On the Chemical and Structural Rearrange of Hg-organyltellurolate Clusters: Synthesis, X-ray Characterization, TGA and Raman Evaluation of [(PhTe)6(Ph3P)2Hg5Cl4]?·?2THF and [(PhTe)8Hg6Py2Cl4]?·?Py (Py = pyridine)

(PhTe)₂Hg reacts with HgCl₂ and triphenylphosphine to give the clusters [(PhTe)₆(Ph₃P)₂Hg₅Cl₄] · 2THF (1) and [(PhTe)₈Hg₆Py₂Cl₄] · Py (Py = pyridine) (2). In 1 each tellurium atom connects two Hg atoms, with Hg–Te distances around 2.75 Å. Phosphorus atoms of the triphenylphosphine groups complete the tetrahedral coordination of the Hg1 atoms. The second set of Hg atoms (Hg2) is also coordinated to chlorine atoms. The three-dimensional assembling of 1 encloses circular channels with medium diameter of 12.5 Å. The cluster 2 results from substitution of the oxidized triphenylphosphine ligands of 1 by one molecule of Hg(PhTe)₂ in the course of the synthetic procedures. The alternated Te–Hg bonds of 2 close a 12-membered ring with two inverted 4-membered rings in the middle. Thermogravimetrical evaluations and Raman scattering lines of 1 and 2 are also discussed.

Interfacial properties and thermal stability of modified poly(m‐phenylene isophthalamide) thin films

Poly(m‐phenylene isophthalamide) (PMIA) is a resistant to high temperatures and chemically stable engineering material. The application as coatings and membranes, however, is limited by its poor interaction with other materials. In this report, we describe the molecular modification of PMIA through reaction with dimsyl sodium and 2‐iodine‐1‐ethanol. The substitution of 58% of amide hydrogen by ethanol (etOH) groups produces a material (MPMIA) able to develop regularly structured films on silicon substrate. The morphology of the films is dependent on the ionic strength of the precursory solution. MPMIA starts a degradation process by losing the etOH group. MPMIA has a better affinity with poly(p‐cresolformaldehyde) than with a pristine one, increasing the range of composition in which thermal stability and miscibility are observed. Thin films of these blends have different morphologies that vary from nanometric porous to two‐phase microstructured grains, according to the composition. Copyright © 2012 John Wiley & Sons, Ltd.     

High throughput screening of beta-amyloid secretion inhibitors using homogenous time-resolved fluorescence

A cell-based assay using homogeneous time-resolved fluorescence has been developed for high throughput screening of putative beta-amyloid (Abeta)production inhibitors. In this assay, total Abeta is detected by simply adding two commercially available antibody complexes. The first was a biotinylated monoclonal antibody (4G8), specifically recognizing an epitope comprising the residues 17-24 of the Abetapeptide, complexed with europium cryptate-streptavidin conjugate. The second was a polyclonal antibody (BioS-N), raised against the N-terminus of the Abeta peptide, complexed with an allophycocyanin-anti rabbit antibody conjugate. Binding of the two complexes to the Abeta peptide brought europium cryptate (fluorescence donor) and allophycocyanin (fluorescence acceptor) into close proximity, consequently a fluorescent resonance energy transfer signal was produced upon excitation at 337 nm. The resulting fluorescence signal (665 nm) was then detected using a Discovery or a ViewLux reader. Detection of Abeta by the proposed method is possible at concentrations of approximately 1 nM. The method was employed for the detection of Abeta secreted from a stable transfected human neuroglioma cell line (H4) overexpressing a mutated form of the human amyloid precursor protein (APP695NL) and developed for robotic automation. At optimized conditions, signal-to-background ratios exceeding 5 and Z' factors around 0.7 were achieved in a 384-well format. High throughput screening of 56,913 potential Abeta production inhibitors led to identification of new non-cytotoxic and cell permeable compounds with potencies in the submicromolar range.     

Solution properties of poly(acrylamide-co-3,5,5-trimethylhexane methacrylate) and its polyelectrolyte derivative

The physicochemical properties of hydrophobically modified polyacrylamide (HAPAM) containing a small amount of hydrophobic groups (3,5,5-trimethylhexane methacrylate) and its partially hydrolyzed derivative (HAPAM-10N500) were investigated. The ¹³C spectrum was used to establish the degree of hydrolysis of HAPAM-10N500. Small-angle X-ray scattering (SAXS) was employed to highlight the polyelectrolyte character of HAPAM-10N500, estimate the chain conformation in the semidilute regime, and evaluate the influence of the ionic strength and the type of salt. The weight average molecular weight, the second virial coefficient, and radius of gyration were determined by static light scattering (SLS). The polymers showed different rheological properties in aqueous solution, with significant increase in viscosity due to partial hydrolysis of HAPAM, however, with strong dependence on ionic strength of the medium. Results showed that the polymers HAPAM and HAPAM-10N500 are suitable for application in processes of moderate temperatures and salinities.     

Design and Characterization of Maltoheptaose-b-Polystyrene Nanoparticles,as a Potential New Nanocarrier for Oral Delivery of Tamoxifen

Tamoxifen citrate (TMC), a non-steroidal antiestrogen drug used for the treatment of breast cancer, was loaded in a block copolymer of maltoheptaose-b-polystyrene (MH-b-PS) nanoparticles, a potential drug delivery system to optimize oral chemotherapy. The nanoparticles were obtained from self-assembly of MH-b-PS using the standard and reverse nanoprecipitation methods. The MH-b-PS@TMC nanoparticles were characterized by their physicochemical properties, morphology, drug loading and encapsulation efficiency, and release kinetic profile in simulated intestinal fluid (pH 7.4). Finally, their cytotoxicity towards the human breast carcinoma MCF-7 cell line was assessed. The standard nanoprecipitation method proved to be more efficient than reverse nanoprecipitation to produce nanoparticles with small size and narrow particle size distribution. Moreover, tamoxifen-loaded nanoparticles displayed spherical morphology, a positive zeta potential and high drug content (238.6 ± 6.8 µg mL⁻¹) and encapsulation efficiency (80.9 ± 0.4 %). In vitro drug release kinetics showed a burst release at early time points, followed by a sustained release profile controlled by diffusion. MH-b-PS@TMC nanoparticles showed higher cytotoxicity towards MCF-7 cells than free tamoxifen citrate, confirming their effectiveness as a delivery system for administration of lipophilic anticancer drugs.     

Thermal Degradation of Natural Polymers

The thermal degradation of sodium hyaluronate, xanthan and methylcellulose was evaluated by thermogravimetric and infrared analysis. Kinetic parameters such as activation energy and pre-exponential factor were determined considering the Ozawa and Freeman–Carroll methods. The results suggest changes in the degradation mechanism with the fraction of mass loss for both the studied polysaccharides. The activation energy values determined by the Freeman–Carroll method are higher than those obtained by the Ozawa method under the same conditions, probably because in the first method a first order reaction was assumed and the thermal history effects were eliminated since only one TG curve was used to determine the kinetic parameters. Low thermal stability was observed for polyanions e.g. sodium hyaluronate (Na-Hy) and xanthan(XT) in comparison with methylcellulose (MC) which is a neutral polysaccharide. By infrared spectroscopy, it was observed that at low temperatures there occured only the scission of the exocyclic groups for both polysaccharides and that the scission of strong links in the backbone occurred at high temperatures, in agreement with the kinetic parameters determined for the degradation reaction. This revised version was published online in July 2006 with corrections to the Cover Date.