The fluorescence distinction of chiral enantiomers: a Zn coordination polymer sensor for the detection of cinchonine and cinchonidine

Abstract

Cinchonine (+Ccn) and cinchonidine (−Ccn) are quinoline alkaloid drugs, which are found in natural products of cinchona bark and are used as specific drugs for treating malaria. As a pair of chiral enantiomers, they show different biological activities and performances in pharmacological applications. In this work, we prepared a fluorescence sensor based on a Zn coordination polymer for the sensitive and selective detection of the above enantiomers, namely, [Zn(PT)(H₂O)₂]_n (IMU-Zn1) (H₂PT = 5-(5-pyrimidyl)-1,3-benzenedicarboxylic acid). +Ccn and −Ccn had a “turn-on” effect on the fluorescence of IMU-Zn1, and the ratio of their fluorescence enhancement rate reached 2.22, and the limits of detection (LOD) for +Ccn and −Ccn were 2.10 μM and 1.90 μM, respectively. In addition, infrared spectroscopy, ¹HNMR spectroscopy, X-ray powder diffraction, fluorescence lifetime, Gaussian calculations, and other characterization methods were used to explore the mechanism of fluorescence enhancement. The results showed that there was a photoelectron transfer process and there were electrostatic interactions between +Ccn and IMU-Zn1. The photoelectron transfer process, the electrostatic interactions, and the stronger hydrogen-bonding interactions between −Ccn and IMU-Zn1 are responsible for a more pronounced fluorescence enhancement. This work provides an alternative strategy for the identification of chiral enantiomers using light-emitting coordination polymers as fluorescent probes.