Selective separation of zwitterionic phospholipid homologues with functional ionic liquids as extractants

Abstract

Natural zwitterionic compounds are widely used as surfactants, drugs and food additives. However, obtaining high-purity zwitterions from biomass remains challenging because of the presence of structurally similar homologues in plants. Here, we developed a novel extraction method to separate zwitterionic phospholipid homologues using ionic liquids (ILs) as extractants. A large distribution coefficient and excellent separation selectivity for phosphatidylcholine (PC) were achieved with hydroxyl-functionalized and carboxyl-functionalized ILs as the extractants. An effective IL–cosolvent extraction strategy was employed in this work to reduce the consumption of IL and improve the extraction efficiency. Additionally, the underlying extraction mechanism was explored using ab initio calculations and dynamic light scattering. The results indicated the existence of multiple hydrogen-bonding interactions between the IL and both the negative and positive moieties of the zwitterion, and the formation of micelles in the IL–cosolvent mixture was also observed. In addition, the effects of the structure and concentration of ILs and the temperature on extraction performance were investigated, and the feasibility of recovery of ILs by electrodialysis was evaluated.