Design, Synthesis And Application Of Novel Fluorescent Probes Based On Coumarin And Naphthalene Derivatives

In biological systems, some cations, anions and biological molecules involve in a variety of physiological or pathological processes. In order to study and understand their roles and influences in physiology and pathology, the development of effective detection methods has become a research hotspot. Among them, fluorescent probe has gotten a lot of attention due to its high sensitivity, non-destructive sample preparation, and fast analysis with high spatiotemporal resolution, which is widely used in analytical chemistry, biochemistry, biology and medicine. In this thesis, we designed and synthesized a series of fluorescent probes based on coumarin, rhodamine, tetraphenylethene and naphthalene derivatives for detection of biological-related cations and molecules. The contents of this thesis are presented as follows:1. In Chapter2, we have reported a coumarin-based fluorescent probe T-CM for high-sensitivity detection of thiophenols based on the thiolysis reaction between thiophenols and2,4-dinitrophenyl ether. The introduction of a2,4-dinitrophenyl ether group into7-hydroxycoumarin would inhibit intramolecular charge transfer (ICT) between electron donor and electron acceptor, resulting in low fluorescence emission from the probe T-CM. After the probe reacts with thiophenols, the2,4-dinitrophenyl ether group is specifically removed, resulting in strong fluorescence emission from7-hydroxycoumarin. The probe shows a high selectivity and a high sensitivity for thiophenols with a linear response concentration range from3.0×10-Mto2.5×10-M and a detection limit of8×10-9M. Moreover, the probe was applied for quantitative detection of thiophenols in real water samples with satisfactory results.2. Nitroxyl (HNO) is involved in a number of important physiological or pharmacological progresses, and the development of efficient analytical methods for HNO detection is critical for understanding its physiological and pathological functions. Although several fluorescence probes have been reported for HNO, most of them suffer from interferences from biological reductants such as glutathione and ascorbate. In Chapter3, we reported a novel coumarin-based fluorescent probe P-CM for quantitative detection of HNO based on the reaction between HNO and triphenylphosphine group. The probe affords a high sensitivity to HNO with a linear response concentration range from5.0×10-8M to5.0×10-6M and a detection limit of2×10M. Also, P-CM exhibits a high selectivity for nitroxyl over other biologically relevant RNS, ROS, metal ions. It is particularly noteworthy that the fluorescence intensity of P-CM was hardly affected by biological reductants, including GSH, AA, and Na2S (a hydrogen sulfide source). Moreover, the probe was applied for quantitative detection of HNO in bovine serum with satisfactory results.3. In eukaryotic cells, lysosomes (pH4.5-5.5) contain numerous enzymes and proteins exhibiting a variety of activities and functions, and abnormal variation in the lysosomal pH causes defects in lysosomal function. Thus, it is important to investigate lysosomal pH in living cells to understand its physiological and pathological functions. In Chapter4, we design a new rhodamine-morpholine fluorescent probe RM to detect lysosomal pH changes with high sensitivity, high selectivity, high photostability and low cytotoxicity. The Probe RM shows a140-fold increase in fluorescence intensity from pH7.4to4.5with a pKa value of5.23. Importantly, RM can detect the chloroquine-induced increase in ysosomal pH and monitor the dexamethasone-induced changes in lysosomal pH during apoptosis in live cells. All these features demonstrate its value of practical application in biological systems.4. Aggregation-induced emission (AIE) dyes such as tetraphenylethene show different emission mechanism from traditional dyes, which are nonemissive when molecularly dissolved but highly emissive when aggregated, and have been well employed to design turn-on fluorescent probes for various targets. In Chapter5, we reported tetraphenylethylene-based AIE probe TA for Al3+for the first time, by employing the tetraphenylethene as the fluorophore and two diethylenetriamine units as the recognition ligand for Al+. In the presence of A13+(1.1equiv), the probe TA shows a32-fold fluorescence enhancement, which together with the low background fluorescence of free probe allow for high sensitivity for Al3+, with a dynamic range from2.0×10-6M to1.1×10-5M observed and a detection limit of5×10-7M for Al3+. The proposed probe shows high selectivity to Al3+, which doesn’t suffer from obvious interferences from other metal ions. Dynamic light scattering measurements and UV-vis absorption spectra experiments were performed to verify the AIE response mechanism of probe TA. Moreover, a1:1stoichiometry was estimated for the TA-Al3+complex via fluorescence Job’s method.5. Two-photon microscopy (TPM), which excites a two-photon (TP) fluorophore by two photons with lower energy (i.e., longer wavelength and smaller frequency) than required in one-photon microscopy, can provide better three-dimensional spatial localization, and observe biological events inside tissues with increased depth (>500μm) and extended time. Thus, two-photon (TP) probes are more favorable for intracellular imaging than one photon fluorescence probes. In Chapter6, we designed and synthesized a new TP bioimaging probe NHSl for H2S with improved sensitivity by employing a D-π-A-structured naphthalene derivative as the TP fluorophore and an azide group as the H2S recognition unit. In the presence of H2S, a significant enhancement for both one photon and TP excited fluorescence were observed, resulting in a high sensitivity to H2S in aqueous solutions with a detection limit of20nM observed, much lower than the previously reported TP probe. The probe also exhibits a wide linear response concentration range (0.1-5μM) to H2S with high selectivity. It was then applied for direct TP imaging of H2S in living cells with satisfactory sensitivity, demonstrating its value of practical application in biological systems.