Theoretical Study On The Complexation Capability Of Azaocrown Ether And Its Derivatives

Azacrown ethers and their derivatives can be used for extraction agent and surfactant with complexation capability. Their complexation capability is mainly depended on the complexation bodies with distinct structure. Azacrown ethers, which possess various rigidity, different substitution heteroatoms, one or more nitrogen atoms, different nitrogen position and alkyl substitution, were calculated to evaluate their complexation capability in this paper. The calculation results found that azacrown ether, especially diazacrown ether, exhibited the best complexation capability in all substitution crown ethers involved. A new parameter,"the ratio of ionization energy and radius"was found to predict the complexatin capability of crown ethers and their derivaties. All results as follow:The investigation on the metallic complexation of heterocyclic compounds with five nitrogen found that the complexation capability increased with the valence of centre metal ions. Their binding energy decreased with the decrescent rigidity of complexation body when the nitrogen involved in a conjugation, but increased with the decrescent rigidity of complexation body when the nitrogen did not involved in a conjugation.The complexation of 12-crown-4 with metal ions and its heterocyclic derivatives containing N, P, and S atoms were studied by the density functional theory that was proved to fit these complexes by theoretical calculations and MS experiments. The results indicated that aza-12-crown-4 exhibited the highest metal binding selectivity, and phospha- or thia- analog of 12-crown-4 ether offered a weaker ligand toward the metal cations. The different hetero-substitution appeared to be crucial in the metal complexation of crown ether. This research indicated that azacrown ether was the preferred parent for complexation surfactant of crown ether and extraction agent.It is necessary to find how many nitrogen atoms can make the crown ether have best complexation capability, since azacrown ether offered the strongest binding ability in 12-crown-4 and its heterocyclic derivatives containing N, P, and S atoms. The results indicated that, in all ionophores involved, diazacrown ethers exhibited the biggest binding ability, offered better metal binding selectivity, and yielded more stable complexes than other ionophores, which means different numbers of nitrogen substitution results in different metal binding capability. It will provide information of the molecular design and synthesis, and the applied engineering.The nitrogen-position effect of diazacrown ethers with 12-, 15-, 18- members on their complexation selectivity and the stability of these complexes were investigated in this section, after the azacrown ether especially diazacrown ethers possess stronger complexation capability was determined above. The calculation results found that 1,10-diaza-18-crown-6, 1,7-diaza-12-crown-4, and 1,4-diaza-15-crown-5 exhibit higher binding selectivity than their corresponding nitrogen position isomers, respectively. Clearly, the position of nitrogen plays an important role in the selectivity of diazacrown ethers to metal ions in the system involved. The binding capability of complexation molecules with a set of metal ions including Li+, Na+, K+, Be2+, Mg2+, Ca2+, Cu2+ and Zn2+ was investigated and their extraction power was evaluated. A new parameter,"the ratio of ionization energy and radius", was found suitable in evaluation of the binding capability of complexation molecules with different ions. It offers a new method to predict the metal binding selectivity of extractant agent and azacrown surfactant, and provides a new idea for their applied research in engineering.The effect of alkyl substitution on the complexation capability of azacrown ethers to alkaline metal ions was evaluated by theoretical and experimental datum. The results showed that the alkyl substitution of azacrown ethers influenced their metal complexation. The errors between theoretical and experimental decreased with the increase of alkyl substitution when the calculation model inclines to fit the true. The results in this section will contribute to the alkyl azacrown ether with bigger position hindrance and their simulation on computer.The B3LYP method of density functional theory is suitable in the systems studied, which gives an approving calculation accuracy and efficiency but less calculated expense. The results found that the azacrown ether especially diazacrown ethers possess stronger complexation capability."The ratio of ionization energy and radius", a new parameter was introduced to evaluate the binding capability of complexation molecules with different ions, which was a better parameter than"size effect"and"ion potential". The work will provide useful information in the design and synthesis for the effectual molecular body that can be used in phase transfer catalyst, ion-selective extractant, ion-selective electrode and ion-exchange resin, and give a new idea in the research of engineering application such as heavy metal pollution, luminesecent material, and isotope diagnose technique.