Technology And Mechanism Study Of Computer Assisted Screening Of Natural Deep Eutectic Solvent For Natural Active Substance Extraction

Natural active substances are an important basis for the development of innovative drugs,foods,flavors and cosmetic products.The progress of modern science and technology has promoted a focus on healthy living and environmental safety,and has also put forward higher requirements for the development and application of natural products.A novel green solvent-natural deep eutectic solvent（NADES）with high solubility for natural products was discovered and applied in extraction and separation.The variety of NADES is increasingly rich with the continuous development of NADES,but this also increases the difficulty of NADES screening.Currently,screening for NADES mainly relies on a sufficiently large number of experiments to determine,which not only consumes a large amount of experimental raw materials,but also the process takes up a lot of manpower and time.To solve this problem,this paper sets hydrophilic small molecule active substance-chlorogenic acid,hydrophobic small molecule active substance-artemisinin,biomacromolecular active substance-Lycium barbarum polysaccharide as the research objects,and computer-assisted to rapid screen suitable NADES.The screened NADES were applied for the extraction of targets,and the antioxidant activity was evaluated.In addition,the synthesis mechanism of NADES and the extraction mechanism of active substances,also the mechanism of intermolecular interaction were calculated and analyzed by quantum chemistry theory,which provided theoretical support for the design of NADES.Firstly,structural models of NADES,chlorogenic acid,artemisinin and Lycium barbarum polysaccharide were constructed.Based on the quantum chemistry theory,the solvation free energy△₇)and intermolecular binding energyΔE were calculated,proline-malic acid（PMH）,sorbitol-choline chloride（So CH）and glucose-choline chloride（GCH）were selected as the preferred solvents for the extraction of chlorogenic acid,artemisinin and Lycium barbarum polysaccharide,and the solvation free energies are-13.04 kcal/mol,-30.12 kcal/mol and-34.23 kcal/mol,respectively.The intermolecular interaction analysis found that the NADES system formed intermolecular hydrogen bonds,and the combination of van der Waals force and steric effects made NADES exist stably in a new liquid form.The strength of the intermolecular hydrogen bond determines the difficulty of NADES synthesis.Secondly,the solubility of chlorogenic acid in several NADES and ethanol solvents was determined.The solubility of chlorogenic acid in ethanol was 194.52 mg/ml and that in PMH was 107.39 mg/ml.The actual extraction effect of PMH（6.83 mg/g）was significantly better than that of ethanol solvent（1.45 mg/g）.By comparing with the solubility parameters,it had reverse dissolution phenomenon,the reliability of computer-aided screening of NADES considering solvent effect was verified.The screened PMH was applied on the ultrasound-assisted extraction of chlorogenic acid from herba artemisiae scopariae,the response surface method was optimized to determine the optimal process:15.01wt%water content,1:10（g/m L）solid-liquid ratio,256.16 W ultrasonic power,25 min ultrasonic time,the yield of 7.68 mg/g was achieved,which was 2-3 times that of traditional water and ethanol extraction.PMH significantly improved the stability and antioxidant activity of chlorogenic acid,the IC₅₀ of DPPH free radical scavenging concentration was 33.95μg/m L（water,94.12μg/m L）,the FRAP value was 0.07～0.13（water,0.01～0.07）,and the IC₅₀ of ABTS free radical scavenging was 35.82μg/m L（water,159.37μg/m L）.Theoretically,the solubilization mechanism of NADES to chlorogenic acid was discussed from the angle of intermolecular interaction.The complex strong hydrogen bond interaction between PMH and chlorogenic acid（9.02 kcal/mol）was formed,while the weak hydrogen bond interaction between ethanol and chlorogenic acid（1.14 kcal/mol）occurred.The screened So CH was applied on ultrasound-assisted extraction of artemisinin,and the extraction rate of artemisinin reached 8.76 mg/g,while 6.15 mg/g,6.05 mg/g,and 5.41 mg/g for petroleum ether,ether,and ethanol,respectively.The optimal process conditions were determined by response surface methodology as 24.84wt%ethanol content,1.49:10（g/m L）solid-liquid ratio,214.21 W ultrasonic power and 15.75 min extraction time.The antioxidant activity of artemisinin obtained by So CH had been improved,that the IC₅₀ value of scavenging DPPH free radicals was 211.29μg/m L（petroleum ether,389.56μg/m L）,FRAP value was 0.07-0.13（petroleum ether,0.04-0.11）,the IC₅₀ value of scavenging ABTS free radical was 107.40μg/m L（petroleum ether,302.59μg/m L）.The Quantum chemical calculation showed that various intermolecular interactions,especially hydrogen bonding,have been formed between artemisinin active molecules and NADES.Cl ion in So CH was the main contribution site of strong interaction,and the existence of hydrogen bond protected the bioactive site of artemisinin.The checked GCH was applied on the ultrasound-assisted extraction of lycium barbarum polysaccharide,the response surface optimized process conditions:water content 15.68wt%,solid-liquid ratio 1.0:10（g/m L）,ultrasonic power 205 W,extraction time 25 min,and the extraction rate of lycium barbarum polysaccharides reached 122.52 mg/g,which was 1.5times that of the traditional hot water extraction（70.4 mg/g）.The molecular weight of lycium barbarum polysaccharide obtained by GCH（9.23 k Da）was much smaller than those obtained by water（138.38 k Da）and ethanol（192.11 k Da）.The IC₅₀ value of scavenging DPPH radical was 0.48 mg/m L（water,2.16 mg/m L）,the FRAP value was 0.07-0.14（water,0.03-0.07）,and the IC₅₀ value of scavenging ABTS radical was 1.12 mg/m L（water,4.97 mg/m L）,also the antioxidant activity was enhanced.The Quantum chemical calculation results showed that the hydrogen bond interaction between GCH and lycium barbarum polysaccharide molecules includes a large number of high-strength hydrogen bond sites（11.11 kcal/mol、8.71 kcal/mol、7.97 kcal/mol、7.96 kcal/mol）and some low strength hydrogen bond sites（1.80 kcal/mol、1.28 kcal/mol、1.46 kcal/mol、1.17 kcal/mol、4.31 kcal/mol）which formed a strong and stable hydrogen bond network,that made lycium barbarum polysaccharide active molecule more stable in GCH solvent environment and had a high extraction selectivity.The calculation provided a theoretical support for further utilization of active substances.