The Studies Of Chromone-3-aldehyde (Heterocyclic Acyl) Hydrazone Ligands As Fluorescent Probes Detecting Zn²⁺,Al³⁺,Fe³⁺ And Cu²⁺

Various metal ions contained in organisms play important roles in cellular activities.For example,the imbalance of Al³⁺not only affects the normal growth of plants and animals,but also damages the central nervous system,Zn²⁺plays a vital role in many protein synthesis and biochemical processes,Fe³⁺can be observed in various proteins and enzymes,and Cu²⁺is related to bone formation,cellular respiration and connective tissue development in the body.In this paper,a series of fluorescent probes have been designed and synthesized based on chromone-3-aldehyde.Their structures of these compounds were characterized by means of instruments(nuclear magnetic spectrometer,mass spectrometer,etc.)and their spectral properties were tested.Mainly as follows:(1)Chromone-3-aldehyde(rhodamine B carbonyl)hydrazone(Ligand 1):1showed high selectivity for Zn²⁺in EtOH/HEPES(9/1,V/V)solution(?_ex=420nm).This may be due to the transfer of lone electrons on the nitrogen atom of the linking group(-C=N-),which hindered the PET process and made the fluorescence recovery.At the same time,1 can also apply to recognize Fe³⁺based on rhodamine ring opening in EtOH/DMSO(3/2,V/V)solution,with obvious color change(?_ex=520 nm).According to the job's curve and ESI-MS analysis,the stoichiometric ratio between 1 and these two metal ions(Zn²⁺,Fe³⁺)was 1:1,and the detection limit was as low as 10^-7 M.In addition,1 can be used as a solid probe to detect Zn²⁺and Al³⁺rapidly.(2)Chromone-3-aldehyde(7'-diethylamine coumarin-3'-formylhydrazine)hydrazone(Ligand 2):Ligand 2 showed high selectivity only for Al³⁺based on ICT mechanism(?_ex=396 nm).The free ligand showed a strong emission peak at 477nm,but the original emission peak disappeared after adding Al³⁺.At the same time,according to the analysis of Job's curve and ESI-MS,the coordination ratio between ligand 2 and Al³⁺was 1:1,and the detection limit and binding constant calculated were 1.44×10^-7 M and 1.32×10⁴ M^-1,respectively.at the same time,a new fluorescence emission peak appeared at 524 nm.Moreover,2 can also be used as a solid probe to detect Al³⁺rapidly.(3)Chromone-3-aldehyde(7'-hydroxy-4'-methyl-8'-methylidene coumarin)hydrazone(Ligand 3):3 can detect Zn²⁺and Cu²⁺in EtOH/H₂O(19/1,V/V)solution based on two mechanisms.It can be used not only as“turn-on”probe to recognize Zn²⁺(?_ex=415 nm),but also as a"colorimetric"probe to detect Cu²⁺.The detection limit of ligand 3 for Zn²⁺and Cu²⁺were 1.83×10^-7 M and 4.80×10^-88 M,respectively.And binding constants of ligand 3 for Zn²⁺and Cu²⁺were 7.51×10⁴M^-1 and 3.63×10⁴ M^-1,respectively.According to the analysis of Job's curve and ESI-MS,the coordination ratio between 3 and these two metal ions(Zn²⁺,Cu²⁺)was1:1.In addition,ligand 3 had AIE effect through fluorescence spectrum experiment.