Design,Synthesis And Bioimaging Applications Of A Series Of Small Molecule Fluorescent Probes Based On The Coumarin Platform

In bio-related research,fluorescence imaging has attracted much attention due to its advantages of non-invasive,visualization and tracking of biological molecules and physiological processes in life systems.Moreover,fluorescence imaging is developing faster and faster because of its high sensitivity,simple operation and good specificity.Nowadays,biofluorescence imaging has been used in many fields,such as small biological molecules,viscosity,various ions in the environment and so on.Coumarin fluorescent dyes have good two-photon properties and large Stokes shift.Therefore,many new fluorescent probes with wide applications can be designed based on the push-pull electronic system of coumarin and its derivatives.In this paper,a series of two-photon fluorescent probes of coumarin were designed and synthesized by modifying the coumarin platform for the detection of various small molecules.In chapter 2,a novel two-photon fluorescence probe Co-Cys was designed and synthesized using coumarin as fluorescence platform and acrylate as recognition site of Cys.Compared with other active sulfur such as GSH,Hcy,SO₂,the probe showed high selectivity and sensitivity to Cys.The fluorescence quenching of the probe Co-Cys is caused by the strong electron pulling ability of the methyl acrylate group and coumarin structure.When the probe interacts with the Cys molecule,the probe Co-Cys is reduced to7-diethylamino-3-hydroxycoumarin.Because of the strong push-pull electron effect of the hydroxyl and coumarin structure,the ICT effect becomes stronger,resulting in a significant increase in the fluorescence intensity,which is realized by fluorescence enhancement.In bioimaging experiments,the probe can detect Cys in HeLa cells,tissues and zebrafishes in a single-photon and two-photon mode.In chapter 3,a novel two-photon fluorescence probe Hy-N2H4 was designed and synthesized using coumarin derivatives as fluorescence platform and aldehyde group as hydrazine?N₂H₄?recognition site.Hydrazine is a common environmental pollutant in chemical and pharmaceutical industries.According to the investigation,N₂H₄ is not only an environmental pollutant,but also a harmful substance.Therefore,monitoring N₂H₄ is an urgent task.In this chapter,a probe Hy-N2H4 was designed and synthesized for monitoring N₂H₄content in aqueous solution and living cells.The selective addition/cyclization reaction of Hy-N2H4 with N₂H₄ can quench probe fluorescence efficiently.The probe has high selectivity and sensitivity.It only takes 5 minutes to react with N₂H₄ in aqueous solution at room temperature.In addition,the fluorescence intensity of the probe changed significantly?about34-fold?before and after identification of N₂H₄.The detection limit can reach 0.33?M.In addition,Hy-N2H4 can be used to monitor N₂H₄ in living cells and tissues.In chapter 4,3-nitro-7-diethylaminocoumarin was designed and synthesized as a fluorescent probe CoNO2-HY for nitroreductase.The two-photon fluorescent probe for detecting nitroreductase described in this chapter emits strong fluorescence in the presence of nitroreductase.This phenomenon indicates that the probe can be appled to biological imaging.Bioimaging experiments on cells and tissues show that the probe can be effectively used to detect endogenous nitroreductase,and the penetration depth of the tissue can reach 90?m.Moreover,the two-photon properties of the probe can also be helpful to further study the physiological and pathological functions of nitroreductase.