Synergistically enhancing hydrogen bonding, hydrophobic interaction and electrostatic association of collagen fiber to flavonoid aglycones for their effective separation by polyethyleneimine modification

Compared with flavonoid glycosides, flavonoid aglycones are difficult to be separated since they have less hydroxyls. Collagen fiber (CF), a natural polymer, was once used as packing material for separation of kaempferol and quercetin (the typical flavonoid aglycones) after crosslinking by glutaraldehyde mainly based on hydrogen bonding and hydrophobic interaction in column length-diameter ratio of 60:1. Hydrophobic modification by grafting alkyl chains was then employed to enhance the hydrophobic interaction between CF and flavonoid aglycones, which can improve the separation efficiency and decrease column length-diameter ratio to 19:1. In order to further improve the adsorption capacity and separation efficiency, the strategy of simultaneously grafting hydrophobic alkyl chains (–CH₂–CH₂–) and alkali groups (–NH₂) was adopted in this work to enhance hydrophobic interaction, hydrogen bonding and electrostatic association to flavonoid aglycones at the same time through grafting polyethyleneimine (PEI). PEI modified CF (PEI-CF) maintained the fiber structure of CF, and had higher adsorption extent and rate to flavonoid aglycones through the enhanced synergetic effect of hydrophobic interaction, hydrogen bonding and electrostatic association. As a result, PEI-CF presented a satisfactory column separation efficiency for kaempferol and quercetin even the length-diameter ratio of column was decreased to 11:1, which was much better than previously developed glutaradehyde-crosslinked collagen fiber and isobutyl-grafted collagen fiber, as well as commonly used polyamide and Sephadex LH-20.

Graphical abstract