The Formation Of Novel Eutectic Deep Solvents/alcohol-based Aqueous Two-phase System And Application In The Extraction Of Phenolic Compounds

As a new type of green solvent,deep eutectic solvent(DES)has been widely applied in the field of extraction of biomolecules because of its excellent properties in recent years.Aqueous two-phase system(ATPS)is an efficient and mild extraction system.Deep eutectic solvent based ATPS combines the excellent characteristics of both deep eutectic solvent and ATPS,and has broad application prospects in the field of extractive separation.Phenolic compounds existed in nature are natural antioxidant active substances and have high medicinal value.Therefore,the extraction technologies of phenolic compounds have attracted much attention.In this paper,a novel ATPS,promising environmentally,simple and efficient,and designable,was constructed with the use of natural deep eutectic solvents and lower alcohols.The mechanism of the DES/alcohol-based ATPSs was discussed primarily and the influence of different factors on the phase behavior is studied,which is in favor of the design and optimization of this kind of ATPS.Finally,the DES/alcohol-based ATPSs were applied to the extraction of phenolic compounds and corresponding extraction mechanism was initially analyzed,for providing technical support for the application of this kind of ATPS to the extraction of phenolic compounds.Betaine-based natural deep eutectic solvents were prepared: betaine-glucose(Bet-Glu),betaine-sorbitol(Bet-Sor),betaine-xylitol(Bet-Xyl),and ATPS were constructed by a combination of deep eutectic solvents and alcohols such as n-propanol(NPA),isopropanol(IPA)and tert-butanol(TBA).The binodal curves and tie-lines were used to characterize the phaseforming ability of DES/alcohol-based ATPS.The lower alcohols were enriched in top phase,while the two components of deep eutectic solvents were enriched in the bottom phase.The formation of ATPS is due to the different ability of deep eutectic solvent and alcohol to bind water,which is related to their hydrophobicity.The greater the difference between the hydrophobicity of the deep eutectic solvent and the lower alcohol,the phase-forming ability of ATPS is stronger.Temperature affects the hydrogen bonding force in ATPS.Increasing the temperature weakens the ability of the deep eutectic solvent to form an ATPS.The increase of the alcohol will promote the phase-forming components to separate in two phases completely,and the density gradient of the two phases will increase accordingly.The research of phase behavior of the DES/alcohol-based ATPS has confirmed its designability.The ATPS we studied is environmentally friendly,low cost and especially without salt,so it will not be affected by ion exchange,and no need to consider the post-treatment of salt.Three ATPSs(Bet-Glu/NPA,Bet-Sor/NPA,Bet-Xyl/NPA)were used to extract nine monocyclic phenol compounds.Result proved high feasibility of this kind of ATPS for the extraction of phenolic compounds.The extraction efficiency of different phenolic compounds showed significant differences,which is related to their molecular structure and properties.There is a hydrogen bonding force between the deep eutectic solvent and the phenolic compound.The phenolic compound,containing more groups with the capability of providing or accepting hydrogen bonding,has lower extraction efficiency in DES/alcohol-based ATPS.Bet-Glu/NPA-based ATPS has the best extraction efficiency on eugenol,which is up to 96.37%.