Schiff Base-type Zn (Ⅱ) Ion Fluorescence Probe Design, Synthesis And Characterization

Zinc is the second most abundant transition metal in the human body, and it plays a myriad of roles in various biochemical processes, such as enzyme regulation, structure and function, neural signal transmission, and gene expression. Although the majority of biological zinc ions are tightly sequestered by proteins, the presence of "free zinc" certain cells may still be possible and is closely related to severe physiological diseases such as Alzheimer’s, amyotrophic lateral sclerosis (ALS), Parkinson’s, ischemia, and epilepsy. Thus, it’s significant to detect the zinc ions.Molecular fluorescent probe technique is a rapid and sensitive detection technology to be developed recent years. The fluorescent probe based on a Schiff base structure has many advantages, such as simple synthesis, excellent light stability, a larger Stocks shift, which has become a good candidate structure in the design of fluorescent probe. Here, we reported multiple zinc ions fluorescent probes based on a Schiff base structure, using naphthol, coumarin, fluorescein as the fluorophore, respectively. The contents mainly including the following three parts:1.2-hydroxy-1-naphthaldehyde was obtained by formylation from the raw material β-naphthol, which then combined with benzoimidazol-2-methanamine and1-methyl-benzoimidazol-2-methanamine, respectively, to produce zinc ions fluorescent probes Cp1and Cp2. Studies showed that the recognization of the zinc ions was based on a PET effect.2.7-hydroxy-8-formylcoumarin-3-carboxylate was synthesized by Knoevenagel condensation and formylation from the raw2,4-dihydroxybenzaldehyde, which then combined with benzoylhydrazine, benzoimidazol-2-methanamine,1-methylbenzoimidazol-2-methanamine and3-amino-7-hydroxy coumarin respectively, to obtain zinc ions fluorescent probes Cp3, Cp4, Cp5and Cp6. Studies showed that Cp3was a dual channel ion fluorescent probe, it could response Ca2+perfectly in the H2O/DMF (1:9) solution and it would be a Zn2+selective probe. For Cp4and Cp5, the recognization of the zinc ions was based on both PET and C=N isomerization effect. However, Cp6is a typical zinc ion fluorescent probe based on a C=N isomerization effect.3. Fluorescent hydrazide was obtained by esterification and hydrazinolysis from the fluorescein, which then combined with benzoimidazol-2-formaldehyde to synthesized zinc ions fluorescent probe Cp7. Studies showed that Cp7was a typically reaction type fluorescent probe, that is to say, before adding Zn2+, a acylation reaction was held and the fluorescence did not take place, however, after putting in Zn2+, the acylation structure was broken up and the special fluorescence of fluorescein appeared. In other words, the fluorescent probe accomplished an OFF-ON shift.