3 research outputs found
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 M<sub>2</sub>NT<sub><i>x</i></sub> 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 Mn<sub>2</sub>NT<sub><i>x</i></sub> with different surface terminations (T = O, OH,
and F), as well as in Ti<sub>2</sub>NO<sub>2</sub> and Cr<sub>2</sub>NO<sub>2</sub>. High magnetic moments (up to 9 μ<sub>B</sub> 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