Polyamines Promote Aragonite Nucleation and Generate Biomimetic Structures

Abstract

Calcium carbonate biomineralization is remarkable for the ability of organisms to produce calcite or aragonite with perfect fidelity, where this is commonly attributed to specific anionic biomacromolecules. However, it is proven difficult to mimic this behavior using synthetic or biogenic anionic organic molecules. Here, it is shown that cationic polyamines ranging from small molecules to large polyelectrolytes can exert exceptional control over calcium carbonate polymorph, promoting aragonite nucleation at extremely low concentrations but suppressing its growth at high concentrations, such that calcite or vaterite form. The aragonite crystals form via particle assembly, giving nanoparticulate structures analogous to biogenic aragonite, and subsequent growth yields stacked aragonite platelets comparable to structures seen in developing nacre. This mechanism of polymorph selectivity is captured in a theoretical model based on these competing nucleation and growth effects and is completely distinct from the activity of magnesium ions, which generate aragonite by inhibiting calcite. Profiting from these contrasting mechanisms, it is then demonstrated that polyamines and magnesium ions can be combined to give unprecedented control over aragonite formation. These results give insight into calcite/aragonite polymorphism and raise the possibility that organisms may exploit both amine-rich organic molecules and magnesium ions in controlling calcium carbonate polymorph.

Formation and properties of spindle-shaped aragonite mesocrystals from Mg-bearing solutions

“…5 and 6) imply that the spindles formed by particle attachment, i.e., in a non-classical crystallization process, as was also suggested by previous authors. 6,12,15,26,35 The formation of mesocrystals via the attachment of crystalline nanoparticles in a crystallographically co-aligned fashion was widely described, e.g., in titanium oxides, 32,48 iron oxides, 34,49,50 and calcium sulphates. 51,51,52 However, the rapid oriented attachment of aragonite nanocrystals is unlikely after their burst nucleation at room temperature, in a weak electrolyte solution, at slightly alkaline pH; moreover, we never observed individual aragonite nanocrystals in our samples.…”

“…[9][10][11][12] These properties have been observed in both natural 13 and synthetic samples, the latter including both abiotically 6,9,11,[14][15][16][17][18][19][20][21][22][23] and biomimetically synthesized aragonite. 12,[24][25][26][27] Whether they formed homogeneously 10 or in the presence of additives (such as polyaspartic and amino acids, 28 solely amino acids, 26 polyamides, 12 or swelling clay minerals 11 ), the mesocrystalline characters of aragonite aggregates were similar. Despite their widespread occurrence, the formation mechanism of aragonite spindles is not clearly understood, even though such an understanding could shed light on important aspects of the formation of mesocrystals.…”

“…The authors suggested that the formation of the spindles was initiated by the aggregation of ACC nanoparticles, and the crystallization of aragonite started within the amorphous aggregate from independent centres, with the amorphous to crystalline transformation taking place in solid state. Huang et al 26 and Nahi et al 12 studied the effect of amino acids and the combined effects of polyamines and dissolved Mg 2+ ions on the formation of aragonite. Both studies reported similar aggregates of aragonite nanocrystals with a typical spindle-shaped external morphology, and observed the presence of small ACC globules on the surfaces or even within the cavities of aragonite aggregates.…”

Silk Protein-Mediated Biomineralization: From Bioinspired Strategies and Advanced Functions to Biomedical Applications

“…Mollusk shells are predominantly composed of CaCO 3 . In recent years, the in vitro biomimetic mineralization process of calcium carbonate has received great attention from researchers. − Studies have shown that silk proteins can also influence the morphology of CaCO 3 crystals. Cheng et al utilized recombinant SF (RSF) as a template to produce a hollow rice-like CaCO 3 /RSF hybrid.…”

Functional mimicry of sea urchin biomineralization proteins with CaCO3-binding peptides selected by phage display

“…aminefunctionalized) polymer additives and their role is increasingly being recognized. [38][39][40] In bioinspired polymer-mediated mineralization, synthetic polyelectrolytes have been shown to exert multiple effects. Examples include the stabilization of transient amorphous precursors of hydrated colloids even in the presence of minute amounts of organic molecules, 41 promotion of the formation and stabilization of an amorphous precursor phase by suppressing crystalline growth, 42 altering the pH value of the reaction solution, 41 or affecting the composition and water content of the mineral phase, resulting in a manifold of different crystal morphologies.…”