Collagen fibers (CFs) were previously used as packing
materials
for the separation of flavonoids based on hydrogen bond and hydrophobic
interactions. However, as for flavonoid aglycones, CFs presented unsatisfactory
adsorption capacity and separation efficiency due to the fact that
they include limited hydroxyls and phenyls. In order to improve the
adsorption capacity and separation efficiency, the hydrophobic modification
strategy was employed in this research to enhance the hydrophobic
interaction of CF with flavonoid aglycones by using silane coupling
agents with different alkyl chains (isobutyl, octyl, and dodecyl).
FT-IR analysis, DSC, TG, SEM, EDS mapping, water contact angle, and
absorption time of solvent proved the successful grafting of alkyl
chains on the CF without disturbing its special fiber structure, leading
to the significantly enhanced hydrophobicity of the CF. The dynamic
adsorption and elution behavior of kaempferol and quercetin (the typical
flavonoid aglycones) on the hydrophobic CF showed that the adsorption
rate and retention rate were largely increased in comparison with
the CF without modification. Molecular dynamic simulations indicated
that the CF grafted with isobutyls could interact with flavonoid aglycones
through the highest synergetic effect of hydrophobic and hydrogen
bond interactions, which exhibited the strongest retention to flavonoid
aglycones. On further increasing the alkyl length (octyl and dodecyl),
the hydrophobic interaction was further enhanced, but the hydrogen
bonds were significantly weakened by steric hindrance, which showed
that the retention to flavonoid aglycones was appropriately increased
but without causing peak tailing. In the column separation of kaempferol
and quercetin, the CF with hydrophobic modification presented a greater
separation efficiency, with the purity of kaempferol increased from
71.99 to 86.57–97.50% and the purity of quercetin increased
from 82.69 to 88.07–99.37%, which was much better than that
of polyamide and close to that of sephadex LH 20. Therefore, the hydrophobicity
of the CF could be controllably adjusted to enhance the adsorption
rate and retention capacity, specifically improving the separation
efficiency of flavonoid aglycones.