Insights into hydrogen bonding and stacking interactions in cellulose.

Area of Science:

• Computational chemistry
• Materials science
• Biopolymer physics

Background:

• Cellulose, a key biopolymer, exists in various crystalline forms (allomorphs) with distinct properties.
• Understanding the intermolecular forces governing cellulose allomorph stability is crucial for materials applications.
• Cellulose I(β) and cellulose III(I) are important allomorphs with differing structural and energetic characteristics.

Purpose of the Study:

• To investigate and quantify hydrogen bonding (H-bonding) and stacking interactions in cellulose I(β) and cellulose III(I) crystalline allomorphs.
• To compare the contributions of intrasheet and intersheet interactions to the stability of these cellulose structures.
• To elucidate the role of nonconventional CH···O H-bonding and analyze chemical reactivity differences.

Main Methods:

• Quantum chemical calculations using hybrid density functional theory (M06-2X/6-31+G(d,p)).
• Modeling of cellulose crystalline cores using six cellobiose units (three layers, two chains/layer).
• Application of the Theory of Atoms-in-Molecules (AIM) for interaction characterization and quantification.
• Molecular dynamics simulations for generating reference structures of hydrated cellulose fibrils.
• Calculation of molecular electrostatic potential maps.

Main Results:

• Individual H-bonds are stronger in cellulose I(β) than in cellulose III(I).
• Cellulose III(I) exhibits greater stabilization from its highly cooperative H-bonding network.
• Cooperative stacking interactions significantly contribute to the stabilization of cellulose I(β).
• AIM analyses confirm the importance of nonconventional CH···O H-bonds in cellulose assemblies.
• Molecular electrostatic potential maps reveal distinct chemical reactivity patterns between the allomorphs.

Conclusions:

• The stability of cellulose allomorphs is governed by a complex interplay of H-bonding and stacking interactions.
• Cooperative effects in H-bonding networks play a critical role in the overall stabilization of cellulose structures.
• Differences in interaction strengths and networks lead to distinct properties and reactivity in cellulose I(β) and III(I).