Design And Synthesis Of Water-stable Metal-Organic Frameworks And Heavy Metal Ions/Tryptophan Sensing

As a multi-functional hybrid material,metal-organic frameworks(MOFs)have rich functional centers,intriguing topologies and high sensitivity to external stimulus.They are widely applied in gas storage/separate,biological medicine,fluorescence sensing and catalysis.Metal ions and small biological molecules are widespred in nature and their concentration sensing is important to human health and environmental safety.Alough many luminescent MOFs probes for metal ions sensing have been developed,most of them could only be used in organic solutions instead of water,which restricts the practical applications of MOFs.Besides,the MOFs sensors for small biological molecules and trivalent metal ions with "turn-on" fluorescence response are relatively less.Through rational selection of organic linkers in this paper,we have developed some water-stable luminescent MOFs and achieved the fluorescence detection with high selectivity and sensitivity for metal ions and small biological molecules.Based on 4,4'-stilbenedicarboxylic acid(H2sdc),two MOFs Mn-sdc-1 and Mn-sdc-2 with reversible structural transformations were synthesized.When induced by trace level of H2O at room temperature,Mn-sdc-1 can transform into Mn-sdc-2.The transformation from Mn-sdc-2 to Mn-sdc-1 is achievable induced by DMF beyond 100 °C.According to the influences of temperature and the volume of H2O in reaction on two phases,we get the first H2O-temperature phase diagram in MOFs.This phase can guide us to target the desired water-stable structure.Besides,Mn-sdc-2 can detect Pb2+ ion in aqueous solution with high sensitivity and selectivity.This work can broaden the applications of luminescent MOFs in sensing hea,vy metal ions in water.By using ligand 6-(4-pyridyl)-terephthalic acid(H2pta),whose LUMO energy level is lower than that of tryptophan,we designed a Zn(?)-based MOF ZJU-108 with excellent water,thermal and pH stabilities.Based on the photoinduced electron transfer(PET)mechanism,ZJU-108 could detect tryptophan in aqueous solution with fluorescence enhancement.The interference of other competitive amino acids including phenylalanine and tyrosine could be ignored.Moreover,ZJU-108 could also sense tryptophan when excited under visible light or in serum,showing great potential for the fluorescence detection of tryptophan in the biological field.A noval Co(II)-based MOF ZJU-109 was developed by using two ligands H2pta and 4,4'-bis(imidazolyl)biphenyl(4,4'-bimbp).The fluorescence of ZJU-109 origins from 4,4'-bimbp.ZJU-109 is water-stable and can simultaneously detect trivalent metal ions M3+ ions(M=Fe,Cr,Al)in water with fluorescence enhancement.These three trivalent metal ions could be discriminated based on different selectivity ratios.Other common metal ions showed negligible influence on the fluorescence of ZJU-109.This work firstly achieved the "turn-on" fluorescence detection for three trivalent metal ions with high selectivity in the world,which shows important theoretical significance and practical application.