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In this study, we demonstrate the ability of polarity inversion of sputtered aluminum scandium nitride thin films through post-fabrication processes with domain widths as small as 220 nm at a periodicity of 440 nm. An approach using photo- and electron-beam lithography to generate sub-quarter micrometer feature size with adjustable duty cycle through a lift-off process is presented. The film with a coercive field Ec+ of 5.35 MV/cm was exercised first with a 1 kHz triangular double bipolar wave and ultimately poled with a 0.5 kHz double monopolar wave using a Radiant Precision Premier II tester. The metal polar (M-polar) and nitrogen polar (N-polar) domains were identified and characterized through potassium hydroxide wet etching as well as piezoresponse force microscopy (PFM). Well-distinguished boundaries between the oppositely polarized domain regions were confirmed through the phase diagram of the PFM results. The relationship between the electrode width, poling voltage, and domain growth was experimentally studied and statistically analyzed, where 7.96 nm/V domain width broadening vs escalating poling voltage was observed. This method produces extremely high domain spatial resolution in III-nitride materials via poling and is transferable to a CMOS-compatible photolithography process. The spatial resolution of the periodically poled Al0.68Sc0.32N is suitable for second-harmonic generation of deep ultraviolet through quasi-phase-matching and RF MEMS operating in the X-Band spectrum. [ABSTRACT FROM AUTHOR]

A novel strategy that combines oxidative aminocatalysis and gold catalysis allows the preparation of chiral α‐quaternary isochromanes, a motif that is prevalent in natural products and synthetic bioactive compounds. In the first step, α‐branched aldehydes and propargylic alcohols are transformed into α‐quaternary ethers with excellent optical purities (>90 % ee) via oxidative umpolung with DDQ and an amino acid‐derived primary amine catalyst. Subsequent gold(I)‐catalyzed intramolecular hydroarylation affords the isochromane products with retention of the quaternary stereocenter. A second approach explores the use of allylic alcohols as reaction partners for the oxidative coupling to furnish α‐quaternary ethers with generally lower enantiopurities. Stereoretentive cyclization to isochromane products is achieved via intramolecular Friedel‐Crafts type alkylation with allylic acetates as a reactive handle. A number of synthetic elaborations and a biological study on these α‐quaternary isochromanes highlight the potential applicability of the presented method. [ABSTRACT FROM AUTHOR]

A fruitful debate took place recently in literature, discussing the enhanced Diels–Alder reactivity of tropone derivatives for which the carbonyl polarity was reversed by means of umpolung. Karas et al. sustained that the umpolung increases the antiaromatic character of the ring, affecting the highest occupied molecular orbital (HOMO)/least unoccupied molecular orbital (LUMO) energies, speeding up the reaction. Tiekink et al. challenged this interpretation by sustaining that the asynchronicity of the reaction mechanisms, rather than orbital energy perturbation, was the main responsible for the smaller reaction barriers. We shed light on this dispute by computing full interaction quantum atom (IQA) and quantum theory of atoms in molecules (QTAIM) analyses over complete intrinsic reaction coordinate (IRC) paths for the Diels–Alder reaction of tropone and its umpolung derivatives, using the same systems studied by Karas et al. and Tiekink et al. Our results confirm that the asynchronicity is indeed very high for those reactions with smaller reaction barriers and offer an atom‐by‐atom and bond‐by‐bond analysis of the entire IRC pathways. Even though asynchronicity and lower reactions barriers seem to be related, antiaromaticity and lower barriers are related as well, but discussing both these interpretations does not necessarily require arguments on HOMO/LUMO energies to be invoked. [ABSTRACT FROM AUTHOR]

Hydrazones as organometallic equivalents have emerged as a general and sustainable strategy to utilize naturally abundant aldehydes and ketones as feedstocks while only releasing water and nitrogen gas as byproducts. Yet the addition of these carbanion equivalents to carbonyl compounds has been limited to the use of precious metals as catalysts and hazardous solvents under an inert atmosphere. Herein, we report the development of a manganese-based catalyst system for the addition of aldehydes to carbonyl compounds producing secondary and tertiary alcohols with yields of up to 91%. Furthermore, this method has proven robust and reproducible under aqueous and aerobic conditions to employ an earth-abundant metal catalyst, hence advancing hydrazone umpolung chemistry to be more sustainable and operationally simple. [ABSTRACT FROM AUTHOR]

An electrochemical three-component reaction involving elemental sulfur is disclosed for achieving a metal-free, oxidant-free synthesis of thioesters in a high atom-economical, step-economical and chemoselective manner. A mechanistic investigation indicates that the use of elemental sulfur to trap acyl radical derived from radical umpolung of α-keto acid with an electrochemical design can efficiently generate a carbonyl thiyl radical, which can further be captured by diazoalkane to afford various thioesters. [ABSTRACT FROM AUTHOR]

Comprehensive Summary Herein, we report rhodium catalyzed N‐arylation via addition of arylboronic acids to electron‐deficient α‐iminoesters which can be prepared in high efficiency by using easily accessible β‐carbonyl esters. The reaction is highly regiospecific to achieve the N‐aryl addition efficiently with up to 99% yield under mild conditions. The corresponding product can be further efficiently converted into indoles and a series of other important building blocks. [ABSTRACT FROM AUTHOR]

Solar flares will cause the change of the photospheric magnetic field and sunspot structure. However, the exact physical processes involved remain unclear. Here, we study the changes of photospheric magnetic field before and after an X1.5 flare caused by a circular filament eruption in the active region NOAA 13006. The magnetic field structure of this active region is a fan-spine structure with a circular polarity inversion line (PIL). We found that the sunspot structure contracted towards the PIL as a whole after the flare. The penumbra away from the PIL gradually disappears, and the umbra and penumbra near the PIL gradually enhances. By analysing the local magnetic field, the Lorentz force (LF), and the photospheric velocity field in these three regions, we find that the magnetic flux in the region of the disappearing penumbra converges and contracts towards the PIL, leading to an enhancement of the umbra, while the enhancement of the penumbra potentially indicates that this region may be the footpoint of a reconnected magnetic field system. We suggest that this contracting motion is driven by the horizontal LF. [ABSTRACT FROM AUTHOR]

Although dearomative functionalizations enable the direct conversion of flat aromatics into precious three‐dimensional architectures, the case for simple arenes remains largely underdeveloped owing to the high aromatic stabilization energy. We herein report a dearomative sequential addition of two nucleophiles to arene π‐bonds through umpolung of chromium–arene complexes. This mode enables divergent dearomative carbonylation reactions of benzene derivatives by tolerating various nucleophiles in combination with alcohols or amines under CO‐gas‐free conditions, thus providing modular access to functionalized esters or amides. The tunable synthesis of 1,3‐ or 1,4‐cyclohexadienes as well as the construction of carbon quaternary centers further highlight the versatility of this dearomatization. Diverse late‐stage modifications and derivatizations towards synthetically challenging and bioactive molecules reveal the synthetic utility. A possible mechanism was proposed based on control experiments and intermediate tracking. [ABSTRACT FROM AUTHOR]

While the nucleophilic addition of ammonia to ketones is an archetypal reaction in classical organic chemistry, the reactivity of heavier group 14 carbonyl analogues (R2E=O; E=Si, Ge, Sn, or Pb) with NH3 remains sparsely investigated, primarily due to the synthetic difficulties in accessing heavier ketone congeners. Herein, we present a room‐temperature stable boryl‐substituted amidinato‐silanone {(HCDippN)2B}{PhC(tBuN)2}Si=O (Dipp=2,6‐iPr2C6H3) (together with its germanone analogue), formed from the corresponding silylene under a N2O atmosphere. This system reacts cleanly with ammonia in 1,2‐fashion to give an isolable sila‐hemiaminal complex {(HCDippN)2B}{PhC(tBuN)2}Si(OH)(NH2). Quantum chemical calculations reveal that the formation of this sila‐hemiaminal is crucially dependent on the nature of the ancillary ligand scaffold. It is facilitated thermodynamically by the hemi‐lability of the amidinate ligand (which allows for the formation of an energetically critical intramolecular N⋅⋅⋅HO hydrogen bond within the product) and is enabled mech‐anistically by a process in which the silanone initially acts in umpolung fashion as a base (rather than an acid), due to the strongly electron‐releasing and sterically bulky nature of the ancillary boryl ligand. [ABSTRACT FROM AUTHOR]

While the nucleophilic addition of ammonia to ketones is an archetypal reaction in classical organic chemistry, the reactivity of heavier group 14 carbonyl analogues (R2E=O; E=Si, Ge, Sn, or Pb) with NH3 remains sparsely investigated, primarily due to the synthetic difficulties in accessing heavier ketone congeners. Herein, we present a room‐temperature stable boryl‐substituted amidinato‐silanone {(HCDippN)2B}{PhC(tBuN)2}Si=O (Dipp=2,6‐iPr2C6H3) (together with its germanone analogue), formed from the corresponding silylene under a N2O atmosphere. This system reacts cleanly with ammonia in 1,2‐fashion to give an isolable sila‐hemiaminal complex {(HCDippN)2B}{PhC(tBuN)2}Si(OH)(NH2). Quantum chemical calculations reveal that the formation of this sila‐hemiaminal is crucially dependent on the nature of the ancillary ligand scaffold. It is facilitated thermodynamically by the hemi‐lability of the amidinate ligand (which allows for the formation of an energetically critical intramolecular N⋅⋅⋅HO hydrogen bond within the product) and is enabled mech‐anistically by a process in which the silanone initially acts in umpolung fashion as a base (rather than an acid), due to the strongly electron‐releasing and sterically bulky nature of the ancillary boryl ligand. [ABSTRACT FROM AUTHOR]

Amidation synthesis stands as a significant area in organic chemistry. Incorporating cutting-edge amidation methods into basic organic chemistry laboratory teaching can enhance educational content and foster integration between undergraduate teaching and research achievements. Herein, we report an experiment focusing on the umpolung of aldehydes catalyzed by N-heterocyclic carbene (NHC) for amide synthesis. Utilizing benzaldehyde and nitrosobenzene as substrates, N-hydroxy-N-phenylbenzoylamide was efficiently synthesized under anhydrous and oxygen-free conditions. The reaction progress was monitored via thin-layer chromatography (TLC), and the product structure was confirmed by infrared and nuclear magnetic resonance spectroscopy. This experiment offers simplicity in operation, mild reaction conditions, high atom economy, and excellent repeatability, rendering it highly suitable for undergraduate laboratory teaching. By amalgamating the pivotal concept of umpolung with the cuttingedge science of N-heterocyclic carbene catalysis, this experiment aims to stimulate and nurture students' interest in scientific inquiry. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Chemodivergent synthesis of benzofurans and 2,3‐dihydrobenzofurans has been realized. Under a reaction system consisting of DBDMH and K2CO3 as promotors, controlled conditions enabled the formation of two sets of valuable heterocycles from the tandem transformation of enaminones and salicylaldehydes. The key to success was the identification of the reaction parameters, in which the imine intermediate which was formed by transient halogenation coupling and substitution processes underwent either aldol condensation/annulation or imine hydrolysis/aldol condensation. The additives NH4Cl or Fe2(SO4)3 controlled the unique selectivity of this reaction. A broad substrate scope of enaminones and salicylaldehydes has been employed in this reaction, demonstrating excellent functional group tolerance and versatility. [ABSTRACT FROM AUTHOR]

Polarity inversion is an interesting phenomenon in non-centrosymmetric wurtzite-structured aluminum nitride (AlN), which offers an important platform to establish acoustic devices with heteropolar junctions. However, previous studies showed that switching polarity generally resulted in only reversing the piezoelectric coefficient (d33) in AlN films. Here, we discovered that appropriate Cr-doping would not only allow to reverse d33 but also improve piezoelectric response in the c-axis oriented AlN films by co-sputtering dual targets of Cr and Al. Specifically, the d33 was reversed from +2.6 pC/N for the undoped AlN to −2.6 pC/N for the 6.2 at. % Cr-doped CrxAl(1−x)N films. As the Cr-doping ratio increased to 9.3 at. %, d33 was −7.0 pC/N, which was 1.7 times higher than that of the undoped AlN films. Independent PFM phase image measurement offered further evidence of the polarity inversion by comparing the undoped and 9.3 at. % Cr-doped CrxAl(1−x)N films. This work offers a simple doping strategy that allows for simultaneous reversal of piezoelectric coefficient and enhancement of piezoresponse. As a result, it establishes a promising foundation for the design and development of acoustic wave devices featuring heteropolar junctions. [ABSTRACT FROM AUTHOR]

A palladium-catalyzed enantioselective umpolung allylation reaction of amido-tethered allyl carbonates with N-2,2,2-trifluoroethylisatin ketimines has been realized herein. The reaction worked well under mild reaction conditions to give various chiral oxindole derivatives in moderate to excellent yields with high enantioselectivities. Notably, this work represents the first Pd-catalyzed asymmetric umpolung allylation reaction of N-2,2,2-trifluoroethylisatin ketimines. [ABSTRACT FROM AUTHOR]

A thiophane‐catalyzed dibromination of olefins using NBS as the sole bromine source has been developed, providing a low‐cost and mild methodology for preparing vicinally dibrominated compounds from electron‐neutral or ‐deficient alkenes. The mechanistic investigation showed that 2,3‐dihydrothiophene generated in situ from the reaction of thiophane with NBS was the actual catalyst, which reversed the polarity of NBS to yield bromide ion. [ABSTRACT FROM AUTHOR]

There is a heated debate regarding the specific roles played by ideal magnetohydrodynamic (MHD) instability and magnetic reconnection in triggering solar eruptions. In the context of a pre-existing magnetic flux rope (MFR) before an eruption, it is widely believed that an ideal MHD instability, in particular, the torus instability, is responsible for triggering and driving the eruption, while reconnection, as invoked in the wake of the erupting MFR, plays a secondary role. Here, we present a new numerical MHD model in which the eruption of a pre-existing MFR is primarily triggered and driven by reconnection. In this model, a stable MFR embedded in a strapping field is set as the initial condition. A surface converging flow is then applied at the lower boundary, pushing magnetic flux towards the main polarity inversion line. It drives a quasi-static evolution of the system, during which a current layer is built up below the MFR with decreasing thickness. Once reconnection starts in the current sheet, the eruption commences, which indicates that the reconnection plays a determining role in triggering the eruption. By further analysing the works done by the magnetic flux of the pre-existing MFR and the newly reconnected flux during the acceleration stage of the eruption, we find that the latter plays a major role in driving the eruption. Such a model may explain observed eruptions in which the pre-eruption MFR has not reached the conditions for ideal instability. [ABSTRACT FROM AUTHOR]

The success and power of homogeneous catalysis derives in large part from the wide choice of transition metal ions and their ligands. This tutorial review introduces examples where the reactivity of a ligand is completely reversed (umpolung) from Lewis basic/nucleophilic to acidic/electrophilic or vice versa on changing the metal and co-ligands. Understanding this phenomenon will assist in the rational design of catalysts and the understanding of metalloenzyme mechanisms. Labelling a metal and ligand with Seebach donor and acceptor labels helps to identify whether a reaction involving the intermolecular attack on the ligand is displaying native reactivity or reactivity umpolung. This has been done for complexes of nitriles, carbonyls, isonitriles, dinitrogen, Fischer carbenes, alkenes, alkynes, hydrides, methyls, methylidenes and alkylidenes, silylenes, oxides, imides/nitrenes, alkylidynes, methylidynes, and nitrides. The electronic influence of the metal and co-ligands is discussed in terms of the energy of (HOMO) d electrons. The energy can be related to the pK LACa (LAC is ligand acidity constant) of the theoretical hydride complexes [H–[M]–L]+ formed by the protonation of pair of valence d electrons on the metal in the [M–L] complex. Preliminary findings indicate that a negative pK LACa indicates that nucleophilic attack by a carbanion or amine on the ligand will likely occur while a positive pK LACa indicates that electrophilic attack by strong acids on the ligand will usually occur when the ligand is nitrile, carbonyl, isonitrile, alkene and η6-arene. [ABSTRACT FROM AUTHOR]

Two Mo(0) phosphenium complexes containing ancillary secondary phosphine ligands have been investigated with respect to their ability to participate in electrophilic addition at unsaturated substrates and subsequent P−H hydride transfer to "quench" the resulting carbocations. These studies provide stoichiometric "proof of concept" for a proposed new metal‐catalyzed electrophilic hydrophosphination mechanism. The more strongly Lewis acidic phosphenium complex, [Mo(CO)4(PR2H)(PR2)]+ (R=Ph, Tolp), cleanly hydrophosphinates 1,1‐diphenylethylene, benzophenone, and ethylene, while other substrates react rapidly to give products resulting from competing electrophilic processes. A less Lewis acidic complex, [Mo(CO)3(PR2H)2(PR2)]+, generally reacts more slowly but participates in clean hydrophosphination of a wider range of unsaturated substrates, including styrene, indene, 1‐hexene, and cyclohexanone, in addition to 1,1‐diphenylethylene, benzophenone, and ethylene. Mechanistic studies are described, including stoichiometric control reactions and computational and kinetic analyses, which probe whether the observed P−H addition actually does occur by the proposed electrophilic mechanism, and whether hydridic P−H transfer in this system is intra‐ or intermolecular. Preliminary reactivity studies indicate challenges that must be addressed to exploit these promising results in catalysis. [ABSTRACT FROM AUTHOR]

Alternation of left and right antimeres of segmental structures, generally known as the glide-reflection symmetry, was found to be unexpectedly widespread in deuterostomes. It occurs in both somatic and visceral organs. Its distribution in echinoderms, acorn worms, cephalochordates, ascidians, hagfishes, and chimaeras might suggest its ancestral nature in deuterostomes. It could have been inherited from Precambrian ancestors. There is a lead of the left segments against their right counterparts in all deuterostomes with glide-reflection symmetry, where the leading side is known. This allows us to presume an inherent left-to-left-side and right-to-right-side homology across all deuterostomes, contradicting a hypothesis of the whole-body dorsoventral inversion in chordates. The features of inversion could be alternatively explained by a transformation of the gastrulation process, which has caused an inversion of dorsoventral polarity in some parts of the body, but did not affect the left–right polarity. It is suggested that this process had involved the animal-vegetal extension of the blastopore along embryonic dorsal side in basal deuterostomes that was followed by the shift of the left–right organizer from the dorsal lip of the blastopore to the anterior tip of archenteron in non-chordate deuterostomes, which has caused roof-to-floor relocation of the notochordal area in their archenteron. [ABSTRACT FROM AUTHOR]

We examine the process during which the solar magnetic field reverses polarity around each solar maximum. We use the McIntosh Archive (McA) of solar synoptic maps over five consecutive solar cycles, SCs 19 – 23, or from 1955 to 2009. This data set allows us to track features such as filaments, polarity inversion lines (PILs), coronal hole (CH) boundaries, and sunspots over many consecutive Carrington rotations (CRs) and solar cycles (SCs). The McA allows tracking of the evolution of the polar magnetic regions and how the rush-to-the-pole (RttP) patterns occur during the period when the polar fields reverse around each activity maximum. We use the McA dataset to determine the timing and lags among these events around the maximum of each SC in each hemisphere: the sunspot number peak, the polarity reversal, the disappearance of the polar crown filaments and PILs, the poleward movement of midlatitude CHs of new-cycle polarity behind the primary PIL, the first appearance of polar CHs of new-cycle polarity, and the earliest persistent complete coverage of each pole by a CH. The goal is to use the RttPs and CH boundary mapping to better constrain solar interior and dynamo models. The end of the PIL RttP, the end of the RttP of the poleward boundary of new-cycle polarity midlatitude CHs, and the first appearance of new-cycle polar CHs are nearly coincident and follow the polarity reversals in each hemisphere by about 1 year. We also show the lag times relative to "terminator" times, which denote when the toroidal magnetic flux built during a given cycle is canceled across the equator, thus beginning the rise of new-cycle flux. This occurs after the start of the RttPs of the polar CH boundaries and near the start of the primary and secondary PIL RttPs. The start of the RttP of the poleward boundary of the new-cycle, midlatitude CH that leads to the new polar CH always occurs later than the terminator time, so the terminator is located near the beginning of the ascending phase. [ABSTRACT FROM AUTHOR]

While hydraulic fracturing (HF) is a widely employed process, the underlying fracturing processes are still heavily contested. The attributes of the HF generated fracture network can exhibit substantial variation when dealing with specific HF propagation regimes encountered in the field. In this study, HF experiments were performed on true-triaxially loaded Barre granite cubes, with microseismic monitoring, to identify and characterize the fracturing mechanisms associated with different viscosity injection fluids. Utilizing fluids with high (oil/1450 cP) and low (water/1 cP) viscosity represented two key HF propagation regimes: viscosity- and toughness-dominated. The experiments conducted with oil involved higher breakdown pressures, larger fluid volumes, and slower fracture propagation speeds. The frequency–magnitude distribution (b value) for all experiments (1.9–2.3) was similar to those encountered for large-scale operations. Slightly larger b values were encountered during the initiation phase (2.4–2.7) relative to the fracture propagation and post-fracturing phases (1.9–2.2). Techniques such as polarity and moment-tensor inversion were utilized to characterize the source mechanisms. For the HF experiments with oil, tensile fractures were most dominant (92%) in the initiation phase compared to fracture propagation and post-fracturing phases (70–75%). Similar tensile fracturing dominancy was not observed with water, attributable to fluid permeation and leak-off. Regardless of the injection fluid or classification criteria employed, tensile fractures were the dominant type consistently, with fewer occurring in water experiments but the specific ratio of crack types varied with different source mechanism criteria employed. Highlights: Evolution of fracturing processes and their source mechanisms during hydraulic fracturing of Barre granite with high and low viscosity fluids. Highlighting the dissimilarity between fracture source mechanisms using multiple classification criteria. The proportion of fracture mechanisms (tensile/shear/compression) varied significantly depending on the classification criteria employed. Tensile fractures were found to be dominant both for high and low viscosity injection experiments. High viscosity fluids resulted in a higher percentage of tensile fractures relative to low viscosity fluids. [ABSTRACT FROM AUTHOR]

Apicobasal epithelial polarity controls the functional properties of most organs. Thus, there has been extensive research on the molecular intricacies governing the establishment and maintenance of cell polarity. Whereas loss of apicobasal polarity is a welldocumented phenomenon associated with multiple diseases, less is known regarding another type of apicobasal polarity alteration - the inversion of polarity. In this Review, we provide a unifying definition of inverted polarity and discuss multiple scenarios in mammalian systems and human health and disease in which apical and basolateral membrane domains are interchanged. This includes mammalian embryo implantation, monogenic diseases and dissemination of cancer cell clusters. For each example, the functional consequences of polarity inversion are assessed, revealing shared outcomes, including modifications in immune surveillance, altered drug sensitivity and changes in adhesions to neighboring cells. Finally, we highlight the molecular alterations associated with inverted apicobasal polarity and provide a molecular framework to connect these changes with the core cell polarity machinery and to explain roles of polarity inversion in health and disease. Based on the current state of the field, failure to respond to extracellular matrix (ECM) cues, increased cellular contractility and membrane trafficking defects are likely to account for most cases of inverted apicobasal polarity. [ABSTRACT FROM AUTHOR]

In this work, a straightforward synthesis of C3−N1' bisindolines is achieved by a formal umpolung strategy. The protocols were tolerant of a wide variety of substituents on the indole and indoline ring. In addition, the C3−N1' bisindolines could be converted to C3−N1' indole‐indolines and C3−N1'‐bisindoles. Also, we have successfully synthesized (±)‐rivularin A through a biomimetic late‐stage tribromination as a key step. [ABSTRACT FROM AUTHOR]

This article discusses the development of a photocatalytic 1,4-addition reaction of aromatic aldehydes or ketones with electron-deficient olefins. The reaction proceeds through the generation of umpoled carbinol anions, which are formed through two successive one-electron reductions. The use of CO2 as an additive enhances the reaction, resulting in the formation of γ-substituted secondary or tertiary alcohols in yields of up to 92%. The findings of this study offer a new avenue in synthetic organic chemistry and provide an alternative to the ketyl Giese reaction. [Extracted from the article]

The implementation of automated methods for sunspot detection is essential to obtain better objectivity, efficiency, and accuracy in identifying sunspots and analysing their morphological properties. A desired application is the contouring of sunspots. In this work, we construct sunspot contours from Solar Dynamics Observatory (SDO)/ Helioseismic and Magnetic Imager intensity images by means of an automated method based on development and application of mathematical morphology. The method is validated qualitatively – the resulting contours accurately delimit sunspots. Here, it is applied to high-resolution data (SDO intensitygrams) and validated quantitatively by illustrating a good agreement between the measured sunspot areas and the ones provided by two standard reference catalogues. The method appears to be robust for sunspot identification, and our analysis suggests its application to more complex and irregular-shaped solar structures, such as polarity inversion lines inside delta-sunspots. [ABSTRACT FROM AUTHOR]

Magnetotactic bacteria are microorganisms that produce intracellular magnetic nanoparticles organized in chains, conferring a magnetic moment to the bacterial body that allows it to swim following the geomagnetic field lines. Magnetotactic bacteria usually display two swimming polarities in environmental samples: the South-seeking (SS) polarity and the North-seeking (NS) polarity, characterized by the bacteria swimming antiparallel or parallel to the magnetic field lines, respectively. It has been observed that in the presence of inhomogeneous magnetic fields, NS magnetotactic bacteria can change their swimming polarity to SS or vice versa. The present study analyzes populations of NS cocci obtained from SS cocci isolated in the presence of a magnet. The aim was to study differences in the swimming characteristics and magnetic moment among both populations of cocci. For that, trajectories were recorded and the velocity and angle among the velocity and the applied magnetic field were calculated. In addition, micrographs from both SS and NS cocci were obtained and their magnetosomes were measured to analyze their length, width, aspect ratio and magnetic moment, to finally obtain the magnetic moment for each coccus. The results showed the following properties of NS relative to SS cocci: higher velocities, narrow bacterial magnetic moment distribution, higher dispersion in the distribution of angles among the velocity and the applied magnetic field and lower magnetic field sensibility. Those differences cannot be explained by the simple change in magnetic polarity of the magnetosome chain and can be related to the existence of an active magnetoreceptive process in magnetotactic bacteria. [ABSTRACT FROM AUTHOR]

The use of trifluoromethyl containing compounds is well established within medicinal chemistry, with a range of approved drugs containing C−CF3 and O−CF3 moieties. However, the utilisation of the N−CF3 functional group remains relatively unexplored. This may be attributed to the challenging synthesis of this unit, with many current methods employing harsh conditions or less accessible reagents. A robust methodology for the N‐trifluoromethylation of secondary amines has been developed, which employs an umpolung strategy in the form of a copper‐catalysed electrophilic amination. The method is operationally simple, uses mild, inexpensive reagents, and has been used to synthesise a range of novel, structurally complex N−CF3 containing compounds. [ABSTRACT FROM AUTHOR]

General methods for the preparation of geminal bis(boronates) are of great interest due to their widespread applications in organic synthesis. While the terminal gem‐diboron compounds are readily accessible, the construction of the sterically encumbered, internal analogues has remained a prominent challenge. Herein, we report a formal umpolung strategy to access these valuable building blocks. The readily available 1,1‐diborylalkanes were first converted into the corresponding α‐halogenated derivatives, which then serve as electrophilic components, undergoing a formal substitution with a diverse array of nucleophiles to form a series of C−C, C−O, C−S, and C−N bonds. This protocol features good tolerance to steric hindrance and a wide variety of functional groups and heterocycles. Notably, this strategy can also be extended to the synthesis of diaryl and terminal gem‐diboron compounds, therefore providing a general approach to various types of geminal bis(boronates). [ABSTRACT FROM AUTHOR]

General methods for the preparation of geminal bis(boronates) are of great interest due to their widespread applications in organic synthesis. While the terminal gem‐diboron compounds are readily accessible, the construction of the sterically encumbered, internal analogues has remained a prominent challenge. Herein, we report a formal umpolung strategy to access these valuable building blocks. The readily available 1,1‐diborylalkanes were first converted into the corresponding α‐halogenated derivatives, which then serve as electrophilic components, undergoing a formal substitution with a diverse array of nucleophiles to form a series of C−C, C−O, C−S, and C−N bonds. This protocol features good tolerance to steric hindrance and a wide variety of functional groups and heterocycles. Notably, this strategy can also be extended to the synthesis of diaryl and terminal gem‐diboron compounds, therefore providing a general approach to various types of geminal bis(boronates). [ABSTRACT FROM AUTHOR]

In the presence of sparteine 2,4,6‐triisopropylbenzoates were lithiated enantioselectively in order to generate chiral d1 reagents. Their reaction with α‐halo boronic esters, resembling chiral a1 reagents, was explored. Enantiomerically enriched α‐halo boronic esters are readily available by Matteson Homologation (MH). A model reaction with α‐bromopentyl pinandiol boronate was optimized to an acceptable yield but proved to be quite sensitive. Generation of the d1 reagent from the corresponding stannane stabilized the protocol and delivered moderate yields for β‐unsubstituted α‐halo boronic esters. Good to excellent yields were obtained for β‐substituted α‐halo boronic esters, which can be generated by iterative MH, thus establishing this method as a useful terminus for an iterative Matteson sequence. [ABSTRACT FROM AUTHOR]

We present a detailed analysis of a partial eruption of a sigmoid filament lying along the polarity inversion line (PIL) of the small active region (AR) NOAA 12734 (with an area of 1.44 × 10 3 square megameters). The active filament was rooted in a dipole sunspot of the AR. The eruption was associated with a C1.3 flare and subsequent large-scale coronal disturbances. During its solar disk passage before the flare, the AR had the following characteristics: (1) Most of the time, the magnetic field lines in the AR showed a sigmoidal structure ('L1') in the low corona and arc-shaped loops (i.e., 'L2') in the upper atmosphere. (2) An 'X'-shaped structure was formed between the original 'S'-shaped magnetic loop ('L1') and the newly rising one ('L3') between the main positive and negative magnetic polarities of the sunspots, and the intersection point of flux ropes 'L1' and 'L3' corresponds well with the area where the initial extreme-ultraviolet (EUV) 1600 Å brightening of the flare occurred. (3) The AR disobeyed the hemispherical helicity rule and had magnetic twist and writhe of the same signs, i.e., its magnetic helicity/current helicity were positive in the northern hemisphere. (4) Sustained magnetic emergence and cancellation occurred before the flare. Therefore, the magnetic reconnection of highly twisted helical flux ropes under the confinement of the overlying magnetic fields is probably responsible for the partial eruption of the filament. [ABSTRACT FROM AUTHOR]

This study revealed that benzyl vinyl ether (BnVE) shows a peculiar isomerization propagation in its radical copolymerization with an electron‐deficient acrylate carrying a pentafluorophenyl group (PFA). The co‐monomer pair inherently exhibits the cross‐over propagation feature due to the large difference in the electron density. However, the radical species of PFA was found to undergo a backward isomerization to the penultimate BnVE pendant giving a benzyl radical species prior to propagation with BnVE. The isomerization brings a drastic change in the character of the growing radical species from electrophilic to nucleophilic, and thus the isomerized benzyl radial species propagates with PFA. Consequently, the two monomers were consumed in the order AAB (A: PFA; B: BnVE) and the unique periodic consumption was confirmed by the pseudo‐reactivity ratios calculated by the penultimate model: r11=0.174 and r21=6600 for PFA (M1) with BnVE (M2). The pentafluorophenyl ester groups of the resulting copolymers are transformed into ester and amide groups by post‐polymerization alcoholysis and aminolysis modifications. The unique isomerization in the AAB sequence allowed the periodic introduction of a benzyl ether structure in the backbone leading to efficient degradation under acid conditions. [ABSTRACT FROM AUTHOR]

This study revealed that benzyl vinyl ether (BnVE) shows a peculiar isomerization propagation in its radical copolymerization with an electron‐deficient acrylate carrying a pentafluorophenyl group (PFA). The co‐monomer pair inherently exhibits the cross‐over propagation feature due to the large difference in the electron density. However, the radical species of PFA was found to undergo a backward isomerization to the penultimate BnVE pendant giving a benzyl radical species prior to propagation with BnVE. The isomerization brings a drastic change in the character of the growing radical species from electrophilic to nucleophilic, and thus the isomerized benzyl radial species propagates with PFA. Consequently, the two monomers were consumed in the order AAB (A: PFA; B: BnVE) and the unique periodic consumption was confirmed by the pseudo‐reactivity ratios calculated by the penultimate model: r11=0.174 and r21=6600 for PFA (M1) with BnVE (M2). The pentafluorophenyl ester groups of the resulting copolymers are transformed into ester and amide groups by post‐polymerization alcoholysis and aminolysis modifications. The unique isomerization in the AAB sequence allowed the periodic introduction of a benzyl ether structure in the backbone leading to efficient degradation under acid conditions. [ABSTRACT FROM AUTHOR]

(2-Methyl-3-oxoisoindolin-1-yl)triphenylphosphonium tetrafluoroborate has been successfully synthesized from Ph3PHBF4 and 3-hydroxy-2-methylisoindolin-1-one. It undergoes smoothly Wittig olefination with a variety of aldehydes when using DBU or t-BuOK as a base to furnish 3-(alkylidene)-2-methyisoindolin-1-ones in 35–93% yields with the stereoselectivity being mostly favorable to (E)-isomer. [ABSTRACT FROM AUTHOR]

An electrochemical Reformatsky‐type reaction of bromodifluoroamides with aldehydes/ketones via electron reductive umpolung is reported, leading to the generation of a series of β‐hydroxy‐α,α‐difluoro amides in moderate to good yields. This protocol tolerated a variety of commercially available alkyl ketone, alkyl and aromatic aldehydes, featuring broad substrate scope and good functional group tolerance under transition metal‐free conditions without metal reduction reagents. Control experiment indicated that the reaction proceeded via an electron reductive umpolung pathway. [ABSTRACT FROM AUTHOR]

Strategies for introducing halogens and other inorganic groups in aromatic systems, usually involve non‐general and strong oxidative protocols which resulted in poor functional group compatibility. Iodine(III) reagents have emerged as an excellent alternative for the aromatic inorganic functionalization due to their low toxicity and strong oxidative character. In this context, the synergistic combination of different iodine(III) reagents and aluminum or ammonium salts including AlCl3, AlBr3, Al(NO3)3, NH4Cl, NH4Br and NH4I have recently demonstrated a great versatility for introducing the chlorine, bromine, iodine and nitro groups in aromatic systems, mainly phenols, anilines and some heterocycles. Using these common salts, their anions are softly oxidated by iodine(III) reagents, allowing the in situ formation of non‐described halogenating and nitrating species and in consequence, the introduction of these inorganic groups under an umpolung reactivity as chemical electrophilic synthons. [ABSTRACT FROM AUTHOR]

This article discusses a study on the synthesis of (2-Nitro-1-AfAlemphenylethyl)malononitriles through a reaction called Michael addition. The researchers optimized the reaction conditions and demonstrated its feasibility using different substances. They also explored the possibility of achieving asymmetric induction in the reaction by using a specific catalyst. The results show promise for the synthesis of (2-Nitro-1-AfAlemphenylethyl)malononitriles as precursors for various compounds with potential biological activities. The authors also mention ongoing research to explore the potential applications of these adducts in the synthesis of chiral β-amino acids. [Extracted from the article]

Herein, for the first time we have explored the umpolung reactivity of the vinylogous carbon center of diazo arylidene succinimide (DAS) through rhodium catalysis to achieve [2,3]‐Stevens rearrangement of α‐thioether esters. The protocol has successfully demonstrated the distal C−H bond functionalization of the α‐thioether esters. Alongside, the carbenoid reactivity of DAS has also been achieved with Doyle‐Kirmse reaction of allyl/propargyl phenyl sulfides. The protocol proved to be practical to synthesize a wide variety of [2,3]‐Stevens rearrangement products exclusively and the possible side products emanating from Pummerer rearrangement and [1,2]‐Stevens rearrangement were not observed. This catalytic protocol works smoothly in environmentally benign solvent under open air to afford the corresponding desired products with excellent diastereo‐, regio‐ and chemo‐selectivities in good to excellent yields. The protocol also proved to be scalable on gram quantity. [ABSTRACT FROM AUTHOR]

The first total synthesis of the proposed structure of unprecedented indolyl derivative bearing 1,2-propanediol moiety is described. Isomerization of 3-alkoxyindolines through indolenium intermediates was the key step in the total synthesis. 1H, 13C-NMR, IR, and HRMS spectra of the synthetic compound drastically differed to those of the originally reported structure, which suggests the natural product requires revision. [ABSTRACT FROM AUTHOR]

Artificial synthesis of carbohydrates has been a long-standing goal for chemists. The formose reaction is an established non-enzymatic one-step route to monosaccharides from a C1 source, where formaldehyde (HCHO) is polymerized under basic conditions. However, bases can lead to multiple side reactions. Thiazolium salts, when activated by a suitable base, can catalyze HCHO condensation to 1,3-dihydroxyacetone (DHA) via umpolung aldehyde activation, but they can slowly lose their activity due to product adsorption on the active sites. Here, we report a heterogeneous, base-free formaldehyde condensation to DHA using a reactor based on a Soxhlet extractor, which quickly separates the product from the solid catalyst during the reaction. This design not only leads to a stable catalytic operation but also constitutes a clean HCHO-to-DHA conversion system. This oligomerization of formaldehyde to DHA completes a critical step in converting CO2 to sugar, including CO2 hydrogenation to methanol (CH3OH), CH3OH oxidation to HCHO, HCHO oligomerization to DHA, and DHA condensation to higher carbohydrates. [ABSTRACT FROM AUTHOR]

Isoporphyrins have recently been identified as remarkable species capable of turning the nucleophile attached to the porphyrin ring into an electrophile, thereby providing umpolung of reactivity (Inorg. Chem. 2022, 61, 8105–8111). They are generated by nucleophilic attack on an iron(III) π‐dication, a class of species that has received scant attention. Here, we explore the effect of the porphyrin meso‐substituent and report a iron(III) π‐dication bearing the meso‐tetraphenylporphyrin (TPP) ligand. We provide an extensive study of the species by UV/Vis absorption, 2H NMR, EPR, applied field Mössbauer, and resonance Raman spectroscopy. We further explore the system's highly dynamic and tunable properties and address the nature of the axial ligands as well as the conformation of the porphyrin ring. The insights presented are essential for the rational design of catalysts for the umpolung of nucleophiles. Such catalytic avenues could for example provide a novel method for electrophilic chlorinations. We further examine the importance of electronic tuning of the porphyrin by nature of the meso‐substituent as a factor in catalyst design. [ABSTRACT FROM AUTHOR]

Isoporphyrins have recently been identified as remarkable species capable of turning the nucleophile attached to the porphyrin ring into an electrophile, thereby providing umpolung of reactivity (Inorg. Chem. 2022, 61, 8105–8111). They are generated by nucleophilic attack on an iron(III) π‐dication, a class of species that has received scant attention. Here, we explore the effect of the porphyrin meso‐substituent and report a iron(III) π‐dication bearing the meso‐tetraphenylporphyrin (TPP) ligand. We provide an extensive study of the species by UV/Vis absorption, 2H NMR, EPR, applied field Mössbauer, and resonance Raman spectroscopy. We further explore the system's highly dynamic and tunable properties and address the nature of the axial ligands as well as the conformation of the porphyrin ring. The insights presented are essential for the rational design of catalysts for the umpolung of nucleophiles. Such catalytic avenues could for example provide a novel method for electrophilic chlorinations. We further examine the importance of electronic tuning of the porphyrin by nature of the meso‐substituent as a factor in catalyst design. [ABSTRACT FROM AUTHOR]

We investigate the interfaces and polarity domains at the atomic scale in epitaxial AlN and GaN/AlN grown by hot-wall metal organic chemical vapor epitaxy on the carbon face of SiC. X-ray diffraction, potassium hydroxide (KOH) wet chemical etching, and scanning transmission electron microscopy combined provide an in-depth understanding of polarity evolution with the film thickness, which is crucial to optimize growth. The AlN grown in a 3D mode is found to exhibit N-polar pyramid-type structures at the AlN–SiC interface. However, a mixed N-polar and Al-polar region with Al-polarity domination along with inverted pyramid-type structures evolve with increasing film thickness. We identify inclined inversion domain boundaries and propose that incorporation of oxygen on the ⟨ 40–41 ⟩ facets of the N-polar pyramids causes the polarity inversion. We find that mixed-polar AlN is common and easily etched and remains undetected by solely relying on KOH etching. Atomic scale electron microscopy is, therefore, needed to accurately determine the polarity. The polarity of GaN grown on mixed-polar AlN is further shown to undergo complex evolution with the film thickness, which is discussed in the light of growth mechanisms and polarity determination methods. [ABSTRACT FROM AUTHOR]

Stream interaction regions (SIRs) are spiral heliospheric structures that arise at the interface between fast and preceding slow solar wind regions. SIR enhancements of density and magnetic field intensity, often with magnetic polarity inversion, are potentially geoeffective and therefore important in the analysis of space weather. We studied an MHD heliospheric simulation containing a well-defined SIR using a new instrument concept based on trans-heliospheric radio sensing: Faraday Effect Tracker of Coronal and Heliospheric structures (FETCH). FETCH uses line-of-sight radio propagation techniques to measure Faraday rotation and electron column density. Analysis of the simulated FETCH observations clearly demonstrated density and magnetic field enhancements, and magnetic polarity reversal, all of which were confirmed in Wind spacecraft measurements at 1 au. FETCH provided 4.5–5.7 days lead times for predicting the arrival of SIR features at Earth. The SIR radial speed was estimated to be 350–390 km s−1. These initial results hold promise that FETCH will be valuable in detecting and characterizing the inner heliosphere SIR properties well ahead of their presentation in the local geospace environment. [ABSTRACT FROM AUTHOR]

We present a new simulation setup using the MURaM radiative MHD code that allows the study of the formation of collisional polarity inversion lines (cPILs) in the photosphere and the coronal response including flares. In this scheme, we start with a bipolar sunspot configuration and set the spots on collision course by imposing the appropriate velocity field at the footpoints in the subphotospheric boundary. We produce different setups with the same initial spot separation by varying physical parameters such as the collision speed and minimum collision distance. While all setups lead to the formation of an EUV and X-ray sigmoid structure, only the cases with a close passing of the spots cause flares and mass eruptions. The energy release is in the 1–2 × 1031 erg range, putting the simulated flares into the upper C-class to lower M-class range of GOES X-ray 1–8 Å flux. While the setup with the more distant passing of the spots does not lead to a flare, the corona is nonetheless substantially heated, suggesting noneruptive energy-release mechanisms. We focus our discussion on two particular setups that differ in spot coherence and resulting cPIL length persistence. We find different timings in the transition from a sheared magnetic arcade to magnetic flux rope (MFR); the setup with a large length but shorter duration cPIL produces a MFR during the eruption, while the MFR is preexisting in the setup with a large length and longer duration cPIL. While both result in flares of comparable strength and the eruption of a coronal mass ejection, the setup with preexisting MFR (and embedded filament) leads to an MFR eruption with a larger mass content. [ABSTRACT FROM AUTHOR]

Reactivity umpolung is an important concept in organic chemistry. Established reactivity umpolung mainly focuses on the aldehyde and umpolung of amide carbonyl group is not known. In this report, we describe a process to obtain the umpolung reactivity of tertiary amide. This process hinges on the efficient reductive stannylation catalyzed by Ir/silane and facile Sn−Li exchange. By leveraging this umpolung reactivity, drug Fluoxetine was derivatized to 12 different analogues via reacting with various electrophiles and four biologically active molecules were prepared concisely. This unlocked umpolung reactivity of tertiary amide is expected to find applications to synthesize complex amines from amides. [ABSTRACT FROM AUTHOR]

Reactivity umpolung is an important concept in organic chemistry. Established reactivity umpolung mainly focuses on the aldehyde and umpolung of amide carbonyl group is not known. In this report, we describe a process to obtain the umpolung reactivity of tertiary amide. This process hinges on the efficient reductive stannylation catalyzed by Ir/silane and facile Sn−Li exchange. By leveraging this umpolung reactivity, drug Fluoxetine was derivatized to 12 different analogues via reacting with various electrophiles and four biologically active molecules were prepared concisely. This unlocked umpolung reactivity of tertiary amide is expected to find applications to synthesize complex amines from amides. [ABSTRACT FROM AUTHOR]

Context. Erupting magnetic flux ropes (MFRs) are believed to play a crucial role in producing solar flares. However, the formation of erupting MFRs in complex coronal magnetic configurations and the role of their subsequent evolution in the flaring events are not fully understood. Aims. We perform a magnetohydrodynamic (MHD) simulation of active region NOAA 12241 to understand the formation of a rising magnetic flux rope during the onset of an M6.9 flare on 2014 December 18 around 21:41 UT (SOL2014-12- 18T21:41M6.9), which was followed by the appearance of parallel flare ribbons. Methods. The MHD simulation was initialised with an extrapolated non-force-free magnetic field generated from the photospheric vector magnetogram of the active region taken a few minutes before the flare. Results. The initial magnetic field topology displays a pre-existing sheared arcade enveloping the polarity inversion line. The simulated dynamics exhibit the movement of the oppositely directed legs of the sheared arcade field lines towards each other due to the converging Lorentz force, resulting in the onset of tether-cutting magnetic reconnection that produces an underlying flare arcade and flare ribbons. Concurrently, a magnetic flux rope above the flare arcade develops inside the sheared arcade and shows a rising motion. The flux rope is found to be formed in a torus-unstable region, thereby explaining its eruptive nature. Interestingly, the location and rise of the rope are in good agreement with the corresponding observations seen in extreme-ultraviolet channels of the Atmospheric Imaging Assembly (AIA) of the Solar Dynamics Observatory (SDO). Furthermore, the foot points of the simulation's flare arcade match well with the location of the observed parallel ribbons of the flare. Conclusions. The presented simulation supports the development of the MFR by the tether-cutting magnetic reconnection inside the sheared coronal arcade during flare onset. The MFR is then found to extend along the polarity inversion line (PIL) through slip-running reconnection. The MFR's eruptive nature is ascribed both to its formation in the torus-unstable region and also to the runaway tether-cutting reconnection. [ABSTRACT FROM AUTHOR]

A photoredox‐catalyzed umpolung strategy for the synthesis of homoallylamines from unactivated imines and allyl bromides is described. This strategy exploited N,N‐diisopropylethylamine (DIPEA) as an auxiliary agent to indirectly realize the cross‐coupling of imines and allyl bromides. Various sterically hindered homoallylamines were synthesized by combining photocatalysis with halogen atom transfer (XAT). Notable characteristics of this approach include water‐insensitive reaction conditions, high yield (up to 99%), wide substrate scope (suitable for N‐aryl/alkyl and C‐aryl ketimines and aldimines, 39 examples), and high tolerance of functional groups (such as cyano, ester, amide, and thioamide). [ABSTRACT FROM AUTHOR]

Herein, organocatalytically achieved polarity reversal of cationic bromine is presented. The proven bromocation source N‐bromosuccinimide (NBS) was converted to a superior bromoanion reagent by H/Br exchange with a secondary amine, substantiated with spectroscopic and computational evidence. The concept has further been used in a successfully accelerated organocatalyzed dibromination of olefins in a non‐hazardous, commercially viable process with a wide range of substrate scope. The reactivity of key entities observed through NMR kinetics and reaction acceleration using only 10 mol % of catalyst account for its major success. The nucleophilicity of the bromoanion was found to be superior in comparison to other nucleophiles such as MeOH and H2O also the protocol dominates over the competing allylic bromination reaction. [ABSTRACT FROM AUTHOR]