Nanoconfined (Bio)Catalysts as Efficient Glucose‐Responsive Nanoreactors

Herein, the design, synthesis, and characterization of bifunctional hybrid nanoreactors used for concurrent one‐pot chemoenzymatic reactions are shown. In the design, the enzyme, glucose oxidase, is wrapped with a peroxidase‐mimetic catalytic polymer. Hemin, the organic catalyst, is linked to the flexible polymeric scaffold through coordination to the imidazole groups that hang out the network. This spatial arrangement, which works as a metabolic channel, is optimized for cooperative chemoenzymatic reactions in which the enzyme catalyzes first. A deep characterization of the integrated nanoreactors demonstrates that the confinement of two distinct catalytic sites in the nanospace is very effective in one‐pot reactions. Moreover, besides its role as scaffold material, the polymeric mantel protects both the biocatalyst and the chemical catalyst from degradation and inactivation in the presence of organic solvents. Furthermore, the polymeric environment of the nanoreactors can be tailored in order to trigger the assembly of those into highly active heterogeneous hybrid catalysts. Finally, the new nanoreactors are applied to the efficient degradation of organic aromatic compounds using glucose as the only fuel.     

Ultra‐Low‐Loss Acrylate Polymers for Planar Light Circuits

We have developed a materials system composed of liquid multifunctional fluorinated acrylate monomers that achieves very low absorption losses within both datacom and telecom wavelength ranges. Identified structure–property relationships have guided the design of polymers that are optimized with respect to their inherent materials properties and their ability to be processed into low‐loss optical waveguides. Together these co‐developed materials and processes combine to produce waveguides that have propagation losses equivalent to planar glass guides, and significantly reduced polarization dependence and improved thermal response needed for the performance of thermo‐optic devices. Extensive environmental studies have demonstrated robustness well beyond that required for normal operating conditions.     

High resistivity magnesium-rich layers and current instability in anodizing a Mg/Ta alloy

Strikingly different morphologies of amorphous anodic films on a Mg/40 at.%Ta alloy are shown to result from single-stage and sequential anodizing procedures. The alloy, prepared by magnetron sputtering, was anodized galvanostatically in ammonium pentaborate (pH 8.3) and sodium silicate (pH 12.6) electrolytes at 293 K and studied by transmission electron microscopy, Rutherford backscattering spectroscopy, glow discharge optical emission spectroscopy and X-ray photoelectron spectroscopy. For one-step anodizing in the pentaborate electrolyte, a single-layered film, of approximate composition Ta₂O₅ · MgO, forms at a ratio of ∼1.8 nm V⁻¹. In the silicate electrolyte, an outer, magnesium-rich layer, containing silicon species, also forms, with a ratio of 0.8 nm V⁻¹. The outer layer can develop due to relatively fast migration of magnesium ions in the inner layer and the stabilization of the pH at the film surface, probably linked to generation of a silica gel that also limits loss of magnesium species to the electrolyte. Further thickening of the anodic film, in ammonium pentaborate electrolyte, produces fingers of low resistivity, inner oxide that penetrate the pre-existing, high resistivity outer layer, with a bi-modal distribution of finger sizes. When fingers reach the film surface, magnesium ions are ejected to the electrolyte. The absence of fingers in films grown in sodium silicate electrolyte is possibly due to prevention, by the silica gel, of their initiation.     

Spike-timing-dependent plasticity and reliability optimization: the role of neuron dynamics

Plastic changes in synaptic efficacy can depend on the time ordering of presynaptic and postsynaptic spikes. This phenomenon is called spike-timing-dependent plasticity (STDP). One of the most striking aspects of this plasticity mechanism is that the STDP windows display a great variety of forms in different parts of the nervous system. We explore this issue from a theoretical point of view. We choose as the optimization principle the minimization of conditional entropy or maximization of reliability in the transmission of information. We apply this principle to two types of postsynaptic dynamics, designated type I and type II. The first is characterized as being an integrator, while the second is a resonator. We find that, depending on the parameters of the models, the optimization principle can give rise to a wide variety of STDP windows, such as antisymmetric Hebbian, predominantly depressing or symmetric with one positive region and two lateral negative regions. We can relate each of these forms to the dynamical behavior of the different models. We also propose experimental tests to assess the validity of the optimization principle.     

Anodic film growth on tantalum in dilute phosphoric acid solution at 20 and 85 °C

The effects of current density and temperature on the anodic films formed on tantalum in dilute H₃PO₄ (0.06%wt) solution have been studied by transmission electron microscopy, using ultramicrotomed sections, and Rutherford backscattering spectroscopy. Two-layered films have been identified, comprising an inner relatively pure Ta₂O₅ layer, adjacent to the metal/film interface, and an outer layer containing incorporated PO₄³⁻ anions. The total amount and depth of incorporated phosphorus species increase with increasing current density and decreasing temperature, in correspondence with the enhancement of the electric field. The formation conditions for the films include those relevant to the commercial anodising of tantalum for capacitors for which the extent of phosphorus incorporation is shown to be comparatively low.     

Solubility and diffusivity of CO2 in carboxylated polyesters

The solubility of CO₂ in saturated polyester resins at different temperatures (306 and 343 K) and pressures (0.1-30 MPa) has been measured using a magnetic suspension balance. The solubility data were used for estimating the binary diffusion coefficients. The results show a good solubility of CO₂ in polymers, up to 0.64 g CO₂/g polymer. The diffusion coefficients of supercritical CO₂ in polymers have generally high values and are in the range from 0.156 × 10⁻⁸ to 10.38 × 10⁻⁸ cm²/s. DSC and XRD analyses of the semi-crystalline polymer samples indicate that amorphous degree of polymers after exposure to CO₂ is increased. The observed structural effects are dependent on pressure, temperature and time of exposure to CO₂.     

Alcohol dehydrogenase in non‐aqueous media using high‐pressure technologies: reaction set‐up and deactivation determination

BACKGROUND: The demand for enantiomerically pure molecules is growing continuously and biocatalysis is a powerful technique for their production. In this work, the catalyst was an enzyme combined with its coenzyme, NADP. High pressure technology, a second clean technology, was applied as well. Dense gases are promising solvents for biocatalysis. They have been investigated extensively as reaction media for lipase‐catalysed reactions, but seldom for reactions, catalysed with alcohol dehydrogenases, as in this work. RESULT: The production of optically pure R‐1‐phenylethanol from acetophenone was investigated. The NADP‐dependent alcohol dehydrogenase from Lactobacillus brevis (LBADH) was used as a catalyst. The hydrogenation was performed with isopropanol as a co‐substrate in different conditions: dense propane with LBADH and NADP co‐immobilized on glass beads and in the biphasic system water/dense propane. The obtained R‐1‐phenylethanol was enantiopure. The conversions were up to 90%. Deactivation of LBADH was also measured in these media. CONCLUSION: Protocols were successfully developed for the testing of alcohol dehydrogenase activity in dense gases. Enantioselectivity of LBADH is excellent in those media but it deactivated quickly. An LBADH‐catalysed reaction was performed in a dense gas for the first time. Copyright © 2010 Society of Chemical Industry     

Atomic layer deposition on biological macromolecules: metal oxide coating of tobacco mosaic virus and ferritin

Decoration of nanoparticles, in particular biomolecules, gathered high attention in recent years.(1-7) Of special interest is the potential use of biomolecules as templates for the fabrication of semiconducting or metallic nanostructures.(1-7,26) In this work we show the application of atomic layer deposition, a gas-phase thin film deposition process, to biological macromolecules, which are frequently used as templates in nanoscale science, and the possibility to fabricate metal oxide nanotubes and thin films with embedded biomolecules.(1-13).