One-step solid state synthesis of capped γ-Fe(2)O(3) nanocrystallites

The thermally induced solid state synthesis of soluble organophilic maghemite (γ-Fe(2)O(3)) nanocrystallites is described. The solvent-free one-step synthesis involves the reaction in the melt state of Fe(NO)(3)·9H(2)O and RCOOH (R = C(11)H(23), C(15)H(31)) at 240?°C. The method yields well-crystallized nanoparticles of γ-Fe(2)O(3) functionalized with the corresponding aliphatic acid. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) observations reveal composite particles with faceted magnetic cores and average size of 20?nm, which are well capped with the surrounding organic sheath. The Fourier transform infrared (FT-IR) spectra and thermal analysis suggest a bimodal configuration of the organic shell including chemically coordinated and physisorbed molecules of aliphatic acid. The chemical bonding of the carboxylate groups to the surface iron atoms is also indicated by a paramagnetic doublet with unchanged area in the variable temperature M?ssbauer spectra. The spinel γ-Fe(2)O(3) particles exhibit perfect structural and magnetic ordering, including the almost ideal ratio of octahedral to tetrahedral positions (5/3) and very low degree of spin canting, as confirmed by in-field M?ssbauer spectroscopy. Magnetic measurements demonstrate the suitable properties required in various (bio)magnetic applications like superparamagnetic behavior at room temperature, high saturation magnetization achievable at low applied fields and suppressed magnetic interactions.     

AC electric field-induced alignment and long-range assembly of multi-wall carbon nanotubes inside aqueous media

The present work examines the behavior of multiwall carbon nanotubes (MWCNT) inside AC electric fields created by three-dimensional electrodes. The response of carbon nanotubes stably suspended in water with the aid of a nonionic surfactant is monitored by combining microscopic observations with on-line measurements of the suspension resistivity. It is found that polarization effects induced by the externally applied AC electric field on MWCNTs can cause their unidirectional orientation and end-to-end contact that result in formations of spatially distributed, long-range, three-dimensional and electrically conducting structures that span the entire gap between the electrodes. The length of the formed structures, which in the present case was approximately 30 times larger than that of an individual carbon nanotube, can be controlled by adjusting the spacing between the electrodes. The influence of main experimental parameters, namely, MWCNT concentration, applied voltage, AC field frequency, and electrode surface topography on the suspension behavior is experimentally examined. Results are demonstrated for applied voltage values, AC field frequencies, and carbon nanotube concentrations in the range 4-40 Vptp, 10 Hz-5 MHz, and 0.001-2.0 wt%, respectively. While higher electric field strengths accelerate the formation of aligned structures, higher frequency values were found to result in suspensions that exhibit smaller electrical resistivity. Carbon nanotube dispersions exposed to an AC electric field exhibit a 100-fold or more decrease in their electrical resistivity, even when carbon nanotube concentrations as low as 0.005 wt% are used.     

Iron changes in natural and Fe(III) loaded montmorillonite during carbon nanotube growth

A detailed elaboration of the transformations of iron species, present in natural and Fe(NO(3))(3) loaded montmorillonite, during carbon deposition and carbon nanotube growth is described. According to transmission electron microscopy results, deposited carbon atoms form fibres in the case of pristine montmorillonite and multiwalled carbon nanotubes in the case of Fe(III) loaded montmorillonite. M?ssbauer and x-ray diffraction analysis results point to an extensive reduction of structural and intercalated Fe(III) cations to Fe(II) with the latter migrating from the interlayer space to the vacant octahedral sites of the mineral's lattice. Such migration of the non-structural iron catalyst prohibits extensive contamination of the final composite with various metal catalyst impurities. The crucial role of the active catalytic centres in the formation of carbon nanotubes is ascribed to a minor quantity of iron, found entrapped in the carbon nanostructures, which, at the end of the reaction, is identified as iron carbide. The interesting formation of a nanometric γ-iron precipitate is also detected, which is probably stabilized through strong interactions with the lattice of montmorillonite. Finally, it is demonstrated that iron-rich natural clay minerals can serve as direct catalysts for carbon nanotube growth.     

Observations and analysis of electrokinetically driven particle trapping in planar microelectrode arrays

In situ observations of submicron fluorescent tracers suspended in high ionic strength media sealed in a confined geometry are combined with 3‐D simulations in order to provide a better understanding of the synergism between dielectrophoresis and electrothermal flows that cause rapid particle transport and trapping on the surface of planar quadrupolar microelectrodes. The influence of electrode design on the microfluidic patterns and observed particle collection is examined by employing two different types of microelectrodes in the experiments. The potential use of quadrupolar microelectrodes as means for achieving accelerated sampling and signal amplification in future surface based biosensor devices is illustrated with an experiment involving stable capture of antigen‐coated polystyrene particles on the surface of an antibody‐functionalized microelectrode array.     

The role of non-covalent interactions and matrix viscosity on the dispersion and properties of LLDPE/MWCNT nanocomposites

Linear low density polyethylene (LLDPE)/multi-walled carbon nanotube (MWCNT) composites were prepared by melt compounding, following two different compatibilization strategies that involved non-covalent interactions between the matrix and the filler. The first approach involved grafting pyridine aromatic moieties on the maleated polyolefin backbone, which are able to interact by π–π stacking with the surface of the nanotubes. The second method implemented non-covalent/non-specific surface functionalization of the MWCNTs with a hyperbranched polyethylene (HBPE). The enhanced interfacial interactions established in the composites containing LLDPE functionalized with pyridine grafts improved the dispersion of the nanotubes within the polymer matrix. Dispersion was also favoured by higher matrix viscosity. Composites containing finely dispersed MWCNTs exhibited an increase in the rheological and electrical percolation thresholds, and a significant improvement in mechanical properties. On the contrary the composites based on the low viscosity matrix contained large amounts of aggregates, which promoted lower percolation thresholds. Manipulation of matrix viscosity and compatibilization resulted in composites with good mechanical properties, and low percolation thresholds.     

The Cardioprotective PKA-Mediated Hsp20 Phosphorylation Modulates Protein Associations Regulating Cytoskeletal Dynamics

The cytoskeleton has a primary role in cardiomyocyte function, including the response to mechanical stimuli and injury. The small heat shock protein 20 (Hsp20) conveys protective effects in cardiac muscle that are linked to serine-16 (Ser16) Hsp20 phosphorylation by stress-induced PKA, but the link between Hsp20 and the cytoskeleton remains poorly understood. Herein, we demonstrate a physical and functional interaction of Hsp20 with the cytoskeletal protein 14-3-3. We show that, upon phosphorylation at Ser16, Hsp20 translocates from the cytosol to the cytoskeleton where it binds to 14-3-3. This leads to dissociation of 14-3-3 from the F-actin depolymerization regulator cofilin-2 (CFL2) and enhanced F-actin depolymerization. Importantly, we demonstrate that the P20L Hsp20 mutation associated with dilated cardiomyopathy exhibits reduced physical interaction with 14-3-3 due to diminished Ser16 phosphorylation, with subsequent failure to translocate to the cytoskeleton and inability to disassemble the 14-3-3/CFL2 complex. The topological sequestration of Hsp20 P20L ultimately results in impaired regulation of F-actin dynamics, an effect implicated in loss of cytoskeletal integrity and amelioration of the cardioprotective functions of Hsp20. These findings underscore the significance of Hsp20 phosphorylation in the regulation of actin cytoskeleton dynamics, with important implications in cardiac muscle physiology and pathophysiology.     

Influence of Oxygen Partial Pressure on the Quasi-Ternary System Cr─Mn─Ti Oxide

The quasi-ternary system Cr─Mn─Ti oxide was investigated at 1000°C under oxygen partial pressures ranging from 0.21 bar to 10^-21 bar (1 bar = 10⁵ Pa). X-ray diffraction analysis was used to identify phases and determine lattice parameters. The positions of phase boundaries as a function of oxygen partial pressure were measured using the emf method. The spinel MnCr₂O₄ may be regarded as the most interesting compound in this system. Part of the chromium can be replaced by trivalent titanium at low oxygen partial pressures and by trivalent manganese at high pressures, and the formation of a limited solid solution with the spinel Mn₂TiO₄ is possible in all cases. As a result, a coherent single-phase spinel region exists over the entire oxygen partial pressure range at 1000°C.     

Merging high doxorubicin loading with pronounced magnetic response and bio-repellent properties in hybrid drug nanocarriers

Hybrid magnetic drug nanocarriers are prepared via a self-assembly process of poly(methacrylic acid)-graft-poly(ethyleneglycol methacrylate) (p(MAA-g-EGMA)) on growing iron oxide nanocrystallites. The nanocarriers successfully merge together bio-repellent properties, pronounced magnetic response, and high loading capacity for the potent anticancer drug doxorubicin (adriamicin), in a manner not observed before in such hybrid colloids. High magnetic responses are accomplished by engineering the size of the magnetic nanocrystallites (～13.5 nm) following an aqueous single-ferrous precursor route, and through adjustment of the number of cores in each colloidal assembly. Complementing conventional magnetometry, the magnetic response of the nanocarriers is evaluated by magnetophoretic experiments providing insight into their internal organization and on their response to magnetic manipulation. The structural organization of the graft-copolymer, locked on the surface of the nanocrystallites, is further probed by small-angle neutron scattering on single-core colloids. Analysis showed that the MAA segments selectively populate the area around the magnetic nanocrystallites, while the poly(ethylene glycol)-grafted chains are arranged as protrusions, pointing towards the aqueous environment. These nanocarriers are screened at various pHs and in highly salted media by light scattering and electrokinetic measurements. According to the results, their stability is dramatically enhanced, as compared to uncoated nanocrystallites, owing to the presence of the external protective PEG canopy. The nanocarriers are also endowed with bio-repellent properties, as evidenced by stability assays using human blood plasma as the medium.     

The Discrete Basis Problem

Matrix decomposition methods represent a data matrix as a product of two factor matrices: one containing basis vectors that represent meaningful concepts in the data, and another describing how the observed data can be expressed as combinations of the basis vectors. Decomposition methods have been studied extensively, but many methods return real-valued matrices. Interpreting real-valued factor matrices is hard if the original data is Boolean. In this paper, we describe a matrix decomposition formulation for Boolean data, the Discrete Basis Problem. The problem seeks for a Boolean decomposition of a binary matrix, thus allowing the user to easily interpret the basis vectors. We also describe a variation of the problem, the Discrete Basis Partitioning Problem. We show that both problems are NP-hard. For the Discrete Basis Problem, we give a simple greedy algorithm for solving it; for the Discrete Basis Partitioning Problem we show how it can be solved using existing methods. We present experimental results for the greedy algorithm and compare it against other, well known methods. Our algorithm gives intuitive basis vectors, but its reconstruction error is usually larger than with the real-valued methods. We discuss about the reasons for this behavior.