Intitulé du poste : Internship Master 2: Syntheses of CaCO3 minerals colored by bio-based organic pigments extracted from sea urchins
Ville : Paris
Laboratoire/Institut : Laboratoire de Chimie de la Matière Condensée de Paris
Description du poste : Sea urchin spines show intense and diverse colors (from purple to green) that are due to a family of organic molecules, the polyhydroxylated-naphthoquinone (PHNQ) [1]. Although the majority of synthetic organic pigments (non-water soluble) hardly disperse in the medium to be colored and fade rapidly under sunlight, PHNQ mass-color and provide long-lasting colors to sea urchin spines.
These remarkable properties are likely due to the encapsulation of the PHNQ molecules within the crystalline biogenic calcite, which protects the organic pigments from the external environment. The PHNQ encapsulation takes place during the coupled pigmentation and biomineralization processes.
PHNQ molecules are first localized in the so-called red-spherule cells and progressively integrate the growing mineral (=biomineralization). Biomineralization in sea urchin involves the presence of amorphous calcium carbonate (ACC) precursors phases [2,3], which are thermodynamically unstable under ambient conditions but can be temporarily stabilized by inorganic ions such as Mg2+ and macromolecules, mostly N-glycosylated proteins [4]. During ACC crystallization, Mg2+ as well as diverse macromolecules (proteins, lipids, polysaccharides, metabolites) and PHNQ are incorporated into the biogenic calcite.

This project aims at synthetizing colored hybrid CaCO3 based materials bio-inspired by the pigmentation and biomineralization processes occurring in sea urchin spines and therefore via the synthesis of ACC-PHNQ samples. PHNQ molecules will be extracted from the red-spherules cells located in the coelomic fluid (≈blood) of the sea urchins by centrifugation techniques and osmotic shock approaches. The molecular structure of the PHNQ molecules will be elucidated by 1H/13C solution state NMR. Based on the literature, two strategies will be employed to synthetize colored CaCO3 crystals with occluded PHNQ via the formation of ACC particles. 1) Spontaneous precipitation by direct mixing of CaCl2 into Na2CO3 solution [5] containing water soluble PHNQ will be performed with a dedicated automatic device that allows the simultaneous measurement of pH and Ca2+ activity during the ACC synthesis. 2) Slow carbonation diffusion methods [6] will be also performed in ethanol with the ethanol-soluble PHNQ fractions. Crystallization of the samples will be induced under heating and/or controlled humidity. Due to the complexity of the natural PHNQ mixture, simplified and commercially available molecules (lawsone and naphthazarin) will also be considered. The PHNQ-ACC hybrid samples will be characterized by ATR-FTIR and the incorporation of the PHNQ within the CaCO3 crystals will be studied by TG analyses and observed by optical microscopy. The likely stabilization effect of the PHNQ on the ACC phases will be determined by DSC. Finally, ACC nanoparticles and faceted CaCO3 crystals will be observed by SEM and the nature of the crystalline polymorphs (calcite, vaterite, aragonite) will be determined by XRD.

[1] T.W. Goodwin, S. Srisukh, A study of the pigments of the sea-urchins, echinus-esculentus l and paracentrotus-lividus lamarck, Biochem. J. 47(1) (1950) 69-76.
[2] Y. Politi, T. Arad, E. Klein, S. Weiner, L. Addadi, Sea urchin spine calcite forms via a transient amorphous calcium carbonate phase, Science 306(5699) (2004) 1161-1164.
[3] M. Albéric, C. Stifler, Z. Zou, C. Sun, C. Killian, P. Gilbert, S. Valencia, M. Mawass, L. Bertinetti, Y. Politi, Growth an regrowth of adult sea urchin psines involve hydrated and anhydrous amorphous calcium carbonate precursors, Journal of structural biology in press (2019).
[4] S. Raz, P.C. Hamilton, F.H. Wilt, S. Weiner, L. Addadi, The Transient Phase of Amorphous Calcium Carbonate in Sea Urchin Larval Spicules: The Involvement of Proteins and Magnesium Ions in Its Formation and Stabilization, Adv. Funct. Mater. 13(6) (2003) 480-486.
[5] Z.Y. Zou, L. Bertinetti, Y. Politi, A.C.S. Jensen, S. Weiner, L. Addadi, P. Fratzl, W. Habraken, Opposite Particle Size Effect on Amorphous Calcium Carbonate Crystallization in Water and during Heating in Air, Chemistry of Materials 27(12) (2015) 4237-4246. [6] S.-F.Chen, H. Cölfen, M. Antonietti, S.-H. Yu, Ethanol assisted synthesis of pure and stable amorphous calcium carbonate nanoparticles, Chemical Communications 49(83) (2013) 9564-9566.
Durée du contrat : 5-6 months
Date de prise de fonction : 02-02-2020
Personne à contacter : Marie Albéric
Téléphone : 0144275675
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