Marcel Van de Put
Biomimetic synthesis of silica hollow spheres
In Nature several examples of biosilica can be found, but probably the most well-known examples are the diatom algae. These eukaryotic species are able to form very well organized and structured silica-based exoskeletons at mildly acidic pH and, moreover, moderate temperature and pressure conditions. Most striking about this species is the high density of the silica network, which in vitro can only be achieved with (thermal) after-treatments.
In the last decades different protein families have been identified in the frustus of these species and the combination of positive (amines) and negative (e.g. phosphates) charges combined with hydrophobic regions is suspected to play a key role in the silica network formation. However, the mechanism and the influence of these interactions on the fast forming diatom frustules are poorly understood. The goal of this project is to study the influence of well defined poly(amino acid)s on the silica mineralization process so that a procedure can be found to produce highly cross-linked silica without after-treatments.
We will make a range of different randomly sequenced poly(amino acid)s with different monomer compositions. In this way, we are able to control both the hydrophilicity of the polymer chains as well as the net charges. By having control on the composition of the polymeric additive by varying the amounts of lysine, glutamic acid, serine and alanine we are able to study the direct influence of these molecular properties on the silica mineralization process. For information on the molecular level we will use solid state 29Si NMR combined with FT-IR spectroscopy to determine the condensation state of the silica species present in solution. The different morphologies and particle growth can be followed in situ by cryoTEM.
Figure 1: SEM image of the highly ordered frustules of the diatom species Thalassiosira Pseudonana. Reproduced with permission from: M. Hildebrand (2008) Diatoms, biomineralization processes, and genomics, Chem Rev, 108:4855-4874. Copyright 2008 American Chemical Society.
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