Synthesis and characterization of phosphorylated galactomannan: The effect of DS on solution conformation and antioxidant activities

Phosphorylated derivatives of galactomannan from guar gum (GG) with the degree of substitution (DS) of 0.35-0.52 were synthesized using POCl3/pyridine. FT-IR, 13C NMR and XPS results revealed that phosphorylation had occurred and C-6 substitution was predominant in phosphorylated guar gum (PGG). PGG showed an increase in Mw and more broad molar mass distribution in size exclusion chromatography (SEC) analysis. Higher reaction temperature (above 60 °C) resulted in a higher MW value in PGG. It might be due to the cross-linking of polysaccharide chains by POCl3 via di-ester which was also supported by monosaccharide composition result. Results of MW−S2z1/2 showed a decrease in fractal dimension (df) values. DS had greater influence on its conformation in aqueous solution. The introduction of -PO3H2 groups improved significantly the stiffness of the chains due to the electrostatic effect. Furthermore, antioxidant experiments revealed that high DS could enhance the scavenging activities of radicals of PGG in vitro