Near-infrared Xanthene Fluorescent Probes:Synthesis、 Biological Small Molecules Recognition And Application

Based on the backbone construction of the fluorescent probe and the specific recognition of the analyte and the reaction site,the near-infrared fluorophore re-modified on the basis of the xanthene structure was selected,and the rhodamine with good"on-off"ring effect was selected.The fluorophore serves as a signal reporter group,or choose a 1,8-naphthylimide fluorophore with good photostability and easy modification,and combine them into a double fluorophore fluorescent probe.Three xanthene-based fluorescent probes were designed and synthesized,and the near-infrared emission of 1,3,3-trimethyl-2-methylene porphyrin-xanthene lactam fluorescent probe RhAN,naphthalimide-rhodamine thiohydrazide reactive fluorescent probe RHSNO and the naphthalimide xanthene fluorescent probe RhSN were both characterized.The fluorescent properties of glutathione(GSH)were investigated by probe RHAN.The recognition mechanism of multi-step tandem reaction,such as Michael conjugate addition and ring-opening reaction of induced rhodamine lactam,was investigated and applied to liver cancer cells(MCF-7)Imaging;specific recognition of ClO-by probe RHSNO,studied ClO-induced intramolecular desulfurization cyclization-through-bond energy transfer recognition mechanism,applied to imaging of liver cancer cells(MCF-7);probe RhSN selectively recognizes the analyte glutathione and is applied to breast cancer cell(HepG2)imaging.The details are as follows:The xanthene was used as a building unit,and the near-infrared xanthene"off-on"fluorescent probe RhAN was synthesized by knoevenagel condensation reaction for detecting GSH;rhodamine and naphthalimide were linked through thiohydrazide to form probe RHSNO based on a double reaction site induced through-bond energy transfer(TBET)system;the probe RhSN was synthesized by naphthalimide group reacting with rhodamine ring-opening structure for selective detection of GSH.The key organic reaction mechanisms used in the synthesis of these probes and the choice of experimental conditions were discussed.1.Glutathione as a biothiol has many key roles in physiological and pathological processes,including combating oxidative stress and maintaining redox homeostasis that is pivotal for cell growth and function,drug metabolism,intracellular signal transduction and gene regulation.Moreover,diseases such as diabetes,stroke,erythrocyte problems,atherosclerosis,inflammation,nervous diseases,and Parkinson’s disease were suggested to be related to abnormal levels of GSH.Therefore,it is important to detect GSH quickly and efficiently.Therefore,this chapter studies the mechanism and properties of probe RhAN recognition.The results show that the probe has"naked eye"recognition ability for glutathione and can be specific detacte from other biothiols,including cysteine and homocysteine.In the presence of GSH,the mechanism of Michael addition and intramolecular amino induced spirolactam opening is triggered.The recognition process exhibits high selectivity,sensitivity,wide working range of PH,and the recognition of response is not affected by other biothiol interferences.In addition,RhAN was used for cell imaging of endogenous and exogenous GSH,and the results indicate that RhAN is a fast and effective biosensor for detecting excess GSH in living cells,maintaining amino acid balance in the body and ensuring normal life activity.2.Hypochlorite(ClO~-)is one of the important reactive oxygen species(ROS).It plays a vital role in the immune defense against pathogens and thus contribute to host defense.Therefore,this chapter designed and synthesized a rhodamine-naphthalimide fluorescent probe for the detection of ClO~-.Studies on the probe RHSNO have shown that in the presence of ClO~-,ClO~--triggered intramolecular desulfurization cyclization of rhodamine-thiohydrazide,the spiro ring of rhodamine was opened and meanwhile desulfurization hydrogenation happened at naphthalimide moiety,naphthalimide and rhodamine transformation from monothio-bishydrazide to 1,2,4-oxadiazole and desulfurization hydrogenation in naphthalimide moiety simultaneously,so that a typical TBET process took place from naphthalimide donor to rhodamine acceptor,resulting in an approximately 260-fold increase in fluorescence emission at 590 nm.The detection limit of probe was 22.1 nM,and it shows high sensitivity and fast response time.It has been successfully applied to the imaging of MCF-7 cells.The results show that the fluorescence sensor RHSNO can be used as a rapid and effective method to detect excessive ClO~-in living cells.It can be used to maintain the balance of hypochlorite in the body and ensure normal life activities.4 The selective recognition of glutathione by fluorescent probe RhSN and its response to PH were studied.Since the rhodamine and naphthalimide linkages form a sulfatide bond,rhodamine is still in an open-loop state,so the fluorescence of the probe is open,and the naphthalimide has a quenching effect on fluoresence of rhodamine.In the case of the tripeptide GSH,the sulfhydryl group of GSH first attacks the carbonyl group of rhodamine,leaving the naphthalimide sulfhydryl group,and the thiol group of GSH and rhodamine undergoes a transesterification reaction and the rhodamine moiety is enhanced at 588 nm(quantum yield:0.64).Furthermore,the chemodosimeter exhibits excellent anti-interference with low detection limit,and it works effectively within a wide pH range.RhSN was successfully applied in clearly imaging of endogenous or exogenous GSH with low toxicity in HepG2 cells.