Fluorescent Recognition Of Thiol-containing Amino Acids Based On Metal Complexes

The thiol-containing amino acids, homocysteine (Hey) and cysteine (Cys), are essential biological molecules and play a crucial multidimensional role in maintaining biological redox homeostasis, An abnormal level of Hey in plasma is an indicator of various disorders, including cardiovascular and Alzheimer's disease, osteoporosis etc.Cys deficiency has been linked to slowed growth in children, liver damage, muscle and fat loss, skin lesions, and weakness. The determination of speci fie thiols is often based on redox chemistry or derivatization with chro mophores or fluorophores in conjunction with HPLC or capillary electrophoresis separations or via immunoassays.Great effort has gone into the detection of Hcy/Cys by various methods. In recent years, a variety of fluorescence sensors have been developed to sense cys/hcy. However, because of the similar structure of Cys as Hey, most of those sensors could not discriminate Cys from Hey.The use of phosphorescent heavy-metal complexes as chemosensors and bioimaging probes has recently attracted considerable interest, because of advantageous photophysical properties such as high luminescence efficiency, the tunable excitation and emission wavelength over the whole visible, significant Stokes shifts, and relatively long lifetimes.In this paper, three metal complexes are synthesized based on ruthenium (II), iridium(III) and platinum(Ⅱ).The recognition to thiol-containing amino acids is addressed by UV-Vis spectroscopy, luminescent methods, and so on. The detailed items are listed as following:1,A ruthenium polypyridine complex [Ru(phen)2(IPBA)](PF6)2(Cl)(IPBA=4-(lH-imidazo[4,5-f][1,9] phenanthroline-2-yl)benzaldehyde), which displays environment-responsive dual emissive properties, was designed and synthesized. In aprotic solvent, such as DMSO, DMF or CH3CN, the complex emits strong cyan light. When in protic solvent, it emits orange light. Similarly, the response of the complex to homocysteine and cysteine (Hcy/Cys) also shows obvious solvent dependence. Both NMR and ESI-MS reveal the recognition mechanism that thiazolidine is formed by the interaction of aldehyde of Cl with Cys/Hcy. Hence, the complex could be used to detect Hcy/Cys in aprotic solvent, as well as in protic solvent.2, A phosphorescent probe [Ir(ppy)2Cl(DMF)](C2) for cysteine(Cys) is synthesized. The recognition is based on the time-dependent emission of C2-Cys. Importantly, this probe can discriminate Cys rapidly from homocysteine (Hey). Probe C2displays a highly selective72nm of luminescent red-shift toward Cys within30min with an obvious emissive color change from green to orange. After30min, the emission band blue shifts gradually with emissive change from orange to green. Detailed analysis suggests that Cys coordinates to C2by two modes with time. The probe can be used to the detection of Cys in semi-aqueous solution.3,A phosphorescent probe [Pt(ppy)(DMSO)Cl](C4) for cysteine(Cys) is synthesized. This probe can discriminate Cys rapidly from homocysteine (Hey). Probe C4displays a dual emission at481nm and513nm. The addition of a little of Cys quenched the emission. With the increment of Cys concentration, a new emission band at600nm appeared and increased gradually with red luminescence. For Hey, with the increment of Cys concentration, the dual emission of C4decreased gradually until the final quenching. The probe can be used to the selective detection of Cys in semi-aqueous solution.