| Calixpyrroles are a class of non-conjugated structure of the flexible macrocyclic compounds which are composed of pyrrole ring and sp3hybridize carbon atom by a-position pyrroles. Calixpyrroles and its derivatives as ion and ion-pair receptors have been widely used in the process of biological life movements, chemical sensors, ion extractions, salt dissolutions, membrane transports and other areas. In this paper, the structure properties and the action mechanism of the electron-rich system of anion and ion-pair recognitions by calixpyrroles and its derivatives were studied by the quantum chemistry methods and molecular dynamics simulations. All results as follows:First of all, equilibrium geometries between halide anions Cl-and octamethyl-calix[4]pyrrole, pyrrole-strapped calix[4]pyrrole, benzene-strapped calix[4]pyrrole and furan-strapped calix[4]pyrrole (the same anion was recognized by different host compounds) were optimized using density functional theory (DFT) at the B3LYP/6-311G**level. And the different halide anions (F-,Cl-,Br-) were recognized by the same host compounds which used the same methods. The conformational changes and the driving force of hydrogen bonds were analyzed by AIM analysis, NBO analysis and EDA analysis in gas phase. The intermolecular interaction energies are predicted by using B3LYP/6-311G**methods with basis set superposition error (BSSE) correction.We found that the1,3-alternate and the similar1,3-alternate conformation were the two most stable structures of the four main compounds, whereas a transition into a cone-like conformation occurs upon capture of a single halide anion to form complexes. In pyrrole-strapped calix[4]pyrrole, the strength of hydrogen bonds between N-H bond of pyrrole-strapped group and halide anions was stronger than the steric repulsion, which enhanced the recognition of halide anion. However, in benzene-strapped and pyrrole-strapped calix[4]pyrrole, the strength of hydrogen bonds between N-H bond of pyrrole-strapped group and halide anions was weaker than the steric repulsion, which reduced the recognition of halide anion. The analysis of hydrogen bonds can be drawn, the N-H bond of pyrrole ring and halide anions can form strong N-H…X-hydrogen bond, and the C-H bond of strapped groups and the bridge carbon atoms with halide anions can form weak C-H…X-hydrogen bond. The natural of this kind of hydrogen bond was mainly by electrostatic interactions.Second, equilibrium geometries between ion-pair (Cs+F-,Cs+Cl-,Cs+Br-) and octamethyl-calix[4]pyrrole were optimized using density functional theory (DFT) at the B3LYP/LANL2DZp level. The conformational changes and the driving force of hydrogen bonds were analyzed by NBO analysis in gas phase. The intermolecular interaction energies were predicted by using B3LYP/LANL2DZp methods with basis set superposition error (BSSE) correction. In the recognitions of ion-pair, the main driving force between host compound and cation Cs+was the electrostatic attraction, the cesium cation as electron-deficient system acting on near the electron-rich groups or an anion, and electrostatic attraction between anion and cesium cation was account for the major part.Third, the simple self-assembly dynamics study was carried out using the solvent molecular dynamics model in dichloromethane (CH2Cl2) solution environment. The results of dynamics simulation can be drawn, the solvent molecules on simple self-assembly conformational influence of complexes Cs+F--OC4P less affected than complexes Cs+Cl--OC4P and Cs+Br--OC4P, which formed a similar "polyline state" assembly. According to the energy principles, the lower is the energy, the more stable is the system, the simple self-assembly of complexes Cs+F--OC4P was the most stable assembly, and the van der Waals interactions played a major role in the whole stability of the system. |
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