A hydrostable samarium(III)-MOF sensor for the sensitive and selective detection of tryptophan based on a "dual antenna effect"

A Eu-MOF-Based Fluorescent Sensing Probe for the Detection of Tryptophan and Cu2+ in Aqueous Solutions

Abnormal tryptophan (Trp) metabolism can be used as an important indicator of chronic hepatitis, paranoia, Parkinson's disease and other diseases. Deficiency or excessive accumulation of Cu2+ can cause diseases such as Wilson's disease and Alzheimer's disease. Eu-based metal-organic framework (Eu-MOF) was successfully prepared for fluorescence sensing of Trp and Cu2+ in an aqueous solution (pH = 7.4). Eu-MOF showed high selectivity and sensitivity for Trp and Cu2+ with detection limits of 0.22 µM and 0.09 µM and Ksv of 6.17 × 103 M- 1 and 2.37 × 104 M- 1 respectively. Trp and Cu2+ had overlapped UV absorption spectra with that of Eu-MOF and competed for the excitation light source. Trp also attenuated the antennae effect of organic ligands on Eu-MOF, thus quenching the red fluorescence of Eu-MOF. This study provides insights into the application of MOFs in bioanalysis and diagnostics.

Fluorescence detection platform of metal-organic frameworks for biomarkers

Sensitive and selective detection of biomarkers is crucial in the study and early diagnosis of diseases. With the continuous development of biosensing technologies, fluorescent biosensors based on metal-organic frameworks have attracted increasing attention in the field of biomarker detection due to the combination of the advantages of MOFs, such as high specific surface area, large porosity, and structure with tunable functionality and the technical simplicity, sensitivity and efficiency and good applicability of fluorescent detection techniques. Therefore, researchers must understand the fluorescence response mechanism of such fluorescent biosensors and their specific applications in this field. Of all biomarkers applicable to such sensors, the chemical essence of nucleic acids, proteins, amino acids, dopamine, and other small molecules account for about a quarter of the total number of studies. This review systematically elaborates on four fluorescence response mechanisms: metal-centered emission (MC), ligand-centered emission (LC), charge transfer (CT), and guest-induced luminescence change (GI), presenting their applications in the detection of nucleic acids, proteins, amino acids, dopamine, and other small molecule biomarkers. In addition, the current challenges of MOFs-based fluorescent biosensors are also discussed, and their further development prospects are concerned.

SCSC Transformation and Post-Synthesis Modification of MOFs with Proton Conduction and Ratiometric Fluorescence-Sensing Properties

The modification of metal-organic framework (MOF) materials to facilitate their practical applications is an extremely challenging and meaningful topic. In this work, two stepwise modification strategies for MOFs were conducted. First, we have demonstrated a single-crystal-to-single-crystal (SCSC) transformation from a microporous three-dimensional (3D) MOF to a two-dimensional (2D) coordination polymer (CP). The centrosymmetric [Cd(3-bpdb)(MeO-ip)]_n (1) transforms into a chiral [Cd₂(3-bpdb)(MeO-ip)₂(CH₃OH)₂]_n (2), which is triggered by the reaction time with methanol that acts as a structure-directing agent. The conversion relationship of 1 to 2 at different reaction times was studied in detail. Density functional theory (DFT) calculations clearly state that the irreversible formation of 2 is thermodynamically favorable. Intriguingly, 2 exhibits good proton conduction of 1.34 × 10^-3 S cm^-1 under 363 K and 98% relative humidity (RH) due to unique H-bond network characteristics. To the best of our knowledge, there are very few cases of 3D to 2D SCSC transformation stimulated by reaction time. The results have important implications for understanding the SCSC transformation mechanism and synthetic chemistry. On the other hand, the lanthanide³⁺-functionalized hybrids (Ln³⁺-MOF), Ln³⁺@1, were continuously prepared by incorporating luminescent Ln³⁺ ions into the structure of 1 through encapsulating post-synthesis modification (PSM). Tb³⁺@1 exhibits double emission in water and shows visual ratiometric fluorescence behavior for sensing glutamic acid (Glu), tryptophan (Trp), and Al³⁺, which is more reliable and accurate than single emission. Our work may not only provide new insights into the multiple modification of MOF materials but also promote the practical application of such materials.

Computational design of the novel building blocks for the metal-organic frameworks based on the organic ligand protected Cu4 cluster

Metal-organic frameworks (MOFs) are tunable porous network compounds composed of inorganic nodes bound by various organic linkers. Here we report the density functional theory (DFT) study of the MOF novel building blocks made of the Cu4 clusters protected by four organic ligands having two phenyl rings and terminated either with Cl or Br atom (precursors 1 and 2, respectively). The research was performed both in the gas phase and with the implicit effects of acetonitrile included, with two functionals, B3LYP and PBE, both with and without the second-order dispersion correction. We analyzed the structural features of the precursors 1 and 2, their electronic structures, molecular electrostatic potential (MEP) distribution, and global reactivity parameters (GRPs). Both functionals resulted in the singlets of the precursors 1 and 2 as the most stable species. The precursor structures optimized with the hybrid functional were found to be quite similar for both halogens, both containing somewhat distorted from planarity Cu4 cluster, with the outer phenyls of the ligands rotated relative to the inner phenyls. With both halogens and both DFT approaches, the frontier molecular orbitals (FMOs) of the precursors 1 and 2 were shown to have quite similar compositions. The change of the substituent from Br to Cl was found to cause slight stabilizations or destabilizations of the HOMOs and LUMOs. The central parts and especially the inner phenyl ring parts of the precursors 1 and 2 were suggested to play a role of nucleophile in various chemical reactions due to the significant accumulation of negative electrostatic potential. Also, weak intermolecular interactions might exist between the ligands of neighboring precursor molecules. Finally, with both substituents the precursors 1 and 2 should be relatively unreactive and demonstrate thermodynamic stability. Further, the precursors 1 and 2 should be quite stable in oxidation reactions and more active in reduction processes. Generally, the substituent nature was shown not to affect significantly the reactivity of the precursors 1 and 2, as well as their other properties.

Pyrazine Functionalization to Boost Antenna Effect in Rare-Earth Metal-Organic Frameworks for Tetracyclines Detection

Here we report a generalizable strategy for the synthesis of rare-earth metal-organic frameworks (RE-MOFs) with 12-connected RE9 clusters and shp-topology. A total of 26 isostructural RE-MOFs (JNU-205-RE and JNU-206-RE) were...