Nerve agents are highly toxic organophosphorus compounds, and the wild-type phosphotriesterase (PTE) enzyme is capable of hydrolyzing these organophosphates but with a low catalytic efficiency. Here the whole enzymatic detoxification process of the G-type nerve agent sarin by the PTE enzyme, including the substrate delivery, the chemical reaction, and the product release, has been explored by extensive QM/MM MD and MM MD simulations. The plausible mechanisms for the chemical and nonchemical steps, the roles of water molecules, and the key residues have been discussed. The enzymatic P–F cleavage of sarin is a two-step exothermic process with the free-energy span of 12.3 kcal/mol, and it should be facile in the whole enzymatic catalysis. On the contrary, the initial degraded product is tightly bound to the binuclear zinc center, and its dissociation experiences multiple chemical steps with the free-energy barriers of 21.0 kcal/mol for the recombination process and 18.3 kcal/mol for the release of the product phosphoester from the active site. Notably, the solvation of hydrophilic products in the bulk water is generally exothermic, which provides the driving force for the release of products from the active site. The side-chain residues Leu271 and Phe132 in the transportation channel function as the entrance gate in PTE and play an important gate-switching role to manipulate the substrate access to the active site and the product release. These mechanistic details for the enzymatic degradation of sarin by PTE provide significant clues to improve its activity toward the nerve agents.

We have introduced a novel water-soluble two-photon photoinitiator based on the host−guest interaction between 3,6-bis[2-(1-methyl-pyridinium)vinyl]-9pentyl-carbazole diiodide (BMVPC) and cucurbit [7]uril (CB7) because most of the commercial photoinitiators have poor two-photon initiating efficiency in aqueous solutions. The binding ratio of BMVPC and CB7 was determined as 1:1 by isothermal titration calorimetry and quantum chemical calculation. The formation of the host−guest complex increases the two-photon absorption cross-section about five times, and improves the water solubility required as the photoinitiator for hydrogel fabrication. The BMVPC−CB7 inclusion complex was used as the one-component photoinitiator, and the polyethylene glycol diacrylate with promising biocompatibility was used as the hydrogel monomer to form the aqueous-phase photoresist system applied to two-photon polymerization microfabrication. A relatively low laser threshold of 4.5 mW, a high fabricating resolution of 180 nm, and the true three-dimensional (3D) fabricating capability in the aqueous solution have been obtained by using the as-prepared photoresist system. Finally, 3D engineering hydrogel scaffold microstructures with low toxicity and good biocompatibility have been fabricated and cocultured with living HeLa cells, which demonstrates the potential for further application in tissue engineering.

We report a novel biscarbazole-based cyanine with a large Stokes shift and TPA cross-section as a light-up probe for DNA and selective TPEF cell imaging.