Host-guest interactions of chiral Schiff-base macrocyclic Zn(II) complexes with α-amino acids

Two chiral Schiff-base macrocyclic Zn(II) complexes ( M _{R , R} and M _{S , S} ) were synthesized from the condensation reaction of 3,3’-methylene-bis(2-hydroxy-5-methylbenzaldehyde) and 1 R ,2 R - or 1 S ,2 S -cyclohexanediamine in the presence of Zn(NO ₃ ) ₂ . The crystal structure of M _{R , R} was determined via single crystal X-ray diffraction technique. In the solution of MeOH/H ₂ O (9:1), the UV-Vis spectra were utilized for the host-guest interaction studies between M _{R , R} or M _{S , S} and a series of α -amino acid enantiomers. The results demonstrated that both M _{R , R} and M _{S , S} exhibited significant binding interactions with D -/ L -Argnine (Arg), D -/ L -Lysine (Lys), and D -/ L -Glutamic acid (Glu), and the binding ratio of these host-guest interaction systems was 1:1. Further studies showed that both M _{R , R} and M _{S , S} exhibited a higher enantioselectivity toward these D -amino acid enantiomers than L -amino acid enantiomers. Moreover, the density functional theory (DFT) calculation indicated that the binding affinity and enantioselectivity of M _{R , R} or M _{S , S} toward these amino acid enantiomers were mainly attributed to the hydrogen-bonding interactions between the amino acid enantiomers with the bridging water molecules located in the binuclear Zn(II) complexes.