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Sujet de stage / Master 2 Internship

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Amorphous intermediate dehydration: a key step in CaCO3 biological crystallisation

Contact: CHEVALLARD Corinne, , corinne.chevallard@cea.fr, +33 1 69 08 52 23
The biological crystallization of calcium carbonate, which allows the development of hard tissues in many invertebrates, takes place from an amorphous material which undergoes dehydration before acquiring a crystalline order. Model syntheses will be conducted in order to specify these mechanisms.
Possibility of continuation in PhD: Oui
Deadline for application:30/04/2022

Full description:
Calcium carbonate is the material that is most widely used by invertebrates to build their hard tissues (shell of molluscs and gastropods, spicules of sponges or corals, love dart of gastropods, etc.) Hundreds of millions of years of evolution have resulted in extremely powerful synthesis strategies, which allow this material to be shaped at will, and which we are just beginning to decipher. The appropriation of these strategies by humans is a huge stake because it would make it possible to carry out environmentally friendly syntheses, without large input of energy, while leading to structures with finely controlled morphologies and mechanical properties.

In the laboratory, we are developing model syntheses of calcium and carbonate ion co-precipitation involving an amorphous intermediate, thus mimicking what happens during the production of the shell by the pearl oyster. The study of these model syntheses should ultimately make it possible to understand the mechanisms of biomineralization by connecting the final structure of the crystal to a path of crystallization.

The aim of this internship is to specify, on the one hand, the mechanisms of appearance of the amorphous intermediate and, on the other hand, its path of crystallization. Particular interest will be paid to the kinetics of dehydration of the amorphous before crystallization, under different environmental conditions (relative humidity, temperature). This will in particular be studied by optical microscopy (fluorescent molecular rotors for probing the local viscosity), Raman spectroscopy or using thermogravimetric analysis coupled with differential calorimetry (ATG-DSC).

1. L. Addadi, S. Raz, S. Weiner, Adv. Mater. 2003, 15, 959–970.
2. H. Du et E. Amstad, Angew. Chem. Int. Ed. 2020, 59, 1798 – 1816 .
3. F. Mastropietro, et al. , Nature 2017, 16, 946-953.

Skills required: good experimental, analysis and reporting skills are mandatory.
Technics/methods used during the internship:
Solution chemistry, optical microscopy, Raman spectroscopy, ATG-DSC, cryo-TEM

Tutor of the internship


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