An accurate coarse-grained model for chitosan polysaccharides in aqueous solution

Area of Science:

• Computational chemistry and biophysics
• Polymer science
• Materials science

Background:

• Molecular conformations and interactions in solution are crucial but often experimentally inaccessible.
• Understanding the behavior of long polysaccharides in aqueous solution requires advanced modeling techniques.
• Physico-chemical conditions like pH and ionic strength significantly impact polysaccharide properties.

Purpose of the Study:

• To develop an efficient and precise coarse-grained model for simulating long polysaccharides in aqueous solution.
• To investigate the influence of pH and ionic strength on polysaccharide structure and properties.
• To explore the effects of polymer length, degree, and pattern of deacetylation on chitosan behavior.

Main Methods:

• Construction of a coarse-grained model based on all-atom simulations of small saccharides.
• Metadynamics sampling of dihedral angles in glycosidic links to capture flexibility.
• Validation against experimental data for chitosan molecules with varying degrees of deacetylation.

Main Results:

• The model closely reproduces experimental data for chitosan solutions.
• Subtle differences in free energy maps of glycosidic links significantly affect measurable polymer properties.
• Free energy maps are updated dynamically based on the charge of titratable monomers.
• Microscopic and mesoscopic structural properties of chitosan were characterized across various solvent conditions.

Conclusions:

• The developed coarse-grained model provides accurate insights into polysaccharide behavior in solution.
• The study highlights the critical role of glycosidic link flexibility and monomer charge in determining polymer properties.
• This model serves as a valuable tool for predicting and understanding the behavior of complex polysaccharides.