Synthesis And Properties Of 4-methyl-7-hydroxycoumarin Schiff Base Fluorescent Prob

Metallic elements play an important role in various basic life processes and are essential elements for many life processes.Certain human diseases are closely related to changes in the content of Zn²⁺in the body.Lack of Zn²⁺can lead to developmental delays and neurological disorders,while excessive Zn²⁺can inhibit immune cell activity and antibacterial ability.As an essential trace element in the human body,copper plays an important role in various physiological processes.However,excessive content of Cu²⁺in the human body can damage organs such as kidneys,heart and liver,and may also lead to diseases such as anemia,gastrointestinal disorders,Alzheimer’s disease,Parkinson’s disease,acute kidney failure,ischemic heart disease and other diseases.In recent years,the detection of analytes by fluorescent probes has become a research hotspot.Compared with traditional detection methods,fluorescent probes have the advantages of high sensitivity,good selectivity,short response time,simple operation and real-time monitoring.Coumarin derivatives are often developed as excellent fluorophores due to their flexible structure,high fluorescence quantum yield,low molecular weight and good photostability.Therefore,in this paper,three novel fluorescence probes were designed and synthesized based on 7-hydroxy-4-methyl coumarin.The structure and optical properties of the three probes were characterized and studied,and the practical applications of the probes were explored.The main contents are as follows:（1）Fluorescent probe CPS was designed and synthesized using 8-formyl-7-hydroxy-4-methylcoumarin and 2-amino-5-methylpyridine as the main raw materials.In DMSO/H₂O（v/v=9:1）solution,probe CPS could accurately and sensitively detect Zn²⁺.Under the excitation at 434 nm wavelength,probe CPS exhibited a maximum emission peak at 518 nm after the addition of Zn²⁺,and the solution changed from non-fluorescent to bright green fluorescence.Probe CPS had strong recognition and anti-interference abilities towards Zn²⁺,with a detection limit of 3.58×10^-7mol·L^-1 and a binding constant of 8.42×10⁴ L·mol^-1.The coordination ratio between CPS and Zn²⁺was determined to be1:1 using the Job’s plot.In addition,experimental results showed that the probe could be used as a test paper or directly for the detection of Zn²⁺in water samples,with certain application potential.（2）Fluorescence probe CBS was synthesized by the reaction of 4-methyl-8-hydrazonomethyl-7-hydroxycoumarin and 2-hydroxy-3-methoxybenzaldehyde.In DMF/H₂O（v/v=9:1）solution,CBS showed weak orange fluorescence emission at 567nm.In the presence of various cations,the probe showed high selectivity for Zn²⁺with significant fluorescence enhancement at 521 nm and a bright green fluorescence.The fluorescence intensity of probe CBS showed a good linear relationship with the concentration of Zn²⁺（R²=0.9966）with a detection limit of Zn²⁺4.83×10^-7 mol·L^-1 and a binding constant of 5.39×10⁴ L·mol^-1.According to ¹H NMR titration experiment,Job’s plot and ESI-MS,the binding ratio of CBS to Zn²⁺was determined to be 1:1.Meantime,probe CBS could also recognize Zn²⁺in a wide range of pH values（6.0-14.0）.In addition,probe CBS could be applied to the detection of Zn²⁺with test paper and in actual water samples.（3）A novel"on-off-on"fluorescent probe CNS was obtained by the reaction of 4-methyl-8-hydrazonomethyl-7-hydroxycoumarin and 2-hydroxy-1-naphthaldehyde.In HEPES（20 mM,pH=7.0）solution,probe CNS not only selectively recognized Cu²⁺but also indirectly recognized EDTA.The probe CNS emitted orange fluorescence at 583 nm under excitation at 420 nm with a Stokes shift of 163 nm.When interacting with Cu²⁺,the fluorescence was quenched,but it could be restored by EDTA.In addition,probe CNS showed high selectivity and sensitivity towards Cu²⁺and EDTA,with detection limits（LOD）of 5.31×10^-7 mol·L^-1 and 3.00×10^-7 mol·L^-1,and binding constants of 4.41×10⁴L·mol^-1 and 2.77×10⁴ L·mol^-1,respectively.The 1:1 coordination ratio between CNS and Cu²⁺was demonstrated by ¹H NMR titration and Job’s plot.Furthermore,probe CNS could also be applied to the detection of Cu²⁺with test papers and in water samples.