Study Of Ab Initio Method And Abeemσπmodel On The Interactions Of Li⁺/Na⁺/k⁺/Be²⁺/Mg²⁺/Ca²⁺with Bases And H₂O

By applying a high levels quantum chemistry（QM）method,MP2/6-311+G（d,p）,the interactions between Li⁺/Na⁺/K⁺/Be²⁺/Mg²⁺/Ca²⁺with five methylated nucleic acid bases and water molecules in gas-phase are investigated in this paper.The structures of the base-M-（H₂O）_n(M=Li⁺/Na⁺/K⁺/Be²⁺/Mg²⁺/Ca²⁺,n=0²)were optimized with the frequency calculation,then the binding energies were determined by the consideration of BSSE correction.The charge distributions were studied by HF/STO-3G method.Results show that the binding energies between the divalent metal ions and its ligand atoms are much bigger than those of monovalent ions;the distances are smaller by 0.3?.With the increasing number of water molecules from 0 to 2,the average distances from metal ions to the ligand atoms（N/O）enlarge gradually and insignificantly.Charge analysis shows that the charge of metal ion is mainly transferred to water.In addition,by comparing the results from MP2 and four DFT methods（B3LYP,B3PW91,M062X,andωB97XD）with the same basis set6-311+G（d,p）,we find that the stability sequences,the structures and binding energies of base-M-（H₂O）_n from the five QM levels are similar;and the binding energies for the monovalent ionic systems fromωB97XD are larger than the other QM methods.Overall,the B3PW91 method can obtain the most similar structures to those from the MP2 method.The interaction potential of Na⁺/K⁺-（H₂O）₄ system is constructed in the frame work of the atom-bond electronegativity equalization fluctuating charge polarizable force field model（ABEEMσπ/MM）,and the related parameters are determined through fitting with the quantum chemistry results.Results of the charge distributions,structures and the binding energies from the constructed potential.For all the compounds,the linear correlation coefficients of the charge distributions are above 0.96,which demonstrates that the molecular charge distribution computes ABEEMσπfrom ab initio results.Meanwhile,the optimized structures by ABEEMσπ/MM are close to those of QM.Then the parameters of Na⁺and K⁺are transferred to base-Na⁺/K⁺-H₂O system,and they performed very well to reproduce the QM results.