Pullulan Oxidation in the Presence of Hydrogen Peroxide and N-Hydroxyphthalimide

The C-6 in the maltotriose unit of pullulan was oxidized in an alkaline medium (pH = 10), utilizing a green method that included hydrogen peroxide (H2O2) as an oxidant and N-hydroxyphthalimide (NHPI) as a catalyst for various reaction times. The structure of the resulting oxidized pullulans (PO) was carefully characterized by titration, intrinsic viscosity, FTIR, C-13-NMR, and zeta potential. The content of carboxyl groups in PO was dependent on reaction time and varied accordingly. Furthermore, a fast reaction rate was found in the first 2-3 h of the reaction, followed by a decreased rate in the subsequent hours. FTIR and C-13-NMR proved that the selective oxidation of the primary alcohol groups of pullulan was achieved. The oxidation also caused the glycoside linkages in the pullulan chain to break, and the viscosity of the pullulan itself went down.

Automated summary

In this study, a green method was used to oxidize pullulan in an alkaline medium. The resulting oxidized pullulans were characterized using various techniques. It was found that the reaction time affected the carboxyl group content in the oxidized pullulans. The oxidation reaction had a fast rate in the first 2-3 hours and achieved selective oxidation of the primary alcohol groups of pullulan.