Abstract
Organisms use inorganic ions and macromolecules to regulate crystallization from amorphous precursors, endowing natural biominerals with complex morphologies and enhanced properties. The mechanisms by which modifiers enable these shape-preserving transformations are poorly understood. We used in situ liquid-phase transmission electron microscopy to follow the evolution from amorphous calcium carbonate to calcite in the presence of additives. A combination of contrast analysis and infrared spectroscopy shows that Mg ions, which are widely present in seawater and biological fluids, alter the transformation pathway in a concentration-dependent manner. The ions bring excess (structural) water into the amorphous bulk so that a direct transformation is triggered by dehydration in the absence of morphological changes. Molecular dynamics simulations suggest Mg-incorporated water induces structural fluctuations, allowing transformation without the need to nucleate a separate crystal. Thus, the obtained calcite retains the original morphology of the amorphous state, biomimetically achieving the morphological control of crystals seen in biominerals.
Highlights
| | | | crystallization biomineralization calcium carbonate magnesium morphology transformation pathways and the evolution of particle composition are largely unknown
The findings reported above reveal that, while for pure solutions and most additives investigated here, amorphous CaCO3 (ACC) transformation into calcite is dominated by dissolution–reprecipitation, doping of Mg2+ into ACC increases the water content, weakens the ionicbinding network, and leads to a direct transformation in the absence of morphological changes (Fig. 6E)
The results show that direct transformation of ACC is a condensation process accompanied by dehydration
Summary
| | | | crystallization biomineralization calcium carbonate magnesium morphology transformation pathways and the evolution of particle composition are largely unknown. Biomineral formation starting from amorphous CaCO3 (ACC) results in diverse morphologies including those of sea urchin spicules and teeth [6], nacre layers [7], and crustacean exoskeletons [8], which are strikingly distinct from the growth shapes of abiotic CaCO3 crystals In these systems, amorphous nanoparticles are deposited within a vesicular space onto the surface of the growing biomineral where they transform to a crystalline material that is shape-preserving with the original ACC precursor and exhibits a microstructure reminiscent of aggregated particles [9, 10]. This in-depth understanding provides an alternative strategy for manufacturing crystals with arbitrary morphologies by design
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