Solid-State NMR Studies of Organic–Inorganic Interactions in Biomineralization
Date Issued
2012
Date
2012
Author(s)
Wen-Tin Tsai, Tim
Abstract
Biomineralization refers to a biological process describing the formation of highly ordered inorganic materials with hierarchical structures in living organisms. Because a biomineralization process typically involves the interfacial interactions of two dissimilar nanophases, it is extremely challenging to obtain the structural information of such organic/inorganic hybrid systems at the molecular level. Therefore, the mechanisms in biomineralization remain largely unknown. In this work, we have developed several solid-state NMR techniques, including homonuclear dipole–dipole recoupling, heteronuclear dipole–dipole recoupling, and torsion angle determination (Chapter 3). These techniques are subsequently employed to extract valuable information, that would be difficult to obtain otherwise, in specific in vitro model systems of calcium phosphate
The first model system describes a phase transformation pathway of calcium phosphate in the presence of glutamic acid under hydrothermal condition (Chapter 4.1). On the basis of experimental data, it is suggested that the transformation is via the dissolution-reprecipitation pathway, which is facilitated in the presence of glutamic acid. This effect is rationalized by the disruption of the water layer that bound on the crystal surface. Chapter 4.2 & 4.3 have utilized solid-state NMR spectroscopy to resolve the molecular structure of octacalcium phosphate incorporated with succinate (OCPS), which is hypothesized as an important model compound of the mineral granules found in mitochondria. Based on the fact that OCPS is more stable than octacalcium phosphate (OCP) under hydrolysis conditions, it is concluded that the hydration layer of OCP is playing the key role in the structural transformation of OCP. Chapter 4.4 discusses the structural dynamics near the N-terminus fragment of statherin (SN15) upon binding on HAp, which are extracted from the spectral analyses of two-dimensional 13C–13C correlation spectra. It has been found that the residue K6 is very close to the mineral surface and its molecular motion, if any, is relatively insensitive to the hydration level of the sample. Consequently, K6 is most likely one of the anchoring sites for SN15 bound on HAp. This result infers that positive charges of polypeptides may also contribute to the peptide–mineral recognition process.
Subjects
Biomineralization
Solid-state NMR
Calcium phosphate
Dipolar recoupling
Hydroxyapatite
Octacalcium phosphate
HAp
OCP
MAS
Water layer ?
Type
thesis
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