Mechanism Preparation And Properties Of Hydrazine Fluorescent Probes Based On Nucleophilic Addition Mechanism

Hydrazine,as an important chemical substance,has been widely used in various fields.Meanwhile,its high toxicity and massive use have caused irreversible pollution to the air,water and soil in the environment,causing serious harm to human body.Organic small molecule fluorescent probes are effective in assessing hydrazine levels in environmental and biological systems and have been extensively studied.Malonitrile group has strong electron-accepting ability and can provide high chemical reactivity for hydrazine.Aldehyde group can react with N₂H₄/HSO₃^-producing hydrazone or hydroxy methanesulfonate group and realizing the double recognition response of hydrazine and bisulfite ion.Chalcone derivatives have good luminescence properties,low biotoxicity,and sensitivity to hydrazine due to the fact that their carbon-carbon double bond groups are easily attacked by nucleophilic attack.Three kinds of hydrazine fluorescent probes malonitrile derivatives,aryl stilbene aldehyde derivatives and chalcone derivative with malonitrile group,aldehyde group and chalcone structure as hydrazine recognition sites,respectively,were developed.The effect and mechanism of compound recognition of hydrazine,as well as the application of sensing hydrazine in environmental and biological fields were comprehensively investigated.（1）Malononitrile derivatives（2）Aryl stilbene aldehyde derivatives（3）Chalcone derivativeA total of four compounds were synthesized in the malonitrile system,among which compounds 1 and 2 could realize the specific recognition of hydrazine.The results showed that the substituted group（1,N-ethyl carbazole;2:hydroxyl naphthalene）effectively promotes the recognition for hydrazine and the recognition is not affected in the presence of other amines.By titration experiments,it was found that the lowest detection limits were0.17μM（1）and 0.14μM（2）,respectively,which were much lower than the threshold limit（TLV）of 10 ppb.Compounds 1 and 2 have excellent p H stability and can recognize hydrazine effectively in 3.0-10.0 p H environment.According to the literature and chromatographic plate,the reaction mechanism was deduced to form hydrazone by addition reaction of malonitrile group and hydrazine.Compounds 1 and 2 were found to be perfect for the naked eye detection of hydrazine through the strip test,greatly increasing the possibility of simple detection of hydrazine in the environment.Two aryl stilbenzoic aldehyde derivatives 5 and 6 were developed.The compounds were proved by ¹H NMR,¹³C NMR,HRMS and crystal structure.It was found that the fluorescence phenomenon was different from that of hydrazine identification when bisulfite was added.Therefore,experimental tests were carried out to identify hydrazine and bisulfite at the same time.Compounds 5 and 6 have high sensitivity,good selectivity and strong anti-interference in recognizing hydrazine.Triphenylamine structural fluorescent probe 5 can detect N₂H₄ and HSO₃^-with low detection limits and distinguishable colors(0.24μM,red to green for N₂H₄;1.71μM,red to blue for HSO₃^-.The aldehyde group reacted with hydrazine and bisulfite as the recognition site to form hydrazone and sulfonate,respectively and the recognition mechanism was proved through in situ ¹H NMR.The reaction mechanism indicates that after reacting with N₂H₄/HSO₃^-,the production of hydrazone or hydroxy methanesulfonate group leads to a different molecular length and intramolecular charge transfer degree and then induces color-differentiated fluorescence emission.Cytotoxicity tests and cell imaging demonstrated that compound 5 can recognize hydrazine and sulfur metabolites in the biological field.Based on the excellent fluorescence properties of coumarin,chalcone derivative 7 was synthesized.The identification mechanism is that the chalcone st ructure was cyclized and dihydropyrazole ring was formed.The compound showed a blue shift of 110 nm before and after recognizing hydrazine.With the increase of hydrazine concentration,the red fluorescence gradually weakened and the blue fluorescence gradually strengthened with detection limit being 0.45μM.In terms of application,compound 7 has achieved hydrazine recognition in living cell,actual water samples,soil,and gaseous hydrazine.In addition,the strip test also shows excellent naked-eye recognition.