Solvation Free Energy for Selection of an Aqueous Two-Phase System: Case in Paeonol Extraction from Cortex Moutan

Aqueous two-phase system(s) (ATPS) has/have been widely employed in the extraction and separation of bioactive molecules from herbs due to its various advantages such as high efficiency and good selectivity. For selecting the type and amount of organics and salts in ATPS, onerous experimental trials are required to ensure the reliability. We intended to develop a theoretical method to select ATPS in the case of paeonol extraction from cortex moutan. The solvation free energies (E _solv) of paeonol in the top phase of 54 ATPS (ATPS-acetone, ATPS-acetone-EA, ATPS-THF, ATPS-THF-EA, ATPS-EtOH, and ATPS-EtOH-EA) were calculated with Gaussian 09, and the extraction yields with 54 ATPS were determined. By comparison of E _solv and yield, the E _solv rank was effective to select the optimal organic type and organic solvent fraction and aqueous salt concentration. With each series of 18 ATPS (ATPS-acetone plus ATPS-acetone-EA; ATPS-THF plus ATPS-THF-EA; or ATPS-EtOH plus ATPS-EtOH-EA), the paeonol yield was correlated with E _solv, suggesting that the optimal organic type and fraction and the aqueous NaH₂PO₄ concentration could be selected by using theoretical E _solv, or at least, the theoretical E _solv rank could offer effective guidance for experimental design, and thus, tedious and onerous experimental work for optimization in ATPS extraction can be significantly reduced.