| Natural deep eutectic solvents aqueous biphasic systems（NADES-ABS）are novel liquid–liquid biphasic systems,which have the characteristics of designability,polarity control,compatibilization,gentleness,high efficiency and environmental protection,and have broad development prospects in the field of extraction and separation.However,only a limited number of NADES-ABS have been developed,and most studies remain at the phenomenological level,lacking in-depth analysis of the mechanism of phase formation and extraction.Therefore,to further explore and study the process mechanism,it is particularly necessary to develop NADES-ABS based on specific objects.Based on above,this paper takes rutin,a flavonoid bioactive substance,as the target object,and proposes to combine several sugar deep eutectic solvents（NADES）with lower alcohols to construct new natural deep eutectic solvents/alcohol-aqueous biphasic systems（NADES/A-ABS）,which are environmentally friendly,mild and recyclable.Based on the analysis of the physical properties of the system,a mathematical model was established based on the excluded volume theory（EEV）,and the phase formation mechanism of the process was studied,the process phenomena were explained from the molecular scale.To study the extraction and separation mechanisms,Hansen solubility,turbidity point thermodynamics and migration thermodynamics were introduced to explore the interaction force between NADES and rutin,which providing a theoretical basis for subsequent application studies and technological developments.This paper mainly carried out the following research:（1）To study phase formation mechanism,a sugar-based NADES/A-ABS is proposed and constructed.Based on the research background of the new sugar-based NADES/ABS,lower alcohols were selected that could constructed ABS with sugar-based NADES.The structural,temperature,NADES composition and stoichiometric ratios of the NADES were investigated for their influence on the liquid-liquid two-phase equilibrium and the physical chemistry of the system.Those results showed that lowering the temperature,increasing the number of hydroxyl groups in hydrogen bond donor（HBD）and increasing the number of alkyl groups in lower alcohols helped improve the phase formation ability of the system.As the separation ability between the lower alcohols and NADES increases,the density difference between the two phases gradually increases as well.Based on the EEV mathematical model and the density properties of the system described above,the EEV mathematical model was modified with the density of the system.The result show that the modified model correlates well with the liquid-liquid two-phase equilibrium data of the system.And the EEV mathematical model study shows that the interaction forces between the phase components of each system are affected by the molecular structure of the HBD and the lower alcohols.Increasing the number of hydroxyl groups of HBD and alkyl groups of lower alcohols is beneficial for reducing the compatibility between the two phases of the system,making the molecular stacking gap of the solution smaller,and enhancing the molecular interaction forces between the constituents.The ability of NADES to eliminate alcohol is enhanced.This model quantifies the phase formation ability of the system and can be used to select the optimal ABS system.（2）The extraction mechanism of the system has been thoroughly explored in order to obtain efficient extraction results.According to the characteristics of rutin,three new ABS were created by choline chloride sucrose（2:1）NADES and tert-butanol,n-propyl alcohol and isopropyl alcohol The temperature variability properties of the system were investigated at different temperatures to improve the extraction efficiency of rutin.The modified EEV mathematical model parameters were used to quantify the phase forming ability of the system at different temperatures,and the linear relationship between the distribution coefficient of the target substance and the phase forming ability of the system was determined.The results showed that the extraction and separation ability of rutin increased linearly with the increase of the phase forming ability of the system.Based on the above studies,the liquid-liquid two-phase system of n-propanol and choline chloride/maltose NADES was established.By adjusting the stoichiometric ratio of the hydrogen bond recipient and temperature,the optimal system was obtained,which made the system adapt to the specific requirements of the target molecule.The distribution behavior of rutin in the system showed that the reduction of temperature and stoichiometric ratio of hydrogen bond donor significantly improved the distribution coefficient and extraction efficiency of rutin in the rich NADES phase.When the temperature was 288.15K,the extraction efficiency of NADES（choline chloride:maltose=1:2）+NPA+H2O system reached 94.27%.Hansen solubility parameter was used to study the interaction mechanism between NADES and rutin,and the results showed that NADES with a stoichiometric ratio of 1:2 had the highest solubility to rutin,which made the corresponding NADES-ABS have efficient extraction ability for rutin.In addition,the interaction between NADES（choline chloride:maltose=1:2）and rutin,dominated by hydrogen bonding force and supplemented by dispersion force,promoted the transfer of rutin to the NADES rich phase.The energy（）,enthalpy（）and entropy（）calculated from the partition data of rutin was consistent with the free energy,enthalpy and entropy changes of system,which confirmed that the driving force of the phase separation of the system drives the transfer of rutin to the rich NADES phase.The results of three cycles show that the extraction efficiency of rutin does not attenuate in each cycle,indicating that the system has the potential of recycling.This research method provides an idea for designing a controllable and efficient aqueous biphasic extraction separation system. |
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