Synthesis And Properties Of Catalytic Self-immolative Reactive Pd²⁺ Fluorescent Probes

Palladium is a metal that is suspected to pose a serious health risk,especially in vulnerable groups such as children.Even very low concentrations can cause various health problems for the human body,including primary skin and eye irritation.Palladium also has a negative impact on the immune system,which may be converted into more toxic derivatives after being absorbed by the organism.The maximum intake of palladium in the diet is limited to about 1.5-15μg per person per day.Therefore,it is of great significance for the detection of palladium ions in the environment and in vivo.Some traditional detection instruments are too expensive,and the operation is relatively complicated.Fluorescent chemical sensors have the advantages of low cost,convenience,and speed in ion detection,and are used as a new method for palladium ion detection.Today,many fluorescent probes for Pd²⁺detection have been reported.However,at present,many probes still have the disadvantages of poor anti-interference,poor water solubility and long response time.It is still challenging to design Pd²⁺fluorescent probes with unique selectivity and high sensitivity.Generally,the coordination type fluorescent probe has better selectivity,but the anti-interference ability needs to be improved,and the palladium-catalyzed self-immolative reaction type fluorescent probe has high selectivity and good anti-interference ability.Therefore,the research work of this paper as follows:1.A new fluorescent probe P1 was designed and synthesized.The probe uses propargyl ether group as Pd²⁺recognition group and 7-amino 4-methylcoumarin as fluorescent group.¹H NMR,¹³C NMR and ESI-MS has characterized its molecular structure.The probe had only weak fluorescence under the excitation of 350 nm excitation light,but after reacting with Pd²⁺,the probe solution emitted blue fluorescence with a fluorescence emission peak of 439 nm.The probe has high selectivity and anti-interference ability for Pd²⁺at physiological environment p H.And the fluorescence emission intensity has a good linear relationship with Pd²⁺in the range of 0-15μM.The detection limit was 0.057μM.At the same time,the detection mechanism of P1 probe was studied by mass spectrometry,and it was confirmed that it is a reactive self-immolative fluorescent probe.2.Based on the P1 probe,a new fluorescent probe P2 was designed and synthesized.The probe also uses propargyl ether group as the Pd²⁺recognition group,and based on the intramolecular 1,4-elimination reaction mechanism,2-Hydroxy-5-methyl-m-xylylene glycol was used as the linking moiety,and 7-amino 4-methylcoumarin was used as the fluorescent group.¹H NMR,¹³C NMR and ESI-MS were used to characterize its molecular structure.The experimental results show that the probe P2 also has high selectivity and anti-interference ability to Pd²⁺.After reacting with Pd²⁺,the maximum fluorescence emission wavelength is 439nm.Its fluorescence emission intensity is directly proportional to the response time and reaches saturation at about 500 minutes.Compared with the P1 probe,the response speed of P2detection is twice as fast.Studies show that this is due to the improvement of its molecular structure,which makes it Self-immolative is based on a 1,4-elimination reaction,which accelerates the degradation rate.3.Based on the mechanism of probes P1 and P2,a hyper-branched polymer based on Pd²⁺response signal amplification was designed and synthesized.A hyperbranched polymer（SID）was synthesized by using a propargyl ether bond as a stimulus-responsive switch and designing a hyperbranched structure of the polymer based on a 1,4-elimination reaction with a fast cleavage rate.¹H NMR and GPC were used for structural characterization and preliminary investigation.The functional design of the modularized polymer has good prospects in the application of fluorescence detection,and its fluorescence detection performance is still under further testing.