Wolfgang Tremel

Formation of siliceous spicules in the marine demosponge Suberites domuncula

The siliceous skeleton of demosponges is constructed of spicules. We have studied the formation of spicules in primmorphs from Suberites domuncula. Scanning electron microscopy and transmission electron-microscopical (TEM) analyses have revealed, in the center of the spicules, an axial canal that is 0.3–1.6xa0μm wide and filled with an axial filament. This filament is composed of the enzyme silicatein, which synthesizes the spicules. TEM analysis has shown that spicule formation starts intracellularly and ends extracellularly in the mesohyl. At the initial stage, the axial canal is composed only of silicatein, whereas membranous structures and fibrils (10–15xa0nm in width) can later also be identified, suggesting that intracellular components protrude into the axial canal. Antibodies against silicatein have been applied for Western blotting; intracellularly, silicatein is processed to the mature form (24xa0kDa), whereas the pro-enzyme with the propeptide (33xa0kDa) is detected extracellularly. Silicatein undergoes phosphorylation at five sites. Immunohistological analysis has shown that silicatein exists in the axial canal (axial filament) and on the surface of the spicules, suggesting that they grow by apposition. Finally, we have demonstrated that the enzymic reaction of silicatein is inhibited by anti-silicatein antibodies. These data provide, for the first time, a comprehensive outline of spicule formation.

Enzymatic production of biosilica glass using enzymes from sponges: basic aspects and application in nanobiotechnology (material sciences and medicine)

Biomineralization, biosilicification in particular (i.e. the formation of biogenic silica, SiO2), has become an exciting source of inspiration for the development of novel bionic approaches following “nature as model”. Siliceous sponges are unique among silica forming organisms in their ability to catalyze silica formation using a specific enzyme termed silicatein. In this study, we review the present state of knowledge on silicatein-mediated “biosilica” formation in marine sponges, the involvement of further molecules in silica metabolism and their potential application in nanobiotechnology and medicine.

Formation of giant spicules in the deep-sea hexactinellid Monorhaphis chuni (Schulze 1904): electron-microscopic and biochemical studies

The siliceous sponge Monorhaphis chuni (Hexactinellida) synthesizes the largest biosilica structures on earth (3xa0m). Scanning electron microscopy has shown that these spicules are regularly composed of concentrically arranged lamellae (width: 3–10xa0μm). Between 400 and 600 lamellae have been counted in one giant basal spicule. An axial canal (diameter: ~2xa0μm) is located in the center of the spicules; it harbors the axial filament and is surrounded by an axial cylinder (100–150xa0μm) of electron-dense homogeneous silica. During dissolution of the spicules with hydrofluoric acid, the axial filament is first released followed by the release of a proteinaceous tubule. Two major proteins (150xa0kDa and 35xa0kDa) have been visualized, together with a 24-kDa protein that cross-reacts with antibodies against silicatein. The spicules are surrounded by a collagen net, and the existence of a hexactinellidan collagen gene has been demonstrated by cloning it from Aphrocallistes vastus. During the axial growth of the spicules, silicatein or the silicatein-related protein is proposed to become associated with the surface of the spicules and to be finally internalized through the apical opening to associate with the axial filament. Based on the data gathered here, we suggest that, in the Hexactinellida, the growth of the spicules is mediated by silicatein or by a silicatein-related protein, with the orientation of biosilica deposition being controlled by lectin and collagen.

Formation of layered titania and zirconia catalysed by surface-bound silicatein

Silicatein immobilised on self-assembled polymer layers using a histidine-tag chelating anchor group retains its hydrolytical activity for the formation of biosilica, and catalyses the formation of layered arrangements of biotitania and biozirconia.

Spectroscopic and microscopic study of vanadium oxide nanotubes

V2O5 nanotubes synthesized via the sol-gel route has been studied by electron energy loss spectroscopy (EELS), x-ray absorption spectroscopy (XAS), and energy dispersive x-ray analysis, in order to understand the local structure of vanadium in the nanotubes. Contrary to our expectation, all the features of the XAS and EELS spectra of the V2O5 nanotubes are in line with that of bulk layered vanadium oxide revealing that vanadium is present in the 5+ oxidation state in the nanotubes. However, V2O5 nanotubes exhibit additional surface states in their electronic structure in comparison with bulk V2O5. A comparison of measured and calculated spectra allows us to distinguish single-wall from multiwall V2O5 nanotubes.V2O5 nanotubes synthesized via the sol-gel route has been studied by electron energy loss spectroscopy (EELS), x-ray absorption spectroscopy (XAS), and energy dispersive x-ray analysis, in order to understand the local structure of vanadium in the nanotubes. Contrary to our expectation, all the features of the XAS and EELS spectra of the V2O5 nanotubes are in line with that of bulk layered vanadium oxide revealing that vanadium is present in the 5+ oxidation state in the nanotubes. However, V2O5 nanotubes exhibit additional surface states in their electronic structure in comparison with bulk V2O5. A comparison of measured and calculated spectra allows us to distinguish single-wall from multiwall V2O5 nanotubes.

From Single Molecules to Nanoscopically Structured Functional Materials

The synthesis of MS 2 (M = Mo, W) onion-like nanoparticles by means of a high temperature MOCVD process starting from W(CO)6 and elemental sulfur is reported. The reaction can also be carried out in two steps where the intermediate amorphous WS 2 nanoparticles formed through the high temperature reaction of tungsten and sulfur in the initial phase of the reaction are isolated and converted in a separate annealing step to onion-type WS2 nanoparticles. Based on a study of the temperature dependence of the reaction a set of conditions could be derived where onion-like structures were formed in a one-step reaction. Onion-like structures obtained in the single-step process were filled, whereas the particles obtained by the two-step procedure were systematically hollow. A model could be devised to rationalize the different outcome of the reactions. The MOCVD approach therefore allows a selective synthesis of open and filled fullerene-like chalcogenide nanoparticles. Furthermore, we demonstrate the novel surface functionalization of WS2 nanotubes with polymeric ligands by complexation with a combination of Ni 2+ via an scorpionate-type nitrilotriacetic acid (NTA) and immobilization of TiO 2 nanoparticles onto the surface of nanotubes. Synthesis of such a functional polymeric ligand was achieved via a reactive polymer precursor route.