Phase transitions in biogenic amorphous calcium carbonate

Yutao Gong(University of Wisconsin–Madison), Christopher E. Killian(University of Wisconsin–Madison), Ian C. Olson(University of Wisconsin–Madison), N. Appathurai(University of Wisconsin–Madison), Audra L. Amasino(University of Wisconsin–Madison), Michael C. Martin(Lawrence Berkeley National Laboratory), Liam J. Holt(University of California, Berkeley), Fred H. Wilt(University of California, Berkeley), Benjamin Gilbert(University of Wisconsin–Madison)
Proceedings of the National Academy of Sciences
April 4, 2012
10.1073/pnas.1118085109
Cited by 295Open Access
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Abstract

Crystalline biominerals do not resemble faceted crystals. Current explanations for this property involve formation via amorphous phases. Using X-ray absorption near-edge structure (XANES) spectroscopy and photoelectron emission microscopy (PEEM), here we examine forming spicules in embryos of Strongylocentrotus purpuratus sea urchins, and observe a sequence of three mineral phases: hydrated amorphous calcium carbonate (ACC · H(2)O) → dehydrated amorphous calcium carbonate (ACC) → calcite. Unexpectedly, we find ACC · H(2)O-rich nanoparticles that persist after the surrounding mineral has dehydrated and crystallized. Protein matrix components occluded within the mineral must inhibit ACC · H(2)O dehydration. We devised an in vitro, also using XANES-PEEM, assay to identify spicule proteins that may play a role in stabilizing various mineral phases, and found that the most abundant occluded matrix protein in the sea urchin spicules, SM50, stabilizes ACC · H(2)O in vitro.

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