Evaluations of calcium phosphate nucleation pathways and kinetics help us understand the biogeochemical cycle of phosphorus in many natural environments and physiological systems. However, due to the lack of in situ analytical tools, calcium phosphate nucleation and crystallization, including the amorphous phase formation in its initial stage, have not been fully explored. Moreover, their evaluation is even more complicated when collagenous and non-collagenous proteins are closely associated with calcium phosphate minerals. Utilizing in situ small angle X-ray scattering, we studied the early stages of calcium phosphate nucleation and growth within fibrillar collagen matrices in the presence and absence of polyaspartic acid. We also used ex situ electron microscopies and Raman spectroscopy to observe morphological changes after nucleation. We found that the pathways of calcium phosphate nucleation, in addition to its kinetics, were strongly influenced by the presence of polyaspartic acid, and these kinetical and morphological differences stemmed from the different nucleation sites in collagen matrices. In other words, whether nucleation occurs within the nanoscale gap channels in collagen fibrils or in extrafibrillar spaces within the matrices will determine the kinetics and shapes of the newly formed calcium phosphate. Our findings indicate that nucleation sites are determined by the interfacial relationships between collagen fibrils and calcium phosphate nucleus surfaces. These nucleation sites and consequent interfacial relationships can also be strongly influenced by the presence of organic compounds, such as non-collagenous proteins and polyaspartic acid. This study provides insights into the behaviors of phosphate minerals in biological systems as well as aqueous environments, where various organic compounds exist. This information is also essential to maintain a more sustainable global phosphorus cycle. Note: Recipient of the Student Travel Award

Influence of biological interfaces on nucleation pathways and kinetics of calcium phosphate minerals

251st National Meeting (2016)

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