Improved magnetosensor for the detection of hydrogen peroxide and glucose

Journal of Solid State Electrochemistry - In this work, the use of neodymium electrodes as a basis for the immobilization of magnetite nanoparticles has been carried out. The sensitivity and...     

Stability of MgAl 2 O 4 Under High-Pressure Conditions

A theoretical investigation of the MgAl 2 O 4 crystal response to high-pressure conditions has been carried out to determine its stability against decomposition towards MgO and f -Al 2 O 3 , and towards recently observed orthorhombic phases. We have evaluated total energy versus volume curves using the density functional formalism under the non-local B3LYP approximation, as implemented in the CRYSTAL package. Numerical and analytical fittings have been carried out to determine the equilibrium unit cell geometry and equation of state parameters for all the structures and compounds involved in the phase diagram. The macroscopic compressibility of the spinel phase is interpreted considering the compressibility of its elementary MgO 4 and AlO 6 coordination polyhedra, and implications to understand the phase stability are suggested.     

Structure, metastability, and electron density of Al lattices in light of the model of anions in metallic matrices

This paper reports a theoretical investigation of the structure, stability, and electron charge density of cubic, rhombohedral, hexagonal, and monoclinic Al lattices. The equations of state and the elastic constants are computed from total energy calculations at different volumes and unit cell strains using the density functional theory approximation. The topology of the electron density is analyzed within the crystalline implementation of the atoms in molecules formalism. The results are discussed in light of the so-called anions in metallic matrices model, which permits the interpretation of the chemical bonding and the explanation of the existence of particular symmetries of inorganic crystals. First, the Al sublattices are identified as the reference building blocks of AlX(3) (X = F, Cl, OH) compounds. The calculations reveal that the equilibrium zero-pressure Al-Al shortest distance is around 2.75 A in all of the Al matrixes, similar to the value observed in the stable face centered cubic structure of Al at room conditions. Second, at their zero-pressure equilibrium geometries, the Al sublattices are found to fulfill the mechanical stability criteria or, alternatively, to show mechanical instabilities that are compatible with the distortions observed for the structures in AlX(3) crystals. However, at the equilibrium volumes of the AlX(3) crystals, all of the Al matrices violate the spinodal condition, and the cohesion and stabilization are provided by the nonmetallic X atoms. Third, the structural anisotropy of the Al sublattices seems to be the main factor to discriminate metallic matrices able to host nonmetallic elements. The inhomogeneities of the electron charge density, which favor the arrival of nonmetallic elements and the crystal formation, are notably enhanced in passing from the fcc structure of pure Al to the less isotropic Al matrices observed in AlX(3) compounds.     

On the Unavoidable Uncertainty of Truth in Dynamic Geometry Proving

The aim of this note is to discuss some issues posed by the emergency of universal interfaces able to decide on the truth of geometric statements. More specifically, we consider a recent GeoGebra module allowing general users to verify standard geometric theorems. Working with this module in the context of Varignon’s theorem, we were driven—by the characteristics of the GeoGebra interface—to perform a quite detailed study of the very diverse fate of attempting to automatically prove this statement, when using two different construction procedures. We highlight the relevance—for the theorem proving output—of expression power of the dynamic geometry interface, and we show that the algorithm deciding about the truth of some—even quite simple—statements can fall into a not true and not false situation, providing a source of confusion for a standard user and an interesting benchmark for geometers interested in discovering new geometric facts.     

Effect of beta-lactoglobulin hydrolysis with thermolysin under denaturing temperatures on the release of bioactive peptides

In this study, bovine beta-lactoglobulin A (beta-Lg A) was hydrolysed with thermolysin under non-denaturing and heat-denaturing conditions. The peptides released during hydrolysis were identified by HPLC-MS/MS. A total of 25 peptides were identified in the hydrolysate obtained at 37 degrees C for 5 min. Some of these peptides survived to further proteolysis even at higher incubation temperatures. Furthermore, novel cleavage sites localised in the most buried zones of beta-Lg and available for thermolysin were recognised when the incubation temperature increased in the range between 60 and 80 degrees C. Three new peptides, LDA, LKPTPEGD, and LQKW, appeared after 30 min hydrolysis at these incubation temperatures, but they were not identified in the 30-min hydrolysates obtained at 37 and 50 degrees C. Of special interest was the peptide LQKW, corresponding to the fragment f(58-61) that had been previously described as a potent angiotensin-converting enzyme-inhibitor (IC50 value of 34.7 microM).     

Engineered biosynthesis of novel polyenes: a pimaricin derivative produced by targeted gene disruption in Streptomyces natalensis.

BACKGROUND: The post-polyketide synthase biosynthetic tailoring of polyene macrolides usually involves oxidations catalysed by cytochrome P450 monooxygenases (P450s). Although members from this class of enzymes are common in macrolide biosynthetic gene clusters, their specificities vary considerably toward the substrates utilised and the positions of the hydroxyl functions introduced. In addition, some of them may yield epoxide groups. Therefore, the identification of novel macrolide monooxygenases with activities toward alternative substrates, particularly epoxidases, is a fundamental aspect of the growing field of combinatorial biosynthesis. The specific alteration of these activities should constitute a further source of novel analogues. We investigated this possibility by directed inactivation of one of the P450s belonging to the biosynthetic gene cluster of an archetype polyene, pimaricin. RESULTS: A recombinant mutant of the pimaricin-producing actinomycete Streptomyces natalensis produced a novel pimaricin derivative, 4,5-deepoxypimaricin, as a major product. This biologically active product resulted from the phage-mediated targeted disruption of the gene pimD, which encodes the cytochrome P450 epoxidase that converts deepoxypimaricin into pimaricin. The 4,5-deepoxypimaricin has been identified by mass spectrometry and nuclear magnetic resonance following high-performance liquid chromatography purification. CONCLUSIONS: We have demonstrated that PimD is the epoxidase responsible for the conversion of 4,5-deepoxypimaricin to pimaricin in S. natalensis. The metabolite accumulated by the recombinant mutant, in which the epoxidase has been knocked out, constitutes the first designer polyene obtained by targeted manipulation of a polyene biosynthetic gene cluster. This novel epoxidase could prove to be valuable for the introduction of epoxy substituents into designer macrolides.