NMR of Biopolymer-Apatite Composites: Developing a Model of the Molecular Structure of the Mineral-Matrix Interface in Calcium Phosphate Biomaterials

Abstract

Nanoparticulate hydroxyapatites (HAps) reproducing some of the subnanometre length scale intermolecular interactions characteristic of hard tissue have been prepared for nuclear magnetic resonance (NMR) structural elucidation. HAps were precipitated at physiological pH and temperature from dilute aqueous solutions, in the presence of acidic polysaccharides (chondroitin sulfate, dermatan sulfate, hyaluronic acid, dextran sulfate, polygalacturonic acid), and of hydrophilic poly aminoacids (poly-l-glutamate, poly-l-asparagine, poly-l-lysine). The HAp resembles that of bone with respect to its 31P NMR properties, broad reflections in X-ray powder diffraction, and the coexistence of an ordered crystalline core, surrounded by a less ordered surface containing water and hydrogen phosphate. 13C{31P} rotational echo double resonance (REDOR) NMR, which probes carbon−phosphorus proximities below ca. 1 nm, shows that all the HAps are molecular composites in which each biopolymer forms intimate intermolecular associations with mineral ions. REDOR effects between mineral phosphorus and ring carbons of the polysaccharides, and the side-chain terminal carboxylate and amide carbonyls of poly-l-glutamate and poly-l-asparagine, and the side chain carbons of poly-l-lysine, closely recapitulate those seen in native bone. Such model HAp−biopolymer composites will prove useful in studies of the role of biopolymers in biomineralization, and in high resolution biomineral structure elucidation.

Enzyme immobilisation on poly-l-lysine-containing calcium phosphate particles for highly sensitive glucose detection

“…Bradley et al prepared the hydroxyapatite composited with polysaccharides (such as chondroitin sulfate and polygalacturonic acid) or poly amino acid (like poly-L-asparagine and poly-L-lysine). 30 Gao et al reported that poly-3-lysine was introduced to the surface of bacterial cellulose nanobers via crosslinking for bone-like apatite deposition, and its nanocomposites were expected to be adapted for applications in bone tissue engineering. 31 Ding et al synthesised poly-L-lysine/HAp/carbon nanotube hybrid biocomposite scaffolds for antibody immobilisation.…”

Depletion of water molecules during ethanol wet-bonding with etch and rinse dental adhesives

“…Recent work on the mineral-matrix interface in calcium phosphate biomaterials shows how the NMR technique is versatile to unravel the complex intermolecular interactions in biological materials [17,18]. Proton NMR studies of collagen fibrils have led to recognize several types or water molecules in collagen.…”

Characterization of the phosphatic mineral of the barnacle Ibla cumingi at atomic level by solid-state nuclear magnetic resonance: comparison with other phosphatic biominerals

“…All experiments were performed using standard SSNMR methodology on a Bruker 9.4 T Avance-400 spectrometer at frequencies of 400.1 ( 1 H), 161.9 ( 31 P) and 100.5 MHz ( 13 C) and at a magic angle spinning (MAS) rate of 12.5 kHz. Experimental parameters were essentially as previously described [23].…”