Solid‐state nuclear magnetic resonance is a promising technique to probe bone mineralization and interaction of collagen protein in the native state. However, many of the developments are hampered due to the low sensitivity of the technique. In this article, we report solid‐state nuclear magnetic resonance (NMR) experiments using the newly developed BioSolids CryoProbe™ to access its applicability for elucidating the atomic‐level structural details of collagen protein in native state inside the bone. We report here approximately a fourfold sensitivity enhancement in the natural abundance 13C spectrum compared with the room temperature conventional solid‐state NMR probe. With the advantage of sensitivity enhancement, we have been able to perform natural abundance 15N cross‐polarization magic angle spinning (CPMAS) and two‐dimensional (2D) 1H–13C heteronuclear correlation (HETCOR) experiments of native collagen within a reasonable timeframe. Due to high sensitivity, 2D 1H/13C HETCOR experiments have helped in detecting several short and long‐range interactions of native collagen assembly, thus significantly expanding the scope of the method to such challenging biomaterials.
Bone is a dynamic
tissue composed of organic proteins (mainly type
I collagen), inorganic components (hydroxyapatite), lipids, and water
that undergoes a continuous rebuilding process over the lifespan of
human beings. Bone mineral is mainly composed of a crystalline apatitic
core surrounded by an amorphous surface layer. The supramolecular
arrangement of different constituents gives rise to its unique mechanical
properties, which become altered in various bone-related disease conditions.
Many of the interactions among the different components are poorly
understood. Recently, solid-state nuclear magnetic resonance (ssNMR)
has become a popular spectroscopic tool for studying bone. In this
article, we present a study probing the interaction of water molecules
with amorphous and crystalline parts of the bone mineral through
31
P ssNMR relaxation parameters (
T
1
and
T
2
) and dynamics (correlation time).
The method was developed to selectively measure the
31
P
NMR relaxation parameters and dynamics of the crystalline apatitic
core and the amorphous surface layer of the bone mineral. The measured
31
P correlation times (in the range of 10
–6
–10
–7
s) indicated the different dynamic
behaviors of both the mineral components. Additionally, we observed
that dehydration affected the apatitic core region more significantly,
while H–D exchange showed changes in the amorphous surface
layer to a greater extent. Overall, the present work provides a significant
understanding of the relaxation and dynamics of bone mineral components
inside the bone matrix.
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