Improvement effect of p-sulfonatocalix[4]arene on the performance of the PEG/salt aqueous two-phase system.

The PEG/salt aqueous two-phase system (ATPS) is the most common ATPS, but its application is still limited due to the restricted polarity difference between the two phases and the poor enhancement effect of adjuvants on ATPS performance so far. Unlike the adjuvants used so far, calixarenes can bind ions and molecules via multiple noncovalent interactions. In the present study, a water-soluble calixarene, p-sulfonatocalix[4]arene (SC[4]), was used for the first time as the adjuvant to improve the performance of the PEG 600/(NH4)2SO4 ATPS through multiple interactions. It is found that when the SC[4] and the SC[4]/imidazole ionic liquid ([Cnmim]Br) complex were used as the adjuvants, the formation of PEG 600/(NH4)2SO4 ATPS was enhanced, and the transfer of the extracts (including S-mandelic acid, L-tryptophan, and L-phenylalanine) into the PEG phase was promoted. Moreover, although the single [Cnmim]Br, a commonly used adjuvant, does not promote the migration of the target molecules into the polymer phase, the SC[4]/[Cnmim]Br complex is superior to SC[4] in enhancing the performance of the ATPS because the SC[4]/[Cnmim]Br aggregates enable more binding sites to combine with the extract. Besides, the partition coefficient of SC[4] in the PEG/trisodium citrate ATPS is much smaller than that in the PEG/(NH4)2SO4 ATPS, which is helpful for the recovery of extracts into the citrate phase.