The Empirical Model For Rapid Evaluation Of The Ionic Noncovalent Complex Interactions

The noncovalent interactions,which exist widely in the natural world,play vital roles in the fields of chemistry,materials science and bioscience.It is essential to rapidly and accurately evaluate the structure and strength of the interactions which could provide for future prospects in science.A polarizable dipole-dipole interaction model was established in our research group and successfully used to estimate the equilibrium intermolecular distances and interaction energies of the neutral noncovalent complexes.In this thesis,the model is further extended to predict the equilibrium intermolecular distances and interaction energies of the ionic noncovalent complexes.The major contents,which can be drawn from this study,are summarized as follows.1.Based on the understanding of ionic noncovalent interactions,the empirical model involving the charge-dipole interaction was developed to evaluate the ionic complexes.Eighteen complexes were selected as the training dimers to define the correlative parameters.2.This empirical model was applied to a series of ionic-π complexes consisting of the spherical monatomic halide ions(F-,Cl-,and Br-)and π systems to investigate the equilibrium intermolecular distances and interaction energies.The calculation results shown that the equilibrium intermolecular distances and interaction energies produced by this empirical model were favorably comparable to the results obtained from high-level ab initio methods.3.This empirical model was then applied to a series of ionic hydrogen-bonded complexes containing the protonated arginine side chain to calculate the equilibrium hydrogen bonding lengths and interaction energies.The calculation results shown that this empirical model could produce the favorable equilibrium hydrogen bonding lengths were compared with those obtained from MP2/6-31+G(d,p)method.The interaction energies obtained from this empirical model and those yielded by MP2.5/CBS method also had a linear correlation in some extent,the linear correlation coefficient was 0.9687.Comparing with the MP2.5/CBS level interaction energy results,the root mean square error for this empirical method is 2.57 kcal/mol.The corresponding linear correlation coefficients of AMBER99 and AMOEBA force field were 0.9370 and 0.4444,and the root mean square errors were 6.84 and 6.30 kcal/mol respectively.4.This empirical model was also applied to the calculation of the equilibrium hydrogen bond lengths and interaction energies of the ionic hydrogen-bonded complexes containing protonated histidine side chain.The calculation results shown that this empirical model could nicely reproduce ab initio equilibrium hydrogen bond lengths and interaction energies results.Comparing with the MP2.5/CBS level results,the linear correlation coefficient for this empirical model is 0.9562 and the root mean square error was 2.12 kcal/mol.The corresponding linear correlation coefficients of AMBER99 and AMOEBA force field were 0.8083 and 0.6963,and the root mean square errors were 11.22 and 6.84 kcal/mol respectively.5.This empirical model was also applied to the calculation of the equilibrium hydrogen bond lengths and interaction energies of the ionic hydrogen-bonded complexes containing protonated lysine side chain.The calculation results shown again that this empirical model could nicely reproduce ab initio equilibrium hydrogen bond lengths and interaction energies results.Comparing with the MP2.5/CBS level results,the linear correlation coefficient was 0.9549,and the root mean square error was 3.60 kcal/mol.The corresponding linear correlation coefficients of AMBER99 and AMOEBA force field were 0.9033 and 0.7630,and the root mean square error were 15.86 and 5.18 kcal/mol respectively.6.Through comparative analysis of computational efficiency between this empirical model and MP2.5/CBS method,the CPU time ratio of this model was improved more than three orders of magnitude.The comparison also illustrates that the efficiency advantage of the empirical model was more obvious than MP2.5/CBS method with the increase of atomic number.It is exhibited that the empirical model is more efficient and speedier than MP2.5/CBS method.The results presented in this thesis prove that this model can efficiently predict the ionic hydrogen bonding and ionic-π interacions.We expect the model developed in this thesis will serve as a new tool for biological process simulations.