title: Molecular design of a "molecular syringe" mimic for metal cations using a 1,3-alternate calix[4]arene cavity.
abstract: 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 the pi-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 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* (1-center Rydberg) or LP* (1-center valence antibond lone pair) 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 a pi-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 the coordination, both the intermolecular electrostatic interactions and the cation-pi interactions between the metal ion and pi-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.
authors.affiliation: Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education, College of Chemistry, Xiangtan University, Xiangtan, Hunan 411105, People's Republic China.
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Zheng
authors.forename: Xueye
authors.initials: X
authors.lastname: Wang
authors.forename: Keqi
authors.initials: K
authors.lastname: Shen
authors.forename: Nuanqing
authors.initials: N
authors.lastname: Wang
authors.forename: Yueming
authors.initials: Y
authors.lastname: Peng
mesh_terms: D001665:Binding Sites; D047250:Calixarenes / Q000737:chemistry*; D002412:Cations / Q000737:chemistry; D017076:Computer-Aided Design; D008024:Ligands; D008670:Metals / Q000737:chemistry*; D018716:Molecular Mimicry; D009584:Nitrogen / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry; D010636:Phenols / Q000737:chemistry*; D011522:Protons; D011789:Quantum Theory; D012834:Silver / Q000737:chemistry; D013816:Thermodynamics
chemical_list: D002412:Cations; D008024:Ligands; D008670:Metals; D010636:Phenols; D011522:Protons; C121325:calix(4)arene; D047250:Calixarenes; D012834:Silver; D009584:Nitrogen; D010100:Oxygen