Search results for "Silice"

Biogenic Inorganic Polysilicates (Biosilica): Formation and Biomedical Applications

2013

The siliceous sponges, the demosponges and hexactinellid glass sponges, are unique in their ability to form biosilica structures with complex architectures through an enzyme-catalyzed mechanism. The biosilica skeleton of these sponges with its hierarchically structure and exceptional opto-mechanical properties has turned out to be an excellent model for the design of biomimetic nanomaterials with novel property combinations. In addition, biosilica shows morphogenetic activity that offers novel applications in the field of bone tissue engineering and repair. In recent years, much progress has been achieved towards the understanding of the principal enzymes, the silicateins that form the spon…

Enzymatically Synthesized Biosilica

2015

Structural biomaterials are hierarchically organized and biofabricated. Biosilica represents the main mineral component of the sponge skeletal elements, the spicules. We summarize recent data on the different levels of molecular, biological, and structural hierarchies controlling the synthesis of the picturesquely and intricately architectured spicules/skeletons.

A cryptochrome-based photosensory system in the siliceous sponge Suberites domuncula (Demospongiae)

2010

Based on the light-reactive behavior of siliceous sponges, their intriguing quartz glass-based spicular system and the existence of a light-generating luciferase [Muller WEG et al. (2009) Cell Mol Life Sci 66, 537–552], a protein potentially involved in light reception has been identified, cloned and recombinantly expressed from the demosponge Suberites domuncula. Its sequence displays two domains characteristic of cryptochrome, the N-terminal photolyase-related region and the C-terminal FAD-binding domain. The expression level of S. domuncula cryptochrome depends on animal’s exposure to light and is highest in tissue regions rich in siliceous spicules; in the dark, no cryptochrome transcri…

Molecular Biomineralization: Toward an Understanding of the Biogenic Origin of Polymetallic Nodules, Seamount Crusts, and Hydrothermal Vents

2011

Polymetallic nodules and crusts, hydrothermal vents from the Deep Sea are economically interesting, since they contain alloying components, e.g., manganese or cobalt, that are used in the production of special steels; in addition, they contain rare metals applied for plasma screens, for magnets in hard disks, or in hybrid car motors. While hydrothermal vents can regenerate in weeks, polymetallic nodules and seamount crusts grow slowly. Even though the geochemical basis for the growth of the nodules and crusts has been well studied, the contribution of microorganisms to the formation of these minerals remained obscure. Recent HR-SEM (high-resolution scanning electron microscopy) analyses of …

Micromorphological approach to the systematics of Mediterranean Isoëtes species (Isoëtaceae, Lycopodiophyta): analysis of the megaspore surface

2012

Megaspore ornamentation is one of the few morphological characters used in the taxonomy of the genus Isoëtes. In the present work, we test the application of this character for distinguishing some Isoëtes species occurring in the Mediterranean: Isoëtes sicula, which according to some authors should be included as a variety in I. histrix, and the recently described I. todaroana, whose affinity with other taxa is currently unknown. Two additional species (I. duriei, I. velata) were also included in the analysis. The megaspores were studied using scanning electron microscopy combined with energy-dispersive X-ray spectroscopy and chemical treatment. In all species, the megaspore surface is cove…

Synthesis of mesoporous silica nanoparticles (MSNs) and encapsulation of cisplatin for targeted cancer therapies

2014

The aim of this PhD thesis is to elaborate mesoporous silica nanoparticles (MSNs) able to sustain the release of cisplatin into the intracellular compartments of solid tumors. The parametric study shows that morphological, structural and textural properties of MSNs-MCM-41, synthesized by sol-gel reaction by using TEOS as a silica source and CTAB as a structure-directing agent, depend on pH, stirring speed, temperature and extraction process of CTAB. The synthesis atmosphere has to be controlled in order to avoid the presence of ethanol and carbonate species which are responsible of necks between particles generating unstable suspensions of MSNs.MSNs were functionalized in order to control t…

Les matières premières siliceuses du site du Petit-Chasseur à Sion (Valais)

2011

Biomineralization events in Recent volcanic and sedimentary settings: textural features and isotope signatures.

2008

Influence of Ge doping level on the EPR signal of Ge(1), Ge(2) and E'Ge defects in Ge-doped silica

2011

Abstract We present an experimental investigation on the Ge doping level dependence of the Electron Paramagnetic Resonance (EPR) signal spectral features of the Ge(1), Ge(2) and E'Ge defects induced in Ge doped silica. We have studied samples produced by sol–gel or PCVD techniques and doped with different amounts of Ge up to 20% by weight. The samples were gamma or beta ray irradiated and successively they were thermally treated to isolate the EPR signals of the different point defects. The data show that the EPR line shapes of the Ge(1) and the Ge(2) centers are progressively modified for doping level higher than 1%, whereas the line shape of the E'Ge defect appears independent from the do…

Irradiation Effects in Optical Fibers

2010

Intrinsic and extrinsic optical fiber-based sensors are promising devices to be used in very different and complex environments, by their very nature: capabilities to work under electromagnetic fields; possibility to carry multiplexed signals (time, wavelength multiplexing); small size and low mass; ability to handle multi-parameter measurements in distributed configuration; possibility to monitor sites far away from the controller. In the case of the optical fibers, the possibility to be incorporated into various types of sensors and actuators, free of additional hazards (i.e. fire, explosion), made them promising candidates to operate in adverse conditions as those required by space appli…