Structural Study of Siliceous Spicules from Marine Sponges
Marine sponges deposit hydrated silica in needle-like objects called spicules. These spicules also contain a protein axial filament which functions as template for silica deposition. Our work deals with the fiber diffraction structural study of the organization of the axial filaments in spicules from different sponges, carried out using a SAXS setup with synchrotron radiation. The analysis of the position and distribution of the spots reveals a hexagonal arrangement with different possible 2D and 3D
dimensional dispositions of the
units
along the main axis of the spicules. Analysis after thermal treatments
reveals a structural ordering accompanying the thermal degradation of
the organic material. This confirms our hypothesis that the protein
units act as template in the formation of an inorganic
structure.Structural Characterization of Bioactive Glasses
Historically the function of biomaterials has been to replace diseased or damaged tissues. When a bioactive glass is implanted in a bone several surface reactions can occur, leading, by a complex mechanism including ion leaching, silica gel formation, Ca++ and PO43- diffusion, to the precipitation of hydroxy-carbonate apatite (HCA) with composition and structure close to the mineral phase of bone. We characterize different kinds of bioactive glasses and glass-ceramics (both massive and porous)
to shed some light on the
structural features of the HCA
film, especially in the early stages of
the deposition. In fact GIWAXS and GISAXS measurements were carried out
in order to study ex situ the different steps of formation of HCA on
the glass surfaces.Examples of Combined Experimental/Theoretical Studies
- Three crystal structures of adducts between fluorene and different electron withdrawing are characterized. The structures result to be disordered and only approximate structures were obtained by refinement of the single crystal data. Their geometry was fully optimised, employing the periodic ab initio CRYSTAL code, to obtain a chemically reliable model with the correct distances and angles. (more..)
- the octakis(Isobutyl)octasilsesquioxane is caratherized with different techniques which indicate that a phase transition at 330K is related to a change in the conformational freedom of the isobutyl chains bonded to the silsesquioxane cage. To confirm this hypothesis, we characterized the conformational mobility of the molecule by molecular dynamic. (more..)