Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 105, Issue 45, Pages 17362-17366Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0806604105
Keywords
biomineralization; Ca L-edge X-ray absorption near-edge structure; XANES; X-PEEM; X-ray photoelectron emission spectromicroscopy
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Funding
- National Science Foundation [CHEDMR-0613972, DMR-0537588]
- Department of Energy [DE-FG02-07ER15899]
- Israel Ministry of Science [777]
- National Institutes of Health
- U.S. Department of Energy (DOE) [DE-FG02-07ER15899] Funding Source: U.S. Department of Energy (DOE)
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Sea urchin larval spicules transform amorphous calcium carbonate (ACC) into calcite single crystals. The mechanism of transformation is enigmatic: the transforming spicule displays both amorphous and crystalline properties, with no defined crystallization front. Here, we use X-ray photoelectron emission spectromicroscopy with probing size of 40-200 nm. We resolve 3 distinct mineral phases: An initial short-lived, presumably hydrated ACC phase, followed by an intermediate transient form of ACC, and finally the biogenic crystalline calcite phase. The amorphous and crystalline phases are juxtaposed, often appearing in adjacent sites at a scale of tens of nanometers. We propose that the amorphous-crystal transformation propagates in a tortuous path through preexisting 40- to 100-nm amorphous units, via a secondary nucleation mechanism.
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