DFT Optimization of Isolated Molecular Chain Sheet Models Constituting Native Cellulose Crystal Structures.

Area of Science:

• Materials Science
• Computational Chemistry
• Biochemistry

Background:

• Cellulose, a highly crystalline biopolymer, is abundant naturally.
• Understanding cellulose allomorphs (Iα and Iβ) is crucial for elucidating its chain packing schemes.
• Theoretical investigations are key to exploring cellulose crystal structures.

Purpose of the Study:

• To systematically optimize cellulose chain sheet models from cellulose Iα and Iβ crystals.
• To investigate the influence of computational methods on cellulose structure.
• To elucidate cellulose chain packing schemes and intermolecular interactions.

Main Methods:

• Density Functional Theory (DFT) was employed for structure optimization.
• Cellulose chain packing structures were partitioned into sheet models (flat and stacked).
• Various basis sets (e.g., 6-31+G(d,p)) and DFT functionals (e.g., CAM-B3LYP, M06-2X) were tested.

Main Results:

• Flat chain sheet models of cellulose Iα (110) and Iβ (100) planes exhibited a right-handed twist, enhanced by diffuse basis functions.
• Intermolecular interactions were more stable with CAM-B3LYP and M06-2X functionals.
• Stacked chain sheet models showed varied results, with some losing sheet integrity.

Conclusions:

• The study provides insights into the stability and structural characteristics of cellulose sheet models.
• Computational methods significantly influence the observed twists and stability of cellulose structures.
• DFT optimization aids in understanding the fundamental packing of cellulose chains in native allomorphs.