The Design And Synthesis Of Conjugated N-heterocyclic Onium Salt-based Fluorescent Probes And Studies On Their Performance

Detection of exogenous or endogenous active sulfur species（RSS）and reactive oxygen species（ROS）can not only effectively prevent the occurrence of related diseases induced by these species,but also provide theoretical guidance for later clinical treatment.Fluorescent probe is a tool for target detection by using fluorescent signals,which has many advantages,including simple operation,low detection cost and low physiological toxicity.However,the reported RSS or ROS fluorescent probes usually use phenyl dense ring structure as the fluorophore skeleton,which have some problems,including aggregation fluorescence quenching,the non-obvious change of fluorescence wavelength,and the unable organelles accurate localization,thus affecting the practical application of probes.N-heterocyclic onium salt are a class of positively charged cations.They can not only achieve obvious changes in fluorescence color（wavelength）for probes by using intramolecular charge transfer effect,but also efficiently locate mitochondria in cells.Based on this,this paper uses conjugated azonium salt as skeleton to develop three different fluorescence probes,which achieve specific and high sensitivity detection of bisulfite ions（RSS）,hydrogen peroxide（ROS）and hypochlorite ions（ROS）,respectively.The specific work of this paper is as follows:（1）A new conjugated polymer-based ratiometric fluorescent probe PFTQ was designed and synthesized,which used quinoline as the framework.The probe achieved high selectivity and high sensitivity detection of HSO₃^-in food by a smartphone detection platform.In the probe PFTQ,the electron-deficient C=C bond energy coupled with the quinolinium unit undergoes a specific 1,2-addition reaction with the nucleophile HSO₃^-,which changes the color of the fluorescence from red to bright blue.At the same time,the fluorescence color signal is converted into the corresponding RGB digital value through the detection platform of smart phone,and the linear relationship between RGB（B/R）and HSO₃^-concentration is established to realize the quantitative detection of HSO₃^-.The probe has good selectivity and low sensitivity for HSO₃^-detection（detection limit is 106 n M）.Finally,the probe used a smartphone detection platform to achieve high precision detection of HSO₃^-content in rock sugar,red wine and beer samples.（2）A mitochondrial-targeted fluorescent probe TBBP-Pro was designed and synthesized,which used pyridonium as the framework.This probe can realize the rapid,specific and highly sensitive detection of endogenous hydrogen peroxide（H₂O₂）in mitochondria,zebrafish and mice.In this probe,the 4-（1-cyanovinyl）pyridonium unit not only acts as the specific reaction site of H₂O₂,but also can efficiently target cell mitochondria.Different from the reported H₂O₂ fluorescence probe,this probe uses olefin oxidative cracking reaction as a new detection mechanism of H₂O₂,which makes it have the advantages of good selectivity,high sensitivity（detection limit is 47 n M）,and short response time（≤5 min）for H₂O₂detection.In addition,the probe TBBP-Pro was successfully used for fluorescence detection of endogenous H₂O₂ in Hep G2 cells and zebrafish.Finally,this probe was successfully used to monitor the dynamic changes of H₂O₂ level in mice with ulcerative colitis,so as to provide theoretical basis for the treatment and diagnosis of related diseases.（3）A mitochondrial-targeted fluorescent probe MTP-BT was designed and synthesized,which used benzothiazonium as the skeleton.This probe can detect exogenous and endogenous hypochlorite ions（Cl O^-）in Hep G2 cells and RAW 264.7 cells.In this probe,the S atom in the phenothiazine ring is specifically oxidized to a sulfoxide structure by Cl O^-,which results in a bright yellow emission within 30 seconds.In addition,benzothiazonium units are highly effective in targeting mitochondria of Hep G2 cells.Finally,the probe was successfully used for the semi-quantitative detection of endogenous Cl O^-in RAW 264.7macrophage.In conclusion,three different N-heterocyclic onium salt-based fluorescent probes have been designed and successfully synthesized,which could selectively and sensitively detected bisulfite ions in food,endogenous H₂O₂ in vivo and endogenous Cl O^-in macrophages,respectively.In addition,the detection mechanism of fluorescence probes was revealed through hydrogen NMR spectroscopy,high resolution mass spectrometry,fluorescence spectroscopy and theoretical calculation methods,our work will provide theoretical guidance for the design of other fluorescence probes...