TY - JOUR

T1 - Colloidal pathways of amorphous calcium carbonate formation lead to distinct water environments and conductivity

AU - Gindele, Maxim B.

AU - Vinod-Kumar, Sanjay

AU - Rochau, Johannes

AU - Boemke, Daniel

AU - Groß, Eduard

AU - Redrouthu, Venkata Subba Rao

AU - Gebauer, Denis

AU - Mathies, Guinevere

N1 - Funding Information: This research was supported by the Deutsche Forschungsgemeinschaft through the Emmy Noether Program awarded to GM (project number 321027114). The authors thank Sarah Busse for providing gold nanoparticles, Thomas Herzog for help with AFM measurements, Stella Kittel for help with ICP-OES measurements, Katharina Nolte for support during TGA-MS-IR experiments, and David McDonogh for help with XRD measurements, and Ilya Kuprov and Albert A. Smith-Penzel for advice and stimulating discussions.

PY - 2024/1/2

Y1 - 2024/1/2

N2 - CaCO3 is the most abundant biomineral and a major constituent of incrustations arising from water hardness. Polycarboxylates play key roles in controlling mineralization. Herein, we present an analytical and spectroscopic study of polycarboxylate-stabilized amorphous CaCO3 (ACC) and its formation via a dense liquid precursor phase (DLP). Polycarboxylates facilitate pronounced, kinetic bicarbonate entrapment in the DLP. Since bicarbonate is destabilized in the solid state, DLP dehydration towards solid ACC necessitates the formation of locally calcium deficient sites, thereby inhibiting nucleation. Magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy of poly-aspartate-stabilized ACC reveals the presence of two distinct environments. The first contains immobile calcium and carbonate ions and structural water molecules, undergoing restricted, anisotropic motion. In the second environment, water molecules undergo slow, but isotropic motion. Indeed, conductive atomic force microscopy (C-AFM) reveals that ACC conducts electrical current, strongly suggesting that the mobile environment pervades the bulk of ACC, with dissolved hydroxide ions constituting the charge carriers. We propose that the distinct environments arise from colloidally stabilized interfaces of DLP nanodroplets, consistent with the pre-nucleation cluster (PNC) pathway.

AB - CaCO3 is the most abundant biomineral and a major constituent of incrustations arising from water hardness. Polycarboxylates play key roles in controlling mineralization. Herein, we present an analytical and spectroscopic study of polycarboxylate-stabilized amorphous CaCO3 (ACC) and its formation via a dense liquid precursor phase (DLP). Polycarboxylates facilitate pronounced, kinetic bicarbonate entrapment in the DLP. Since bicarbonate is destabilized in the solid state, DLP dehydration towards solid ACC necessitates the formation of locally calcium deficient sites, thereby inhibiting nucleation. Magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy of poly-aspartate-stabilized ACC reveals the presence of two distinct environments. The first contains immobile calcium and carbonate ions and structural water molecules, undergoing restricted, anisotropic motion. In the second environment, water molecules undergo slow, but isotropic motion. Indeed, conductive atomic force microscopy (C-AFM) reveals that ACC conducts electrical current, strongly suggesting that the mobile environment pervades the bulk of ACC, with dissolved hydroxide ions constituting the charge carriers. We propose that the distinct environments arise from colloidally stabilized interfaces of DLP nanodroplets, consistent with the pre-nucleation cluster (PNC) pathway.

UR - http://www.scopus.com/inward/record.url?scp=85181243660&partnerID=8YFLogxK

U2 - 10.1038/s41467-023-44381-x

DO - 10.1038/s41467-023-44381-x

M3 - Article

C2 - 38167336

AN - SCOPUS:85181243660

VL - 15

JO - Nature Communications

JF - Nature Communications

SN - 2041-1723

M1 - 80

ER -