Fluorescence Recognition Of L-Amino Acids By Zn/Cd Complexes And Their Modifications

Complexes（CPs）are widely used in the recognition of nitro compounds,heavy metal ions and amino acids because of their unique porous structure and modifiability,which give them excellent fluorescence properties.However,the sensitivity and selectivity of CPs based fluorescent probes cannot meet the needs of practical applications.In this paper,seven CPs with novel structures were constructed with aromatic polycarboxylic acid tri（4-benzoic acid）phosphoxy compounds（H₃TPO）,5,5’-（1,3,6,8-tetracarboxylic acid[lmn][3,8]phenol-2-7-di）di-1,3-benzoic acid（H₄BIPA-TC）and nitrogen containing heterocyclic coligands and Zn/Cd salts under hydrosolvothermal method.At the same time,the structures of CPs were characterized by X-ray single crystal diffraction（XRD）,powder X-ray diffraction（PXRD）,Thermogravimetric（TG）and Fourier infrared spectroscopy（FT-IR）.Finally,the fluorescence recognition properties and mechanism of CPs and its modifier for L-amino acids were systematically studied.The specific research content and results are as follows:1.Under hydrosolvothermal conditions,nine CPs were constructed:{[Cd₃TPO]·6H₂O·5NMP}_n（CP1）,{[Cd₃（TPO）₂（4,4’-biyb）（H₂O）₂]·0.5H₂O·1.5（C₂H₃N）·（C₄H₈O₂）}_n（CP 2）,{[Cd（HTPO）（1,4-bdmb）]·3H₂O}_n（CP 3）and{[Cd₃（TPO）₂（1,4-bmiyb）（H₂O）₂]·2（C₂H₃N）·12H₂O}_n（CP4）,{[Zn₃（TPO）₂]·4C₄H₈O₂·2H₂O}_n（CP 5）,{[Zn（BIPA-TC）_0.5（1,3-bimb）]·0.75DMF}_n（CP 6）{[Zn（BIPA-TC）_0.5（1,3-bimb）]·0.5Et OH·DMF·H₂O}_n（CP7）,{[Zn（HTPO）（1,4-bipb）]·0.5DMSO}_n（CP 8）and{[Zn（HTPO）（2,6-dipp）]·1.5Et OH}_n（CP 9）.2.The fluorescence recognition performance of CPs 1-8 for L-amino acid showed that The identification performance of CP 3 for L-lysine is better than that reported in the literatures,namely,the fluorescence quenching constant(K_sv)was 2.12×10⁵ M^-1,and the detection limit（LOD）was 0.17μM;CPs 6-7 showed significant fluorescence enhanced recognition effect on L-glutamic acid,LOD=0.10μM and LOD=0.13μM,separately.In addition,the fluorescence recognition mechanism of CPs was analyzed by PXRD characterization,UV spectrum,fluorescence lifetime test and density functional theory calculation,combined with their fluorescence recognition performance.The results show that the excellent fluorescence recognition performance of CP 3 for L-lysine is mainly attributed to the synergistic effect of the energy resonance transfer from analyte to ligand and the dynamic quenching process,the remarkable fluorescence recognition performance of CPs 6-7 on L-glutamate was attributed to the synergistic effect of photoelectron transfer（PET）and dynamic quenching process.3.In order to study the effect of the post-modification of CPs on the fluorescence recognition performance,CP 8 and CP 9 were taken as representatives.Eu@CP 8 was synthesized by CP 8 and europium nitrate under hydrothermal conditions,with CP 8（LOD=0.49μM）,compared to the Eu@CP 8,the recognition of L-lysine（LOD=0.19μM）significantly improved sensitivity,LOD decreased 0.30μM.In addition,Rh B@CP 9（LOD=0.05μM）was prepared by in situ sealing Rhodamine B dye into the channel of CP 9,and its sensitivity to L-tyrosine was higher than that of CP 9（LOD=0.14μM）.The improved sensitivity of Eu@CP 8 to L-lysine is mainly attributed to fluorescence resonance and the synergistic effect between Eu³⁺and L-lysine,while the improved sensitivity of Rh B@CP 9 to L-tyrosine is mainly attributed to the electron transfer and double emission characteristics from Rh B to CP 9.4.In order to recover fluorescent probes effectively,Rh B@CP 9/CTS complex was prepared by disperses Rh B@CP 9 in chitosan（CTS）aqueous solution under magnetic agitation.The results showed that the recovery rate of this complex was close to 100%after 5 fluorescence recognition cycles.