Design, Synthesis And Application Of Rhodamine-based Ratiometric Fluorescent Probes For PH, Hypochlorite Anion

Intracellular pH homeostasis is essential for maintaining cellular functions. Eukaryotic cells contain organelles that function within various pH ranges. Abnormal pH values are known to be implicated in common diseases. Hence, sensing and monitoring pH changes in cells is of great significance.HOCl can be formed from hydrogen peroxide and chloride ions by the catalysis of MPO. HOCl plays a vital role in the immune defense against pathogens. However, the excessive production of HOCl is involved in numerous diseases. Quantitative determination of HOCl is thus highly important.Fluorescent probes have been extensively employed to measure the intracellular analyte concentration. The framework of rhodamine dyes is an ideal model to fabricate fluorescent probes due to the excellent photophysical properties. Moreover, rhodamine derivatives can transform from the spirocyclic (non-fluorescent) form to ring-opening (fluorescent) form. However, the fluorescence signal of probes based on single-fluorophore tends to be affected by many factors, making the detection inaccurate. To alleviate the above-mentioned problems, we introduce naphthalimide or coumarin into rhodamine framework to develop two ratiometric probes for pH and ’OC1, respectively.Chapter 1, an overview of the components and recognition mechanisms of fluorescent probes was presented, as well as the review about fluorescent probes for pH and HOCl/-OCl in recent years.Chapter 2, an FRET-based fluorescent pH probe (RNL), comprising of naphthalimide donor and rhodamine acceptor, was developed. RNL was suitable for the ratiometric detection of pH in the range of 4.5-5.5. It has been applied to monitor intracellular pH fluctuations and can selectively stain lysosome due to the introduction of 4-(2-aminoethyl)morpholine moiety, which is a lysosome-targetable group.Chapter 3, a novel hypochlorite fluorescent probe (RCP) based on FRET mechanism was presented. The probe was constructed by integrating coumarin moiety (FRET donor) with rhodamine moiety (FRET accepter). RCP exhibited high selectivity and sensitivity toward hypochlorite as well as brilliant water-solubility. Furthermore, the introduction of the quaternized pyridine moiety achieved the mitochondrial targetability.