Design,Synthesis And Biological Application Of Novel Fluorescent Probes For Ferrous Ion And Cysteine

The labile iron pool,mainly in the form of Fee+,binds weakly to cellular ligands and exists at the center of iron metabolic network.The labile iron pool plays pivotal roles in a diverse array of physiological and pathological processes in the human body.However,the biological function of labile iron pool is not completely clear.Therefore,detection of Fe2+ in the labile iron pool is helpful for undestanding the biological functions of the labile iron pool.Fluorescent probes are attractive tools to visualize Fe2+ in the labile iron pool.Cysteine(Cys)is an important amino acid and biothiol which plays a vital roles in physiological processes such as protein synthesis,cellular detoxification and metabolism.Deficiency of Cys might lead to many health problems including slow growth in children,liver damage,lethargy as well as edema.On the other hand,aberrantly high level of Cys is associated with neurotoxicity.Thus,it is of great significance to develop highly selective and sensitive fluorescent Cys probes for understanding the physiological and pathological functions of Cys.This work mainly covers the following two parts:1.Two reaction-based TPE probes Coum-Nox and Acedan-Nox were designed and synthesized for labile Fe2+ based on Fee+-triggered reduction of N-oxide and recovery of the parent fluorophore 7-diethylamino-4-methylcoumarin or 2-acetyl-7-diethylaminonaphthalene(Acedan).Coum-Nox and Acedan-Nox exhibited a high signal to background ratio(about 17 fold),fast response(within 15 min),long stocks shift,and high sensitivity(with a detection limit of 0.06 or 0.07?M)in aqueous solution.More meaningfully,Coum-Nox and Acedan-Nox could be used for TPE imaging of labile Fe2+ in living cells with high selectivity,low toxicity and good biocompatibility.To extend the potential biological application,Coum-Nox was used to investigate the transferrin receptor induced(TfR)iron uptake process in HepG2 cells and L02 cells by two-photon real-time visualization of the cellular labile Fe2+pools.The results showed that HepG2 cells and L02 cells loaded with iron and holotransferrin and incubated with Coum-Nox exhibited gradual enhancement in fluorescence and the fluorescent enhancement rate of HepG2 cells is faster than that of L02 cells,which could be blocked by pretreatment of the cells with anti-transferrin receptor polyclone antibody,indicating that the expression level of transferrin receptor on normal hepatic cells is lower than that of cancerous hepatic cells.2.A simple near-infrared fluorescent probe HCA-A was developed for rapid and specific detection of cysteine(Cys).4-Dimethylamino-2'-hydroxychalcone(HCA),which displays both excited intramolecular proton transfer(ESIPT)and aggregation induced emission(AIE)effect,was ultilized as the fluorophore,and an acrylate group was used as the blocking agent as well as the responsive moiety.Cys could trigger the removal of the acryl group and release of fluorophore HCA.The ESIPT and AIE process of HCA were thus restored,rendering the probe a high signal to noise ratio and low detection limit for Cys(0.04 ?M).More importantly,the high selectivity of the probe for Cys over homocysteine(Hcy)and glutathione(GSH)enables it to image the endogenous Cys in living cells.