Invited talk: Role of the amyloid region in the formation and propagation of Als adhesive nanodomains on Candida albicans

The most prevalent fungal pathogen in humans Candida albicans expresses on its surface Als (Agglutinin-like sequence) proteins which mediate both yeast-to-host tissue adherence and yeast aggregation. Although adhesins often show weak binding to specific ligands, Als mediate remarkably strong adherence. By combining single-molecule atomic force microscopy (AFM) with the tools of genetics and cell biology, we unraveled the various Als protein domains to understand how they synergize to strengthen the cell adhesion and aggregation. The complementary role of the ligandbinding domains, amyloid-forming regions and the less specific hydrophobic tandem repeat domains give raise to a fascinating new mechanism of cell-activation resulting in force-activated clustering of hundreds of adhesion molecules. The amyloid heptapeptide sequence plays a crucial role in this mechanism providing a cohesive strength to the Als protein by forming molecular zipper that mediates protein interactions between cells

Preparation, characterization and catalytic properties of Co-Nb2O5-SiO2 catalysts

Co-Nb(2)Q(5)-SiO2 catalysts were prepared using three different sol-gel procedures: (i) the colloidal sol-gel method using NbCl5 and SiCl4 as precursors; (ii) the polymeric sol-gel method using niobium ethoxide and tetraethyl-orthosilicate (TEOS); (iii) an intermediate procedure between the colloidal and polymeric sol-gel method in which the precursors were those utilized in the CSG but dissolved in a mixture of anhydrous ethanol and CCl4. In all procedures, the elimination of the solvent carried out between 80 and 110 degrees C was followed by a reduction in hydrogen flow (30 ml min(-1)) at 773 K. Following these procedures, samples containing 10 wt.% Co and 15 wt.% niobium oxide (expressed as Nb2O5) were obtained. The characterization of the catalysts was performed using various techniques: N-2 adsorption and desorption curves at 77 K, NH3- and H-2-chemisorption, TPO, XPS, XRD, and solid state H-1 MAS-NMR. Hydrogenolysis of butane was evaluated. The low reaction rates are assigned to the effect of the metal size, whereas the isobutane selectivity as well as the relatively high stability is due to the acidity of the support. (C)2000 Elsevier Science B.V. All rights reserved

Sol-gel synthesis of cobalt-niobia catalysts

Cobalt-niobia catalysts were prepared using different variants of the colloidal sol-gel technique and wetness impregnation. Characterization of these catalysts by XRD, FT-IR, XPS and TEM showed that phases structure as well as superficial composition depended on the preparation route. It was found that niobia exhibits a strong metal support interaction effect and this effect depends on the dimension of the metallic cobalt on the support surface. Reactivity of these catalysts was checked in n-butane hydrogenolysis, a well known structural sensitive reaction. The catalytic tests showed the influence of the catalysts features both on the reaction rate and selectivity

Comparative behavior of silica-embedded tert-butyldimethylsilyltrifluoro-methanesulfonate and lanthanum triflate catalysts

A series of hybrid catalysts containing tert-butyldimethylsilyltrifluoro-methanesulfonate (BDMST) or lanthanum triflate (LaT), hex adecyltrimethylammonium bromide and silica were obtained by sol-gel immobilization. The catalysts were characterized by nitrogen adsorption-desorption isotherms at 77 K, TG-DTA, H-1, C-13, and Si-29 solid state MAS-NMR, XRD, TEM, scanning electron microscopy (SEM), XPS and, FT-IR after adsorption of NH3. The catalytic tests were carried out in the reaction of the methyl ester of 1-cyclopentenylacetic acid in various solvents. The results revealed a completely different behavior of the hybrid catalysts compared with catalysts without surfactant or with free tert-butyldimethylsilyltrifluoro-methanesulfonate, or lanthanum triflate, or triflic acid, indicating a behavior for a typical heterogeneous catalyst. (C) 2002 Elsevier Science B.V. All rights reserved

Preparation and characterization of WOX-CeO2 catalysts

Tungsten-ceria catalysts were prepared by co-precipitation and impregnation techniques looking for the effect of the tungsten loading and calcination temperature. The catalysts were characterized by adsorption-desorption isotherms of N-2 at 77 K, in-situ XRD, NH3-DRIFT, Raman spectroscopy, and XPS. It was found that the preparation method influences the texture of the catalyst, the tungsten loading, the dispersion of the WO, domains which correspond to a different interaction with ceria, and the temperature of formation of the Ce-2(WO4)(3) species which seem to be responsible for the strong Lewis/Bronsted acid sites

Co-Nb2O5/SiO2 sol-gel catalysts: preparation implications on the texture and acidity of the support and dimension of the metal particle

Colloidal and polymeric sol-gel, an intermediate technique between the colloidal and the polymeric sol-gel and the clasical incipient wetness impregnation method were used to prepare a set of Co-Nb2O5/SiO2 catalysts with various characteristics. Modifications in the preparation procedure and its parameters have determined significant changes of the texture and the acidity of the support as well as of the Co metal particle size. Textural and structural characterization and catalytic data from butane hydrogenolysis were used to reveal the main differences among the catalysts obtained by the various techniques applied for preparation