Synthesis And Property Of Nitroxyl, Cysteine Molecular Fluorescent Probes Based On The Excited State Intramolecular Proton Transfer

Excited state intramolecular proton transfer (ESIPT) is a process involving the proton transfer through a pre-existing hydrogen bond to adjacent atoms, giving rise to a proton-transfer tautomer. Instantaneous electron configuration and relaxation then occurrs in the excited ESIPT molecules, which leads to a large Stokes shift between absorption and tautomer emission. Meanwhlie, the ESIPT molecules is free from fluorescence quenching effectively caused by self absorption, with the detection pricision being improved. Therefore, ESIPT molecules are ideal molecular fluorescent probe materials. Fluorescence probes are a class of molecules that express molecular recognition events with fluorescence signals. It has the advantages of good selectivity, high sensitivity, simply operation and especially situ detection and so on. Combining fluorescent probes with micro-imaging technique makes it easier to study the bioactive small molecules in vivo. Nitroxyl and cysteine, bioactive small molecules, play important roles in physiological and pathophysiological processes. It is hence meaningful to develop fluorescent probes that can efficiently detect nitroxyl and cysteine, in order to analyze their distribution and fluctuation level in vivo, which is of great significance for the disease prevention and clinical medical research. In this dissertation, the main task is to design new ESIPT dyes and construct fluorescent probes for nitroxyl and cysteine. The main contents and innovative results are as follows:(1) Many reported probes for nitroxyl are selectively limited and susceptible to interference from biological reductants. To improve this drawback, a novel fluorescent probe HBT-HNO based on the ESIPT mechanism for the detection of nitroxyl was developed for the first time, with triarylphosphine acting as the specific reactive site for nitroxyl. It consists of 2-(2'-hydroxyphenyl)-benzothiazole as fluorophore, and links to diphenylphosphinobenzoyl group via an ester moiety. The probe exhibits high sensitivity, good selectivity toward nitroxyl. Moreover, the probe can penetrate membranes and successfully apply for fluorescence bioimaging of nitroxyl in living cells.(2) To solve the problem that some reported probes for Cys lack the properties of highly specific recognition of Cys, a novel fluorescent probe, Pl-Cys, was developed on the basis of the ESIPT mechanism for the detection of Cys. PI-Cys consists of a phenanthrene derivative, with acrylate group acting as the functional recognition moiety. The probe exhibits high sensitivity and selectivity toward Cys over homocysteine and glutathione, and achieves specific recognition of Cys. In addition, the potential for biological applications of the probe is confirmed by employing it for fluorescence imaging of Cys in living cells.