Surface and structural analysis of epitaxial La1−xSrx (Mn1−yCoy)zO3 films

In the present study were studied the ferromagnetic La_1−xSr_x (Mn_1−yCo_y)_zO₃ (LSMCO) films with Co content y = 0 to 0.18, grown on LaAlO₃ substrates by advantageous pulsed-injection metalorganic chemical vapor deposition technique. The LSMCO films exhibit negative colossal magnetoresistance effect; therefore, they are interesting as potential material for the applications in magnetic field sensing. The changes of lattice volume in the investigated LSMCO films were monitored by X-ray diffraction measurements revealing a transition from tensile to compressive strain with increase of Co content. Additionally, from the atomic force microscopy images, the surface smoothening with increase of y was determined. Despite the reduction of the out-of-plane lattice parameter of LSMCO, the increase of lattice volume in the whole Co-doping range was observed. The X-ray photoelectron spectroscopy combined with Ar⁺ ion sputtering was used for the investigation of chemical composition of the LSMCO films and demonstrated the change and redistribution of oxidation states of Mn and Co on the surface and in the volume of the films. Regardless of the structural changes and charge distribution of Co and Mn cations, epitaxial LSMCO exhibits ferromagnetic properties and magnetoresistance values increases with augmenting Co content in the range of y = 0 to 0.18.     

Bifunctional Ligand Enables Efficient Gold‐Catalyzed Hydroalkenylation of Propargylic Alcohol

Using the previously designed biphenyl‐2‐ylphosphine ligand, featuring a remote tertiary amino group, the first gold‐catalyzed intermolecular hydroalkenylation of alkynes has been developed. Synthetically valuable conjugated dienyl alcohols are formed in moderate to good yields. A range of alkenyltrifluoroborates are allowed as the alkenyl donor, and no erosion of alkene geometry and/or the propargylic configuration are detected. DFT calculations confirm the critical role of the remote basic group in the ligand as a general‐base catalyst for promoting this novel gold catalysis with good efficiency.     

Charged molecular films on brownian particles: structure, interactions, and relation to stability

The interfacial film of physically adsorbed ionic amphiphilic molecules on submicron particles dispersed in water was studied by a combination of surface tension measurements, laser light scattering (LLS) and high-shear experiments in a microchannel. General features in the structure and morphology of the molecular film are identified and understood in the framework of the two-step Langmuir adsorption model deduced from the adsorption isotherm. On the basis of this approach, the phase transitions and structural ordering of the film at the solid-liquid interface are analyzed in detail. A novel methodology based on high-shear aggregation experiments subsequently analyzed by means of LLS is proposed and turns out to be able to provide significant information on the phase transitions and structural arrangements of the adsorbed molecules (in substantial agreement with the adsorption isotherm model) as well as on the resulting interactions. Particularly important for applications is the result that, with no added salt, the films on two particles can adhere/fuse, leading to aggregation as long as an uncovered (hydrophobic) patch is present (unsaturated molecular layers). In the opposite case of fully developed layers, by analyzing the mechanism of shear aggregation of charged particles in the low-salt limit, we show that, when the hydrophobic attraction is absent, short-range hydration repulsive forces dominate over Derjaguin-Landau-Verwey-Overbeek (DLVO) forces and adhesion can never be achieved even upon application of very high collision energies. Consistently, a lower limiting boundary for the hydration interaction is calculated and found to be in agreement with data in the literature.     

Redox state of coenzyme Q10 determines its membrane localization

The interaction between oxidized (ubiquinone-10) and reduced (ubiquinol-10) coenzyme Q 10 with dimyristoylphosphatidylcholine has been examined by differential scanning microcalorimetry, X-ray diffraction, infrared spectroscopy, and (2)H NMR. Microcalorimetry experiments showed that ubiquinol-10 perturbed considerably more the phase transition of the phospholipids than ubiquinone-10, both forms giving rise to a shoulder of the main transition peak at lower temperatures. Small angle X-ray diffraction showed an increase in d-spacing suggesting a thicker membrane in the presence of both ubiquinone-10 and ubiquinol-10, below the phase transition and a remarkable broadening of the peaks indicating a loss of the repetitive pattern of the lipid multilamellar vesicles. Infrared spectroscopy showed an increase in wavenumbers of the maximum of the CH 2 stretching vibration at temperatures below the phase transition, in the presence of ubiquinol-10, indicating an increase in the proportion of gauche isomers in the gel phase, whereas this effect was smaller for ubiquinone-10. A very small effect was observed at temperatures above the phase transition. (2)H NMR spectroscopy of perdeuterated DMPC showed only modest changes in the spectra of the phospholipids occasioned by the presence of coenzyme Q 10. These small changes were reflected, in the presence of ubiquinol-10, by a decrease in resolution indicating that the interaction between coenzyme Q and phospholipids changed the motion of the lipids. The change was also visible in the first spectral moment (M1), which is related with membrane order, which was slightly decreased at temperatures below the phase transition especially with ubiquinol-10. A slight decrease in M 1 values was also observed above the phase transition but only for ubiquinol-10. These results can be interpreted to indicate that most ubiquinone-10 molecules are localized in the center of the bilayer, but a considerable proportion of ubiquinol-10 molecules may span the bilayer interacting more extensively with the phospholipid acyl chains.     

On the regularity of the pressure field of Brenier’s weak solutions to incompressible Euler equations

In this paper we improve the regularity in time of the gradient of the pressure field arising in Brenier’s variational weak solutions (Comm Pure Appl Math 52:411–452, 1999) to incompressible Euler equations. This improvement is necessary to obtain that the pressure field is not only a measure, but a function in . In turn, this is a fundamental ingredient in the analysis made by Ambrosio and Figalli (2007, preprint) of the necessary and sufficient optimality conditions for the variational problem by Brenier (J Am Mat Soc 2:225–255, 1989; Comm Pure Appl Math 52:411–452, 1999).     

Fabrication, structural characterization, and applications of langmuir and langmuir-blodgett films of a poly(azo)urethane

The synthesis of a poly(azo)urethane by fixing CO(2) in bis-epoxide followed by a polymerization reaction with an azodiamine is presented. Since isocyanate is not used in the process, it is termed "clean method" and the polymers obtained are named "NIPUs" (non-isocyanate polyurethanes). Langmuir films were formed at the air-water interface and were characterized by surface pressure vs mean molecular area per mer unit (Pi-A) isotherms. The Langmuir monolayers were further studied by running stability tests and cycles of compression/expansion (possible hysteresis) and by varying the compression speed of the monolayer formation, the subphase temperature, and the solvents used to prepare the spreading polymer solutions. The Langmuir-Blodgett (LB) technique was used to fabricate ultrathin films of a particular polymer (PAzoU). It is possible to grow homogeneous LB films of up to 15 layers as monitored using UV-vis absorption spectroscopy. Higher number of layers can be deposited when PAzoU is mixed with stearic acid, producing mixed LB films. Fourier transform infrared (FTIR) absorption spectroscopy and Raman scattering showed that the materials do not interact chemically in the mixed LB films. The atomic force microscopy (AFM) and micro-Raman technique (optical microscopy coupled to Raman spectrograph) revealed that mixed LB films present a phase separation distinguishable at micrometer or nanometer scale. Finally, mixed and neat LB films were successfully characterized using impedance spectroscopy at different temperatures, a property that may lead to future application as temperature sensors. Principal component analysis (PCA) was used to correlate the data.     

Speeding up biomolecular interactions by molecular sledding

Numerous biological processes involve association of a protein with its binding partner, an event that is preceded by a diffusion-mediated search bringing the two partners together. Often hindered by crowding in biologically relevant environments, three-dimensional diffusion can be slow and result in long bimolecular association times. Similarly, the initial association step between two binding partners often represents a rate-limiting step in biotechnologically relevant reactions. We demonstrate the practical use of an 11-a.a. DNA-interacting peptide derived from adenovirus to reduce the dimensionality of diffusional search processes and speed up associations between biological macromolecules. We functionalize binding partners with the peptide and demonstrate that the ability of the peptide to one-dimensionally diffuse along DNA results in a 20-fold reduction in reaction time. We also show that modifying PCR primers with the peptide sled enables significant acceleration of standard PCR reactions.     

Theoretical elastic moduli for disordered packings of interconnected spheres

A theoretical model has been developed which provides analytical expressions for the elastic moduli of disordered isotropic ensembles of spheres interconnected by physical bonds. Young's and shear moduli have been derived assuming an ideal random isotropic network and the radial distribution function for disordered packings of spheres. The interparticle interactions are accounted for in terms of surface forces for the two distinct cases of perfectly rigid spheres and spheres deformable at contact. A theoretical expression is also derived in a similar way for the bulk or compressibility modulus. In this case, an atomistic approach has been followed based on the analogy with noble gas solids and colloidal crystals. Also in this case, disordered spatial distribution of the spheres is described statistically. For the case of colloidal aggregates, a total two-body mean-field interaction potential is used which includes the Born repulsion energy. This latter contribution plays an essential role in determining the compression behavior of systems of particles aggregated in the primary minimum of the potential well and, therefore, must not be neglected. Both the expression of the Young's modulus and that of the compressibility modulus derived in this work are found to be consistent with two distinct sets of experimental data which recently appeared in the literature.