Single Atomic Vacancy Catalysis.

Single atom catalysts provide exceptional activity. However, measuring the intrinsic catalytic activity of a single atom in real electrochemical environments is challenging. Here, we report the activity of a single vacancy for electrocatalytically evolving hydrogen in two-dimensional (2D) MoS2. Surprisingly, we find that the catalytic activity per vacancy is not constant but increases with its concentration, reaching a sudden peak in activity at 5.7 × 1014 cm-2 where the intrinsic turn over frequency and Tafel slope of a single atomic vacancy was found to be ∼5 s-1 and 44 mV/dec, respectively. At this vacancy concentration, we also find a local strain of ∼3% and a semiconductor to metal transition in 2D MoS2. Our results suggest that, along with increasing the number of active sites, engineering the local strain and electrical conductivity of catalysts is essential in increasing their activity.

Stimulus-responsive self-assembly of protein-based fractals by computational design.

Fractal topologies, which are statistically self-similar over multiple length scales, are pervasive in nature. The recurrence of patterns in fractal-shaped branched objects, such as trees, lungs and sponges, results in a high surface area to volume ratio, which provides key functional advantages including molecular trapping and exchange. Mimicking these topologies in designed protein-based assemblies could provide access to functional biomaterials. Here we describe a computational design approach for the reversible self-assembly of proteins into tunable supramolecular fractal-like topologies in response to phosphorylation. Guided by atomic-resolution models, we develop fusions of Src homology 2 (SH2) domain or a phosphorylatable SH2-binding peptide, respectively, to two symmetric, homo-oligomeric proteins. Mixing the two designed components resulted in a variety of dendritic, hyperbranched and sponge-like topologies that are phosphorylation-dependent and self-similar over three decades (~10 nm-10 µm) of length scale, in agreement with models from multiscale computational simulations. Designed assemblies perform efficient phosphorylation-dependent capture and release of cargo proteins.

Nonuniform Composition Profiles in Amorphous Multimetal Oxide Thin Films Deposited from Aqueous Solution.

Metal oxide thin films are ubiquitous in technological applications. Often, multiple metal components are used to achieve desired film properties for specific functions. Solution deposition offers an attractive route for producing these multimetal oxides because it allows for careful control of film composition through the manipulation of precursor stoichiometry. Although it has been generally assumed that homogeneous precursor solutions yield homogeneous thin films, we recently reported evidence of nonuniform electron density profiles in aqueous-deposited films. Herein, we show that nonuniform electron densities in lanthanum zirconium oxide (LZO) thin films are the result of inhomogeneous distributions of metal components. Specifically, La aggregates at the film surface, whereas Zr is relatively evenly distributed throughout single-layer films. This inhomogeneous metal distribution persists in stacked multilayer films, resulting in La-rich interfaces between the sequentially deposited layers. Testing of metal-insulator-semiconductor devices fabricated from single and multilayer LZO films shows that multilayer films have higher dielectric constants, indicating that La-rich interfaces in multilayer films do not detrimentally impact film properties. We attribute the enhanced dielectric properties of multilayer films to greater condensation and densification relative to single-layer films, and these results suggest that multilayer films may be preferred for device applications despite the presence of layering artifacts.

Biological control of aragonite formation in stony corals.

Little is known about how stony corals build their calcareous skeletons. There are two prevailing hypotheses: that it is a physicochemically dominated process and that it is a biologically mediated one. Using a combination of ultrahigh-resolution three-dimensional imaging and two-dimensional solid-state nuclear magnetic resonance (NMR) spectroscopy, we show that mineral deposition is biologically driven. Randomly arranged, amorphous nanoparticles are initially deposited in microenvironments enriched in organic material; they then aggregate and form ordered aragonitic structures through crystal growth by particle attachment. Our NMR results are consistent with heterogeneous nucleation of the solid mineral phase driven by coral acid-rich proteins. Such a mechanism suggests that stony corals may be able to sustain calcification even under lower pH conditions that do not favor the inorganic precipitation of aragonite.

Mitochondria Protection after Acute Ischemia Prevents Prolonged Upregulation of IL-1ß and IL-18 and Arrests CKD.

The innate immune system has been implicated in both AKI and CKD. Damaged mitochondria release danger molecules, such as reactive oxygen species, DNA, and cardiolipin, which can cause NLRP3 inflammasome activation and upregulation of IL-18 and IL-1ß It is not known if mitochondrial damage persists long after ischemia to sustain chronic inflammasome activation. We conducted a 9-month study in Sprague-Dawley rats after 45 minutes of bilateral renal ischemia. We detected glomerular and peritubular capillary rarefaction, macrophage infiltration, and fibrosis at 1 month. Transmission electron microscopy revealed mitochondrial degeneration, mitophagy, and deformed foot processes in podocytes. These changes progressed over the study period, with a persistent increase in renal cortical expression of IL-18, IL-1ß, and TGF-ß, despite a gradual decline in TNF-α expression and macrophage infiltration. Treatment with a mitoprotective agent (SS-31; elamipretide) for 6 weeks, starting 1 month after ischemia, preserved mitochondrial integrity, ameliorated expression levels of all inflammatory markers, restored glomerular capillaries and podocyte structure, and arrested glomerulosclerosis and interstitial fibrosis. Further, helium ion microscopy vividly demonstrated the restoration of podocyte structure by SS-31. The protection by SS-31 was sustained for ≥6 months after treatment ended, with normalization of IL-18 and IL-1ß expression. These results support a role for mitochondrial damage in inflammasome activation and CKD and suggest mitochondrial protection as a novel therapeutic approach that can arrest the progression of CKD. Notably, SS-31 is effective when given long after AKI and provides persistent protection after termination of drug treatment.

Non-uniform Composition Profiles in Inorganic Thin Films from Aqueous Solutions.

A variety of metal oxide films (InGaOx, AlOx, "HafSOx") prepared from aqueous solutions were found to have non-uniform electron density profiles using X-ray reflectivity. The inhomogeneity in HafSOx films (Hf(OH)4-2x-2y(O2)x(SO4)y·zH2O), which are currently under investigation as inorganic resists, were studied in more detail by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and medium-energy ion scattering (MEIS). The HAADF-STEM images show a greater concentration of heavy atoms near the surface of a single-layer film. MEIS data confirm the aggregation of Hf at the film surface. The denser "crust" layer in HafSOx films may directly impact patterning resolution. More generally, the phenomenon of surface-layer inhomogeneity in solution-deposited films likely influences film properties and may have consequences in other thin-film systems under investigation as resists, dielectrics, and thin-film transistor components.