Revealing the Hierarchical Mechanical Strength of Single Cellulose Acetate Electrospun Filaments through Ultrasonic Breakage

The tensile strength of single cellulose acetate electrospun fibers is determined through sonication‐induced fragmentation in water using a model previously developed by Terentjev and co‐workers. The fragmentation of the electrospun fibers results in a gradual shortening of their length until a constant modal length is achieved. A single electrospun CA fiber tensile strength of ≈150 MPa (55–280 MPa) is determined based on fracture statistics. It is also observed that the fragmented fibers show bunches of nanofilaments at their ends with similar diameters to those of round structures observed in the cross‐section of the initial electrospun fibers (≈38 nm). The sonication of these nanofilaments gives rise to spherical particles with similar diameter dimensions, which allows the estimation of a value of the tensile strength of the order of 2 MPa for these nanostructures. The aggregation and the alignment of the nano filaments inside the electrospun fiber should be the source of its higher strength value.

     

Dielectric and thermal characterization of low density ethylene/10‐undecen‐1‐ol copolymers prepared with nickel catalysts

Ethylene and 10‐undecen‐1‐ol copolymers, prepared using a nickel complex as catalyst, were studied using differential scanning calorimetry (DSC), X‐ray diffraction, and dielectric relaxation spectroscopy. The behavior exhibited by copolymers containing incorporated 10‐undecen‐1‐ol amounts within 0.5 and 4.6 mol % was compared with neat polyethylene. DSC revealed that a new crystalline region with lower thickness lamellae emerges in copolymers due to the side‐chains crystallization. Nevertheless, the global crystallization degree decreases due to the loss of crystallinity that occurs in a greater extent in PE‐like regions. Dielectric relaxation spectroscopy detected two processes, a low activation energy process below ?20 °C related with localized mobility increasing in intensity and deviating to higher temperatures with the increase in 10‐undecen‐1‐ol amount, and a high activation energy process ascribed to the glass transition, located at higher temperatures for the different copolymers relatively to neat polyethylene. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2802–2812, 2007     

Cytotoxic Mechanism of Sphaerodactylomelol,an Uncommon Bromoditerpene Isolated from Sphaerococcus coronopifolius

Marine natural products have exhibited uncommon chemical structures with relevant antitumor properties highlighting their potential to inspire the development of new anticancer agents. The goal of this work was to study the antitumor activities of the brominated diterpene sphaerodactylomelol, a rare example of the dactylomelane family. Cytotoxicity (10–100 µM; 24 h) was evaluated on tumor cells (A549, CACO-2, HCT-15, MCF-7, NCI-H226, PC-3, SH-SY5Y, SK-ML-28) and the effects estimated by MTT assay. Hydrogen peroxide (H₂O₂) levels and apoptosis biomarkers (membrane translocation of phosphatidylserine, depolarization of mitochondrial membrane potential, Caspase-9 activity, and DNA condensation and/or fragmentation) were studied in the breast adenocarcinoma cellular model (MCF-7) and its genotoxicity on mouse fibroblasts (L929). Sphaerodactylomelol displayed an IC₅₀ range between 33.04 and 89.41 µM without selective activity for a specific tumor tissue. The cells’ viability decrease was accompanied by an increase on H₂O₂ production, a depolarization of mitochondrial membrane potential and an increase of Caspase-9 activity and DNA fragmentation. However, the DNA damage studies in L929 non-malignant cell line suggested that this compound is not genotoxic for normal fibroblasts. Overall, the results suggest that the cytotoxicity of sphaerodactylomelol seems to be mediated by an increase of H₂O₂ levels and downstream apoptosis.     

Copolymerization of ethylene/unsaturated alcohols using nickel catalysts: effect of the ligand on the activity and comonomer incorporation

The nickel complexes {bis[N,N′-di(2-t-butylphenyl)imino]acenaphthene} dibromonickel (1-NiBr₂) and {bis[N,N′-di(2-phenylphenyl)imino]acenaphthene} dibromonickel (2-NiBr₂) were studied in homo-, co- and terpolymerization of ethylene and propylene with polar monomers and the results compared to those previously obtained with another catalyst precursor [bis(N,N′-dimesitylimino)acenaphthene] dibromonickel (3-NiBr₂). In order to understand the effect of the ligand in the activity and rate of comonomer incorporation some theoretical studies, using both a semi-empirical molecular orbital method and a density-functional theory model, were performed. Good agreement was found between the computed parameters and the experimental results for the order of homo-polymerization, the differences in polymer molecular weight distribution, and, in some cases, the incorporation of functionalized copolymers in the case of copolymerization, and also on the inhibition effects caused by these copolymers.     

Correlation between i.r. spectra and thermal decomposition of cobalt(II), nickel(II), copper(II) and mercury(II) complexes with piperidinedithiocarbamate and pyrrolidinedithiocarbamate

The thermal decomposition of pyrrolidinedithiocarbamate and piperidinedithiocarbamate complexes of Co^II, Ni^II, Cu^II and Hg^II have been studied by thermogravimetry and differential scanning calorimetry. The decomposition intermediates and final products were identified by their X-ray diffraction patterns. The i.r. spectra are discussed in terms of the thermal decomposition pathways.     

Natural Approaches for Neurological Disorders—The Neuroprotective Potential of Codium tomentosum

Parkinson’s disease (PD) is the second most common neurodegenerative disorder, and is characterized by a progressive degeneration of the dopaminergic neurons in the substantia nigra. Although not completely understood, several abnormal cellular events are known to be related with PD progression, such as oxidative stress, mitochondrial dysfunction and apoptosis. Accordingly, the aim of this study was to evaluate the neuroprotective effects of Codium tomentosum enriched fractions in a neurotoxicity model mediated by 6-hydroxydopamine (6-OHDA) on SH-SY5Y human cells, and the disclosure of their mechanisms of action. Additionally, a preliminary chemical screening of the most promising bioactive fractions of C. tomentosum was carried out by GC-MS analysis. Among the tested fractions, four samples exhibited the capacity to revert the neurotoxicity induced by 6-OHDA to values higher or similar to the vitamin E (90.11 ± 3.74% of viable cells). The neuroprotective effects were mediated by the mitigation of reactive oxygen species (ROS) generation, mitochondrial dysfunctions and DNA damage, together with the reduction of Caspase-3 activity. Compounds belonging to different chemical classes, such as terpenes, alcohols, carboxylic acids, aldehydes, esters, ketones, saturated and unsaturated hydrocarbons were tentatively identified by GC-MS. The results show that C. tomentosum is a relevant source of neuroprotective agents, with particular interest for preventive therapeutics.     

Titanium and zirconium ketimide complexes: synthesis and ethylene polymerisation catalysis

The syntheses of ketimide titanium complexes of the type Ti(NC^tBu₂)₃X (X = Cl, Cp, Ind), Ti(NC^tBu₂)₄ and the zirconium complex CpZr(NC^tBu₂)₂Cl are described. When activated by MAO, all compounds are ethylene polymerisation catalysts. In the conditions studied, the most active catalyst is CpZr(NC^tBu₂)₂Cl, with an activity of 2.7 × 10⁵ kg/(molZr [E] h). Titanium complexes are less active by about two orders of magnitude. The polyethylene produced is linear, as determined by NMR spectroscopy. Molecular structures of Ti(NC^tBu₂)₃X (X = Cl, Cp, Ind) and Ti(NC^tBu₂)₄ were determined by X-ray single crystal diffraction.     

Photodegradation of Ethylene/Propylene/Polar Monomers Co‐ and Terpolymers. I—Prepared by Group 4 Catalyst Systems

The photooxidative degradation behavior of polyethylene, its copolymers (propylene/polar monomers) and terpolymers, synthesized by a group 4 catalyst system, has been studied by Fourier transform infrared spectroscopy and confirmed with scanning elecrton microscopy for morphological changes. The kinetics of photodegradation has also been studied. Surface damage caused by polychromatic (≥290 nm) at 55°C in air is presented in different micrographs. The rate of photodegradation is very fast in terpolymers containing polar monomers as compared with copolymers and polyethylene. Morphological study of these photodegraded samples showed a very good relation with photodegradation results.