Theoretical study on noncovalent interaction of molecular tweezers by Zn(II) salphen-azo-crown ether triads receptor.

A novel zinc(II)-salphen-azo-benzo-15-crown-5 triad receptor was studied theoretically as ditopic recognition of hydrophobic amino acid. And density functional theory was used to investigate the Zn(II) salphen-crown ether complex (L1), complex L2 (L1 with the alkaline metal cation Na+), and the corresponding 1:1 sandwich complex (complex L with tryptophan). In this work, geometrical optimization was carried out using ωB97XD functional and def2-SVP basis set for all atoms. The absorption spectra and excited-states were calculated using time-dependent density functional theory and ωB97XD/def2-TZVP level. The absorption spectra data show some significantly shifts in the absorption band due to the present of Na+ or tryptophan. In addition, interfragment interactions between receptor L and tryptophan were analyzed in detail by Independent Gradient Model and topological properties of Bader's atoms in molecules theory, which is found to contribute to forming the metal-ligand bonds, intermolecular H-bond, and van der Waals interaction in 1:1 sandwich complex. The above results demonstrate that the L2 complex is a ditopic receptor to be utilized to recognize amphiphilic molecule - tryptophan.