Organopolysiloxanes as Chemically Sensitive Coatings for Optical Fibers

Various types of UV-curable organically modified siloxanes have been synthesized by the sol-gel method with the aim of fabricating chemically sensitive coatings for silica optical fibers. The refractive index of the coating material can be tailored in the range from 1.46 to 1.56 and sensitivity towards CO2 is achieved by incorporation of amino groups. The interaction of the cured layers with CO2 or with hydrocarbons has been studied in immersion experiments. Both the reaction of CO2 with incorporated amino groups and the penetration of hydrocarbons into the layer induce changes of the light absorption coefficient and the refractive index of the coating which are detected by measuring the output light intensity from the fiber.     

Effect of synthesis conditions on the microstructure of TEOS derived silica hydrogels synthesized by the alcohol-free sol–gel route

Silica matrices synthesized from a pre-hydrolysis step in ethanol followed by alcohol removal at low pressure distillation, and condensation in water, are suitable for encapsulation of biomolecules and microorganisms and building bioactive materials with optimized optical properties. Here we analyze the microstructure of these hydrogels from the dependence of I(q) data acquired from SAXS experiments over a wide range of silica concentration and pH employed in the condensation step. From the resulting data it is shown that there is a clear correlation between the microscopic parameters—cluster fractal dimension (D), elementary particle radius (a) and cluster gyration radius (R)—with the attenuation of visible light when the condensation step proceeds at pH < 6. At higher pHs, there is a steep dependence of the cluster density (~R ^D−3) with the condensation pH, and non-monotonous changes of attenuance are less than 20%, revealing the complexity of the system. These results, which were obtained for a wide pH and silica concentration range, reinforce the idea that the behavior of gels determined in a restricted interval of synthesis variables cannot be extrapolated, and comparison of gelation times is not enough for predicting their properties.     

Identification of phosphorylation sites of equine β‐casein isoforms

Equine β‐casein is phosphorylated at variable degrees and isoforms carrying 3 to 7 phosphate groups (3P–7P) have been found in milk, but the phosphorylated amino acid residues of each isoform are not yet identified. In the present work, the different phosphorylation variants were first isolated by ion‐exchange chromatography and then hydrolysed by trypsin to generate caseinophosphopeptides (CPPs), each containing all the potential phosphorylation sites. The equine CPPs were prepared by metal oxide affinity chromatography, a method based on the affinity of phosphate groups towards titanium dioxide immobilized onto a micro‐column. This method turned out to be an efficient tool to separate the CPPs Arg¹–Lys³⁴ and Glu⁴–Lys³⁴ from non‐phosphorylated peptides. Purification was achieved by reversed‐phase high‐performance liquid chromatography (RP‐HPLC) and each CPP was hydrolyzed by endoproteinase Glu‐C. Finally, the digests were analyzed by RP‐HPLC/electrospray ionization mass spectrometry (RP‐HPLC/ESI‐MS) and identified by nano‐electrospray ionization tandem mass spectrometry (nESI‐MS/MS) to locate the phosphorylated sites of the β‐casein isoforms 4P–7P with accuracy. Thus, the isoform 4P was found to be phosphorylated on residues Ser⁹, Ser²³, Ser²⁴, and Ser²⁵. Addition of phosphate groups on Ser¹⁸, Thr¹², and Ser¹⁰ led to the formation of the isoforms 5P–7P, respectively. The results indicated that the in vivo phosphorylation of the equine β‐casein follows a sequential way and is not randomly performed. Copyright © 2010 John Wiley & Sons, Ltd.     

Partially Hydrogenated Graphene Materials Exhibit High Electrocatalytic Activities Related to Unintentional Doping with Metallic Impurities

Partially hydrogenated graphene materials, synthesized by the chemical reduction/hydrogenation of two different graphene oxides using zinc powder in acidic environment or aluminum powder in alkaline environment, exhibit high electrocatalytic activities, as well as electrochemical sensing properties. The starting graphene oxides and the resultant hydrogenated graphenes were characterized in detail. Their electrocatalytic activity was examined in the oxygen reduction reaction, whereas sensing properties towards explosives were tested by using picric acid as a redox probe. Findings indicate that the high electrocatalytic performance originates not only from the hydrogenation of graphene, but also from unintentional contamination of graphene with manganese and other metals during synthesis. A careful evaluation of the obtained data and a detailed chemical analysis are necessary to identify the origin of this anomalous electrocatalytic activity.     

Modified Guanines as Constituents of Smart Ligands for Nucleic Acid Quadruplexes

Repetitive guanine‐rich nucleic acid sequences play a crucial role in maintaining genome stability and the cell life cycle and represent potential targets for regulatory drugs. Recently, it has been demonstrated that guanine‐based ligands with a porphyrin core can be used as markers of G‐quadruplex assemblies in cell tissues. Herein, model systems of guanine‐based ligands are explored by DFT methods. The energies of formation of modified guanine tetrads and those of modified tetrads stacked on the top of natural guanine tetrads have been calculated. The interaction energy has been decomposed into contributions from hydrogen bonding, stacking, and ion coordination and a twist–rise potential energy scan has been performed to find the individual local minima. Energy decomposition analysis reveals the impact of various substituents (F, Cl, Br, I, Me, NMe₂) on individual energy terms. In addition, cooperative reinforcement in forming the modified and stacked tetrads, as well as the frontier orbitals participating in the hydrogen‐bonding framework involving the HOMO–LUMO gap between the occupied σ_HOMO on the proton‐accepting C=O and =N? groups and unoccupied σ_LUMO on the N?H groups, has been studied. The investigated systems are demonstrated to have a potential in ligand development, mainly due to stacking enhancement compared with natural guanine, which is used as a reference.     

Elysiapyrones from Elysia diomedea. Do such metabolites evidence an enzymatically assisted electrocyclization cascade for the biosynthesis of their bicyclo[4.2.0]octane core?

[structure: see text] Biogenetically interesting polypropionate-derived metabolites 1 and 2, featuring an unprecedented skeleton, have been isolated from the sea slug Elysia diomedea. Their enantiomeric character indicates that the current spontaneous electrocyclization cascade biogenetic hypothesis for the bicyclo[4.2.0]octane core must be enzymatically aided. These compounds are isomeric with the 15-nor-9,10-deoxytridachione/15-norphotodeoxytridachione pair of metabolites and encourage speculation about their biosynthetic relationship.     

Proteomic analysis reveals metabolic changes during yeast to hypha transition in Yarrowia lipolytica

Fungal dimorphism is important for survival in different environments and has been related to virulence. The ascomycete Yarrowia lipolytica can grow as yeast, pseudomycelial or mycelial forms. We have used a Y. lipolytica parental strain and a Deltahoy1 mutant, which is unable to form hypha, to set up a model for dimorphism and to characterize in more depth the yeast to hypha transition by proteomic techniques. A two-dimensional gel electrophoresis (2-DE) based differential expression analysis of Y. lipolytica yeast and hyphal cells was performed, and 45 differentially expressed proteins were detected; nine with decreased expression in hyphal cells were identified. They corresponded to the S. cerevisiae homologues of Imd4p, Pdx3p, Cdc19, Sse1p, Sol3p, Sod2p, Xpt1p, Mdh1p and to the unknown protein YALIOB00924g. Remarkably, most of these proteins are involved in metabolic pathways, with four showing oxidoreductase activity. Furthermore, taking into account that this is the first report of 2-DE analysis of Y. lipolytica protein extracts, 35 more proteins from the 2D map of soluble yeast proteins, which were involved in metabolism, cell rescue, energy and protein synthesis, were identified.