Adsorption mechanisms of alginate oligosaccharides with specific degree of polymerizations on a novel ion-exchange resin: Experiments and simulations

Abstract

Alginate oligosaccharides (AOS) with a specific degree of polymerization (DP) have unique physiological activity, but industrialization and high-value applications of AOS are restricted due to the paucity of study on its precise separation mechanism. In the process design of adsorption separation chromatography, the adsorption behaviors of the adsorbent are crucial. Herein, the adsorption properties of AOS with DPs 1–4 (AOS1-4) on novel SM-7 resin were clarified by combining adsorption experiments and theoretical calculations. The effect of various parameters on the adsorption process of AOS1-4 was investigated using a series of static adsorption tests. Molecular dynamics modeling was implemented to determine the interaction energy and diffusion between AOS1-4 and SM-7 resin. The results of the adsorption equilibrium demonstrated that the adsorption of AOS1-4 complied with the Langmuir model and exhibited ion dependency and pH stability. The saturation adsorption capacities of AOS1-4 on SM-7 resin were 1.144 mmol/g, 0.810 mmol/g, 0.730 mmol/g, and 0.582 mmol/g, respectively. The external diffusion was the primary rate-limiting phase in the adsorption kinetics of AOS1-4, which followed the pseudo-second-order kinetic model. As the increasing of DPs of AOS, the hydroxyl, carboxyl, and molecular volume rose, which decreased the adsorption capacity and rate. Simulation results showed that interaction energies between SM-7 resin and AOS enhanced while the diffusion coefficient declined with rising DPs of AOS. Hydrogen bond interaction and electrostatic attraction promoted the adsorption of AOS on the novel resin. The fundamental theoretical data in this study can provide guidance for the large-scale preparation of AOS with specific DPs.