Molecular Simulation And Experimental Study On The Inclusion Of Rution With β-cyclodextrin And Its Derivative

Rutin is a is a natural flavonoid glycoside which widely exists in buckwheat,rut leaves,tomato,orange peel and other plants.Rutin has strong antioxidant activity and has various pharmacological activities such as anti-cancer,antibacterial,anti-inflammatory,hypoglycemic,and so on.However,the water solubility of rutin is poor,which typically cause low bioavailability and limited application in the fields of health care products and medicine.Cyclodextrin is a cyclic oligosaccharide with a hydrophobic cavity and a hydrophilic outer wall,which can include insoluble substances to form water-soluble inclusion complexes.Complexing with cyclodextrin（CD）is an effective method to solubilize rutin.In this study,we explored the inclusion mechanisms betweenβ-cyclodextrin（β-CD）,its derivative 2,6-dimethyl-β-cyclodextrin（DM-β-CD）and rutin through various experiments combined with simulation analysis.Furthermore,the modification effects of different cyclodextrins on rutin are evaluated.Details of the research content are described below.（1）The Flory-Huggins interaction parameters（χ）and mixing free energy(ΔG_mix)of CDs and rutin were calculated by Monte Carlo simulation（MC）.The results show that both cyclodextrins have excellent miscibility with rutin and DM-β-CD is easier to combine with rutin thanβ-CD.From molecular docking simulation,it can be found that bothβ-CD and DM-β-CD can form inclusion complexes with rutin.A part of molecular of rutin was encapsulated by the cavity of the two CDs and inclusion complexes exhibit a semi-inclusion structure.Through molecular dynamics simulation（MD）,the binding energy(E_binding)and solubility parameters（）of two CD/rutin inclusion complex systems were calculated.The results showed that the E_bindingof the DM-β-CD/rutin inclusion complex system was 2.22 times that of theβ-CD/rutin inclusion complex system,indicating that the DM-β-CD/rutin inclusion complex was more stable.The solubility parameter difference（Δ）with water showed that the DM-β-CD/rutin inclusion complex was completely soluble in water,and its water solubility was higher than that of the partially water-solubleβ-CD/rutin inclusion complex.The radial distribution function（RDF）calculated by MD simulation showed that compared with theβ-CD/rutin inclusion complex system,the intermolecular hydrogen between host and guest in the DM-β-CD/rutin inclusion complex system is stronger.Based on the above analysis,it can be speculated that that DM-β-CD is a better solubilizing carrier for rutin.（2）The phase solubility study showed thatβ-CD and its derivative DM-β-CD can form inclusion complexes with rutin in a molar ratio of 1:1,and the solubilization efficiency of DM-β-CD to rutin was 146%higher than that ofβ-CD.The stability constant（K_S）of the DM-β-CD/rutin inclusion complex was found to be higher thanβ-CD/rutin inclusion complex,indicating that the DM-β-CD/rutin inclusion complex was more stable,which was consistent with the larger E_bindingvalue obtained in the MD simulation.The Gibbs free energy（ΔG）of both inclusion complex systems are negative,revealing that the complexation process of two CDs with rutin can proceed spontaneously.The more negativeΔG of DM-β-CD/rutin inclusion complex corresponded to theΔG_mixin the MC simulation.Two inclusion complexes,β-CD/rutin and DM-β-CD/rutin,were prepared and proved by FT-IR,XRD and DSC experiments that they had completely different structure from the simple physical mixtures.The results of in vitro dissolution experiments showed that encapsulation ofβ-CD and DM-β-CD with rutin improve the dissolution rate in water and the DM-β-CD/rutin inclusion complex had the highest water solubility,which verified the analysis based onΔin the MD simulation.The order of antioxidant activity shown by DPPH experiments was:DM-β-CD/rutin inclusion complex>β-CD/rutin inclusion complex>rutin.Since intermolecular hydrogen bonds can weaken the covalent bond of hydroxyl groups and improve the hydrogen-donating ability of antioxidants,the stronger antioxidant activity of DM-β-CD/rutin inclusion complex may be due to the stronger intermolecular hydrogen bonding as shown in the RDF results calculated by MD simulation.In summary,the molecular simulation method visualized the inclusion structure,predicted the stability and water solubility of the two CD/rutin inclusion complexes,and provided theoretical analysis at the molecular level for the improvement of the antioxidant activity of the inclusion complexes.A series of experiments also proved the inference of molecular simulation,indicating that DM-β-CD is a better solubilizing carrier for rutin,which can also improve the antioxidant activity while increasing the water solubility of rutin.The molecular simulation analysis method used in this study can also provide some theoretical guidance for the screening of solubilizing carriers for other poorly soluble small molecule drugs.