Search

Anisotropic materials with low symmetries hold significant promise for next-generation electronic and quantum devices. 2M-WS 2 , which is a candidate for topological superconductivity, has garnered considerable interest. However, a comprehensive understanding of how its anisotropic features contribute to unconventional superconductivity, along with a simple, reliable method to identify its crystal orientation, remains elusive. Here, we combine theoretical and experimental approaches to investigate angle- and polarization-dependent anisotropic Raman modes of 2M-WS 2 . Through first-principles calculations, we predict and analyze the phonon dispersion and lattice vibrations of all Raman modes in 2M-WS 2 . We establish a direct correlation between their anisotropic Raman spectra and high-resolution transmission electron microscopy images. Finally, we demonstrate that anisotropic Raman spectroscopy can accurately determine the crystal orientation and twist angle between two stacked 2M-WS 2 layers. Our findings provide insights into the electron-phonon coupling and anisotropic properties of 2M-WS 2 , paving the way for the use of anisotropic materials in advanced electronic and quantum devices.

Leveraging the reciprocal-space proximity effect between superconducting bulk and topological surface states (TSSs) offers a promising way to topological superconductivity. However, elucidating the mutual influence of bulk and TSSs on topological superconductivity remains a challenge. Here, we report pioneering transport evidence of a thickness-dependent transition from conventional to unconventional superconductivity in 2M-phase WS 2 (2M-WS 2 ). As the sample thickness reduces, we see clear changes in key superconducting metrics, including critical temperature, critical current, and carrier density. Notably, while thick 2M-WS 2 samples show conventional superconductivity, with an in-plane (IP) upper critical field constrained by the Pauli limit, samples under 20 nm exhibit a pronounced IP critical field enhancement, inversely correlated with 2D carrier density. This marks a distinct crossover to unconventional superconductivity with strong spin-orbit-parity coupling. Our findings underscore the crucial role of sample thickness in accessing topological states in 2D topological superconductors, offering pivotal insights into future studies of topological superconductivity.

The potential of memristive devices for applications in nonvolatile memory and neuromorphic computing has sparked considerable interest, particularly in exploring memristive effects in two-dimensional (2D) magnetic materials. However, the progress in developing nonvolatile, magnetic field-free memristive devices using 2D magnets has been limited. In this work, we report an electrostatic-gating-induced nonvolatile memristive effect in CrI 3 -based tunnel junctions. The few-layer CrI 3 -based tunnel junction manifests notable hysteresis in its tunneling resistance as a function of gate voltage. We further engineered a nonvolatile memristor using the CrI 3 tunneling junction with low writing power and at zero magnetic field. We show that the hysteretic transport observed is not a result of trivial effects or inherent magnetic properties of CrI 3 . We propose a potential association between the memristive effect and the newly predicted ferroelectricity in CrI 3 via gating-induced Jahn-Teller distortion. Our work illuminates the potential of 2D magnets in developing next-generation advanced computing technologies.

Ice adhesion on aerospace-relevant materials is both complex and not well understood. Measuring such adhesion and understanding the underlying physics involved require reliable testing techniques that can yield multifaceted data sets. The latter includes the surface morphology, that is, roughness, and its spatial correlation structure, resolving substrate-induced strain, and direct mechanical testing of adhesion. As part of a continuing investigation of ice adhesion on a relevant surface, we performed time-dependent stress ramps on aluminum surfaces. The temperature range explored, from -20 to -7 °C, allowed spontaneous icing and ice morphologies, namely, below or above -15 °C. Additionally, we characterized the spatial correlation surface roughness maps of the specimens. Our novel test protocol yields reproducible and high-precision results when compared with alternative methods reported throughout the literature. The stress-ramp test data using the proposed protocol show that the apparent average critical stress (proportional to the adhesion strength) depends on both stress-ramp rate and temperature. More specifically, the adhesion strength is higher for higher stress rates and increases with decreasing temperature. The stress-ramp test yields the full span of the time-dependent adhesive behavior of ice and particularly the upper bound. Additional stress-concentration analysis is needed to correct for this effect and thereby yield the critical stress rather than the average value produced by our procedure. The results in this work should aid to improve our understanding of ice adhesion mechanisms.

Recently, a newly discovered VIB group transition metal dichalcogenide (TMD) material, 2M-WS 2 , has attracted extensive attention due to its interesting physical properties such as topological superconductivity, nodeless superconductivity, and anisotropic Majorana bound states. However, the techniques to grow high-quality 2M-WS 2 bulk crystals and the study of their physical properties at the nanometer scale are still limited. In this work, we report a new route to grow high-quality 2M-WS 2 single crystals and the observation of superconductivity in its thin layers. The crystal structure of the as-grown 2M-WS 2 crystals was determined by X-ray diffraction (XRD) and scanning tunneling microscopy (STM). The chemical composition of the 2M-WS 2 crystals was determined by energy dispersive X-ray spectroscopy (EDS) analysis. At 77 K, we observed the spatial variation of the local tunneling conductance (d I /d V ) of the 2M-WS2 thin flakes by scanning tunneling spectroscopy (STS). Our low temperature transport measurements demonstrate clear signatures of superconductivity of a 25 nm-thick 2M-WS 2 flake with a critical temperature ( T C ) of ∼8.5 K and an upper critical field of ∼2.5 T at T = 1.5 K. Our work may pave new opportunities in studying the topological superconductivity at the atomic scale in simple 2D TMD materials., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

Human leukocyte elastase (HLE) has been proposed to be a primary mediator of pulmonary emphysema, and inhibitors of this enzyme should be effective in the treatment of emphysema and other pulmonary diseases. We have discovered a novel class of alicyclic and heterocyclic leaving groups which share one common structural feature, a cyclic beta-dicarbonyl. This design concept for leaving groups has not been previously reported. A structure-activity relationship has been developed and the concept extended to several types of alicyclic and heterocyclic beta-dicarbonyl systems. This work led to the identification of a potent (K*i of 0.066 nM) and tissue stable (in vitro: blood t1/2 = 160 min, liver t1/2 > 240 min) benzisothiazolone HLE inhibitor, WIN 65936 (13b).

Aminoalkylindoles (AAIs) are a novel series of cannabinoid receptor ligands. In this report we disclose the structural features of AAIs which are important for binding to this receptor as measured by inhibition of binding of [3H]Win 55212-2 (5). Functional activity in the mouse vas deferens is also noted and used to distinguish agonists from potential antagonists. The key structural features for potent cannabinoid activity in this series are a bicyclic (naphthyl) substituent at the 3-position, a small (H) substituent at the 2-position, and an aminoethyl (morpholinoethyl) substituent at the 1-position. A 6-bromo analog, Win 54461 (31), has been identified as a potential cannabinoid receptor antagonist. Modeling experiments were done to develop a pharmacophore and also to compare AAI structures with those of classical cannabinoids. The fact that the cannabinoid AAIs arose out of work on a series of cyclooxygenase inhibitors make sense now that an endogenous cannabinoid ligand has been identified which is a derivative of arachidonic acid. Because of their unique structures and physical properties, AAIs provide useful tools to study the structure and function of the cannabinoid receptor(s).

Syntheses of 5'-acyl furanosteroids are described from the corresponding unsubstituted [3,2-b]furanosteroids using acid anhydrides and acid chlorides in the presence or absence of Lewis acids. New methods have been developed to prepare 5'-acetyl derivatives: reduction of a 5'-trichloroacetyl intermediate either by sodium formaldehyde sulfoxylate or with 10% Pd/C. Most of these 5'-acyl derivatives bind to the rat ventral prostate androgen receptor. However the antiandrogenic activity was diminished when compared with 4,5'-methylsulfonyl furanosteroid. Biological studies revealed that 5'-acyl furanosteroids were either androgens or modest antiandrogens. The electrostatic potential maps of the substructures of 3, 4, and 5'-acetyl syn- and anti-furanosteroids showed striking differences which may explain, to some extent, the lack of significant antiandrogenic activity of 5'-acyl furanosteroids.

The steroidal sulfonylpyrazole 1 bound to the rat ventral prostate androgen receptor in vitro; it inhibited testosterone propionate induced increases in ventral prostate weight in vivo in the castrated, immature male rat with an ED50 of 15 mg/kg po. Compound 1 lacked androgenic activity in vivo in contrast to the parent steroidal pyrazole 5, which was both androgenic and antiandrogenic. The 2'- and 5'-methylsulfonyl isomers 6 and 6a did not bind to the androgen receptor. Introduction of an alkylsulfonyl at the N-1'-position has served, therefore, to isolate the intrinsic antiandrogenic properties of the steroidal heterocycle free of apparent hormone agonist properties. Structure-activity relationship studies revealed that a methylsulfonyl group at N-1' together with a C-17 alpha-substituent were the optimal combination for in vitro androgen receptor binding, in vivo antiandrogenic potency, and a lack of androgenic activity.

The carbon-13 NMR spectrum of oxaloacetate bound in the active site of citrate synthase has been obtained at 90.56 MHz. In the binary complex with enzyme, the positions of the resonances of oxaloacetate are shifted relative to those of the free ligand as follows: C-1 (carboxylate), -2.5 ppm; C-2 (carbonyl), +4.3 ppm; C-3 (methylene), -0.6 ppm; C-4 (carboxylate), +1.3 ppm. The change observed in the carbonyl chemical shift is successively increased in ternary complexes with the product [coenzyme A (CoA)], a substrate analogue (S-acetonyl-CoA), and an acetyl-CoA enolate analogue (carboxymethyl-CoA), reaching a value of +6.8 ppm from the free carbonyl resonance. Binary complexes are in intermediate to fast exchange on the NMR time scale with free oxaloacetate; ternary complexes are in slow exchange. Line widths of the methylene resonance in the ternary complexes suggest complete immobilization of oxaloacetate in the active site. Analysis of line widths in the binary complex suggests the existence of a dynamic equilibrium between two or more forms of bound oxaloacetate, primarily involving C-4. The changes in chemical shifts of the carbonyl carbon indicate strong polarization of the carbonyl bond or protonation of the carbonyl oxygen. Some of this carbonyl polarization occurs even in the binary complex. Development of positive charge on the carbonyl carbon enhances reactivity toward condensation with the carbanion/enolate of acetyl-CoA in the mechanism which has been postulated for this enzyme. The very large change in the chemical shift of the reacting carbonyl in the presence of an analogue of the enolate of acetyl-CoA supports this interpretation.