Design, Synthesis And Applications Of Fluorescent Probes For Sensing Redox-active Molecules

Fluorescent probes have become effective tools for monitoring biomolecules because of its high sensitivity and high-speed spatiotemporal resolution.In recent years,the fluorescent assays based on synthesized organic probes have been gained a great deal of attentions.But some of the developed fluorescent probes suffered from seceral drawbacks,such as poor water-solubility,low quantum yield,tedious synthesis routes,and so on.Therefore,it is highly required to develop new fluorescent probes which could overcome these above-mentioned disadvanteges.This thesis is aimed to continually construct fluorescent probes with advanteges of facile synthetic route,excellent water-solubility,ratiometric response mode,large Stocks shift,and/or near-infrared emission character by tuning and optimating the structure of the fluorephore,and further apply these probes for detecting some important small redox-active molecules and explore their biological applications.The detail works are as follows:(1)Coumarin-based fluorophores has the advanteges of facile synthetic route,tunable structure and favorable optical features.It is expected that by introducing hydroxyl group to its benzene ring could improve the water solubility of the coumarin-based fluorophores.And further using 8-hydroxyjulolidine instead of the traditional 3-diethylaminophenol a emmision red-shifted fluorophore is obtained.By coupling the recognition moiety of 2,4-dinitrobenzenesulfonyl ester(DNBS)to this fluorophore,a trun-on fluorescent probe was synthesized for the detection of Cysteine(Cys).The probe shows a significant fluorescence off-on response(~52-fold)by reaction with Cys in 100% aqueous buffer media.This probe also features high selectivity for Cys over other species(including glutathione),as well as high sensitivity with a low detection limit of 23 nM.Moreover,cell cytotoxicity and imaging tests indicate that the probe is biocompatible and can be utilized for imaging Cys in live cells.(2)A new ratiometric fluorescent probe was developed for the detection of hydrazine.The probe was obtained by incorporating the recognition moiety of acetyl group onto the above-mentioned coumarin fluorophore.The probe displayed a distinct cyan emission in a 100% aqueous phosphate buffer solution.In the presence of hydrazine,probe undergoes a hydrazinolysis process to release the coumarin fluorophore,which exhibited significant hypsochromic shifts in both absorption and emission spectra,and thus achieving a ratiometric response.This ratiometric probe is highly selective and sensitive toward hydrazine detection.The limit of detection(LOD)was calculated to be 34 nM.Moreover,cellular toxicity and imaging experiments suggested that the probe can be used to monitor hydrazine in living cells.(3)To conquer the problem of signal interference from the exciting light,a new green-emitting fluorescent probe was developed for biothiols detection.The sensing mechanism is based on thiols induced the cleavage of 2,4-dinitrobenzenesulfonate group in the probe thereby eliminating the photoinduced electron transfer(PET)process to release the fluorescent dye.The probe exhibited favorable properties such as excellent selectivity,highly sensitive(0.12 ?M),large Stokes shift(117 nm)and remarkable turn-on fluorescence signal(148-fold).Furthermore,confocal fluorescence imaging indicated that the probe was membrane-permeable and suitable for visualization of thiols in living HeLa cells.(4)To surmount the problem of signal interference from the distribution of probes,a novel ratiometric fluorescent probe was prepared for the detection of benzoyl peroxide(BPO).The probe was obtained by coupling the recognition unit of arylboronate to a benzothiazole-derived fluorophore.The probe solution is colorless and displays weak blue fluorescence at 460 nm.Upon addition of BPO,the arylboronate substituent can be removed via the oxidation and 1,4-elimination processes.The released fluorophore emits strong yellow–greenish fluorescence at 545 nm.The ratiometric response of the probe is highly selective and sensitive for BPO.The dynamic range was fitted in the range of 1.0 ~ 75.0 ?M with a detection limit of 0.26 ?M.In addition,the probe was applied to quantitative detection of BPO in real samples of wheat flour and antimicrobial agent.Cellular experiments further demonstrated that the probe can be effectively utilized for imaging BPO in living cells.(5)NIR fluorescent probes have the merits of excellent cell-penetrating ability and non-invasive characteristic.And NIR fluorescent probes has large Stock shift would further eliminate signal interferences.Herein,a novel NIR fluorescent with large Stock shift was devised and synthesized by condensing 4-(diethylamino)salicylaldehyde with a electron withdrawing moiety.Further incorporating 2,4-dinitrofluorobenzene to the fluorepore,a trun-on NIR fluorescent probe was obtained for sensing thiophenol.The porbe displayed excellent selevtivity for thiophenol without interference of other relevant species including biothiols and hydrogen sulfide.The LOD was calculated to be 17 nM.The probe also has been exploited for monitoring thiophenol in living HeLa cells.