Laboratoire Matière et Systèmes Complexes

Patrick Guenoun (LIONS, CEA Saclay, SIS2M-UMR CEA CNRS 3299)

In biominerals, organic matter is a minority key element in the controlled nucleation and growth of the mineral phase. Because of this matter, the hierarchical organization, the shape and the nanostructure of the biomineral composite is found very different from the synthetic counterparts[1].

At LIONS, in collaboration with biologists and mineralogists, we have tried to understand what role organic matter plays in the case of nacre shells. In this presentation, after describing some generic features of nacre, I will present two recent attempts we have carried out. The first one is concerned with the coupled evolution of the organic and inorganic structures during the nucleation and growth of CaCO3 under a monolayer of acidic β-sheet forming peptides that mimic some natural conformations found in nacre. The investigation is carried out using in situ analytical techniques (X-ray diffraction and IR spectroscopy) in order to provide molecular scale structural information over the whole course of the mineralization process. Mineralization is shown to coexist with β-sheet order while inducing other conformational changes to the peptide assembly. Peptides are observed to promote the growth of unoriented vaterite crystals (Figure 1) ; no templating effect of the β-sheet order is observed[2].

In another attempt, we used soluble organic extracts of Pinctada margaritifera shells for modulating in vitro growth of calcium carbonate[3]. Because of acidic residues these extracts greatly modify the crystal shapes. In particular an organisation made of nanodomains is found (Figure 2), these nanodomains being oriented so well such as a monocrystal-like diffraction is obtained. This is reminiscent of some generic features found in biominerals and nacre in particular.

1 C . Chevallard, P. Guenoun, Les matériaux biomimétiques, Bulletin de la S.F.P. (155) juillet-août 2006

2 N. Chevalier, C. Chevallard, M. Goldmann, G. Brezesinski, P. Guenoun, to appear in Crystal Growth and Design

3 Y.H. Tseng, C. Chevallard, Y. Dauphin, P. Guenoun, in preparation