(558b) A Highly-Tunable Coarse-Grained Model of Chitosan for Applications in Water Treatment

Chitosan is a versatile biopolymer that has gained the attention of researchers in fields ranging from drug delivery and wound healing to water purification and oil spill remediation.  It consists of a random sequence of glucosamine (GlcN) and N-acetylglucosamine (GlcNAc) monomers. The solution behavior of chitosan has been shown to depend strongly on both the solution pH and chitosan degree of acetylation (defined as the ratio of GlcNAc monomers to the total number of monomers).  GlcN monomers contain a primary amine that becomes protonated in solution, causing electrostatic repulsion between monomers.  In contrast, GlcNAc monomers contain acetyl groups that introduce hydrophobic and hydrogen bonding interactions, leading to self-association between monomers.  The amine group on GlcN can also be hydrophobically-modified to further influence its behavior in solution.  We have developed a coarse-grained model of chitosan that can account for the experimental conditions that are relevant to applications in water treatment and oil spill remediation.  Our results show that at low degrees of acetylation hydrophobically-modified chitosan can bridge the gap between oil droplets, leading to the formation of an oil/chitosan gel that could be physically removed from water.  At higher degrees of acetylation the chitosan backbone is less extended (due to less cationic repulsion between monomers), making it well suited for use in flocculating oil droplets in solution, potentially leading to more effective water filtration.  Our model allows easy adjustment of the chitosan degree of acetylation and solution pH, and is currently being used to explore the design of chitosan architectures for various water treatment applications.