Theoretical Study On A Seriers Of Crown Ethers Compounds Molecular Recognition And Supramolecular Devices

Recently, the study of molecular recognition and supramolecular devices in supramolecule chemistry becomes one of the most active fields. The paper applied the quantum chemistry mothods and systematically studied the following five systems: (1) The molecular recognition of the carbon- and nitrogen-pivot lariat crown ethers and the alkali metal cations: Na+, K+; (2) The molecular recognition of the tetraprotonated spheroidal macrotricyclic ligand and halide anions: F–, Cl–, Br–; (3) The molecular recognition of calix[4]arene-N-azacrown-5, calix[4]arene-N-phenyl- azacrown-5 with alkali metal cations: Na+, K+, Rb+; (4) The molecular recognition of potassium complexation of an unsymmetrical 1,3-alternate calix[4]-crown-5-N-azacrown-5 bearing two different crown-5 rings; (5) Molecular design of a molecular syringe mimic for metal cations using a 1,3-alternate calix[4]arene cavity.Firstly, in the present work, a quantum mechanical research of five lariat crown ethers (LCEs), A, B, C, D, E, which are based on either 15-crown-5 or 18-crown-6 frameworks and contain various pendant arms extending from either carbon or nitrogen atoms on the crown frameworks, had been done using DFT with B3LYP/6-31G(d) method in order to obtain the electronic and geometrical structures of the LCEs and their complexes with alkali metal ions: Na+ and K+. The nucleophilicity of LCEs had been investigated by the Fukui functions. For complexes, the match between the cation and cavity size, the status of interaction between Na+, K+ and donor atoms in the LCEs and the sidearm effect of the LCEs had been analyzed through the other calculated parameters, such as the ionization potentials, highest occupied molecular orbital energy, lowest unoccupied molecular orbital energy and energy gaps. In addition, the enthalpies of complexation reaction had been studied by the calculated thermodynamic data (298K). The calculated results are all in a good agreement with the experimental data for the complexes.Secondly, theoretical studies of the macrotricyclic tetramine hexaether (SC), its tetraprotonated form SC-4H+ and the corresponding complexes X–?SC-4H+ of SC-4H+ with the halide anions: F–, Cl– and Br– have been performed using DFT with B3LYP/6-31G method implemented in the Gaussian 03 program package. The optimized geometric structures obtained from DFT calculations are used to perform NBO analysis. The three main types of hydrogen bonds +N–H…F–, +N–H…Cl–, and +N–H…Br– are investigated. The results indicate that hydrogen bonding interactions are dominant and the halide anions: F–, Cl–, and Br– offer lone pair electrons to the contactingσ* (N–H) antibond orbital of SC-4H+. For all the structures, the most pronounced changes in geometric parameters upon interaction are observed in the proton-donor molecule. The intermolecular interaction energies are predicted by using B3LYP/6-31G methods with basis set superposition error (BSSE) and zero-point energy (ZPE) correction.Thirdly, theoretical studies of 1,3-alternate-25,27-bis(1-methoxyethyl)calix[4] arene-azacrown-5 (L1), 1,3-alternate-25,27-bis(1-methoxyethyl)calix[4]arene-N-phenyl -azacrown-5 (L2) and the corresponding complexes M+/L of L1 and L2 with Na+, K+ and Rb+ have been performed using DFT at B3LYP/6-31G(d) level. The optimized geometric structures obtained from DFT calculations are used to perform NBO analysis. The two main types of driving force metal-ligand and cation-πinteractions are investigated. The results indicate that intermolecular electrostatic interactions are dominant and the electron-donating oxygen offer lone pair electrons to the contacting RY* or LP* orbitals of M+ (Na+, K+, Rb+). What's more, the cation-πinteractions between the metal ion andπ-orbitals of the two rotated benzene rings play a minor role. For all the structures, the most pronounced changes in geometric parameters upon interactions are observed in calix[4]arene molecule. The calculated results of hydrated cation exchange reaction are in a good agreement with the experimental data for the complexes.Forthly, theoretical studies of an unsymmetrical calix[4]-crown-5-N-azacrown-5 (1) in a fixed 1,3-alternate conformation and the corresponding complexes: 1·K+(a), 1·K+(b), 1·K+(c) and 1·K+K+ have been performed using density functional theory (DFT) at B3LYP/6-31G(d) level. The optimized geometric structures obtained from DFT calculations are used to perform NBO analysis. The two main types of driving force metal-ligand and cation-πinteractions are investigated. The electron-donating heteroatoms O and N offer lone pair electrons to the contacting RY* or LP* orbitals of K+. In addition, the intermolecular interactions energies are prodicted by frequency analysis at B3LYP/6-31G(d) level. For all the structures, the most pronounced changes in geometric parameters upon interaction are observed in the calix[4]arene molecule. The results indicate that both the intermolecular electrostatic interactions and the cation-πinteractions between K+ andπ-orbitals of the two pairs facing inverted benzene rings play a significant role.At last, the chemically-switchable actions well imitate the function of a molecular syringe, has been studied in theory using the 1,3-alternate calix[4]arene bearing a nitrogen-containing crown cap at one side and a bis(ethoxyethoxy) group at another side by theπ-basic calixtube as a pipette and the crown ring as a rubber cap. The model is characterized by geometry optimization using density functional theory (DFT) at B3LYP/6-31G(d) level. The obtained optimized structures are used to perform natural bond orbital (NBO) and frequency analysis. The electron-donating heteroatoms: O and N offer lone pair electrons to the contacting RY* or LP* orbitals of K+, Ag+. The results indicate that when the nitrogen atom in the crown ring is protonated, K+ and Ag+ will be pushed out to the bis(ethoxyethoxy) side through aπ-basic calixtube. When the nitrogen·H+ in the crown ring is deprotonated, K+ and Ag+ are sucked back to the crown-capped side again. In the course of coordination, both the intermolecular electrostatic interactions and the cation-πinteractions between the metal ions andπ-orbitals of the two pairs facing inverted benzene rings play a significant role. It is believed that this prototype of a molecular syringe is a novel molecular architecture for the action of metal cations.