd sequence were infectious and induced the typical symptoms of the CChM disease. CChMVd can form hammerhead structures in both polarity strands. Plus and minus monomeric CChMVd RNAs self-cleaved during in vitro transcription and after purification as predicted by these structures, which are stable and most probably act as single hammerhead structures as in peach latent mosaic viroid (PLMVd), but not in avocado sunblotch viroid (ASBVd). Moreover, the plus CChMVd hammerhead structure also appears to be active in vivo, because the 5′ terminus of the linear plus CChMVd RNA isolated from infected tissue is that predicted by the corresponding hammerhead ribozyme. Both hammerhead structures of CChMVd display some peculiarities: the plus self-cleaving domain has an unpaired A after the conserved A9 residue, and the minus one has an unusually long helix II. The most stable secondary structure predicted for CChMVd is a branched conformation that does not fulfill the rod-like or quasi-rod-like model proposed for the in vitro structure of most viroids with the exception of PLMVd, whose proposed secondary structure of lowest free energy also is branched. The unusual conformation of CChMVd and PLMVd is supported by their insolubility in 2 M LiCl, in contrast to ASBVd and a series of representative non-self-cleaving viroids that are soluble under the same high salt conditions. These results support the classification of self-cleaving viroids into two subgroups, one formed by ASBVd and the other one by PLMVd and CChMVd.

The nitrite reductase from Pseudomonas aeruginosa: Essential role of two active-site histidines in the catalytic and structural properties

Cd1 nitrite reductase catalyzes the conversion of nitrite to NO in denitrifying bacteria. Reduction of the substrate occurs at the d1-heme site, which faces on the distal side some residues thought to be essential for substrate binding and catalysis. We report the results obtained by mutating to Ala the two invariant active site histidines, His-327 and His-369, of the enzyme from Pseudomonas aeruginosa. Both mutants have lost nitrite reductase activity but maintain the ability to reduce O2 to water. Nitrite reductase activity is impaired because of the accumulation of a catalytically inactive form, possibly because the productive displacement of NO from the ferric d1-heme iron is impaired. Moreover, the two distal His play different roles in catalysis; His-369 is absolutely essential for the stability of the Michaelis complex. The structures of both mutants show (i) the new side chain in the active site, (ii) a loss of density of Tyr-10, which slipped away with the N-terminal arm, and (iii) a large topological change in the whole c-heme domain, which is displaced 20 Å from the position occupied in the wild-type enzyme. We conclude that the two invariant His play a crucial role in the activity and the structural organization of cd1 nitrite reductase from P. aeruginosa.

Role of hydrophobic interactions and desolvation in determining the structural properties of a model alpha beta peptide.

Model AB, a 20-amino acid peptide that was designed to adopt an alpha beta tertiary structure stabilized by hydrophobic interactions between residues in adjacent helical and extended segments, exhibited large pKa shifts of several ionizable groups and slow hydrogen/deuterium exchange rates of nearly all the peptide amide groups [Butcher, D. J., Bruch, M. D. & Moe, G. T. (1995) Biopolymers 36, 109-120]. These properties, which depend on structure and hydration, are commonly observed in larger proteins but are quite unusual for small peptides. To identify which of several possible features of the peptide design are most important in determining these properties, several closely related analogs of Model AB were characterized by CD and NMR spectroscopy. The results show that hydrophobic interactions between adjacent helical and extended segments are structure-determining and have the additional effect of altering water-peptide interactions over much of the peptide surface. These results may have important implications for understanding mechanisms of protein folding and for the design of independently folding peptides.

Thermodynamic, surface and structural properties of liquid Co-Si alloys

The knowledge of thermophysical properties of liquid Co-Si alloys is a key requirement for manufacturing of composite materials by infiltration method. Despite this need, the experimental and predicted property data of the Co-Si system are scarce and often inconsistent between the various sources. In the present work the mixing behaviour of Co-Si melts has been analysed through the study of the concentration dependence of various thermodynamic, surface (surface tension and surface composition) and structural properties (concentration fluctuations in the long-wavelength limit and chemical short-range order parameter) in the framework of the Compound Formation Model (CFM) and Quasi Chemical Approximation for regular solutions (QCA). In addition, the surface tension of the Co22·5Si77.5 (in at%) eutectic alloy, that is proposed to be used as the infiltrant, has been measured by the pendant drop method at temperatures ranging from 1593 to 1773 K. The results obtained were discussed with respect to both, temperature and concentration, and subsequently compared with the model predictions and literature data.

Structural properties of a family of hydrogen-bonded co-crystals formed between gemfibrozil and hydroxy derivatives of t-butylamine, determined directly from powder X-ray diffraction data

We report the formation and structural properties of co-crystals containing gemfibrozil and hydroxy derivatives of t-butylamine H2NC(CH3)3-n(CH2OH)n, with n=0, 1, 2 and 3. In each case, a 1:1 co-crystal is formed, with transfer of a proton from the carboxylic acid group of gemfibrozil to the amino group of the t-butylamine derivative. All of the co-crystal materials prepared are polycrystalline powders, and do not contain single crystals of suitable size and/or quality for single crystal X-ray diffraction studies. Structure determination of these materials has been carried out directly from powder X-ray diffraction data, using the direct-space Genetic Algorithm technique for structure solution followed by Rietveld refinement. The structural chemistry of this series of co-crystal materials reveals well-defined structural trends within the first three members of the family (n=0, 1, 2), but significantly contrasting structural properties for the member with n=3. © 2007 Elsevier Inc. All rights reserved.