Synthesis and Characterization of Composite Materials HDPE/HA and PMMA/HA Prepared by Sonochemistry

Summary : In the present work, the synthesis and characterization of composite materials based on HDPE, and PMMA with nanometric hydroxyapatite, are studied. Composites preparation was carried out by dilutions of the commercial polymers, using decaline as solvent for the polyolefin and 2-butanone for PMMA. In the synthesis of Hydroxyapatite (HA), ammonium phosphate [(NH₄)₂HPO₄] and calcium hydroxide [Ca(OH)₂] were used as precursors. Composites with 20, 30 and 40 wt% of HA were prepared. The polymer dilutions and the precursors of the HA were placed simultaneously in a reactor under ultrasonic radiation at 20 kHz, for periods of 15, 25 and 35 min. The products obtained were characterized by FTIR, TGA, TEM, XRD and biocompatibility studies were also carried out. The results showed the presence of nanometric HA and clear interactions between HA and PMMA polymers were observed by FTIR. These results were corroborated by TEM showing that nanometric HA particles are encapsulated into the polymeric PMMA matrix. For the composites of HDPE, these interactions were not observed.     

Atomic-scale simulations of material behaviors and tribology properties for BCC metal film

This work has two main purposes:(i) introducing the basic concepts of molecular dynamics analysis to material scientists and engineers, and(ii) providing a better understanding of instrumented indentation measurements, presenting an example of nanoindentation and scratch test simulations. To reach these purposes, three-dimensional molecular dynamics(MD) simulations of nanoindentation and scratch test technique were carried out for generic thin films that present BCC crystalline structures. Structures were oriented in the plane(100) and placed on FCC diamond substrates. A pair wise potential was employed to simulate the interaction between atoms of each layer and a repulsive radial potential was used to represent a spherical tip indenting the sample. Mechanical properties of this generic material were obtained by varying the indentation depth and dissociation energy. The load-unload curves and coefficient of friction were found for each test; on the other hand, dissociation energy was varied showing a better mechanical response for films that present grater dissociation energy. Structural change evolution was observed presenting vacancies and slips as the depth was varied.     

Phosphorus heterocycles from 2‐(2‐hydroxyphenyl)‐1H‐benzimidazole

Sixteen different P(III) and P(V) heterocycles derived from 2‐(2‐hydroxyphenyl)‐1H‐benzimidazole ( 1 ) are reported. In these heterocycles the phosphorus atom is part of a six‐membered unsaturated ring. They were mainly studied by multinuclear NMR. The X‐ray diffraction of 3,4‐ benzimidazole‐5,6‐benzo‐2‐dimethylamino‐2‐seleno‐ 1,3,2‐oxazaphosphorinane is reported. Phosphoranes derived from 1 and 3,5‐di‐tert‐butylcatechol, and bearing Cl, NMe₂, or phenyl as substituent at phosphorus are presented. © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:307–320, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20021     

Sandwich,Triple-Decker and Other Sandwich-like Complexes of Cyclopentadienyl Anions with Lithium or Sodium Cations

Density functional theory, DFT, calculations were carried out on complexes containing cyclopentadienyl anions and lithium or sodium cations; half-sandwich, sandwich and sandwich-like complexes (among them triple-decker ones) are analyzed. Searches performed through the Cambridge Structural Database revealed that crystal structures containing these motifs exist, mostly structures with sodium cations. The DFT calculations performed here include geometry optimization and frequency calculations of the complexes at the ωB97XD/aug-cc-pVTZ level, followed by the partitioning of the energy of interaction via the Energy Decomposition Analysis scheme, EDA, at the BP86-D3/TZ2P level. Additional calculations and analyses were performed using both the Quantum Theory of Atoms in Molecules, QTAIM, and the Natural Bond Orbital analyses, NBO. The results of this work show that the electrostatic interaction energy is the most important attractive contribution to the total interaction energy of each of the complex systems analyzed here, and that complexation itself leads to minor electron charge shifts.     

Calmness of the Feasible Set Mapping for Linear Inequality Systems

In this paper we deal with parameterized linear inequality systems in the n-dimensional Euclidean space, whose coefficients depend continuosly on an index ranging in a compact Hausdorff space. The paper is developed in two different parametric settings: the one of only right-hand-side perturbations of the linear system, and that in which both sides of the system can be perturbed. Appealing to the backgrounds on the calmness property, and exploiting the specifics of the current linear structure, we derive different characterizations of the calmness of the feasible set mapping, and provide an operative expresion for the calmness modulus when confined to finite systems. In the paper, the role played by the Abadie constraint qualification in relation to calmness is clarified, and illustrated by different examples. We point out that this approach has the virtue of tackling the calmness property exclusively in terms of the system’s data.     

Atisideritol,a new ent-atis-13-ene from a sideritis pusilla (Lag) Pau ssp

From Sideritis pusilla subspecia has been isolated an ent-11β, 16α,17-trihydroxy-atis-13-ene diterpenoid, and the trivial name atisideritol is proposed for it.     

Design and characterization of a lactate biosensor based on immobilized lactate oxidase onto gold surfaces

The design and characterization of a lactate biosensor and its application to the determination of this analyte in wine and beer are described. The biosensor is developed through the immobilization of lactate oxidase (LOx) using two different strategies including direct adsorption and covalent binding. The characterization of the resulting lactate oxidase monolayers was performed in aqueous phosphate buffer solutions using atomic force microscopy (AFM) and quartz crystal microbalance (QCM) techniques. In presence of lactate and using hydroxymethylferrocene as a redox mediator, biosensors obtained by either direct adsorption or by covalent binding exhibit a clear electrocatalytic activity, and lactate could be determined amperometrically at 300 mV versus SSCE. Results obtained under these conditions give a linear current response versus lactate concentration up to 0.3 mM, with a detection limit of 10 μM of lactate and a sensitivity of 0.77 ± 0.08 μA mM⁻¹. Finally, biosensors were applied to the determination of lactate in wine and beer. The results obtained are in good agreement with those obtained by a well-established enzymatic-spectrophotometric assay kit.     

Gelled emulsions with a high water content

The structure of a gel containing 99% water, 0.5% of a nonionic surfactant and 0.5% of a hydrocarbon was investigated by analysis of its equilibrium phases and their state of dispersion by liquid helium freeze fracture electron microscopy.The gel consisted of aqueous droplets of micron size separated by a thin membrane of a lamellar liquid crystal and a W/O microemulsion with droplets varying between 200 and 1000 Å in diameter.