Dynamic Nucleophilic Aromatic Substitution of Tetrazines

A dynamic nucleophilic aromatic substitution of tetrazines (SN Tz) is presented herein. It combines all the advantages of dynamic covalent chemistry with the versatility of the tetrazine moiety. Indeed, libraries of compounds or sophisticated molecular structures can be easily obtained, which are susceptible to post-functionalization by inverse electron demand Diels-Alder (IEDDA) reaction, which also locks the exchange. Additionally, the structures obtained can be disassembled upon the application of the right stimulus, either UV irradiation or a suitable chemical reagent. Moreover, SN Tz is compatible with the imine chemistry of anilines. The high potential of this methodology has been proved by building two responsive supramolecular systems: A macrocycle that displays a light-induced release of acetylcholine; and a truncated [4+6] tetrahedral shape-persistent fluorescent cage, which is disassembled by thiols unless it is post-stabilized by IEDDA.

Rational Design of Dual-Emission Lanthanide Metal-Organic Framework for Visual Alkaline Phosphatase Activity Assay

The alkaline phosphatase (ALP) activity assay is very significant for disease diagnosis and biomedical research. Lanthanide metal-organic framework (Ln-MOF) based fluorescence sensors have great application potential in ALP activity assays. However, it is critical but challenging to investigate the emission law of Ln-MOFs for revealing rational design principles and selecting an appropriate MOF. Here, we describe a reasonable design strategy for dual-emission Ln-MOFs based on theoretical calculations. This strategy combines Reinhoudt empirical rule, intramolecular charge transfer theory, and aggregation/coordination-induced emission theory; reveals the luminescence law of Ln-MOFs; and provides theoretical guidance for the rational design of dual-emission Ln-MOFs. On the basis of this strategy, we create a dual-emission Tb-MOF fluorescent probe used for ALP activity assay and investigate the detection mechanism. The probe shows ultrasensitive (limit of detection 0.002 mU mL^-1) and selective response to ALP, and it suits for point-of-care visual detection coupled with a self-designed portable enzyme activity assay kit and smartphone-assisted visual device. The kit-based visual assay method can accurately quantify the activity of ALP in real serum samples (recovery >93%, and relative error is less than 6.8% compared with the results of fluorescence spectrometer-based method) and consumes only 25 μL of serum. In addition, a logical decoder based on the "dual-key unlocking strategy" is designed, providing a feasible solution for the development of intelligent ALP activity detection equipment. As far as we know, this is the first report of a theoretical calculation-guided versatile design strategy for dual-emission Ln-MOFs and a portable enzyme activity assay kit for visual detection.