The influence of zwitterions on the partition of biomolecules in aqueous biphasic systems

Abstract

The use of hydrophilic zwitterionic compounds (ZI) to act as phase forming components of aqueous biphasic systems (ABS) has been attracting increased interest. Although previous works studied the phase behavior of ZI, there is still a lack of knowledge on the partition behavior of compounds in ZI-based ABS. This work reports a study on the influence of ZI structure for the extraction of 7 different biomolecules selected as molecular probes – 2 alkaloids (nicotine and caffeine), 2 phenolic compounds (gallic acid and vanillic acid) and 3 amino acids (L-tryptophan, L-tyrosine and L-phenylalanine). The partition and extraction efficiencies of these biomolecules were evaluated in ternary systems composed of hydrophilic ZI constituted by ammonium, imidazolium, pyridinium and piperidinium cationic and SO3− anionic groups, K2CO3 and water. The obtained results show that all the biomolecules preferentially partition to the ZI-rich phase, and the extent of their partition was closely related with the octanol–water partition coefficients of both biomolecules and ZI. It was demonstrated that the partition of biomolecules in ZI-based ABS is firstly ruled by hydrophobic/hydrophilic effects and only in some particular cases specific interactions between the biomolecule and the ZI affect their partition. Furthermore, despite the similarity between ZI and ionic liquids behavior as phase forming compounds of ABS for the extraction of biomolecules, ZI-based ABS presented a better performance in the extraction of phenolic compounds in alkaline environment.