Transformation mechanism of amorphous calcium carbonate into calcite in the sea urchin larval spicule.
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.
Politi
Yael
Y
Department of Structural Biology, Weizmann Institute of Science, Rehovot 76100, Israel.
Metzler
Rebecca A
RA
Abrecht
Mike
M
Gilbert
Benjamin
B
Wilt
Fred H
FH
Sagi
Irit
I
Addadi
Lia
L
Weiner
Steve
S
Gilbert
P U P A
PU
Gilbert
Pupa
P
D000825:Animal Structures / Q000737:chemistry / Q000648:ultrastructure*; D000818:Animals; D002113:Calcification, Physiologic; D002119:Calcium Carbonate / Q000737:chemistry*; D004577:Electron Probe Microanalysis; D007814:Larva / Q000737:chemistry / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D047270:Strongylocentrotus purpuratus / Q000737:chemistry*
D002119:Calcium Carbonate