Design And Synthesis Of ITC-based Near-infrared Fluorescent Probes And Study On Fluorescence Imaging

Near-infrared fluorescent probes are widely used in biomedical applications because of their high tissue penetration,low background fluorescence and low optical energy.In recent years,various NIR fluorescent probes for small molecules and enzymes have been developed to study the mechanism of action of beacon molecules in organisms with disease or pharmacology.In this thesis,NIR fluorescent probes for small molecules,nucleic acids and enzymes were developed by designing different NIR fluorophores.Also through the specific targeting of nucleic acids,we designed and synthesised nucleic acid-targeted NIR photosensitizers for photodynamic therapy studies on living tumours.Details of the research are as follows.1.The fluoride ion（F-）plays an essential role in biological systems as one of the smallest and strongest electron-absorbing anions.In this chapter,a NIR fluoride ion fluorescent probe,Mito-FP,was designed using a near-infrared semi-flora dye as the fluorescent moiety,tert-butyldimethylsilyl（TBDMS）as the recognition site for the fluoride ion,and linked to the fluorescent moiety via a 4-hydroxybenzyl alcohol autocyclic linker.The probe Mito-FP is essentially non-fluorescent on its own due to blocked intramolecular charge transfer in the fluorophore.However,the specific cleavage of the Si-O bond by fluoride ions triggers the elimination of the intermediate of quinone methylation and the production of a fluorescent moiety semiflorocyanine dye with significant intramolecular charge transfer and concomitant fluorescence activation.In vitro spectroscopic exploration and analysis were culminated in the introduction of the probe Mito-FP into He La cells and cytofluorimetric imaging studies of fluoride ions in the cells.The experimental results indicate that the probe Mito-FP can provide a useful tool for studying fluoride ions in cells.2.G-quadruplexes（G4s）are DNA or RNA structures formed from guanine-rich sequences that play an indispensable regulatory role in many biological processes.In this chapter,we developed a G4s near-infrared fluorescent probe（TAQ）to enable activatable imaging of G4s in living cells.The probe TAQ fluoresces in aqueous solution with basic matter emission and its fluorescence was significantly enhanced upon binding to G4s structures at 677 nm.TAQ interacted extensively with different G4s structures and does not respond to single or double stranded nucleic acids.The linear response of the probe TAQ to G4s was shown to be between 5.0-600 n M,with a detection limit of 0.51 n M.Live cell experiments showed that TAQ emits a strong fluorescent signal upon interaction with specific G4s structures.We further used the probe TAQ to image the dynamics of RNA/DNA G4s in live cells in real time,and this NIR fluorescent probe could provide a valuable tool for monitoring the dynamics of G4s structures in live cells.3.Photodynamic therapy（PDT）with type Ⅰ photosensitizers（PSs）is a promising modality for the treatment of hypoxic solid tumours.However,near-infrared（NIR）typeⅠphotosensitizers are still limited and their efficacy needs to be improved by new targeting strategies.We developed a novel G-quadruplex（G4s）-targeted NIR typeⅠphotosensitizer by designing acridinium derivatives with a modifiable donor-π-acceptor system.Density functional calculations revealed the PS exhibited an effective intersystem crossing from S₁to T₁via a T₂intermediate.In vitro and in vivo cell studies showed that the photosensitiser was able to detect fluorescence activation of G4s under normoxic and hypoxic conditions and effectively produce superoxide anions,leading to cellular necrosis and ablation of G4s structures.The photosensitiser has strong potential for use in cancer therapy through targeted ablation of functional biomolecules.4.Intracellular histone deacetylase（HDAC）plays a critical role in chromatin remodelling,signal transduction and cellular homeostasis.Abnormal levels of HDAC are thought to be associated with a variety of diseases,including cancer,metabolic syndrome and neurodegenerative disorders.Due to the important role of HDAC in biomedical research and clinical treatment,it is important to design responsive probes of HDAC for living cells.However,the existing activated HDAC fluorescent probes are all in visible light excitation,which hinders the study of HDAC to some extent.Therefore,we provided a reliable and practical NIR fluorescent probe for HDAC research by optimising the NIR fluorophore,chemically coupling the HDAC response site,acetylaminohexanoic acid,to the NIR fluorophore,and performing fluorescence imaging studies on relevant cells and living tumours.