The Synthesis of a Coumarin Carbohydrazide Dinuclear Copper Complex Based Fluorescence Probe and Its Detection of Thiols

Small-molecule thiols, such as cysteine (CYS) and glutathione (GSH), are essential for maintaining the cellular redox environment and play important roles in regulating various cellular physiological functions. A fluorescence probe (compound 1-Cu2+) for thiols based on coumarin carbohydrazide dinuclear copper complex was developed. Compound 1 was synthesized from the reaction of 7-(diethylamino)-2-oxo-2H-chromene-3-carbohydrazide with 4-tert-butyl-2,6- diformylphenol. Accordingly, the copper complex (compound 1-Cu2+) was prepared by mixing compound 1 with 2 equivalents copper ions. Compound 1 had strong fluorescence while compound 1-Cu2+ hardly possessed fluorescence owing to the quenching nature of paramagnetism Cu2+ to the fluorescence molecule excited state. However, the fluorescence intensity of compound 1-Cu2+ was increased dramatically after the addition of thiol-containing amino acids, but not the other non-sulfhydryl amino acids. UV-vis absorption and fluorescence spectra indicated that compound 1-Cu2+ had good selectivity and sensitivity for thiols such as glutathione in CH3CN:H2O (3:2, v/v) PBS solution. The fluorescence imaging experiments implied that compound 1-Cu2+ has potential application in thiol-containing amino acids detection in living cells.