Density functional theory study of a molecular allosteric switch for 2,2'-bipyridyl-3,3'-15-crown-5

A classical model of "molecular machine," which acts as an ON-OFF switch for 2,2'-bipyridyl-3,3'-15-crown-5 (L), has been theoretically studied. It is highly important to understand the mechanism of this switch. The alkali-metal cations (Na(+) and K(+) ) and W(CO)(4) fragment are introduced to coordinate with the different active sites of L, respectively. The density functional theory (DFT) method is used for understanding the stereochemical structural natures and thermodynamic properties of all the target molecules at B3LYP/6-31G(d) and SDD (Stuttgart-Dresden) level, together with the corresponding effective core potential (ECP) for tungsten (W). The fully optimized geometries have been performed with real frequencies, which indicate the minima states. The nucleophilicity of L has been investigated by the Fukui functions. The natural bond orbital analysis is used to study the intermolecular charge-transfer interactions and explore the origin of the internal forces of the molecular switch. In addition, the binding energies, enthalpies, Gibbs free energies, and the cation exchange energies have been studied for L, W(CO)(4) L, and their corresponding complexes. The properties of the complexes displayed by in presence or absence of the W(CO)(4) fragment are also analyzed. The calculated results of allosterism displayed by L are in a good agreement with the experimental results.