Publications

Ultrahigh-resolution transmission electron microscopy and atomic-scale spectroscopy are used to investigate the origin of the toughness in rare-earth doped silicon carbide (RE-SiC) by examining the mechanistic nature of the intergranular cracking events which we find to occur precisely along the RE-decorated interface between the SiC grains and the nanoscale grain-boundary phase. We conclude that, for optimal toughness, the relative elastic modulus across the grain-boundary phase and the interfacial fracture toughness are the most critical material parameters; both can be altered with judicious choice of rare-earth elements.

The catalytic transformation of C–H to C–N bonds offers rapid access to fine chemicals and high-performance materials, but achieving high selectivity from undirected aminations of unactivated C(sp3)–H bonds remains an outstanding challenge. We report the origins of reactivity and selectivity of a Cu-catalyzed C–H amidation of simple alkanes. Using a combination of experimental and computational mechanistic studies and energy decomposition techniques, we uncover a switch in mechanism from inner-sphere to outer-sphere coupling between alkyl radicals and the active Cu(II) catalyst with increasing substitution of the alkyl radical. The combination of computational predictions and detailed experimental validation shows that simultaneous minimization of both Cu–C covalency and alkyl radical size increases the rate of reductive elimination, and that both strongly electron-donating and electron-withdrawing substituents on the catalyst accelerate the selectivity-determining C–N bond formation process as a result of a change in mechanism. These findings offer design principles for the development of improved catalyst scaffolds for radical C–H functionalization reactions.

Targeting proteins at the other sulfur As the only amino acid with a thiol (SH) group, cysteine is easily targeted for site-selective protein modifications. Hydrophobic methionine also has sulfur in its side chain, but its capping methyl group has hindered analogous targeting efforts. Lin et al. introduce a complementary protocol to tether new substituents exclusively to methionine, even in the presence of cysteine. They used an oxaziridine group as an oxidant to form sulfimide (S=N) linkages. The approach allowed antibody-drug conjugation and chemoproteomic screening for reactive methionine surface residues. Science , this issue p. 597

We present multi-epoch, multi-colour pre-outburst photometry and\npost-outburst light curves and spectra of the luminous blue variable (LBV)\noutburst Gaia16cfr discovered by the Gaia satellite on 1 December 2016. We\ndetect Gaia16cfr in 13 epochs of Hubble Space Telescope imaging spanning phases\nof 10 yr to 8 months before the outburst and in Spitzer Space Telescope imaging\n13 years before outburst. Pre-outburst optical photometry is consistent with an\n18 Msun F8 I star, although the star was likely reddened and closer to 30 Msun.\nThe pre-outburst source exhibited a significant near-infrared excess consistent\nwith a 120 AU shell with 4x10-6 Msun of dust. We infer that the source was\nenshrouded by an optically-thick and compact shell of circumstellar material\nfrom an LBV wind, which formed a pseudo-photosphere consistent with S Dor-like\nvariables in their "maximum" phase. Within a year of outburst, the source was\nhighly variable on 10-30 day timescales. The outburst light curve closely\nmatches that of the 2012 outburst of SN 2009ip, although the observed\nvelocities are significantly slower than in that event. In Halpha, the outburst\nhad an excess of blueshifted emission at late times centred around -1500 km/s,\nsimilar to that of double-peaked Type IIn supernovae and the LBV outburst SN\n2015bh. From the pre-outburst and post-outburst photometry, we infer that the\noutburst ejecta are evolving into a dense, highly structured circumstellar\nenvironment from precursor outbursts within years of the December 2016 event.\n

Abstract Copper‐tantalate, Cu 2 Ta 4 O 11 (CTO), shows significant promise as an efficient photocathode for multi‐carbon compounds (C 2+ ) production through photoelectrochemical (PEC) CO 2 reduction, owing to its suitable energy bands and catalytic surface. However, synthesizing CTO poses a significant challenge due to its metastable nature and thermal instability. In this study, this challenge is addressed by employing a flux‐mediated synthesis technique using a sodium‐based flux to create sodium‐doped CTO (Na‐CTO) thin films, providing enhanced nucleation and stabilization for the CTO phase. To evaluate the PEC performance and catalytic properties of the films, copper(II) oxide (CuO) at the Na‐CTO surface is selectively etched. The etched Na‐CTO shows a lower dark current, with decreased contribution from photocorrosion, unlike the non‐etched Na‐CTO which has remaining CuO on the surface. Furthermore, Na‐CTO exhibits 7.3‐fold ethylene selectivity over hydrogen, thus highlighting its promising potential as a photocathode for C 2+ production through PEC CO 2 reduction.

Silver-copper (AgCu) bimetallic catalysts hold great potential for electrochemical carbon dioxide reduction reaction (CO₂RR), which is a promising way to realize the goal of carbon neutrality. Although a wide variety of AgCu catalysts have been developed so far, it is relatively less explored how these AgCu catalysts evolve during CO₂RR. The absence of insights into their stability makes the dynamic catalytic sites elusive and hampers the design of AgCu catalysts in a rational manner. Here, we synthesized intermixed and phase-separated AgCu nanoparticles on carbon paper electrodes and investigated their evolution behavior in CO₂RR. Our time-sequential electron microscopy and elemental mapping studies show that Cu possesses high mobility in AgCu under CO₂RR conditions, which can leach out from the catalysts by migrating to the bimetallic catalyst surface, detaching from the catalysts, and agglomerating as new particles. Besides, Ag and Cu manifest a trend to phase-separate into Cu-rich and Ag-rich grains, regardless of the starting catalyst structure. The composition of the Cu-rich and Ag-rich grains diverges during the reaction and eventually approaches thermodynamic values, i.e., Ag_0.88Cu_0.12 and Ag_0.05Cu_0.95. The separation between Ag and Cu has been observed in the bulk and on the surface of the catalysts, highlighting the importance of AgCu phase boundaries for CO₂RR. In addition, an operando high-energy-resolution X-ray absorption spectroscopy study confirms the metallic state of Cu in AgCu as the catalytically active sites during CO₂RR. Taken together, this work provides a comprehensive understanding of the chemical and structural evolution behavior of AgCu catalysts in CO₂RR.

Abstract Herein, we report the synthesis of a nitrone‐linked covalent organic framework, COF‐115, by combining N , N′ , N′ , N ′′′‐(ethene‐1, 1, 2, 2‐tetrayltetrakis(benzene‐4, 1‐diyl))tetrakis(hydroxylamine) and terephthaladehyde via a polycondensation reaction. The formation of the nitrone functionality was confirmed by solid‐state 13 C multi cross‐polarization magic angle spinning NMR spectroscopy of the 13 C‐isotope‐labeled COF‐115 and Fourier‐transform infrared spectroscopy. The permanent porosity of COF‐115 was evaluated through low‐pressure N 2 , CO 2 , and H 2 sorption experiments. Water vapor and carbon dioxide sorption analysis of COF‐115 and the isoreticular imine‐linked COF indicated a superior potential of N ‐oxide‐based porous materials for atmospheric water harvesting and CO 2 capture applications. Density functional theory calculations provided valuable insights into the difference between the adsorption properties of these COFs. Lastly, photoinduced rearrangement of COF‐115 to the associated amide‐linked material was successfully demonstrated.

<p>Supplementary Table 3. The Adjusted Associations of Scaled Body Composition Measurements (Per SD Increase) with Reduced RDI and Relative Changes (%) in the Number of Moderate and Severe Adverse Events</p>

A nanoscale, visible-light, self-sensing stress probe would be highly desirable in a variety of biological, imaging, and materials engineering applications, especially a device that does not alter the mechanical properties of the material it seeks to probe. Here we present the CdSe–CdS tetrapod quantum dot, incorporated into polymer matrices via electrospinning, as an in situ luminescent stress probe for the mechanical properties of polymer fibers. The mechanooptical sensing performance is enhanced with increasing nanocrystal concentration while causing minimal change in the mechanical properties even up to 20 wt % incorporation. The tetrapod nanoprobe is elastic and recoverable and undergoes no permanent change in sensing ability even upon many cycles of loading to failure. Direct comparisons to side-by-side traditional mechanical tests further validate the tetrapod as a luminescent stress probe. The tetrapod fluorescence stress–strain curve shape matches well with uniaxial stress–strain curves measured mechanically at all filler concentrations reported.