Role of Ovalbumin in the Stabilization of Metastable Vaterite in Calcium Carbonate Biomineralization

Abstract

The role of proteins in biomineralization has been examined in this work by studying the effect of ovalbumin on the stabilization of metastable CaCO(3) phases. In the absence of ovalbumin, the mixing of Na(2)CO(3) with CaCl(2) in an aqueous solution led to the formation of metastable phases that swiftly transformed into stable calcite crystals within 4 h under the experimental conditions. However, ovalbumin was found to favor the formation and stabilization of spherical vaterites, and the effect was concentration dependent. In the presence of 2 g/L ovalbumin, for example, vaterite microspheres with diameters ranging from 0.9 to 3.0 mum, composed of much smaller nanosized particles, were produced and stabilized even after 24 h following the initial mixing. In addition, the influence of ovalbumin on the CaCO(3) mineralization process from the very beginning was carefully examined. Both amorphous calcium carbonate (ACC) and vaterite were favored with ovalbumin present, but the ACC phase formed predominantly at the initial stage of mixing followed by the vaterite formation. Vaterite could then be embedded further in the mineralization process and become stabilized many hours afterward. The stabilizing effect of ovalbumin could arise from the strong binding between carboxylate groups of ovalbumin and the calcium ions on the CaCO(3) surface, preventing the metastable CaCO(3) from transformation via dissolution-recrystallization processes. The strong ovalbumin adsorption on vaterite microspheres was revealed from transmission electron microscopy imaging and thermogravimetric analysis, thereby providing useful evidence to support the proposed stabilizing mechanism.

Quantitative proteomics provides new insights into chicken eggshell matrix protein functions during the primary events of mineralisation and the active calcification phase

“…The calcium cations are the starting points for the subsequent formation of ACC nuclei which then undergo a series of phase transitions to the stable crystalline polymorphs [64]. The ability of OVAL to stabilise unstable calcium carbonate phases was further confirmed using in vitro experiments [65,66]. In our study, we observed that ovalbumin, which is overabundant at 7h p.o., is a major protein with high emPAI values at all stages (5 th , 6 th , 2 nd and 7 th most abundant protein at 5, 6 and 7 and 16 hours p.o.…”

“…calcium carbonate formation and ACC stabilisation has been investigated [63][64][65][66]. Calcium is bound by ovalbumin and this accumulation creates a nucleation centre for the minerals [64].…”

Investigating vaterite phase stabilisation by a tetrazole molecule during calcium carbonate crystallisation

“…The mechanism of vaterite stabilisation, therefore, appears to be due to the greater adsorption of the tetrazole after formation of the vaterite and this adsorption impedes its dissolution, thereby hindering any transformation to calcite. While this is sometimes used to explain the impact of large protein molecules on vaterite stabilisation [23,24], templating effects tend to be cited more often [25][26][27][28][29][30]. Our hypothesis, however, is supported by both the visual appearance of the vaterite after 14 days in the presence of the tetrazole and by the adsorption of the tetrazole onto the vaterite surface from DRIFT analysis.…”

Symmetry-breaking assembled porous calcite microspheres and their multiple dental applications

“…However, since vaterite is rather unstable in a humid environment, this porous CaCO3 will easily convert to non-porous rhombohedral calcite overnight [16]. Recently, several modification approaches, such as layer-by-layer electrostatic adsorption, double hydrophilic block copolymers coating, and nanodots embedding, have been attempted to stabilize vaterite MPs [14,[17][18][19]. The above foreign impurities can inhibit the nucleation of calcite from metastable vaterite phase.…”