Biomimetics silica

Furthermore, diatoms and radiolaria exert strict species-specific control over the patterns and pore sizes of the silica, which is precipitated at ambient conditions. Controlled industrial synthesis of silica, on the other hand, requires extreme pHs and/or temperatures. Biomimetic silica synthesis has, therefore, attracted much interest among materials scientists and phycologists for potential industrial applications, such as components of industrial separators, catalysts, and electronic devices.64-67... 

Knecht, M. R. Wright, D. W., Functional analysis of the biomimetic silica precipitating activity of the R5 peptide from Cylindrotheca fiisiformis. Chem. Commun. 2003, (24), 3038-3039. 

Yang SH, Choi IS (2010) Thickness control of biomimetic silica thin films grafting density of poly (2-(dimethylamino)ethyl methacrylate) templates. Anglais 31 753... 

Luckarift, H.R., Spain, J.C., Naik, R.R. and Stone, M.O. (2004) Enzyme immobilization in a biomimetic silica support. Nature Biotechnology, 22,... 

Jan, J.-S. and Shantz, D.F. (2007) Biomimetic silica formation effect of block copolypeptide chemistry and solution conditions on silica nanostructure. Advanced Materials, 19, 2951-6. 

Lutz, K., Groger, C., Sumper, M. and Brunner, E. (2005) Biomimetic silica formation analysis of the phosphate-induced self-assembly of polyamines. Physical Chemistry Chemical Physics, 7, 2812-15. 

Bernecker, A., Wieneke, R., Riedel, R., Seibt, M., Geyer, A., and Steinem, C. (2010) Tailored synthetic polyamines for controlled biomimetic silica formation. /. Am. Chem. Soc., 132,1023-1031. 

The major differences between biological and biomimetic silica formation mainly lies in precursor concentrations (undersaturated in biosilicification), time required for biosilica deposition, involvement of other molecules (ions, organic molecules, and membranes), and the presence of a confined environment in diatoms. Nonetheless, proteins that direct biomineralization in nature can be used to control the production of nanostructured materials and fecilitate the febrica-tion of new structures in vitro under ambient conditions. Indeed, polycationic silaffins and silicateins isolated from diatoms and sponges, respectively, were shown to generate networlcs of silica nanospheres within seconds when added to a solution of silicic acid. 

Cha JN, Stucky GD, Morse DE, Deming TJ (2000) Biomimetic synthesis of ordered silica structures mediated by block copolypeptides. Nature 403 289-292... 

Altunbas A, Sharma N, Lamm MS et al (2010) Peptide-silica hybrid networks biomimetic control of network mechanical behavior. ACS Nano 4 181-188... 

Similarly to the above-mentioned entrapment of proteins by biomimetic routes, the sol-gel procedure is a useful method for the encapsulation of enzymes and other biological material due to the mild conditions required for the preparation of the silica networks [54,55]. The confinement of the enzyme in the pores of the silica matrix preserves its catalytic activity, since it prevents irreversible structural deformations in the biomolecule. The silica matrix may exert a protective effect against enzyme denaturation even under harsh conditions, as recently reported by Frenkel-Mullerad and Avnir [56] for physically trapped phosphatase enzymes within silica matrices (Figure 1.3). A wide number of organoalkoxy- and alkoxy-silanes have been employed for this purpose, as extensively reviewed by Gill and Ballesteros [57], and the resulting materials have been applied in the construction of optical and electrochemical biosensor devices. Optimization of the sol-gel process is required to prevent denaturation of encapsulated enzymes. Alcohol released during the... 

Coradin, T., Durupthy, O. and Livage, J. (2002) Interactions of amino-containing peptides with sodium silicate and colloidal silica A biomimetic approach to silicification. Langmuir, 18, 2331-2336. 

E. (2003) Biomimetic control of size in the polyamine-directed formation of silica nanospheres. Angewandte Chemie-Intemational Edition, 42, 5192— 5195. 

As mentioned earlier, biological systems have developed optimized strategies to design materials with elaborate nanostructures [6]. A straightforward approach to obtaining nanoparticles with controlled size and organization should therefore rely on so-called biomimetic syntheses where one aims to reproduce in vitro the natural processes of biomineralization. In this context, a first possibility is to extract and analyze the biological (macro)-molecules that are involved in these processes and to use them as templates for the formation of the same materials. Such an approach has been widely developed for calcium carbonate biomimetic synthesis [13]. In the case of oxide nanomaterials, the most studied system so far is the silica shell formed by diatoms [14]. 

In fact, such biomimetic molecules demonstrate the ability to tailor the growth of silica nanoparticles in a way that is very similar to diatom-extracted species. However, they demonstrate the same limitations in terms of morphological control of nanoparticle assembly. This is because the diatom shell architecture results not only from interactions of silica precursors with templating molecules but also benefits from a cell-driven molding of the vesicular compartment where silicification occurs [29]. Thus, it is very likely that diatom-like synthetic silica will only be achieved when such confinement/molding effects are taken into account in the design of biomimetic experiments [30]. 

However, it has to be realized that biological templates remain inserted in the final nanoparticles and this is not acceptable for many applications. Nevertheless, some recent examples indicate that such biomimetic materials may be suitable for the design of biotechnological and medical devices [32]. For instance, it was shown that silica gels formed in the presence of p-R5 were excellent host matrices for enzyme encapsulation [33]. In parallel, biopolymer/silica hybrid macro-, micro- and nanocapsules were recently obtained via biomimetic routes and these exhibit promising properties for the design of drug delivery materials (see Section 3.1.1) [34,35],... 

Knecht, M.R. and Wright, D.W. (2004) Amine-terminated dendrimers as biomimetic templates for silica nanospheres formation. Langmuir, 20, 4728-4732. 

Abdoul-Aribi, N. and Livage, J. (2005) Gelatine thin films as biomimetic surfaces for silica particles formation. Colloids and Sufaces B-Biointerfaces, 44, 191-196. 

Gautier, C., Lopez, P.J., Hemadi, M., Livage and J., Coradin, T. (2006) Biomimetic growth of silica tubes in confined media. Langmuir, 22, 9092-9095. 

Allouche, J., Boissiere, M., Helary, C., Livage, J. and Coradin, T. (2006) Biomimetic core-shell gelatine/silica nanoparticles a new example of biopolymer-based nanocomposites. Journal of Materials Chemistry, 16, 3121-3131. 

Roth, K.M., Zhou, Y., Yang, W. and Morse, D.E. (2005) Bifunctional small molecules are biomimetic catalysts for silica synthesis at neutral pH. Journal of the American Chemical Society, 127, 325-330. 

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