Abstract
We examined the mineralization performance of a nacre protein, AP7, within seawater mineralization assays that form aragonite and magnesium calcite. Under these conditions AP7 forms hydrogel particles that vary in size and complexity depending upon ionic conditions. These hydrogels “hijack” the mineralization process by limiting nucleation in bulk solution and promoting nucleation within the hydrogels.
Highlights
We examined the mineralization performance of a nacre protein, AP7, within seawater mineralization assays that form aragonite and magnesium calcite
The equilibrium form of calcium carbonate, calcite, forms from the assembly of nanometer-sized mineral clusters, known as prenucleation clusters, (PNCs)[11,12,13,14,15,16,17] into an amorphous calcium carbonate (ACC) precursor that subsequently transforms into calcite under ambient conditions.[18,19,20,21]. Stabilizing agents, such as MgIJII) ions, can promote aragonite formation instead.[7]. This is clearly seen in invertebrate organisms that live in seawater, where the ratio of MgIJII) to CaIJII) is approximately 5 : 1 and a Mg : Ca ratio >2 is known to promote aragonite and magnesium calcite (MgC) nucleation and inhibit calcite nucleation.[1,7,8,9,10]
MgIJII) : CaIJII)] at pH ∼ 8.0–8.5.7 Note that the actual MgIJII) : CaIJII) ratio in the mollusk nacre matrix is not known at present[7] and our selection of the 5 : 1 MgIJII) : CaIJII) seawater ratio represents an initial starting point for nacre protein – aragonite studies
Summary
We examined the mineralization performance of a nacre protein, AP7, within seawater mineralization assays that form aragonite and magnesium calcite. We conclude the following: since mineral nanoparticles form within AP7 hydrogel particles during this same time period (Fig. 2), and we know that AP7 can assemble mineral nanoparticles in solution,[27] the nucleation of ACC in bulk solution is severely restricted as a result of the recruitment or capture of ion clusters or PNCs by the AP7
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