QCM based enantioselective discrimination of enantiomers by a pair of serine derived homochiral coordination polymers

Decoding enantioselective molecular interactions between sensors and guests into readable signal represents a great challenge in developing selective sensing technology. In this work, a pair of serine derivatives based homochiral coordination polymer (HCP) enantiomers, (L)-SA-Cd and (D)-SA-Cd, were synthesized and explored as enantioselective sensors towards guest enantiomers. Quartz crystal microbalance (QCM) technology was employed to indicate the gravimetric change of (L)- and (D)-SA-Cd towards variable chiral guests, and an enantioselective factor of 1.72 ± 0.15, 1.81 ± 0.08, 1.37 ± 0.03 and 2.89 ± 0.09 were achieved for lactic acid, menthol, valinol and 1-phenylethylamine (PEA), respectively. PEA was further selected to comprehensively study the enantioselectivity via electrochemical tests, HPLC analysis and theoretical calculations. By comparison with state-of-art works, the enantioselective discrimination for PEA enantiomers is better than a vast majority of similar reports. (L)- and (D)-form of SA-Cd exhibited mirror behaviors towards guest enantiomers, and control experiments indicated the role of HCP construction in enhancing enantioselectivity. H-bonding effect was found to be the binding force between SA-Cd and PEA, as verified by FT-IR and UV-Vis titration studies. Further DFT calculations revealed the existence of conformation oriented H-bonding between the chiral -OH groups of serine fragment and -NH₂ group of PEA. The findings indicate that HCP construction represents an effective strategy for promoting enantioselectivity, and monitoring gravimetric change could be a promising general method in decoding most of the enantioselective recognition process.