Molecular dynamics of polycrystalline cellobiose studied by solid-state NMR

Area of Science:

• Solid-state Nuclear Magnetic Resonance (NMR) Spectroscopy
• Materials Science
• Biophysics

Background:

• Cellobiose is a disaccharide crucial for understanding carbohydrate structure and dynamics.
• Investigating molecular motions provides insights into material properties and biological functions.
• Polycrystalline materials present complex dynamics due to varied molecular environments.

Purpose of the Study:

• To elucidate the molecular dynamics of polycrystalline cellobiose.
• To characterize the motion of hydroxyl and methylene groups.
• To assess the crystalline structure and identify potential polymorphs.

Main Methods:

• Proton spin-lattice relaxation times (T1 and T1rho) were measured over a temperature range of 120-380 K.
• Second moment (M2) analyses were performed on protonated and deuterated cellobiose.
• Carbon-13 Cross-Polarization Magic Angle Spinning (13C CPMAS) NMR was employed.

Main Results:

• Hydroxyl group motions dominated T1 relaxation (150-380 K) and T1rho relaxation (120-300 K), indicating a distribution of dynamics.
• Methylene group motion was observed around 350 K with a distinct activation energy.
• Analysis suggested discrepancies with existing X-ray data regarding inter-proton distances.
• 13C CPMAS spectra revealed the presence of a second crystalline form in deuterated cellobiose.

Conclusions:

• The study provides detailed insights into the complex molecular motions within polycrystalline cellobiose.
• NMR relaxation data offer a complementary perspective to crystallographic studies, highlighting potential structural inaccuracies.
• The identification of a second crystalline form warrants further investigation into cellobiose polymorphism.