Structure of an amorphous calcium carbonate phase involved in the formation of Pinctada margaritifera shells

Type Article
Date 2022-11
Language English
Author(s) Grünewald Tilman A.ORCID1, Checchia StefanoORCID2, Dicko Hamadou1, Le Moullac GillesORCID3, Sham Koua Manaarii3, Vidal-Dupiol JeremieORCID4, Duboisset Julien1, Nouet Julius5, Grauby Olivier6, Di Michiel Marco2, Chamard VirginieORCID1
Affiliation(s) 1 : Aix-Marseille Univ, CNRS, Centrale Marseille, Institut Fresnel, Marseille, F-13013 France
2 : ESRF – The European Synchrotron, Grenoble Cedex, F-38043 France
3 : Ifremer, IRD, Institut Louis‐Malardé, Univ Polynésie française, EIO, F-98719 Taravao Tahiti, Polynésie française, France
4 : IHPE, University Montpellier, CNRS, IFREMER, University Perpignan Via Domitia, Montpellier, France
5 : Geosciences Paris Saclay, Université Paris-Saclay, CNRS, 91405 Orsay, France
6 : Aix-Marseille Univ, CNRS, CINaM, Campus Luminy, Marseille, France
Source Proceedings Of The National Academy Of Sciences Of The United States Of America (0027-8424) (Proceedings of the National Academy of Sciences), 2022-11 , Vol. 119 , N. 45 , P. e2212616119 (10p.)
DOI 10.1073/pnas.2212616119
WOS© Times Cited 9
Keyword(s) biomineralization, nonclassical crystallization, calcium carbonate, amorphous calcium carbonate

Some mollusc shells are formed from an amorphous calcium carbonate (ACC) compound, which further transforms into a crystalline material. The transformation mechanism is not fully understood but is however crucial to develop bioinspired synthetic biomineralization strategies or accurate marine biomineral proxies for geoscience. The difficulty arises from the simultaneous presence of crystalline and amorphous compounds in the shell, which complicates the selective experimental characterization of the amorphous fraction. Here, we use nanobeam X-ray total scattering together with an approach to separate crystalline and amorphous scattering contributions to obtain the spatially resolved atomic pair distribution function (PDF). We resolve three distinct amorphous calcium carbonate compounds, present in the shell of Pinctada margaritifera and attributed to: interprismatic periostracum, young mineralizing units, and mature mineralizing units. From this, we extract accurate bond parameters by reverse Monte Carlo (RMC) modeling of the PDF. This shows that the three amorphous compounds differ mostly in their Ca–O nearest-neighbor atom pair distance. Further characterization with conventional spectroscopic techniques unveils the presence of Mg in the shell and shows Mg–calcite in the final, crystallized shell. In line with recent literature, we propose that the amorphous-to-crystal transition is mediated by the presence of Mg. The transition occurs through the decomposition of the initial Mg-rich precursor into a second Mg-poor ACC compound before forming a crystal.

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Grünewald Tilman A., Checchia Stefano, Dicko Hamadou, Le Moullac Gilles, Sham Koua Manaarii, Vidal-Dupiol Jeremie, Duboisset Julien, Nouet Julius, Grauby Olivier, Di Michiel Marco, Chamard Virginie (2022). Structure of an amorphous calcium carbonate phase involved in the formation of Pinctada margaritifera shells. Proceedings Of The National Academy Of Sciences Of The United States Of America, 119(45), e2212616119 (10p.). Publisher's official version : , Open Access version :