Construction And Application Of Positive Charged Small Molecular Fluorescent Probes

In this present work, we designed and synthesized four kinds of small molecular fluorescent probes, based on Michael addition and ICT effect, for sensing some important species in food, enviroments, and biological systems, such as cysteine, cyanide, sulfite, and cellular viscosity, and further investigated their sensing process, mechanisms and applications.1. A new strategy for fast fluorescent detection of Cysteine (Cys), based on a noval response-assisted electrostatic attraction, was demonstrated. By utilizing this strategy, we designed and synthesized three fluorescent probes for specific detecting Cys in actual physiological conditions. The probe MCP showed highly selective and sensitive detection for Cys over homocysteine (Hey) and glutathione (GSH). The kinetic analysis indicated that the sensing process was highly accelerated (response time less than1min) by the response-assisted electrostatic attraction. Control studies of neutral precursors (PI, P2, and P3) and isomers (OCP and PCP) firstly revealed that, both electrostatic attraction and spatial charge configuration played important roles in Cys preferred selectivity and kinetic rate acceleration. Furthermore, the practical utility of the probe in fluorescent detection the microenvironment of Cys34within BSA was demonstrated. Particularly, non-reactive protein without free Cys but disulphide bonds showed a remarkable fluorescent response after DTT treatment. Finally, the ability of the probe in determining the subcellular distribution of active thiols was investigated with HeLa cells. The probe displayed satisfied cell permeability and enabled to distinguish active thiols in cytoplasm, nucleus and mitochondria.2. We designed and synthesized a series of fluorescent probs (MEBP, OEBP, and PEBP) for monitoring viscosity, based on intramolecular charge transefor (ICT) effect. These probes contain a BODIPY moiety (fluorophore) and a pyridinium moiety (molecular rotor) conjugated through a freely rotatable single carbon bond. The fluorescent quntum yields of MEBP and PEBP were not affected by solvent polarity, and kept stable in a wide pH rang from1to10. More importantly, the fluorescent enhancement of MEBP and PEBP showed a good linear relationship with a wide solvent viscosity range from1to1000CP. Finally, MEBP and PEBP were further used for monitoring cellular viscosity in Hela cells. The results indicated that both MEBP and PEBP displayed satisfied cell permeability, and they can image cellular viscosity distributions, and response to viscosity changes induced by peroxide.3. A colorimetric and ratiometric fluorescent cyanide probe based on a unique F-CN substitution mechanism of BODIPY was designed and synthesized. PEBP shows highly sensitive and selective to CN". After addition of cyanide, PEBP changed its fluorescent emission from orange to green, and turned its solution color from red to yellow. Based on the1H and19F NMR titrations, for the first time, we concluded that the sensing process of cyanide to PEBP was through a novel F-CN replacement reaction mechanism. More interesting, common BODIPY cannot undergo the similar replacement reaction just like PEBP does, which means PEBP is special for cyanide sensing. This specificity of PEBP maybe attributed to the pyridinium moiety, such a strong electron withdraw group improve the ICT effect, which makes the center boron more reactive. Moreover, OEBP and MEBP also showed response to cyanide, but in different manners. Cyanide just quenched their fluorescence through a Michael addition mechanism.4. We designed and synthesized a near infared flurescent probe CHCN for high sensitively and selectively sensing sulfite in absolute physiological condition. CHCN contains a hemicyanine moiety conjugated with coumarin group, gives a red emission at638nm. After addition of sulfite, CHCN changes its emission from red to cyan, and truns its solution color from bluish violet to faint yellow. CHCN shows a colorimetric and flurescent rariometic response to sulfite. Moreover, CHCN shows different flurescent response to sulfide and cyanide.