Host-guest interactions of chiral Schiff-base macrocyclic Zn(II) complexes with α-amino acids
摘要
Two chiral Schiff-base macrocyclic Zn(II) complexes (MR,R and MS,S) were synthesized from the condensation reaction of 3,3’-methylene-bis(2-hydroxy-5-methylbenzaldehyde) and 1R,2R- or 1S,2S-cyclohexanediamine in the presence of Zn(NO3)2. Their structures were characterized using 1H/13C NMR, ESI-MS, and elemental analysis, and the crystal structure of MR,R was further determined via single-crystal X-ray diffraction. In the solution of MeOH/H2O (9:1), the UV-Vis spectra were utilized for the host-guest interaction studies between MR,R or MS,S and a series of α-amino acid enantiomers. The results demonstrated that both MR,R and MS,S exhibited quantifiable binding interactions with D-/L-Arginine (Arg), D-/L-Lysine (Lys), and D-/L-Glutamic acid (Glu), and the binding ratio was consistently 1:1. Moreover, the density functional theory (DFT) calculation indicated that the binding affinity as well as the observed enantioselectivity of MR,R or MS,S toward these amino acid enantiomers was mainly attributed to the hydrogen-bonding interactions between the amino acid enantiomers with the bridging water molecules located in the binuclear Zn(II) complexes.