Study On Ion Recognition Of Coumarin Compounds And Inclusion Complexes Of Coumarin With Cucurbiturils

1.Fluorescent probe,it is a kind of fluorescence analysis method based on molecular recognition,which uses the specific interaction between host and guest to change the fluorescence performance of the system,so as to selectively analyzing and identifying target compounds.It is mainly suitable for qualitative or quantitative analysis of ions and small molecules.It has the advantages of low cost,small amount experimental sample,simple operation,good selectivity and high sensitivity,can perform real-time monitoring and in-situ detection of samples.Coumarin is a benzopyranone structure with good photostability,large Stokes shift,high fluorescence intensity and good fluorescence quantum yield.It is considered as an ideal and easily modified fluorescent group.In this paper,natural coumarin compounds such as Osthol（OST）,Esculetin（ESC）and Psoralen（PSA）as well as their inclusion complexes with Cucurbit[7]uril（Q[7]）or Cucurbit[8]uril（Q[8]）were selected as fluorescence probes.Their recognition performance and mechanism of metal ions were systematically studied by fluorescence spectroscopy,UV-vis spectrophotometry（UV）,mass spectrometry（Ms）,nuclear magnetic resonance hydrogen spectroscopy（¹HNMR）,Infrared Spectroscopy（IR）and X-ray crystal diffraction,in order to obtain a highly selective and sensitive method for metal ion detection.The main research content are as follows:The recognition performance and mechanism of OST,ESC and PSA as small molecule fluorescent probes for metal ions were studied by fluorescence spectrum,UV,¹HNMR,IR,isothermal calorimetric titration（ITC）and MS.The results show that（a）:OST can specifically recognize the Hg²⁺ion at p H=4.0-8.0,and other metal cations hardly interfere with the detection of Hg²⁺by OST with a detection limit of 5.04×10^-8mol·L^-1.The recognition mechanism is that OST and Hg²⁺ions form a stable complex with an interaction ratio of 1:1,and the binding constant is 1.552×10⁵L·mol^-1.The recovery rate of Hg²⁺in the aqueous solution is 98%-99%by standard addition method.（b）:ESC has fluorescence and fluorescent responses to various metal ions,so it cannot realize specific recognition of a single metal ion.（c）:PSA has a certain fluorescence intensity.At p H=4.0-9.0,it can be used as a small molecule fluorescent probe to specifically identify Fe³⁺ions with a detection limit of 1.06×10^-7mol·L^-1,and the recognition process is not affected by other common interfering ions.The recognition mechanism is the complexation between PSA and Fe³⁺ions,which changes its electronic arrangement,resulting in fluorescence quenching.2.The identification performance and mechanism of supramolecular probes constructed by OST,ESC and PSA with Q[7]and Q[8]for metal ions were investigated by fluorescence spectroscopy,UV,¹H NMR,MS,IR and X-ray crystal diffraction,the results show that（a）:OST does not interact with Q[7]or Q[8],and cannot construct supramolecular fluorescent probes with Q[7]or Q[8],（b）:ESC can interact with Q[7]and Q[8]to form stable inclusion complexes with interaction ratios of 1:1 and 2:1,and the binding constant are 2.931×10⁶L·mol^-1and 1.733×10⁶L²·mol^-2respectively.ESC@Q[7]and ESC₂@Q[8]can excite Al³⁺ions to emit indigo fluorescence,which enhances the fluorescence emission intensity and the relative fluorescence quantum yield.and can be used as supramolecular fluorescence probes to selectively detect Al³⁺ions,the detection limits are 1.74×10^-8mol·L^-1and 9.39×10^-9mol·L^-1,respectively.The recognition mechanism of ESC@Q[7]may be that Al³⁺ions form a 1:1 complex with two hydroxyl groups of ESC through coordination bonds,causing ESC to depart from the Q[7]cavity,which is a chelated fluorescence enhancement mechanism.Different from the action mode of ESC@Q[7]@Al³⁺,the crystal structure of ESC₂@Q[8]@Al³⁺shows that the recognition mechanism is that the hydroxyl oxygen atom on ESC and the carbonyl oxygen atom of Q[8]port are interact with Al³⁺at the same time,forming a 2:1:1 chain-like structure complex leading to fluorescence enhancement.Using ESC@Q[7]and ESC₂@Q[8]as fluorescent probes,the recovery rates of Al³⁺ions in tap water were both 97%-99%by standard addition method.（c）:PSA and Q[8]formed a 2:1 stable inclusion complex with a binding constant of 1.830×10⁶L²·mol^-2.Compared with PSA,PSA₂@Q[8]has more obvious specific recognition and stronger quenching effect on Fe³⁺,and detection limit of Fe³⁺ions is 1.05×10^-8mol·L^-1,and the recovery rate of Fe³⁺ions in tap water by standard addition method is 97%-99%.The recognition mechanism may be due to the interaction between Fe³⁺ion and the oxygen atom on the PSA lactone ring and port Q[8]to generate a stable complex with an action ratio of 1:2,which changes the electron configuration of PSA and leads to fluorescence quenching.Taking natural compounds as fluorescent probes has the characteristics of non-toxic or low toxicity,good biocompatibility and environmental friendliness.They are a class of green fluorescent probes,which can be used for the quantitative detection and monitoring of metal ions in environment.