Prediction of Enhanced Catalytic Activity for Hydrogen Evolution Reaction in Janus Transition Metal Dichalcogenides

Significant efforts have been made in improving the hydrogen evolution reaction (HER) catalytic activity in transition metal dichalcogenides (TMDs), which are promising nonprecious catalysts. However, previous attempts have exploited possible solutions to activate the inert basal plane, with little improvement. Among them, the most successful modification requires a careful manipulation of vacancy concentration and strain simultaneously. To fully realize the promise of TMD catalysts for HER in an easier and more effective way, a new means in tuning the HER catalytic activity is needed. Herein, we propose exploiting the inherent structural asymmetry in the recently synthesized family of Janus TMDs as a new means to stimulate HER activity. We report a density functional theory (DFT) study of various Janus TMD monolayers as HER catalysts, and identify the WSSe system as a promising candidate, where the basal plane can be activated without large applied tensile strains and in the absence of significant density of vacancies. We predict that it is possible to realize a strain-free Janus TMD-based catalyst that can readily provide promising intrinsic HER catalytic performance. The calculated density of states and electronic structures reveal that the introduction of in-gap states and a shift in the Fermi level in hydrogen adsorbed systems due to Janus asymmetry is the origin of enhanced HER activity. Our results should pave the way to design high-performance and easy-accessible TMD-based HER catalysts

Tunable Magnetism and Transport Properties in Nitride MXenes

Two-dimensional materials with intrinsic and robust ferromagnetism and half-metallicity are of great interest to explore the exciting physics and applications of nanoscale spintronic devices, but no such materials have been experimentally realized. In this study, we predict several M₂NT_<i>x</i> nitride MXene structures that display these characteristics based on a comprehensive study using a crystal field theory model and first-principles simulations. We demonstrate intrinsic ferromagnetism in Mn₂NT_<i>x</i> with different surface terminations (T = O, OH, and F), as well as in Ti₂NO₂ and Cr₂NO₂. High magnetic moments (up to 9 μ_B per unit cell), high Curie temperatures (1877 to 566 K), robust ferromagnetism, and intrinsic half-metallic transport behavior of these MXenes suggest that they are promising candidates for spintronic applications, which should stimulate interest in their synthesis

Heparinoids Activate a Protease, Secreted by Mucosa and Tumors, via Tethering Supplemented by Allostery

Activation by glycosaminoglycans (GAGs) is an emerging trend among extracellular proteases important in disease. ProMMP-7, the zymogen of a matrix metalloproteinase secreted by mucosal epithelial and tumor cells, is activated at their surfaces by sulfated GAGs, but how? ProMMP-7 is activated in <i>trans</i> by representative heparin oligosaccharides in a length-dependent manner, with a large jump in activation at lengths of 16 monosaccharides. Imaging by atomic force microscopy visualized small complexes of proMMP-7 molecules linked by 8-mer lengths of heparinoids and extended assembles formed with 16-mer lengths of heparin. Complexes of proMMP-7 with polydisperse heparin or heparan sulfate were more diverse. Heparinoids evidently accelerate activation by tethering multiple proMMP-7 molecules together for proteolytic attack among neighbors. Removal of either the prodomain or C-terminal peptide sequence of KRSNSRKK from MMP-7 prevents formation of the long arrays induced by heparin 16-mers or heparan sulfate. The role of the C-terminus in activation assays suggests it contributes to remote, allosteric binding of GAGs. Enhancement of proteolytic velocity of MMP-by GAGs indicates them to be effectors of V-type allostery. GAGs from proteoglycans appear to assemble proMMP-7 molecules for activation, an event preceding its tumorigenic or antibacterial proteolytic activities at cell surfaces