Development And Application Of ABEEM/MM To Study The Interaction Of Halide Ions With Water And NMA

Ionic aqueous solution exists widely in nature,in which halogen inorganic salts plays a pivotal role in maintaining ecological balance.In order to explore the hydration of halogen ion and its interaction with protein,the fluctuating charge polarizable force field of fluorion was constructed in this thesis.The main contents are as follows:1.The structures and binding energies of[X（H₂O）_1-6]^-（X^-=F^-/Cl^-/Br^-/I^-）was calculated by the MP2/aug-cc-p VTZ//B3LYP/6-311++G（d,p）level of quantum mechanics（QM）theory.Based on the atom-bond electronegativity equalization fluctuating charge molecular force field（ABEEM/MM）,three theoretical models of F^--H₂O system are designed to describe the anisotropic distribution of water molecules in the hydration shell of fluorion:（1）the single-site model with local-charge-conservation constraint（ABEEM/MM-I）;（2）the single-site model with global-charge-conservation constraint（ABEEM/MM-II）;（3）the multi-site model with global-charge-conservation constraint（ABEEM/MM-III）.The difference between models I and II lies in whether there is charge transfer between F^-and its first hydration layer.Both of models I and II adopt a single charge site to describe F^-,while seven charge sites are employed in model III.The potential energy functions were constructed and the force field parameters are iteratively optimized to fit the QM charge distributions,structures and binding energies.The structures and binding energies of[F（H₂O）_3-6]^-were calculated using the above three models.Compared with the QM results,the average absolute deviations（AADs）of the average distance between F^-and H of its first hydration shell,R_F-H,from the three models are 0.015?,0.015?and 0.068?,respectively.The AADs of the bond angle between F^-and H-O in its first hydration shell,?_{-F H-O},are 0.94o,0.18oand 1.75o,respectively.The relative root mean square deviations（RRMSDs）of the average binding energies between F^-and water molecules（（35）E）are 0.69%,5.93%and 69.54%,respectively.The linear correlation coefficients of the ABEEM/MM charge distributions and QM results are 0.96,0.99 and 0.99,respectively.The average charge transfer（（35）q）of F^-are 0.404 a.u.and0.349 a.u.from models II and III,respectively,and that of QM is 0.384 a.u..The performance of model II is obviously better than that of model I,which shows that it is necessary to take account of the charge transfer between fluorion and its first hydration layer.For model III,further improvements on the potential energy function and the parameters are requisite,especially to refine the performances on structures and binding energies.2.The structures,charge distributions and binding energies of[X（NMA）_1-4]^-（X^-=F^-/Cl^-/Br^-/I^-）are calculated at the same QM level.Based on the performance of the ABEEM/MM-Ⅱmodel in hydrated fluorion,its parameters are transferred to study[F（NMA）_1-4]^-.Compared with the QM results,the AADs of （?） are 0.204 ?and 0.69o,respectively,and the RRMSD of （?）E is 58.90%.The linear correlation coefficient between the ABEEM/MM charge distribution and that of QM is larger than 0.98.The relevant parameters still need to be further adjusted and optimized.We attempted to develop the ABEEM/MM single-site model to the multi-site model for the fluorion,and the fluctuating charge potential functions are constructed preliminarily.This provides an important reference to establish the ABEEM/MM force field of halogen ion,to discuss the structures and properties of aqueous electrolytes solution containing halogen ions.