Solid state NMR and X-ray diffraction studies of alpha-D-galacturonic acid monohydrate

Area of Science:

• Solid-state chemistry
• Molecular dynamics
• Crystallography

Background:

• Alpha-D-galacturonic acid monohydrate is a key component in plant cell walls.
• Understanding its solid-state properties is crucial for material science applications.
• Previous studies have not fully elucidated its molecular dynamics and hydrogen bonding network.

Purpose of the Study:

• To investigate the molecular dynamics of crystalline alpha-D-galacturonic acid monohydrate.
• To characterize its hydrogen bonding network and crystal structure.
• To correlate molecular motion with structural properties.

Main Methods:

• 13C Cross-Polarization Magic-Angle Spinning (CPMAS) Nuclear Magnetic Resonance (NMR) spectroscopy.
• Measurement of 13C spin-lattice relaxation in the rotating frame (T1rho).
• X-ray crystallography at ambient temperature and 150 K.

Main Results:

• Limited molecular motions were detected in the low frequency range (< 10(4) Hz).
• 13C relaxation times (T1rho) and chemical shift anisotropy properties indicated restricted dynamics.
• X-ray analysis confirmed a chair-shaped pyranose ring conformation.
• An extensive hydrogen-bonded lattice was observed, linking acid and water molecules via O-H groups.

Conclusions:

• The crystalline structure of alpha-D-galacturonic acid monohydrate is characterized by a stable pyranose ring and a robust hydrogen bond network.
• Molecular dynamics are significantly restricted in the solid state.
• NMR and X-ray crystallography provide complementary insights into the structural and dynamic properties.