Synthesis, characterization and solution behaviour of oxidized pullulan.

Area of Science:

• Polymer Chemistry
• Carbohydrate Chemistry
• Materials Science

Background:

• Pullulan is a non-ionic, water-soluble polysaccharide with diverse applications.
• Controlled chemical modification of polysaccharides is crucial for tailoring their properties.
• Oxidation is a common method to introduce functional groups into polysaccharides.

Purpose of the Study:

• To introduce varying amounts of carboxyl groups onto pullulan at the C-6 position.
• To characterize the oxidized pullulan derivatives.
• To investigate the impact of oxidation on pullulan's physicochemical properties.

Main Methods:

• TEMPO-mediated oxidation using sodium hypochlorite/sodium bromide.
• Characterization using FT-IR, 1H NMR, and 13C NMR spectroscopy.
• Molecular weight determination via multiangle laser light scattering (MALLS).
• Dynamic light scattering (DLS) for zeta potential and hydrodynamic radius.
• Viscosity measurements of dilute aqueous solutions.
• Determination of intrinsic viscosity and interaction parameter using the Wolf approach.

Main Results:

• Successful introduction of carboxyl groups onto pullulan, increasing water solubility.
• Oxidation degree correlated with reaction time.
• Significant decrease in molecular weight observed with prolonged oxidation.
• Increased second virial coefficients (A2) in oxidized samples.
• Demonstrated polyelectrolyte behavior in oxidized pullulan solutions, except for highly degraded samples.
• Intrinsic viscosity and interaction parameter showed dependence on ionic strength following a Boltzmann sigmoid model.

Conclusions:

• TEMPO oxidation provides a controlled method to functionalize pullulan with carboxyl groups.
• Oxidation significantly impacts pullulan's molecular weight, solubility, and solution behavior.
• The modified pullulan exhibits tunable properties suitable for various applications, with potential polyelectrolyte characteristics.