Atomic Resolution of Cotton Cellulose Structure Enabled by Dynamic Nuclear Polarization Solid-State NMR

Area of Science:

• Biomaterials Science
• Solid-State Chemistry
• Polymer Science

Background:

• Conventional methods struggle with low-resolution structural analysis of cellulose, particularly in native cell walls or low-crystallinity samples.
• Isotope-labeled solid-state NMR offers insights but is impractical for unlabeled cellulose due to sensitivity limitations.

Purpose of the Study:

• To investigate the molecular structure of unlabeled cotton cellulose without isotope labeling.
• To develop a widely applicable strategy for analyzing cellulose-rich materials.
• To understand structural changes in cellulose during mechanical processing.

Main Methods:

• Utilized natural abundance 13C-13C 2D correlation solid-state NMR spectroscopy.
• Employed dynamic nuclear polarization (DNP) to enhance sensitivity for unlabeled samples.
• Combined NMR data with statistical analysis of chemical shifts and literature values.

Main Results:

• Achieved atomic resolution insights into unlabeled cotton cellulose structure.
• Monitored the loss of Iα and Iβ allomorphs and the formation of a novel structure during ball-milling.
• Identified partial order within previously considered 'disordered' cellulose domains.

Conclusions:

• Demonstrated the importance of large crystallite size for maintaining cellulose Iα and Iβ allomorph structures.
• Presented a sensitive and broadly applicable NMR strategy for analyzing unlabeled cellulose-rich materials.
• Provided high-resolution structural insights into cotton cellulose, complementing previous studies.