Abstract
Low molecular water-soluble chitosan was prepared by the depolymerization of chitosan in the presence of a series of catalysts with active W(O2) sites. Both the peroxo species [W2O3(O2)4]2- and {PO4[WO(O2)2]4}3- showed high efficiency in the degradation of chitosan, indicating that the degradation mechanism did not follow the radical mechanism. That means •OH is not the active species, which has been proven by the fluorescence spectra. H2O2 acted as an oxidant to regenerate the active W(O2) sites in the depolymerization of chitosan. The developed catalyst (TBA)3{PO4[WO(O2)2]4} is recoverable.
Highlights
Chitosan is a biopolymer obtained by partial deacetylation of chitin, which is the second most abundant polysaccharide in nature after cellulose[1,2]
Huang et al reported that a Keggin heterpoly acid, H3PW12O40, can efficiently catalyze oxidative degradation of chitosan with H2O2 to the LMWSC[16,17,18]
The authors presumed that 1) the peroxo species {PO4[WO(O2)2]4}32 formed by phosphotungstic acid in the presence of H2O2 is the real catalyst. 2) the peroxo species {PO4[WO(O2)2]4}32 accelerates the formation of free radicals by the disassociation of hydrogen peroxide. 3) the free radicals can attack the b-(1–4) glucosidic bond of chitosan to obtain the LMWSC
Summary
Chitosan is a biopolymer obtained by partial deacetylation of chitin, which is the second most abundant polysaccharide in nature after cellulose[1,2]. Huang et al reported that a Keggin heterpoly acid, H3PW12O40, can efficiently catalyze oxidative degradation of chitosan with H2O2 to the LMWSC[16,17,18]. The isolated peroxo species (TBA)3{PO4[WO(O2)2]4} and K2[W2O3(O2)4] were directly employed as the catalyst to degrade chitosan.
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