The Xanthene Lo Lactam Optical Probe Synthesis And Applied Research

Optical probes play the important role in analytical biochemistry, environment monitoring, disease diagnosis, medicine screening, and so on. Rhodamine B, the common xanthene dye, has the large molar extinction coefficient, long excitation wavelength and higher fluorescence quantum yield. Rhodamine spirolactams optical probes were developed to detect Cu²⁺, Hg²⁺, HSO₃^-, cysteine, melamine and ClO^- in this dissertation. This dissertation summarized as follows:A general introduction to the research progress on xanthene spirolactams optical was presented. Based on referring to the relative literatures, the objective of this dissertation was proposed.Firstly, a rhodamine-based chemosensor for copper ion 1-(rhodamine B)- lactam -thiosemicarbazide (1), was designed and synthesized. Compound 1 is a colorless, non-fluorescent compound and was synthesized via the one-step reaction of rhodamine B hydrazide with KSCN in acidic medium. Upon mixing Cu²⁺ in acetonitrile-water (30:70, v/v) solution, the spirolactam ring of 1 was opened, which resulted in the dramatic increases in both fluorescence and absorbance of the mixing solution. Based on this mechanism, a chromo- and fluorogenic chemosensor for Cu²⁺ was developed. Compound 1 displays excellent selective and sensitive response toward Hg²⁺ over other transition metal ions in neutral aqueous solution. 1 itself is a colorless, nonfluorescent compound. Upon addition of Hg²⁺ to the solution of 1, the thiosemicarbazide moiety of 1 would undergo an irreversible desulfurization reaction to form its corresponding 1,3,4-oxadiazole (2), a colorful and fluorescent product, causing instantaneous development of visible color and strong fluorescence emission. Based on this mechanism, a fluorogenic probe for Hg²⁺ was developed.Secondly, a rhodamine-based fluorescent probe with a aldehyde functionality as a recognition unit has been developed for the selective detection of bisulfite in aqueous media. The new fluorescent probe shows an excellent selectivity for bisulfite anion over other anions. The bisulfite-induced ring opening of spirolactam of the rhodamine moiety resulted in the dual chromo- and fluorogenic observation. A new rhodamine derivative (3) containg a aldehyde moiety as the signalling unit has been developed for the selective detection of cysteine in aqueous media. The interaction of Cys with probe 3 induces ring opening of spirolactam of the rhodamine moiety and results in the dual chromo- and fluorogenic observation. The new fluorescent probe displays an excellent selectivity for cysteine over other amino acids including homocysteine. A new rhodamine derivative (3) containg a aldehyde moiety as the recognition unit has been developed for the selective detection of melamine in acid media. The interaction of amino group in melamine with aldehyde in probe 3 results in the fluorescence enhancement of the reaction mixture. The proposed method is proved to be simple, selective and sensitive.Finally, a new rhodamine-based fluorescent probe (6) for hypochlorite ion was designed and synthesized. Compound 6 was a colorless, non-fluorescent compound. Upon addition of ClO^- to the solution of 6, the reaction between 6 and hypochlorite ion gives its corresponding product 7, a colorful and fluorescent product, causing instantaneous development of visible color and strong fluorescence emission. The fluorescence increase is linear with hypochlorite ion concentration in the range 0.5 - 10.0μmol L^-1. Based on the above mechanism, a fluorogenic method for the determination of hypochlorite ion was developed. This probe is highly selective for hypochlorite ion over other reactive oxygen species (ROS).