The Hofmeister anion effect and the growth of polyelectrolyte multilayers

The influence of a variety of counteranions on the properties of polyelectrolyte multilayers deposited by layer-by-layer technique is studied by using ellipsometry and AFM. We found out that in thin dry multilayers (20-90 nm) ofpoly(4-styrenesulfonate) (PSS) and poly(diallyldimethylammonium) (PDADMA), the thickness follows reasonably well the position of the counteranion in the Hofmeister series. The polyelectrolyte-counteranion interaction is studied by means of viscosity measurements of semidilute solutions of PDADMA in the presence of different anions. The dynamic viscosities follow the Hofmeister series of anions and correlate with the thickness of multilayers. Two parameters describing the interaction of ions with water, the Jones-Dole viscosity B coefficient and the hydration entropy, are used to explain the anion effect on the developing multilayer thickness. Reasonably smooth and monotonic functional dependence is observed between the layer thickness and these two parameters.     

Oils from Wild,Micropropagated Plants,Calli, and Suspended Cells ofEuphorbia characias L.

Applied Biochemistry and Biotechnology - Micropropagated Euphorbia characias plants gave higher yields of crude oil than did wild ones. Leaves of either wild and micropropagated plants contained...     

Gold(I)-catalyzed intramolecular cyclopropanation of dienynes

Gold(I) complexes are the most active catalysts for the biscyclopropanation of dienynes to form tetracyclic compounds. PtII and ZnII are also able to promote the biscyclopropanation, although less efficiently. The configurations obtained in all cases with the use of gold(I) catalysts can be explained by the pathway proceeding through anti cyclopropyl gold carbenes. Similar intermediates are most probably involved in reactions catalyzed by RuII and PtII. Two different cyclopropanation pathways have been found; they depend on the structures of the cyclopropyl gold carbenes (anti or syn) and the relative arrangements of the metal carbenes and the alkenes.     

Long-Range Lateral Correlation between Self-Assembled Domains of Fluorocarbon-Hydrocarbon Tetrablocks by Quantitative GISAXS

The structure and lateral correlation of fluorocarbon-hydrocarbon tetrablock di(F10Hm) domains at the air/water interface have been determined by quantitative analysis of grazing incidence small-angle X-ray scattering (GISAXS) data. The measured GISAXS signals can be well represented by the full calculation of the form and structure factors. The form factor suggests that di(F10Hm) domains take a hemiellipsoid shape. Both major and minor axes of the hemiellipsoids monotonically increased in response to the elongation of the hydrocarbon blocks, which can be explained by the concominant increase in van der Waals interaction. The structure factor calculated from the GISAXS signals suggests that the domains take an orthorhombic lattice. Remarkably, the lateral correlation can reach over a distance that is more than 14 times longer than the distance to the nearest neighbors. Our data suggest that quantitative GISAXS enables the optimal design of mesoscopic self-assemblies at the air/water interface by fine-tuning of the structures of molecular building blocks.     

Anticancer β-hairpin peptides: membrane-induced folding triggers activity

Several cationic antimicrobial peptides (AMPs) have recently been shown to display anticancer activity via a mechanism that usually entails the disruption of cancer cell membranes. In this work, we designed an 18-residue anticancer peptide, SVS-1, whose mechanism of action is designed to take advantage of the aberrant lipid composition presented on the outer leaflet of cancer cell membranes, which makes the surface of these cells electronegative relative to the surface of noncancerous cells. SVS-1 is designed to remain unfolded and inactive in aqueous solution but to preferentially fold at the surface of cancer cells, adopting an amphiphilic β-hairpin structure capable of membrane disruption. Membrane-induced folding is driven by electrostatic interaction between the peptide and the negatively charged membrane surface of cancer cells. SVS-1 is active against a variety of cancer cell lines such as A549 (lung carcinoma), KB (epidermal carcinoma), MCF-7 (breast carcinoma), and MDA-MB-436 (breast carcinoma). However, the cytotoxicity toward noncancerous cells having typical membrane compositions, such as HUVEC and erythrocytes, is low. CD spectroscopy, appropriately designed peptide controls, cell-based studies, liposome leakage assays, and electron microscopy support the intended mechanism of action, which leads to preferential killing of cancerous cells.     

The effect of stoichiometry on curing and properties of epoxy–clay nanocomposites

Epoxy–clay nanocomposites have been prepared with an organically modified montmorillonite. The epoxy network was based on diglycidyl ether of bisphenol A (DGEBA) cured with diaminodiphenylmethane (DDM). The stoichiometry DGEBA–DDM was varied, the molar ratio of amine hydrogen/epoxy groups, r, ranged from 0.85 to 1.15. The influence of stoichiometry on curing and properties of the nanocomposites was studied using differential scanning calorimetry, dynamic mechanical thermal analysis and X-ray diffraction. All nanocomposites had intercalated clay structures. The clays accelerated the curing reaction whose rate was also increased when increasing r. The heat of reaction, −ΔH (J/g epoxy), increased as r increased, reaching a constant value for r ≥ 1. In the presence of clays −ΔH was lower than in the neat DGEBA–DDM. The glass transition temperature (T _g) of the neat epoxy thermosets reached a maximum at r = 1; however, the nanocomposites showed the T _g maximum at 0.9 < r < 1. The presence of clay lowered the T _g for r > 0.94 and raised T _g for r ≤ 0.85. The elastic modulus of neat epoxy thermosets reached a maximum in the rubber state and a minimum in the glassy state at r = 1. The nanocomposites showed similar behavior, but the maximum and the minimum values of the elastic modulus were reached at stoichiometry r < 1. The comparison of the properties of neat epoxy with those of the nanocomposites varying the stoichiometry indicates that the clay itself induces stoichiometric changes in the system.     

Existence and uniqueness of solutions of nonlinear elliptic equations without growth conditions at infinity

In this paper, we consider the nonlinear elliptic problem $$ - \Delta u + {\left| u \right|^{p - 1}}u + {\left| {\nabla u} \right|^q} = f$$ in ? ^N , where p > 1 and q > 0. We show that if f ?? L _loc ^r (? ^N ) for suitable r ?? 1, then there exists a distributional solution of the equation, independently of the behavior of f at infinity. We also analyze the uniqueness of this solution in some cases.     

Iron-related toxicity effects of single-walled carbon nanotubes in human placental cells (BeWo) investigated by X-ray fluorescence microscopy

As the prospect of human beings exposed to new nanomaterials increases, there are growing concerns about the foetal exposure and effects of such nanomaterials during pregnancy. Among others, due to their ample usage, it becomes urgent to address the vulnerability of the human placental barrier to carbon nanotubes (CNTs). Recently, by applying a combination of advanced synchrotron-based X-ray microscopy and X-ray fluorescence (XRF) techniques, we demonstrated that raw single-walled CNTs (SWCNTs) may cause an asbestos-like iron-related toxicity in mesothelial (MeT5A) cells. This work shows the results obtained with the same approach and experimental conditions in human choriocarcinoma (BeWo) cells as a placental model. XRF microscopy in mild and soft X-ray regimes was used to map the distribution of P, S, Ca, and Fe in exposed and control cells, whereas absorption and phase-contrast imaging (soft X-ray microscopy) provided simultaneous morphological information. The findings show that exposure to SWCNTs affects cell viability and causes a small increase in intracellular iron content, further confirmed by the stimulation of the ferritin protein. It is interesting to note that the iron changes are negligible when highly purified SWCNTs are used. In all tested conditions, including exposure to iron sulfate, the iron accumulation or ferritin increase was much lower in BeWo cells than in MeT5A ones, suggesting a different iron metabolism and possibly a lower vulnerability of the placental barrier to iron-rich nanomaterials.     

Development of a solid-phase microextraction method for determination of volatile oxidation compounds in fish oil emulsions

Headspace solid-phase microextraction (HS-SPME) is proposed for isolating and determining the headspace volatiles formed during oxidation of fish-oil-in-water emulsions. Three different fiber coatings were tested and compared for sensitivity and reproducibility. A carboxen/polydimethylsiloxane (CAR-PDMS) fiber coating was found to be the most suitable for the analysis of emulsion volatiles. The main factors affecting the microextraction process on CAR-PDMS were then evaluated by a factorial design: amount of sample, time and temperature of extraction and stirring. The incubation of 0.5 g of emulsion at 60 degrees C during 30 min leads to the most effective extraction of volatiles associated with lipid oxidation of fish oil emulsions. The HS-SPME method coupled with GC-MS allowed the qualitative and quantitative analysis of the volatiles derived from oxidation of real fish oil enriched foods such as milk and mayonnaise. The method here proposed is very fast and simple and yields high sensitivity, with good repeatability for all target compounds.