The Applications Of ABEEM??/MM On The Interactions Of K⁺ With N-methylacetamide/H₂O And Halide Ions With Water

Monovalent ions play a decisive role in many life processes,and it is still a challenge to accurately simulate the structures and properties of the ion-containing aqueous electrolyte solutions and biomolecular systems.Based on the results of high-level ab initio methods,this thesis developed and applied the atom-bond electronegativity equalization fluctuating charge force field?ABEEM??/MM?,and related parameters were further optimized to study the structures,binding energies and charge distributions of[K?H₂O?_n]⁺?n=3-8?,[K?NMA?_n]⁺?n=3-8?and[K?NMA?_m?H₂O?_n]⁺?m+n=6?complexes.Results show that the results of ABEEM??/MM are in good agreement with those of QM,in which the average absolute deviations?AAD?of bond lengths,bond angles and binding energies are less than 0.03?,2.1°and 9.5 kcal/mol,respectively,and the relative root mean square deviations?RRMSD?are less than 1.9%,1.6%and 14.8%,respectively.The linear correlation coefficient of the charge distributions of the above systems is nearly 0.94.Molecular dynamics simulation on a series of aqueous solutions of NMA were carried out by using ABEEM??/MM,and results show that the first peaks of the radial distribution function?RDF?between K⁺and oxygen atom of NMA and water locate at 3.0?.In pure water,4M,6M,and 8M aqueous solutions of NMA,for K⁺,the coordination number of first hydration shell is 5.7,6.7,8.8 and 11.0,respectively.The structures,binding energies and charge distributions of[X?H₂O?_3-8]^-?X=F,Cl,Br,I?complexes were studied in terms of four popular QM methods,namely B3LYP,B3PW91,M062X and MP2 respectively.Based on the QM results,the ABEEM??potential energy function and related parameters of the interactions between halide ions and water were further optimized,including adjusting and determing the ABEEM??charge parameters and force field parameters.It is show that the ABEEM??/MM results are in good agreement with QM results,in which the AADs of bond lengths,bond angles and binding energies are less than0.05?,0.6°and 12.8 kcal/mol,respectively,and the RRMSDs are less than 2.6%,0.5%and22.3%,respectively.The linear correlation coefficients of the charge distributions of the above systems are nearly 0.97.Molecular dynamics simulation on aqueous solutions of halide ions had been performed by using ABEEM??/MM,and the preliminary results show that the first peaks of the RDF between F^-,Cl^-,Br^-and hydrogen atom of water locate at 2.20,2.70 and 2.75?,respectively,and the first peaks of the RDF between F^-,Cl^-,Br^-and oxygen atom of water locate at 3.00,3.65 and 3.70?,respectively.For F^-,Cl^-,Br^-,the coordination number of first hydration shell in 216/500 water is 3.8/3.9,4.6/5.0,4.0/4.5,respectively.