Study On The Recognition Of Different Metal Cations By Citrulline Based Fluorescence Sensor

Cucurbit[n]urils?Q[n]s?,a class of macrocyclic hosts with a rigid hydrop Hobic cavity and two identical carbonyl-fringed portals,have attracted much attention since the first member of the Q[n]-family,cucurbit[6]uril?Q[6]?,was structurally identified in 1981 by Mock and co-workers.The structure characteristics of the rigid hydrop Hobic cavity and the electrostatic potential negative portals of Q[n]s leads to the formation of two research directions:the Q[n]-based coordination chemistry and the Q[n]-based host-guest chemistry.The investigations revealed that the interaction between host Q[n]s and guests may be affected by the coordination between the Q[n]s and metal ions,and in turn,the coordination between host Q[n]s and metal ions can also be affected by the inclusion of the Q[n]s on guests.Thus a new branch is derived from the interaction among three components of Q[n]-G-Mⁿ⁺,including the interaction between Q[n]/Mⁿ⁺complexes and guests?G?;interaction of G@Q[n]inclusion complexes and metal ions(Mⁿ⁺).This thesis focuses on the interaction systems of Mⁿ⁺and G@Q[n]with fluorescence characteristics.The fluorescence quenching or enhancement of G@Q[n]after interaction with Mⁿ⁺makes it possible to be used as a supramolecular fluorescence probe.The main research contents of this paper include:investigation of the response of G@Q[n]to various Mⁿ⁺metal ions,the interaction mode between G@Q[n]and Mⁿ⁺,and the mechanism that causes the fluorescence change of the system.Based on the study of a known host–guest inclusioncomplex comprising cucurbit[6]uril?Q[6]?and a hemicyanine dye,trans-4-[4-?dimethylamino?styryl]-1-pyridinium iodide?t-DSMI?,a water-soluble symmetric tetramethylcucurbit[6]uril?TMe Q[6]?,was selected to construct a t-DSMI@TMe Q[6]-based probe to test the response to various metal cations in neutral water.The experimental results revealed that the probe responded to Cs⁺cations in alkali metal systems,Ba²⁺and Sr²⁺cations in alkaline earth metal systems,Eu³⁺,Tm³⁺and Yb³⁺cations in lanthanide systems,and Cr³⁺,Fe³⁺and Hg²⁺cations in systems containing transition and other metal cations.The investigation on the response mechanism shows that for Cs⁺,Ba²⁺and Sr²⁺cations,the partial exchange becomes the main response mode;for Eu³⁺,Tm³⁺and Yb³⁺,Cr³⁺and Fe³⁺cations,the ternary synergy becomes the main response mode;for Hg²⁺cation,these two response modes coexist.The host-guest interaction between the Q[8]host and the guest palmatine?PAL?was investigated.The results revealed the formation of a 1:2 host-guest inclusion complex?PAL@Q[8]?accompanied by strong fluorescence emission.Using the PAL@Q[8]as a fluorescent probe,we detected various metal cations,including alkali?A⁺?,alkaline earth(AE²⁺),transition(Trⁿ⁺)and lanthanides(Ln³⁺)metal cations.The probe underwent fluorescence quenching only with ferric metal cations,demonstrating its ability to specifically detect Fe³⁺ions.Thus establishing a unique Fe³⁺detection method.Metal cations in aqueous solutions at different p Hs?1.5,4.5 and 7.2?can be detected using the known inclusion complex H33258@Q[8]as a fluorescent probe?H33258=Hoechst-33258?.Indeed,the fluorescence intensity of H33258 increases rapidly upon increasing the amount of Q[8]up to a Q[8]:H33258 ratio of 2:1,even at p H 1.5.The experimental results reveal that the probe exhibited selective recognition of metal cations at different p H.Namely the probe can selectively identify metal ions under different p H conditions.At p H 7.2,the probe responded to quite a variety metal cations,including one of the thirdmain group elements,Al³⁺,four transition metal cations,Hg²⁺,Fe³⁺,Fe²⁺,and Cr³⁺and three lanthanide cations Eu³⁺,Tm³⁺and Yb³⁺;At p H 4.5,the probe responded to only two transition metal cations,Hg²⁺and Fe³⁺.Unexpectedly,the probe lost its recognition properties at pH 1.5.