Synthesis And Application Of Pyrazol-3-Carboxylic Acid Derivatives

Metal ions exist widely in the natural environment and life activities,while they may also cause irreversible damage to the environment or organisms.In recent years,fluorescent probes have been widely used for the detection of metal ions in the environment and in vivo due to their high selectivity,sensitivity and rapid real-time monitoring.In this paper,five fluorescent probes based on pyrazole-3-carboxylic acid derivatives were designed and synthesized by modifying and transforming the N-1,C-3 and C-5 of the pyrazole ring skeleton.The structures of the synthesized fluorescent probes were identified by characterization methods such as nuclear magnetic resonance hydrogen spectrum（¹H NMR）,nuclear magnetic resonance carbon spectrum(¹³C NMR)and mass spectroscopy（MS）.At the same time,their fluorescence properties were studied in DMSO/H₂O（p H=7.4,v/v=9/1,tris=10 m M）buffer system using fluorescence spectra and UV-vis spectra,and their recognition mechanism was discussed.The five probes showed unique fluorescence responses to the target metal ions,and exhibited different characteristics due to the differences in structure.Probe W1 exhibited high selectivity and sensitivity to Ga³⁺.It could be used as a“turn-on”fluorescent sensor to detect Ga³⁺,and could be well distinguished from In³⁺and Al³⁺of the same family.The detection limit of W1 for Ga³⁺was 1.45×10^-8 M.Probe W2 had a good recognition effect on Al³⁺and Fe³⁺,and could sequentially identify these two target ions through the“off-on-off”response mechanism.The detection limits of W2 on Al³⁺and Fe³⁺were 9.42×10^-9 M and 2.10×10^-8 M.Both probe W3 based on salicylaldehyde and probe W4 based on 4-（diethylamino-salicylaldehyde）had significant fluorescence enhancement effect on Ga³⁺,and the detection limits of both the two probes were 8.85×10^-7 M and 1.21×10^-8 M,respectively.The difference was that the presence of N-diethylamino made probe W4 had better selectivity and anti-interference ability than W3.The difference of sensing performance between the two probes was further explained by theoretical research.In addition,based on the excellent fluorescence response of W4 to Ga³⁺and P₂O₇^4-,a molecular logic gate had been constructed,and a test paper for detecting Ga³⁺had been prepared successfully.Probe W5 could recognize Al³⁺through obvious fluorescence enhancement phenomenon,and its in situ generated complex W5[Al³⁺]could be used as a new secondary platform to detect Fe³⁺through efficient fluorescence quenching behavior.The detection limits of probe W5 for Al³⁺and Fe³⁺were 1.10×10^-8 M and 4.45×10^-8 M,respectively.The five fluorescent probes were combined with metal ions in a stoichiometric ratio of 1:2by Job’s plot curve and high-resolution mass spectrometry,and the feasible complexation model between probes and target ions was clarified.Gaussian 09 software was used to optimize the structure of the five probes and their complexes formed with metal ions and calculate the orbital energy,which further verified the proposed complex sensing model.The results showed that probe molecules with similar molecular structure but different fluorescence modification groups had higher selectivity and sensitivity for the recognition of target ions,which provided an excellent design idea and technical guarantee for the future design of multifunctional and highly sensitive chemical sensors for metal ion detection.