Ln-MOFs Based On Rigid Carboxylic Acid Ligands For Fluorescence Sensing Of Biomolecules

Biomolecules widely exist in natural science and daily life,and are important substances for revealing the biochemical processes of organisms.The realization of highly selective detection of specific biomolecules will have far-reaching significance in disease prevention,medical diagnosis,and environmental safety and so on.Lanthanide metal-organic frameworks（Ln-MOFs）have the characteristics of large specific surface area,high porosity,rich and diverse structures and designable functions,while inheriting the excellent optical properties of lanthanides.As a fluorescent sensing material,Ln-MOFs is favored because of its high sensitivity,strong selectivity and short response time,showing great application potential and development space in the field of biosensing.Selecting suitable ligands is a necessary condition for the construction of Ln-MOFs with novel structures,stable frameworks,and outstanding performances.Rigid carboxylic acid ligands have firm structure,stable groups,and excellent coordination ability,which is easy to form high-quality single crystals in the process of complex preparation and is helpful to predict and analyze its topological structure.In this work,a series of Ln-MOFs with good stability are constructed by using a variety of rigid ligands and lanthanide metals,aiming to realize the detection of biomolecules by using their unique structure,excellent fluorescence properties and abundant functional sites,so as to obtain high-sensitivity,high-selectivity,and recyclable fluorescent biosensing materials.It is expected to provide new detection methods in biological analysis and clinical disease diagnosis while providing ideas for the synthesis of efficient Ln-MOFs materials.The main results are as follows:（1）A series of isomorphic Ln-MOFs were synthesized using the rigid polycarboxylic acid ligand 2,5-dihydroxyterephthalic acid（H₂DHBDC）,all of which had a three-dimensional pcu topological grid structure.The experimental results showed that Eu-MOF had excellent thermal and water stability,and exhibited green emission generated by the ligandπ-π*transition under the excitation of ultraviolet light source,while the characteristic fluorescence peak of Eu³⁺was completely shielded.This phenomenon was explained by density functional theory（DFT）calculation.Interestingly,the addition of 2,6-Pyridine dicarboxylic acid（DPA）,the main component of bacillus anthracis spores,could effectively restore the characteristic red light of Eu³⁺,achieving rapid,sensitive and selective detection of DPA in the presence of other potential interferers.In addition,combined with density functional theory（DFT）,the powder X-ray diffraction（PXRD）,infrared spectroscopy（FT-IR）,Xray photoelectron spectroscopy（XPS）,UV-visible absorption spectrum（UV-vis）were used to detailly investigate the detection mechanism of DPA.（2）A kind of novel Ln-MOFs was synthesized for the first time by using Pyromellitic acid（H₄btec）and nicotinic acid（Hntca）with rigid structure as mixed dual-ligands.The complex was an infinitely extended 3D supramolecular network formed by the interaction of coordination bonds and a variety of hydrogen bonds,which was simplified by Topos Pro software to obtain a unique and novel topological structure.Eu-MOF could achieve high sensitivity detection of uric acid（UA）in aqueous solution through significant fluorescence quenching effect,and had excellent anti-interference ability.More importantly,Eu-MOF showed excellent recyclability in the cycling experiment of detecting UA,and was expected to become an efficient,sensitive and environmental-friendly fluorescent sensing material.（3）Two isomorphic Ln-MOFs were prepared by solvothermal self-assembly using rigid pyromellitic acid（H₄BTEC）as ligand.The complex had a 3D structure and there were a large number of coordinated and free water molecules.A novel topological type was obtained after simplification by Topos Pro software.The fluorescence test results showed that Sm-MOF emitted the characteristic fluorescence of Sm³⁺at the optimal excitation wavelength.The DFT calculation results proved that the T₁ energy level of the ligand matches the ⁴G_5/2 vibration energy level of Sm³⁺,which could carry out the effective energy transfer process.Interestingly,Sm-MOF could distinguish tryptophan（Trp）from other natural amino acids in aqueous solution by significant fluorescence enhancement,and had fast response time,excellent detection sensitivity and anti-interference ability.More importantly,Sm-MOF could effectively detect Trp in real milk samples,marking it as a potential Trp sensing material.