Determination Of Thiol Compounds Synthesis Of Fluorescent Probes And Applied Research

Thiols are an important component of many proteins and small molecules in organisms and play an important role in the antioxidant system in biological system.Intracellular thiols such as glutathione(GSH),cysteine(Cys),and homocysteine(Hcy) play a crucial role in maintaining biological redox homeostasis.Thiols are also active in the catalytic sites of enzymes,and play important roles in metabolic pathways.The levels of certain thiols,such as homocysteine,have been linked to a number of diseases,including cancer,Alzheimer's, cardiovascular disease and so on.Because fluorimetric analysis has many advantages such as high sensitivity,high selectivity,wide range of dynamic response as well as real-time detecting,the detection of biological thiols based on fluorescence techniques has received special attention.The development of fluorescent probes which have advantages such as high sensitivity,high selectivity and real-time detecting has become an active realm.It was reported that strongly electron-withdrawing 2,4-dinitrobenzenesulfonyl group is the most effective in labilizing the carbon-sulfur bond,and the resulting benzenesulfonate can be readily cleaved by nucleophile reagents.Based on this mechanism,we designed and synthesized some fluorescent probes for thiols.Firstly,we synthesized a fluorescent probe 2,4-dinitrobenzenesulfonyl-fluorescein(Ⅰ) according to the literature,which was utilized as a new chemodosimeter for sulfide anion. 2,4-Dinitrobenzenesulfonate in compound I can be efficiently cleaved by sulfide anion to give the corresponding hydroxy-containing compound,resulting in the formation of highly fluorescent fluorescein and hence leading to a dramatic increase in absorbance and fluorescence intensity simultaneously.The enhancement value of the fluorescence intensity (△F) is directly proportional to the sulfide anion concentration.In addition,a color change from light yellow to yellow-green appeared upon addition of sulfide anion to the solution of I, indicating that compound I can be used as a "naked-eye" indicator for sulfide anion.The probe I can be readily cleaved by tiopronin(as a nucleophile reagent) through a nucleophilic substitution process,resulting in the formation of the parent dye fluorescein and hence leading to dramatic increases in both fluorescence and absorbance of the reaction mixture.The proposed method has been successfully applied to the tiopronin determination in pharmaceutical preparations.Secondly,three 4-methylumbelliferyl-based compounds (including 4-methylumbelliferyl-2,4-dinitrobenzenesulfonate,4-methylumbelliferyl-p-toluen-esulfonate,and 4-methylumbelliferyl-2-nitrobensulfonate) were designed and synthesized. Among them,4-methylumbelliferyl-2,4-dinitrobenzenesulfonate(4-MUDNBS) was developed as a novel fluorogenic probe for captopril.At the same time,the effect of substituents on the thiolate-induced cleavage reaction was studied and the results showed that the electro-withdrawing groups on the benzenesulfonyl moiety of the probe markedly facilitate the nucleophilic reaction.In basic media,SNH was decomposed to produce sodium sulfite,which then reacted with 4-MUDNBS to yield highly fluorescent 4-MU,hence leading to the fluorescence increase of the reaction solution.A new fluorimetric method for determination of sodium houttuyfonate was established.