Theoretical Study On A Seriers Of Cyclodextrins Compounds Interctions Between Host And Guest

The paper applied the quantum chemistry mothods and systematically studied the following three systems:(1) interactions ofβ-cyclodextrin with Helicobacter Pylori Eradicating Agent (TG44); (2) the inclusion processes of niflumic acid with cyclodextrins; (3) the regioselectivity of reactions and the ratios of products for cyclodextrins.Firstly, the inclusion complex ofβ-cyclodextrin (β-CD) and TG44 had been investigated by using densify functional theory (DFT) and PM3 semiempirical method. The results indicate that theβ-CD includes predominantly the biphenyl moiety of TG44, and the inclusion complex formed by TG44 entering into the cavity ofβ-CD from its narrow side (the primary hydroxyl group side) is more stable than that formed by TG44 entering into the cavity ofβ-CD from its wide side (the secondary hydroxyl group side). The negative enthalpy changes calculated from the statistical thermodynamic calculations at 1 atm and 298.15K suggest that the inclusion complexes are favored enthalpy-driven processes. The molecular modeling results are in good agreement with the experiment for 2D 1H-13C H HETCOR spectroscopic and H-NMR spectroscopic observations.Secondly, the inclusion complexes of cyclodextrins (CDs) and niflumic acid (2-[3-(trifluoromethyl) anilino]nicotinicacid, NA) had been investigated by using densify functional theory (DFT), hybrid method (ONIOM) and PM3 semiempirical method. The results indicate that theβ-CD is a more suitable complexating agent thanα-CD,γ-CD and HP-β-CD (Hydroxypropyl-beta-cyclodextrin). The inclusion complex formed by NA entering into the cavity ofβ-CD from its wide side (the secondary hydroxyl group side) is more stable than that formed by NA entering into the cavity ofβ-CD from its narrow side (the primary hydroxyl group side). The negative enthalpy changes calculated from the statistical thermodynamic calculations at 1 atm and 298.15 K suggest that the complexation of HP-β-CD with NA is characterized by a less negative enthalpy thanβ-CD since the hydroxypropyl groups prevent the penetration of NA inside macrocyclic cavity. Besides, both phenyl and pyridine residues of niflumic acid molecule have been inserted in the macrocyclic cavity of theβ-CD. However, the inclusion of the former residue is more preferential. The molecular modeling results are in good agreement with the corresponding experimental.At last, the regioselectivity of reactions and the ratios of the products of bromination for cyclodextrins are studied by use of quantum mechanics densify functional theory (DFT) and PM3 semiempirical method. Theβ-CD is more stable for complexation with compound 1 (3-methylanisole-4-bromo) thanα-CD. Compound 1 guest fit the host size ofβ-CD cavity better than that ofα-CD. The ability ofβ-CD is bigger than that ofα-CD in the aspect of improve ratios of the products. The stability of l/β-CD is higher than that of 2/β-CD and 3/β-CD means that bromination at the para position is favoured over ortho substitution and theβ-CD restrict access of the reagent adjacent to the methoxy groups. The inclusion complex formed by compound 1 entering into the cavity ofβ-CD from its narrow side (the primary hydroxyl group side) is more stable than that formed by compound 1 entering into the cavity ofβ-CD from its wide side (the secondary hydroxyl group side). The negative enthalpy changes from the statistical thermodynamic calculations at 1 atm and 298.15K suggest that the formation of the inclusion complex is an enthalpy entropy -driven process. The molecular modeling results are in good agreement with the corresponding experimental.