Magneto-Optical Sensing of the Pressure Driven Magnetic Ground States in Bulk CrSBr.

Competition between exchange interactions and magnetocrystalline anisotropy may bring new magnetic states that are of great current interest. An applied hydrostatic pressure can further be used to tune their balance. In this work, we investigate the magnetization process of a biaxial antiferromagnet in an external magnetic field applied along the easy axis. We find that the single metamagnetic transition of the Ising type observed in this material under ambient pressure transforms under hydrostatic pressure into two transitions, a first-order spin-flop transition followed by a second-order transition toward a polarized ferromagnetic state near saturation. This reversible tuning into a new magnetic phase is obtained in layered bulk CrSBr at low temperature by varying the interlayer distance using high hydrostatic pressure, which efficiently acts on the interlayer magnetic exchange and is probed by magneto-optical spectroscopy.

Synthesis of Tricyclic Tetrazoles by Cascade Diazotization/Intramolecular Radical C-H Heteroarylation of Arenes.

A cascade diazotization/intramolecular radical C-H heteroarylation of 1-benzyloxy-5-aminotetrazoles and 1-phenethyl-5-aminotetrazoles as substrates using sodium nitrite and acetic acid without any heating, catalysis, irradiation, or electrolysis is reported. This one-pot reaction afforded the desired tricyclic tetrazole products in good yields (up to 94%) without isolation of the diazonium salt intermediate under mild reaction conditions.

Spectroscopic fingerprint of chiral Majorana modes at the edge of a quantum anomalous Hall insulator/superconductor heterostructure.

With the recent discovery of the quantum anomalous Hall insulator (QAHI), which exhibits the conductive quantum Hall edge states without external magnetic field, it becomes possible to create a topological superconductor (SC) by introducing superconductivity into these edge states. In this case, 2 distinct topological superconducting phases with 1 or 2 chiral Majorana edge modes were theoretically predicted, characterized by Chern numbers (N) of 1 and 2, respectively. We present spectroscopic evidence from Andreev reflection experiments for the presence of chiral Majorana modes in an Nb/(Cr0.12Bi0.26Sb0.62)2Te3 heterostructure with distinct signatures attributed to 2 different topological superconducting phases. The results are in qualitatively good agreement with the theoretical predictions.

Observation of Reentrant Correlated Insulators and Interaction-Driven Fermi-Surface Reconstructions at One Magnetic Flux Quantum per Moiré Unit Cell in Magic-Angle Twisted Bilayer Graphene.

The discovery of flat bands with nontrivial band topology in magic-angle twisted bilayer graphene (MATBG) has provided a unique platform to study strongly correlated phenomena including superconductivity, correlated insulators, Chern insulators, and magnetism. A fundamental feature of the MATBG, so far unexplored, is its high magnetic field Hofstadter spectrum. Here, we report on a detailed magnetotransport study of a MATBG device in external magnetic fields of up to B=31 T, corresponding to one magnetic flux quantum per moiré unit cell Φ_{0}. At Φ_{0}, we observe reentrant correlated insulators at a flat band filling factors of ν=+2 and of ν=+3, and interaction-driven Fermi-surface reconstructions at other fillings, which are identified by new sets of Landau levels originating from these. These experimental observations are supplemented by theoretical work that predicts a new set of eight well-isolated flat bands at Φ_{0}, of comparable band width, but with different topology than in zero field. Overall, our magnetotransport data reveal a qualitatively new Hofstadter spectrum in MATBG, which arises due to the strong electronic correlations in the reentrant flat bands.

Nodal and Nematic Superconducting Phases in NbSe_{2} Monolayers from Competing Superconducting Channels.

Transition metal dichalcogenides like 2H-NbSe_{2} in their two-dimensional (2D) form exhibit Ising superconductivity with the quasiparticle spins being firmly pinned in the direction perpendicular to the basal plane. This enables them to withstand exceptionally high magnetic fields beyond the Pauli limit for superconductivity. Using field-angle-resolved magnetoresistance experiments for fields rotated in the basal plane we investigate the field-angle dependence of the upper critical field (H_{c2}), which directly reflects the symmetry of the superconducting order parameter. We observe a sixfold nodal symmetry superposed on a twofold symmetry. This agrees with theoretical predictions of a nodal topological superconducting phase near H_{c2}, together with a nematic superconducting state. We demonstrate that in NbSe_{2} such unconventional superconducting states can arise from the presence of several competing superconducting channels.

Synthesis of α-Trifluoromethylthio-α,ß-Unsaturated Carbonyl Compounds by DABCO-Mediated Electrophilic Trifluoromethylthiolation with N-SCF3-Dibenzenesulfonimide.

A DABCO-mediated electrophilic α-trifluoromethylthiolation of α,ß-unsaturated carbonyl compounds comprising no ß-substituents has been achieved using N-trifluoromethylthio-dibenzenesulfonimide as the SCF3 source. The direct trifluoromethylthiolation provides the corresponding α-trifluoromethylthio-α,ß-unsaturated carbonyl products in good yields (up to 88%). Furthermore, the vinyl group in the α-trifluoromethylthio-α,ß-unsaturated carbonyl product was successfully transformed into diverse functional groups in good to excellent yields (70-95%) by reactions such as epoxidation, aziridination, hydrocyanation, and hydrogenation.

A Combined Experimental and Theoretical Study of the Versatile Reactivity of an Oxocerium(IV) Complex: Concerted Versus Reductive Addition.

A combined experimental and theoretical investigation on the cerium(IV) oxo complex [(LOEt )2 Ce(=O)(H2 O)]⋅MeC(O)NH2 (1; LOEt - =[Co(η5 -C5 H5 ){P(O)(OEt)2 }3 ]- ) demonstrates that the intermediate spin-state nature of the ground state of the cerium complex is responsible for the versatility of its reactivity towards small molecules such as CO, CO2 , SO2 , and NO. CASSCF calculations together with magnetic susceptibility measurements indicate that the ground state of the cerium complex is of multiconfigurational character and comprised of 74 % of CeIV and 26 % of CeIII . The latter is found to be responsible for its reductive addition behavior towards CO, SO2 , and NO. This is the first report to date on the influence of the multiconfigurational ground state on the reactivity of a metal-oxo complex.

WITHDRAWN: Application of deep learning to predict advanced neoplasia using big clinical data in colorectal cancer screening of asymptomatic adults.

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Organocatalytic enantioselective synthesis of acyclic pyrimidine nucleosides by aza-Michael reaction.

An efficient diarylprolinol triphenylsilyl ether-catalyzed enantioselective aza-Michael reaction of pyrimidines as N-centered nucleophiles to α,ß-unsaturated aldehydes, followed by reduction, provided chiral acyclic pyrimidine nucleosides in good yields (51-78% yields for two steps) and excellent enantioselectivities (91-98% ee). In addition, the chiral acyclic pyrimidine nucleoside having the tert-butyldiphenylsilyl-protected hydroxyl substituent was successfully applied to the synthesis of the corresponding chiral cyclic pyrimidine nucleoside analogue bearing the tetrahydrofuranyl ring.

Catalytic enantioselective synthesis of carboxy-substituted 2-isoxazolines by cascade oxa-Michael-cyclization.

An efficient quinidine-based phase-transfer-catalyzed enantioselective cascade oxa-Michael-cyclization reaction of hydroxylamine with various ß-carboxy-substituted α,ß-unsaturated ketones has been achieved for the preparation of chiral carboxy-substituted 2-isoxazolines. This cascade reaction provided the desired products in good yields (up to 98%) with excellent enantioselectivities (91-96% ee). In addition, the cascade reaction was effectively applied to the first catalytic asymmetric synthesis of the herbicide (S)-methiozolin.

5-Bromo-4',5'-bis(dimethylamino)fluorescein: Synthesis and Photophysical Studies.

In this study, three new fluorescein derivatives-5-bromo-4',5'-dinitrofluorescein (BDNF), 5-bromo-4',5'-diaminofluorescein (BDAF), and 5-bromo-4',5'-bis(dimethylamino)fluorescein (BBDMAF)-were synthesized and their pH-dependent protolytic equilibria were investigated. In particular, BBDMAF exhibited pH-dependent fluorescence, showing strong emission only at pH 3-6. BBDMAF bears a bromine moiety and thus, can be used in various cross-coupling reactions to prepare derivatives and take advantage of its unique emission properties. To confirm this, the Suzuki and Sonogashira reactions of BBDMAF with phenylboronic acid and phenylacetylene, respectively, were performed, and the desired products were successfully obtained.

Thermodynamic Evidence for the Fulde-Ferrell-Larkin-Ovchinnikov State in the KFe_{2}As_{2} Superconductor.

We investigate the magnetic phase diagram near the upper critical field of KFe_{2}As_{2} by magnetic torque and specific heat experiments using a high-resolution piezorotary positioner to precisely control the parallel alignment of the magnetic field with respect to the FeAs layers. We observe a clear double transition when the field is strictly aligned in the plane and a characteristic upturn of the upper critical field line, which goes far beyond the Pauli limit at 4.8 T. This provides firm evidence that a Fulde-Ferrell-Larkin-Ovchinnikov state exists in this iron-based KFe_{2}As_{2} superconductor.

Enantioselective Phase-Transfer-Catalyzed Synthesis of Chiral N-Substituted 3,3-Dinitroazetidines by Aza-Michael Reaction.

An efficient and highly enantioselective phase-transfer-catalyzed aza-Michael reaction of 3,3-dinitroazetidine, as N-centered nucleophile, to α,ß-unsaturated ketones has been achieved using a quinidine-based phase-transfer catalyst (0.5-1 mol %), providing chiral N-substituted 3,3-dinitroazetidines in good yields (up to 99%) and excellent enantioselectivities (90-95% ee). This is the first example of the use of azetidines as N-centered nucleophiles in catalytic enantioselective aza-Michael reactions.

Efficient Syntheses of 1,2,3-Triazoloamide Derivatives Using Solid- and Solution-Phase Synthetic Approaches.

Efficient synthetic routes for the preparation of secondary and tertiary 1,2,3-triazoloamide derivatives were developed. A secondary α-1,2,3-triazoloamide library was constructed and expanded by a previously developed solid-phase synthetic route and a tertiary 1,2,3-triazoloamide library was constructed by a parallel solution-phase synthetic route. The synthetic routes rely on amide formation with secondary amines and chloro-acid chlorides; SN2 reaction with sodium azide; and the selective [3 + 2] Hüisgen cycloaddition with appropriate terminal alkynes. The target secondary and tertiary 1,2,3-triazoloamide derivatives were obtained with three-diversity points in excellent overall yields and purities using the reported solid- and solution-phase synthetic routes, respectively.

Cinchona-based primary amine-catalyzed asymmetric cascade aza-Michael-aldol reactions of enones with 2-(1H-pyrrol-2-yl)-2-oxoacetates: synthesis of chiral pyrrolizines with multistereocenters.

Cinchona-based primary amine-catalyzed cascade aza-Michael-aldol reactions of α,ß-unsaturated ketones with 2-(1H-pyrrol-2-yl)-2-oxoacetates provided highly functionalized chiral pyrrolizines bearing multistereocenters including a chiral quaternary carbon center in good yields (up to 92%) with excellent levels of stereocontrol (90-95% ee, >20:1 dr in all cases). The ketone group in the cascade product was asymmetrically reduced to chiral secondary hydroxyl groups in good yields.

Recyclable rhodium nanoparticles: green hydrothermal synthesis, characterization, and highly catalytic performance in reduction of nitroarenes.

In this work, rhodium nanoparticles were synthesized using hydrothermal method that is simple and easy to manipulate reaction and use nontoxic supercritical water. The rhodium nanoparticles were formed in uniform size and shape. These Rh NPs also acted as a efficient heterogenous catalyst in reduction of 4-nitrophenol to 4-aminophenol. Moreover, the rhodium nanoparticles can be recycled without any loss in catalytic activity, and showed highly catalytic activity for various nitroarenes. Therefore, this method will contribute greatly to the development of environmental field and be suitable for use in the industry.

Exploration for the salt stress tolerance genes from a salt-treated halophyte, Suaeda asparagoides.

Salinity stress severely affects plant growth and development causing crop loss worldwide. Suaeda asparagoides is a salt-marsh euhalophyte widely distributed in southwestern foreshore of Korea. To isolate salt tolerance genes from S. asparagoides, we constructed a cDNA library from leaf tissues of S. asparagoides that was treated with 200 mM NaCl. A total of 1,056 clones were randomly selected for EST sequencing, and 932 of them produced readable sequence. By sequence analysis, we identified 538 unigenes and registered each in National Center for Biotechnology Information. The 80 salt stress related genes were selected to study their differential expression. Reverse transcription-PCR and Northern blot analysis revealed that 23 genes were differentially expressed under the high salinity stress conditions in S. asparagoides. They are functionally diverse including transport, signal transduction, transcription factor, metabolism and stress associated protein, and unknown function. Among them dehydrin (SaDhn) and RNA binding protein (SaRBP1) were examined for their abiotic stress tolerance in yeast (Saccharomyces cerevisiae). Yeast overexpressing SaDhn and SaRBP1 showed enhanced tolerance to osmotic, freezing and heat shock stresses. This study provides the evidence that SaRBP1 and SaDhn from S. asparagoides exert abiotic stress tolerance in yeast. Information of salt stress related genes from S. asparagoides would contribute for the accumulating genetic resources to improve osmotic tolerance in plants.

Two-dimensional localization in GeSn.

Localization behaviour is a characteristic feature of thep-type GeSn quantum well (QW) system in a metal-insulator-semiconductor device. The transition to strongly localized behaviour is abrupt with thermally activated conductivity and a high temperature intercept of 0.12 ×e2h-1at a hole carrier density 1.55 × 1011cm-2. The activation energy for the conductivity in the localized state is 0.40 ± 0.05 meV compared to an activation energy of ∼0.1 meV for conductivity activation to a mobility edge at carrier densities >1.55 × 1011cm-2. Insulating behaviour can occur from a system that behaves as though it is in a minimum metallic state, albeit at high temperature, or from a conductivity greater than a minimum metallic state behaviour showing that local disorder conditions with local differences in the density of states are important for the onset of localization. In the presence of a high magnetic field, thermally activated conductivity is present down to Landau level filling factor <1/2but without a magnetic-field-dependent carrier density or a variable range hopping (VRH) transport behaviour developing even with conductivity ≪e2h-1. In the localized transport regime inp-type doped Ge0.92Sn0.08QWs the VRH mechanism is suppressed at temperatures >100 mK and this makes this two-dimensional system ideal for future many body localization studies in disordered hole gases that can be thermally isolated from a temperature reservoir.

Organocatalytic enantioselective formal synthesis of bromopyrrole alkaloids via aza-Michael addition.

An unprecedented organocatalytic enantioselective formal synthesis of bromopyrrole alkaloid natural products is reported. An organocatalytic aza-Michael addition using pyrroles as the N-centered nucleophile is utilized as the enantioselective step to construct the nitrogen-substituted stereogenic carbon center in bromopyrrole alkaloids in good yield and excellent enantioselectivity. The aza-Michael product is converted via lactamization using a Staudinger-type reductive cyclization to the key intermediate, which was previously used in the total synthesis of bromopyrrole alkaloid natural products.

Synthesis of N-Trifluoromethanesulfinyl Ketimines by Cascade Trifluoromethylthiolation/Rearrangement of Ketoximes.

A new and efficient cascade electrophilic trifluoromethylthiolation/radical rearrangement reaction of ketoximes is reported using N-trifluoromethylthio-dibenzenesulfonimide as the SCF3 source without any additives. This simple one-pot reaction provides the corresponding N-trifluoromethanesulfinyl ketimine products in good yields with high E selectivity under mild reaction conditions.