The impact of multivalent counterions, Al3+, on the surface adsorption and self-assembly of the anionic surfactant alkyloxyethylene sulfate and anionic/nonionic surfactant mixtures

The impact of multivalent counterions, Al(3+), on the surface adsorption and self-assembly of the anionic surfactant sodium dodecyl dioxyethylene sulfate, SLES, and the anionic/nonionic surfactant mixtures of SLES and monododecyl dodecaethylene glycol, C(12)E(12), has been investigated using neutron reflectivity, NR, and small angle neutron scattering, SANS. The addition of relatively low concentrations of Al(3+) counterions induces a transition from a monolayer to well-defined surface bilayer, trilayer, and multilayer structures in the adsorption of SLES at the air-water interface. The addition of the nonionic cosurfactant, C(12)E(12), partially inhibits the evolution in the surface structure from monolayer to multilayer interfacial structures. This surface phase behavior is strongly dependent upon the surfactant concentration, solution composition, and concentration of Al(3+) counterions. In solution, the addition of relatively low concentrations of Al(3+) ions promotes significant micellar growth in SLES and SLES/C(12)E(12) mixtures. At the higher counterion concentrations, there is a transition to lamellar structures and ultimately precipitation. The presence of the C(12)E(12) nonionic cosurfactant partially suppresses the aggregate growth. The surface and solution behaviors can be explained in terms of the strong binding of the Al(3+) ions to the SLES headgroup to form surfactant-ion complexes (trimers). These results provide direct evidence of the role of the nonionic cosurfactant in manipulating both the surface and solution behavior. The larger EO(12) headgroup of the C(12)E(12) provides a steric hindrance which disrupts and ultimately prevents the formation of the surfactant-ion complexes. The results provide an important insight into how multivalent counterions can be used to manipulate both solution self-assembly and surface properties.     

Thermodynamics and Kinetics of the Complexation Reaction of Lead by Calix‐DANS4

The thermodynamics and kinetics of the complexation reaction between lead ions and the fluorescent sensor Calix‐DANS4 are determined to optimize the geometry of the microreactor used for the flow‐injection analysis of lead and to tune the working conditions of this microdevice. Under our experimental conditions (pH 3.2, low concentration of Calix‐DANS4) the 1:1 Pb²⁺‐Calix‐DANS4 complex is predominantly formed with a high stability constant (log K_1:1=6.82) and a slow second‐order rate constant (k=9.4×10⁴ L mol^?1 s^?1). Due to this sluggish complexation reaction, the microchannel length must be longer than 130 mm and the flow rate lower than 0.25 mL h^?1 to have an almost complete reaction at the output of the microchannel and a high sensitivity for the heavy metal detection. After determination of the values of the reaction times in our different microdevices, it is possible to simulate the calibration curves for the fluorimetric detection of lead under different conditions. An original method is also presented to determine mixing times in microreactors.     

A quantitative CE method to analyse tau protein isoforms using coated fused silica capillaries

We evaluated the potential of CE to analyse different isoforms of unphosphorylated recombinant tau protein and for separating one phosphorylated tau from the respective unphosphorylated protein. Different capillary coatings such as polyacrylamide, poly‐(ethylene oxide) and polybrene (PB) were evaluated to overcome the poor efficiencies obtained with fused‐silica capillary. Although peak asymmetry values were quite similar for the three investigated coatings, the peak efficiencies were 35‐fold and 5‐fold higher with PB coating than with polyacrylamide and poly(ethylene oxide) coatings, respectively. The recovery percentage (over 97%) was satisfactory and confirmed the efficacy of PB coating to limit the adsorption of tau protein to capillary walls. Moreover, PB coating produced higher repeatability for migration times (RSD values <1.2%) in comparison to the neutral coatings. The potential of PB‐modified capillary in producing high resolutive separations of one phosphorylated tau isoform from its unphosphorylated counterpart and of a mixture of phosphorylated and unphosphorylated tau peptides was demonstrated with 50 mM phosphate buffer pH 3.0. The separation of unphosphorylated tau isoform 352 (Tau‐352) from Tau‐352 phosphorylated in vitro by the mitogen‐activated protein kinase ERK2, was accomplished in less than 15 min.     

Single walled carbon nanotube length determination by asymmetrical-flow field-flow fractionation hyphenated to multi-angle laser-light scattering

Asymmetrical flow field-flow fractionation (AFlFFF) hyphenated to multi-angle laser-light scattering (MALS) was evaluated in order to determine single walled carbon nanotube (SWCNT) length distribution. Fractionation conditions were investigated by examining mobile phase ionic strength and pH, channel components and cross-flow rate. Ammonium nitrate-based mobile phase with 10(-5)molL(-1) ionic strength and pH 6 allows the highest sample recovery (89±3%) to be obtained and the lowest loss of the longest SWCNT. A cross-flow rate of 0.9mLmin(-1) leads to avoid any significant membrane-sample interaction. Length was evaluated from gyration radius measured by MALS by comparing SWCNT to prolate ellipsoid. In order to validate the fractionation and the length determination obtained by AFlFFF-MALS, different SWCNT aliquots were collected after fractionation and measured by dynamic light scattering (DLS). AFlFFF is confirmed to operate in normal mode over 100-2000nm length. MALS length determination after fractionation is found to be accurate with 5% RSD. Additionally, a shape analysis was performed by combining gyration and hydrodynamic radii.     

Caryophyllene oxide-rich essential oils of Lithuanian Artemisia campestris ssp. campestris and their toxicity

The chemical composition of the essential oils of aerial parts of Artemisia campestris ssp. campestris, collected from ten different locations in Lithuania is detailed in this paper. The major component in all the oils was caryophyllene oxide (8.5-38.8%), whereas compounds with the caryophyllane skeleton ranged from 10.2 to 44.5%. Other representative constituents were germacrene D (< or = 15.0%), humulene epoxide II (< or = 8.1%), beta-ylangene (< or = 7.7%), spathulenol (< or = 6.8%), beta-elemene (< or = 6.8%), beta-caryophyllene (< or = 6.2%), junenol (< or = 6.1%) and alpha- or beta-pinene (< or = 5.5%). Eighty-seven compounds were identified, comprising 73.6-92.3% of the oils. The chemical composition was highly variable depending on the sample location. Toxicity of A. campestris oils was determined using the brine shrimp (Artemia sp.) assay. LC50 values ranging to 20 microg/mL were obtained for three of the oils after 24 hours of exposure. Data of this test revealed that A. campestris ssp. campestris essential oils with dominant caryophyllene oxide are notably toxic.     

Dielectric behaviour of copolymers based on 2,2,2-trifluoroethyl methacrylate and cyano co-monomers

In the frame of a research aiming at developing new dielectric polymers containing CCN and CF substituents with strong dipole moment, statistical copolymers based on cyano monomers such as acrylonitrile (AN), methacrylonitrile (MAN), methylvinylidene cyanide (MVCN) and 2,2,2-trifluoroethylmethacrylate (MATRIF), were synthesized and characterized. Elemental analysis has shown that the molar percentages of AN and MAN in the copolymers were 45 mol.%, while only 5 mol.% of MVCN was incorporated in the poly(MVCN-co-MATRIF) copolymer. These copolymers exhibit glass transition temperatures, T_g, in the range of 70-90 °C. The dynamic dielectric analyses and their complex permittivities of these copolymers were studied versus the temperature and the frequency. Evidence of an α-relaxation phenomenon in the glass transition region, which is confirmed by the Vogel-Fulcher-Tammann (VFT) temperature dependence of the relaxation times, was assigned to the cooperative reorientation motions of the cyano groups. The values of dielectric strength (Δε) for the copolymers based on MATRIF were determined by Havriliak-Negami (HN) fitting from the dispersion curves, and can be related to the polarity of the monomer unit and to the packing of the macromolecular chains. These relaxations are sometimes overlapped by conduction phenomena due to ionic impurities at low frequencies and high temperatures dipolar losses. In the glassy state, the permittivity values of AN and MAN copolymers show an increase of polarity which makes them candidates for some applications amongst advanced electrical materials such as dielectric layer for capacitors.     

The Soave,Twu and Boston–Mathias alpha functions in cubic equations of state: Part I. Theoretical analysis of their variations according to temperature

A theoretical analysis of the strengths and weaknesses of the Soave, Twu and Boston–Mathias attractive terms was performed with the Redlich–Kwong EoS. Special attention was paid to the variations of the alpha functions and their first and second derivatives with respect to temperature. Contrary to the Soave function, abnormal behaviors of the derived Twu and Boston–Mathias functions were evidenced in the temperature range commonly covered by industrial applications. The unsuccessful variations of the derived alpha functions observed with these two last models strengthen the interest of the Soave equation for the modeling of derived thermodynamic properties. The accuracy of pure component data modeling by means of the cubic equation of state is discussed in a second part.     

Characterization of biomaterials polar interactions in physiological conditions using liquid–liquid contact angle measurements: Relation to fibronectin adsorption

Wettability of biomaterials surfaces and protein-coated substrates is generally characterized with the sessile drop technique using polar and apolar liquids. This procedure is often performed in air, which does not reflect the physiological conditions. In this study, liquid/liquid contact angle measurements were carried out to be closer to cell culture conditions. This technique allowed us to evaluate the polar contribution to the work of adhesion between an aqueous medium and four selected biomaterials widely used in tissue culture applications: bacteriological grade polystyrene (PS), tissue culture polystyrene (tPS), poly(2-hydroxyethyl methacrylate) film (PolyHEMA), and hydroxypropylmethylcellulose-carboxymethylcellulose bi-layered Petri dish (CEL). The contributions of polar interactions were also estimated on the same biomaterials after fibronectin (Fn) adsorption. The quantity of Fn adsorbed on PS, tPS, PolyHEMA and CEL surfaces was evaluated by using the fluorescein-labeled protein. PolyHEMA and CEL were found to be hydrophilic, tPS was moderately hydrophilic and PS was highly hydrophobic. After Fn adsorption on PS and tPS, a significant increase of the surface polar interaction was observed. On PolyHEMA and CEL, no significant adsorption of Fn was detected and the polar interactions remained unchanged. Finally, an inverse correlation between the polarity of the surfaces and the quantity of adsorbed Fn was established.     

Novel Functional Mesoporous Materials Obtained from Nanostructured Diblock Copolymers

Summary: Novel carboxy (COOH)-functionalized mesoporous polystyrene membranes were prepared from polystyrene-block-poly(D,L-lactide) (PS-b-PLA) diblock copolymers through the selective degradation of the PLA block. The combination of atom transfer radical polymerization (ATRP) and ring-opening polymerization (ROP) techniques enabled the synthesis of nanostructured diblock copolymers possessing carboxylic acid functionality at the junction between both blocks. Such copolymers were subjected to shear flow through the use of a channel die to align their nanodomains. Under mild alkaline conditions, the quantitative hydrolysis of the polyester nanodomains afforded mesoporous materials with COOH-coated pore walls. The PS-b-PLA precursors as well as the resulting porous systems were carefully analyzed by size exclusion chromatography (SEC), ¹H NMR, scanning electron microscopy (SEM), and two-dimensional small-angle X-ray scattering (2-D SAXS). Moreover, the specific surface area and pore size distribution were determined by nitrogen sorption porosimetry.     

Effects of nanocracks on the magnetic and electrical properties of single crystals

An investigation of the physical properties of La_0.8Sr_0.2MnO₃ single crystals grown by the molten zone technique is realized close to the metal-to-insulator transition temperature (T_MI). In this paper, we review the effect of the structural defects through magnetotransport and local magnetic microstructures. From electron microscopy observations, some ‘nanocrack’ defects (i.e. defects at a nanometer scale) were found, essentially in the center part of the single crystals. At room temperature, magnetic force microscopy measurements have shown that the absence of defects allowed a magnetic ordering of the domains at the crystal edge, which is the best-crystallized region. In addition, the magnetization loops have permitted us to verify that the crystal was ferromagnetically weaker in the center. On analyzing the electrical resistivity data, we observed in the linear current regime a sensitive variation of the resistivity due to defects, by comparing the center and the edge of the material at T_MI. Additionally, at strong current, non-linearity phenomena have been supposed to be related to local heating. Finally, we discuss the structural disorder effect on the relaxation of the ferromagnetic domains.