Chemical structure analyses of phosphorylated chitosan

Area of Science:

• Biomaterials Science
• Polymer Chemistry
• Organic Synthesis

Background:

• Chitosan modification generates novel bio-functional materials with tailored properties.
• Phosphorylated chitosan is of recent interest, with established synthesis routes.
• Previous studies suggest hydroxyl groups are the primary substitution sites in chitosan phosphorylation.

Purpose of the Study:

• To systematically investigate and compare the chemical structures of phosphorylated chitosan synthesized via three distinct reaction routes.
• To elucidate the substitution sites (hydroxyl vs. amino groups) under different phosphorylation conditions.

Main Methods:

• Synthesis of phosphorylated chitosan using three different reaction routes: H3PO4/urea, H3PO4/Et3PO4/P2O5, and P2O5/CH3SO3H.
• Comprehensive structural characterization using infrared (IR) spectroscopy, X-ray photoelectron (XPS) spectroscopy, and Carbon-13 Nuclear Magnetic Resonance ((13)C NMR) spectroscopy.

Main Results:

• Phosphorylation using H3PO4/urea and H3PO4/Et3PO4/P2O5 resulted in substitution at the amino groups of chitosan.
• The P2O5/CH3SO3H route led to phosphorylation of the C-6 hydroxyl groups, with amino groups shielded via ionic binding.
• Distinct chemical structures were identified for phosphorylated chitosan based on the chosen synthesis pathway.

Conclusions:

• The reaction route critically determines the site of phosphorylation in chitosan.
• Amino groups are susceptible to substitution under certain phosphorylation conditions.
• The P2O5/CH3SO3H method offers a route to selectively phosphorylate hydroxyl groups, yielding structurally unique phosphorylated chitosan.