Selenylation of Guar Gum Mediated by N-Methyl-2-pyrrolidone Hydrosulfate: Insights into Regulation of Selenium Content and Molecular Weight

Selenylation is an important modification strategy of polysaccharide, however, one of the main obstacles is that the weak esterification ability of selenide reagent, which leads to the low Se conversion efficiency during reaction. Here, we used N-methyl-2-pyrrolidone hydrosulfate ([HNMP]HSO4) as acid catalyst efficiently synthesized selenized guar gum (Se-GGs) to improve the activity of selenide reagent. The chemical structure of GG and selenized derivatives was investigated using FT-IR, 1D/2D NMR spectrometry and atomic force microscopy (AFM). The results indicated that selenite groups existed in Se-GGs and the substitution position was at C6. Furthermore, it was also demonstrated that [HNMP]HSO4 had a dual influence on GG by increasing the Se content (from 181.3 to 9072.8 mu g/g) and regulating the molecular weight, which was due to strong Bronsted acidic proton (H+). These results illustrated a new synthetic method for preparing functional polysaccharides with a broad range of potential applications.