NMR investigations of biological and synthetic phosphate -based nanocomposites

The study of complex organic, inorganic and composite systems is greatly facilitated by solid state nuclear magnetic resonance (NMR) spectroscopy. This is especially true for materials lacking crystalline long-range order or having low atomic mass contrast, such as amorphous organic materials, which renders other methods such as x-ray diffraction (XRD) and transmission electron microscopy (TEM) incapable of comprehensive characterization. In this dissertation, a variety of oneand two-dimensional (2D) solid-state NMR measurements are applied to investigate the composition and nanometer-scale structure of a variety of organic-inorganic hybrid systems as well as complex inorganic phases. Bone, which is a natural nanocomposite of an inorganic apatitic phosphate and the organic protein collagen, has been studied by H single-resonance, H-P and H-C double-resonance, as well as H-C-P triple-resonance experiments. Analysis of P dephasing by heteronuclear recoupling with dephasing by strong homonuclear interactions of protons (HARDSHIP) has provided information about the size of the apatite nanocrystals. The concentrations of various moieties in the composite, such as the OH, CO3, HPO4, H2O-PO4, and Na in the inorganic apatite, were determined by quantitative spectroscopy via spectral selection of specific chemical moieties. X{H} HARDSHIP NMR was used to prove their incorporation into the apatite nanocrystals. P chemical shift anisotropy (CSA) dephasing experiments as well as H{P} rotational echo double resonance (REDOR) experiments have identified and quantified the hydrogen and phosphate species located at the surface and the interior of the apatite crystal. Strongly bound H2O, as well as a layer of viscous water, is present at the organic-inorganic interface, as proven by H spin-diffusion detected via C and P nuclei. Investigation of the proximity of organic moieties to the apatite surface via C{P} heteronuclear recoupling experiments provide a structural insight of the organic–inorganic interface.