Controllably Adjusting the Hydrophobicity of Collagen Fibers for Enhancing the Adsorption Rate, Retention Capacity, and Separation Performance of Flavonoid Aglycones

Abstract

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.

Differences in Performance and Conductivity Persistence of New Reduced Graphene Oxide Air Filter Materials before and after Eliminating Static Electricity

“…The filtration efficiency for PM 10 decreased by 8.5% to 11.8%, the filtration efficiency for PM 2.5 decreased by 4.3% to 7.2%, and the filtration efficiency for PM 1.0 decreased by 3.6% to 8.0%, with the greatest impact on PM 10 . This is because the isopropanol solution neutralizes the positive and negative charges on the fibers, causing their charges to permanently decay [30]. After eliminating static electricity, the surface of the fiber does not carry static electricity, causing the fiber to become inactive.…”

“…From Figure 7, it can be seen that the electric resistance value after eliminating static electricity was greater than the electric resistance value before eliminating static electricity, with an overall increase of 7.0 KΩ to 9.4 KΩ and an average of 8.1 KΩ. This is because the process of eliminating static electricity has a certain impact on the fiber structure [30], leading to damage to the reduced graphene oxide coating and part of the fiber structure breaking, which makes it difficult to form a complete circuit between the fibers. As a result, based on the above actual situation, the overall increase in fiber surface resistance has been caused.…”

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

“…Because of the fullness of hydrophilic groups like peptide bond, − NH 2 , − COOH, − OH and hydrophobic groups like alkyl and benzyl, as well as the inherently excellent biocompatibility, biodegradability and mechanical strength, collagen fiber could be also developed for other utilizations. It was previously developed as a packing material for separating flavonoids mainly through the hydrogen bond and hydrophobic interactions [15][16][17][18][19][20][21]. Before practical application, collagen fiber needs crosslinking to further improve the mechanical strength and thermal stability.…”

“…For example, a GCF column with length-diameter ratio of 60:1 can separate kaempferol and quercetin [19]. Hydrophobic modification by using silane coupling agent with alkyl chains was once adopted to enhance the hydrophobic interaction, and thus improve the separation efficiency to flavonoid aglycones, and it could reduce the length-diameter ratio of collagen fiber-based column for separation of kaempferol and quercetin to 19:1 [21]. Interestingly, when the grafted alkyl chain is short like isobutyl, it is also beneficial to the formation of hydrogen bond, showing excellent synergistic effect of hydrophobic and hydrogen bond interactions.…”

“…Interestingly, when the grafted alkyl chain is short like isobutyl, it is also beneficial to the formation of hydrogen bond, showing excellent synergistic effect of hydrophobic and hydrogen bond interactions. However, increasing the grafted alkyl chain length to octyl and dodecyl can further enhance the hydrophobic interaction, but the hydrogen bond interaction was largely weakened due to the steric hindrance of long carbon chains [21]. So, further increasing the hydrophobicity of collagen fiber could not be considered as a good way to further improve the separation ability to flavonoid aglycones.…”