Influence of DNA, Alginate, Lysozyme and Bovine Serum Albumin on Sodium Silicate Condensation
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Influence of DNA, Alginate, Lysozyme and Bovine Serum Albumin on Sodium Silicate Condensation Thibaud Coradin, AurŽlie CoupŽ and Jacques Livage Laboratoire de Chimie de la Mati•re CondensŽe, CNRS-UMR 7574, UPMC, F-75252 Paris cedex 05, France. ABSTRACT The interaction of DNA, alginate, Lysozyme and Bovine Serum Albumin with diluted solutions of sodium silicate was studied using the molybdosilicate method. DNA and alginate showed very weak interactions with silica precursors whereas both proteins were able to form silica gels. Both electrostatic interactions and hydrogen bonds are suggested to arise between peptide chain and polysilicates, bringing new informations on the nature of inorganic and bioorganic species involved in the natural biosilicification processes. INTRODUCTION Biomineralization processes often occur at the interface between inorganic precursors and biological macromolecules [1]. For instance, bone formation involves hydroxyapatite deposition in a collagen proteinaceous matrix whereas the β-chitin polysaccharide and calcium carbonate are associated within crab cuticles. The formation of the silica skeleton of diatoms was shown to take place mainly at the interface with proteins, even though the presence of sugars in the cell wall was reported [2-3]. Aiming at understanding the interactions that may arise between the naturally-occurring form of silica precursors, i.e. silicic acids, and proteins, we have undertaken the study of the effect of various biopolymers on the behaviour of sodium silicate diluted solutions. We have first focused on amino acids and poly-amino acids and shown that poly-lysine and poly-arginine were able to induce silica formation, the catalytic effect increasing with polymer chain length [4-5]. These results correlate well with the fact that the silaffin proteins that were extracted from diatom cells are characterized by lysine and arginine patches along the peptide chain [6]. In order to get a better understanding of the possible silica-biopolymers interactions, we have selected two proteins that bear an important number of lysine and arginine groups, as well as a polysaccharide macromolecule and DNA. The evolution of the silicic acid content of a diluted sodium silicate solution in the presence of these polymers was monitored using the molybdosilicate method [7]. Depending on the solution pH, only the two proteins were able to induce silica formation. These results are discussed in terms of electrostatic interactions and hydrogen bonds.
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EXPERIMENTAL Waterglass (27% SiO2, 10 % NaOH) from Riedel-de Ha‘n was chosen as the source of silicic acid. Aqueous silicate solutions were preferred to silicon alkoxide precursors because they correspond to the usual form of soluble silica in nature. For similar reasons, diluted soluti
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