Sliding plate rheometry of planar oriented concentrated fiber suspension

The rheology of concentrated planar fiber suspensions is investigated. A new experimental technique for fiber suspensions based on a sliding plate rheometer incorporating a shear stress transducer is developed. It is shown that this instrument works well for the tested material systems. The rheological behavior in steady shear is subsequently investigated. The results can be largely explained by a combination of frictional and hydrodynamic interaction. Despite this evidence of friction no yield stress could be detected for the investigated shear rates. It was also found that the fiber aspect ratio did not influence the steady shear viscosity.     

Substructure of a rubidium-ion-exchanged form of the silicate nepheline hydrate I

X-Ray structure analysis of a nepheline hydrate I crystal, Rb⁺-exchanged at 80°C, was performed making use only of the main diffractions. The resulting substructure was found to be orthorhombic with a = 8.0802(8), b = 15.259(2), c = 5.1584(5) Å, V = 636.0ų, space group Pnm2₁. Fourier and least-squares techniques gave the residuals R = 0.048 and R_w = 0.058, and a tentative formula of RbNa₂Al₃Si₃O₁₂ · H₂O (Z = 2, D_c = 2.65 g cm^?3). Tetrahedral distances were consistent with Al,Si alternation in the framework. Of the channel species, Na(1) and Na(2) were found not to be exchangeable at the current temperature. These sodium atoms are located in the small cages, formed by 6-rings of O atoms which connect the 8-ring channels parallel to c into two-dimensional pore systems. In the larger tunnels the replacement was complete and these contain a Rb⁺ ion and probably a water molecule in symmetry-related positions. According to this model, Rb⁺ coordinates four oxygens of an 8-ring and two water molecules, with RbO distances in the range 2.81–3.36 Å. Additional O atoms are found at greater distances.     

Mean-field nucleation theory with nonlocal interactions

Mean-field nucleation theory has for a long time been successfully used to extract microscopic parameters from island density data in growth experiments. However, it produces grossly incorrect results when used to analyze weakly corrugated systems, where adsorbate interactions cannot be neglected. Here, a mean-field theory that includes nonlocal adsorbate interactions is developed and successfully tested against kinetic Monte Carlo growth simulations for a realistic adsorbate system.     

Structure of a potassium-ion-exchanged nepheline hydrate I crystal

A nepheline hydrate I crystal, ion-exchanged using KCl(aq) at 80°C, was found to be orthorhombic, space group Pnm2₁, a = 8.113(3), b = 15.223(2), c = 5.1817(7)Å and showed no superlattice X-ray reflections. Structure analysis by means of Fourier and least-squares methods led to the composition K_1.1Na_1.9Al₃Si₃O₁₂ · H₂O (Z = 2, D_c = 2.40 g cm^?3) and the agreement factors: R = 0.032 and R_w = 0.040. Species assigned to the observed extra framework sites were K(1), K(2), and W(1) in the 8-ring tunnels along c plus Na(1) and Na(2) in the smaller 6-ring voids forming connections in the b direction. The atoms Na(1) and Na(2) coordinated framework oxygens exclusively and were but little affected by the ion-exchange process; K(1) was found near the center of an 8-ring and had five O atoms and two water molecules as closest neighbors, while the weakly occupied K(2) site was near a 6-ring and was found to have a coordination consisting of at least five oxygens and one water. The 10% vacancy of Na(2) is compensated for by an equal amount of K(2), which does not enter the Na(2) site for sterical reasons.     

Activation energies for quantum diffusion of hydrogen in metals and on metal surfaces using delocalized nuclei within the density-functional theory

Hydrogen diffusion on the Cu(001) surface and in bulk Nb and Ta is studied in the quantum regime using first-principles electronic-structure calculations. We present, for the first time, a direct density-functional calculation of the activation energy required to establish the quantum-mechanically delocalized hydrogen coincidence configuration and of the corresponding tunneling matrix element. For the two bulk systems a direct comparison can be made with nuclear magnetic resonance data, and we find excellent agreement for both the coincidence energy and the tunneling matrix element.     

Co-adsorption of cadmium(II) and glyphosate at the water-manganite (gamma-MnOOH) interface

The co-adsorption of Cd(II) and glyphosate (N-(phosphonomethyl)glycine, PMG) at the manganite (gamma-MnOOH) surface has been studied in the pH range 6-10 at 25 degrees C and with 0.1 M Na(Cl) as ionic medium. Batch adsorption experiments, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS) spectroscopy were used for the quantitative analysis and the determination of the molecular structure of the surface complexes. The adsorption of Cd(II) and PMG in the ternary Cd(II)-PMG-manganite system was compared with the adsorption in the binary Cd(II)-manganite and PMG-manganite systems. The formation of three inner sphere surface complexes was observed, a ternary Cd(II)-PMG-manganite complex, a binary Cd(II)-manganite complex and a binary PMG-manganite complex. The surface concentration of the ternary complex and the Cd(II)-manganite complex was more or less constant throughout the pH range studied. However, the surface concentration of the binary PMG-manganite complex decreased with increasing pH. The major part of the binary PMG-surface complex was protonated. The ternary surface complex displayed a type B structure (Cd(II)-PMG-manganite). The average Cd-Mn distance obtained from EXAFS (3.26 A) indicates that the binary and ternary Cd(II)-surface complexes are formed by edge-sharing of Mn and Cd octahedra on the (010) plane of the manganite crystals.     

Bacterial quorum sensing and interference by naturally occurring biomimics

Bacteria are able to coordinate gene expression as a community through the secretion and detection of signalling molecules so that the members of the community can simultaneously express specific behaviours. This mechanism of regulation of behaviour appears to be a key trait for adaptation to specific environments and has been shown to regulate a variety of important phenotypes, from virulence factor production to biofilm formation to symbiosis related behaviours such as bioluminescence. The ability to communicate and communally regulate gene expression is hypothesised to have evolved as a way for organisms to delay expression of phenotypes until numerical supremacy is reached. For example, in the case of infection, if an invading microorganism were to express virulence factors too early, the host may be able to mount a successful defence and repel the invaders. There is growing evidence that bacterial quorum sensing (QS) systems are involved in cross-kingdom signalling with eukaryotic organisms and that eukaryotes are capable of actively responding to bacteria in their environment by detecting and acting upon the presence of these signalling molecules. Likewise, eukaryotes produce compounds that can interfere with QS systems in bacteria by acting as agonists or antagonists. An exciting new field of study, biomimetics, takes inspiration from nature’s models and attempts to design solutions to human problems, and biomimics of QS systems may be one such solution. This article presents the acylated homoserine lactone and autoinducer 2 QS systems in bacteria, the means of intercepting or interfering with bacterial QS systems evolved by eukaryotes, and the rational design of synthetic antagonists. Figure Natural products, furanones, from the red alga Delisea pulchra inhibit the quorum sensing regulated production of violacein by Chromobacterium violaceum “The proof of evolution lies in those adaptations that arise from improbable foundations”—Stephen Jay Gould     

Microchip electroseparation of proteins using lipid-based nanoparticles

Porous liquid crystalline lipid-based nanoparticles are shown here to enable protein analysis in microchip electroseparation by reducing sample adsorption. Additionally, higher stability and reproducibility of the separations were observed. The method was tested by separating green fluorescent protein (GFP) in hot embossed cyclic olefin polymer microchips with integrated fiber grooves for LIF detection. The sample adsorption was indirectly quantified by measuring the height, width and asymmetry of the separation peaks for various concentrations of nanoparticles in the sample and background electrolyte. Without nanoparticles, electropherograms displayed typical signs of extensive adsorption to the channel walls, with low, broad tailing peaks. Higher, narrower more symmetric peaks were generated when 0.5-10% nanoparticles were added, showing a dramatic reduction of sample adsorption. The current through the separation channel decreased with nanoparticle concentration, reducing to half its value when the nanoparticle concentration was increased from 0.5 to 4%. Addition of nanoparticles enabled separations that were otherwise hindered by extensive adsorption, e.g. separation of GFP mutants differing by only one amino acid. It was also observed that increasing the nanoparticle concentration increased the number of impurities that could be resolved in a GFP sample. This indicates that the adsorption is further reduced, and/or that the nanoparticles provide an interacting pseudostationary phase for electrochromatography.