Nucleation and growth of CaCO3 mediated by the egg-white protein ovalbumin: a time-resolved in situ study using small-angle neutron scattering.
Mineralization of calcium carbonate in aqueous solutions starting from its initiation was studied by time-resolved small-angle neutron scattering (SANS). SANS revealed that homogeneous crystallization of CaCO 3 involves an initial formation of thin plate-shaped nuclei which subsequently reassemble to 3-dimensional particles, first of fractal and finally of compact structure. The presence of the egg-white protein ovalbumin leads to a different progression of mineralization through several stages; the first step represents amorphous CaCO 3, whereas the other phases are crystalline. The formation and dissolution of the amorphous phase is accompanied by Ca (2+)-mediated unfolding and cross-linking of about 50 protein monomers showing the characteristic scattering of linear chains with a large statistical segment length. The protein complexes act as nucleation centers for the amorphous phase because of their enrichment by Ca (2+) ions. SANS revealed the sequential formation of CaCO 3 starting from the amorphous phase and the subsequent formation of the crystalline polymorphs vaterite and aragonite. This formation from less dense to more dense polymorphs follows the Ostwald-Volmer rule.
Pipich
Vitaliy
V
Institute of Solid State Research of the Helmholtz Research Center Jülich GmbH, D-52425 Jülich, Germany.
Balz
Mathias
M
Wolf
Stephan E
SE
Tremel
Wolfgang
W
Schwahn
Dietmar
D
D002119:Calcium Carbonate / Q000737:chemistry*; D002122:Calcium Chloride / Q000737:chemistry; D003460:Crystallization; D033363:Neutron Diffraction; D010047:Ovalbumin / Q000737:chemistry*; D011487:Protein Conformation; D017510:Protein Folding; D053838:Scattering, Small Angle; D014867:Water / Q000737:chemistry
D014867:Water; D010047:Ovalbumin; D002119:Calcium Carbonate; D002122:Calcium Chloride