The Initial Stages of Template-Controlled CaCO ₃ Formation Revealed by Cryo-TEM

Abstract

Biogenic calcium carbonate forms the inorganic component of seashells, otoliths, and many marine skeletons, and its formation is directed by an ordered template of macromolecules. Classical nucleation theory considers crystal formation to occur from a critical nucleus formed by the assembly of ions from solution. Using cryotransmission electron microscopy, we found that template-directed calcium carbonate formation starts with the formation of prenucleation clusters. Their aggregation leads to the nucleation of amorphous nanoparticles in solution. These nanoparticles assemble at the template and, after reaching a critical size, develop dynamic crystalline domains, one of which is selectively stabilized by the template. Our findings have implications for template-directed mineral formation in biological as well as in synthetic systems.

Reconciling disparate views of template-directed nucleation through measurement of calcite nucleation kinetics and binding energies

“…4). Consequently, despite the recent reports of prenucleation clusters (41)(42)(43), liquid-liquid separation (44)(45)(46), and multiphase aggregationbased pathways of calcite formation (41,42,47) in bulk solutions, the results presented here provide strong evidence that the classical theory of nucleation provides a good description of calcite formation on ionized surfaces and that interfacial energy is a useful concept even when critical nuclei are in the nanometer range. Calculations of γ assume rhombohedral nuclei.…”

Rice-like hollow nano-CaCO 3 synthesis

“…Once the CO 2 bubble was introduced into the Ca(OH) 2 solution, it will dissolve and its concentration increases around the bubbles, which reacts with the available Ca þ þ ions in the solution. The newly produced CaCO 3 particles would be CaCO 3 crystallite particles [7,10,37] of about 40 nm as we calculated from the (104) peak of the XRD pattern of the CaCO 3 particles using the Sheerer Equation [38]. As shown in Fig.…”

“…Therefore, production of nano calcite can be achieved by recrystallization; such that the mineral CaCO 3 is converted to calcium oxide (CaO) by calcination, hydrated to calcium hydroxide (Ca(OH) 2 ) and recrystallize by carbon dioxide (CO 2 ) [3][4][5][6]. Obtaining CaCO 3 particles in nano sizes with homogeneous size distribution and different morphologies is difficult due to agglomeration of newly synthesized clusters [7][8][9][10], which is related to the surface potential of the colloidal CaCO 3 particles [11][12][13][14]. Also, there is a huge effort to produce hollow nano-CaCO 3 particles with homogenous size distribution and different morphologies, which is rare in the literature.…”

How does an amorphous surface influence molecular binding? – ovocleidin-17 and amorphous calcium carbonate

“…ACC exists in two different phases 7 : a stable phase with a high level of water content (∼50% or greater) which is found in living organisms 8 ; and a transient phase (with a low level of water content) that undergoes a rapid transition to calcite or another CaCO 3 polymorph. Debate continues in the literature as to the role of ACC phases in the crystallisation process with observations of crystallisation occurring within the amorphous phase 5 or potentially at the ACC/water interface while in other cases the ACC may have no major controlling function 9 . Calcite growth is expected to occur in regions with higher local concentrations of Ca and CO 3 ions but the major debate remains concerned with the structure/phase of this region.…”