X-ray microfluorescence (μXRF) imaging of Aspergillus nidulans cell wall mutants reveals biochemical changes due to gene deletions

We used synchrotron X-ray fluorescence to create the first semiquantitative, submicron resolution, element distribution maps of P, S, K, and Ca, in situ, in fungal samples. Data collection was performed at the European Synchrotron Radiation Facility beam line ID21, Grenoble, France. We studied developing hyphae, septa, and conidiophores in Aspergillus nidulans, comparing wild type and two cell wall biosynthesis gene deletion strains. The latter encode sequential enzymes for biosynthesis of galactofuranose, a minor wall carbohydrate. Each gene deletion caused hyphal morphogenesis defects, and reduced both colony growth and sporulation 500-fold. Elemental imaging has helped elucidate biochemical changes in the phenotype induced by the gene deletions that were not apparent from morphological examination. Here, we examined S as a proxy for protein content, P for nucleic acid content, as well as Ca and K, which also have important metabolic roles. Element distributions in wild-type fungi reflect biological aspects already known or expected from other types of analysis; however, the application of X-ray fluorescence (XRF) imaging reveals aspects of gene deletion phenotypes that were not previously available. We have demonstrated that deleting a dispensable gene involved in galactose metabolism (ugeA) and one involved in biosynthesis of a minor cell wall component (ugmA) led to changes in hyphal elemental distribution that may have resulted from compromised wall composition.     

Subfemtomolar electrochemical detection of target DNA by catalytic enlargement of the hybridized gold nanoparticle labels

After showing the failure of conventional gold-enhancement procedures to amplify the gold nanoparticle-based electrochemical transduction of DNA hybridization in polystyrene microwells, a new efficient protocol was developed and evaluated for the sensitive quantification of a 35 base-pair human cytomegalovirus nucleic acid target (tDNA). In this assay, the hybridization of the target adsorbed on the bottom of microwells with an oligonucleotide-modified Au nanoparticle detection probe (pDNA-Au) was monitored by the anodic stripping detection of the chemically oxidized gold label at a screen-printed microband electrode (SPMBE). Thanks to the combination of the sensitive Au(III) determination at a SPMBE with the large amount of Au(III) released from each pDNA-Au, picomolar detection limits of tDNA can be achieved. Further enhancement of the hybridization signal based on the autocatalytic reductive deposition of ionic gold (Au(III)) on the surface of the gold nanoparticle labels anchored on the hybrids was first envisaged by incubating the commonly used mixture of Au(III) and hydroxylamine (NH(2)OH). However, due to a considerable nonspecific current response of poor reproducibility it was not possible to significantly improve the analytical performances of the method under these conditions. Complementary transmission electronic microscopy experiments indicated the loss of most of the grown gold labels during the post-enlargement rinsing step. To circumvent this drawback, a polymeric solute containing polyethyleneglycol and sodium chloride was introduced in the growth media to act as an aggregating agent during the catalytic process and thus retain the enlarged labels on the bottom of the microwell. This strategy, which led to an efficient increase of the hybridization response, allowed detection of tDNA concentrations as low as 600 aM (i.e., 10(4) lower than without amplification), and thus offers great promise for ultrasensitive detection of other hybridization events.     

[Ni(H2O)4]3[U(OH,H2O)(UO2)8O12(OH)3], crystal structure and comparison with uranium minerals with U3O8-type sheets

The new U(VI) compound, [Ni(H₂O)₄]₃[U(OH,H₂O)(UO₂)₈O₁₂(OH)₃], was synthesized by mild hydrothermal reaction of uranyl and nickel nitrates. The crystal-structure was solved in the P-1 space group, a=8.627(2), b=10.566(2), c=12.091(4) Å and α=110.59(1), β=102.96(2), γ=105.50(1)°, R=0.0539 and wR=0.0464 from 3441 unique observed reflections and 151 parameters. The structure of the title compound is built from sheets of uranium polyhedra closely related to that in β-U₃O₈. Within the sheets [(UO₂)(OH)O₄] pentagonal bipyramids share equatorial edges to form chains, which are cross-linked by [(UO₂)O₄] and [UO₄(H₂O)(OH)] square bipyramids and through hydroxyl groups shared between [(UO₂)(OH)O₄] pentagonal bipyramids. The sheets are pillared by sharing the apical oxygen atoms of the [(UO₂)(OH)O₄] pentagonal bipyramids with the oxygen atoms of [NiO₂(H₂O)₄] octahedral units. That builds a three-dimensional framework with water molecules pointing towards the channels. On heating [Ni(H₂O)₄]₃[U(OH,H₂O)(UO₂)₈O₁₂(OH)₃] decomposes into NiU₃O₁₀.     

Copper(I) Zeolites as Heterogeneous and Ligand‐Free Catalysts: [3+2] Cycloaddition of Azomethine Imines

Clicking in zeolites : Copper(I)‐exchanged zeolites proved to be practical and efficient catalysts for the cycloaddition of azomethine imines with alkynes, providing a convenient access to N,N‐bicyclic pyrazolidinone derivatives (see scheme). With high regioselectivity, 100 % atom economy, and convenient product isolation, this heterogeneously catalyzed version of the Dorn cycloaddition corresponds to click‐chemistry criteria.

     

Biaxial stretching of pet films: A molecular description

Biaxially oriented poly(ethylene terephthalate) films were prepared under well defined stretching conditions in order to mimic the three stages of the industrial inverse drawing process. Molecular orientation has been characterized through X-ray diffraction and infrared dichroism. The main orientation mechanisms in the constant-speed drawing of an amorphous film as well as in the constant-force transverse drawing of monodrawn samples are described. It is shown that relaxation phenomena dominate the orientation of an amorphous sample. Reorientation along the second drawing direction involves rotation of crystalline blocks along the draw direction and further crystalline growth. The high-temperature heating stage leads to an almost four-fold increase in the size of the crystallites. The orientation of the amorphous phase is controlled by the mechanisms occurring during crystallization (relaxation followed by extension).     

Physical simulation of precipitation of radioactive element oxalates by using the harmless neodymium oxalate for studying the agglomeration phenomena

Oxalic precipitation is usually applied in nuclear industry to process radioactive wastes or to recover actinides from a multicomponent solution. This paper deals with the development of methods adapted to a nuclear environment in order to study the agglomeration phenomena during actinide oxalic precipitation. These methods are previously setup with harmless elements that simulate the actinide behaviour: the lanthanides. A parametric study is carried out to quantify the influence of operating parameters on the agglomeration kernel and to determine a kinetic law for this mechanism. The experimental study is performed in a continuous-MSMPR precipitator at steady-state. The method is based on the resolution of two population balances using the moment approach, one for elementary crystals and the other for agglomerates. Provided that the kinetic rates of nucleation and growth are known, the agglomeration kernel can be obtained from a mathematical treatment of the experimental particle size distributions. Results point out that experimental crystal sizes are consistent with an independent kernel. It appears that the agglomeration kernel is directly proportional to supersaturation, increases with temperature but is limited by ionic strength and shear rate.     

Impact of Peptide Micropatterning on Endothelial Cell Actin Remodeling for Cell Alignment under Shear Stress

HSVEC behavior under physiological shear stress in vitro is investigated on PET surfaces micropatterned with both RGDS and WQPPRARI peptides. This technique allows (i) creating geometries on surface to guide cell orientation under shear stress and (ii) controlling surface chemical composition in order to modulate cell behavior. Under shear stress, endothelial cells adhere on patterned PET surfaces and present a more rapid orientation in flow direction in comparison to cells cultured on homogeneous surfaces. Micropatterned surfaces presenting a large surface area ratio of RGDS/WQPPRARI peptides induce fibrillar adhesion, while surfaces presenting an equal RGDS/WQPPRARI peptides surface area ratio preferentially induce focal adhesion.

     

Microstructure and chemical composition of giant avian eggshells

The microstructure and composition of the layers of two giant avian eggshells were investigated using a combination of scanning electron microscopy, electron probe microanalyses, and X-ray absorption near-edge structure spectroscopy (XANES). The two species have some similarities and differences in their microstructure and composition; the composition is not homogeneous throughout the eggshell thickness. XANES studies show that sulfur is associated with amino acids in the inner organic membranes, whereas in the mineralised layers the sulfur is mainly associated with sulfated polysaccharides. These results are similar to those obtained on chicken eggshells, and confirm the active role of sulfated acidic polysaccharides in biomineralisation processes of carbonate skeletons.