Sp2 Carbon Research Articles

One-step synthesis of [15]paracyclophane and [16]paracyclophane via Pd-catalyzed C(sp2)–C(sp3) coupling and the cyclohexane-encapsulating crystal structure of [16]paracyclophane

Abstract Macrocycles consisting of methylene-bridged aromatic rings had been synthesized by aromatic electrophilic substitution reactions, thus limiting the substrates to electron-rich aromatic compounds. In this work, we developed a novel method for 1-step synthesis of [15]paracyclophane (PCP) and [16]PCP by the self-condensation of 4-bromobenzyl bromide via a Pd-catalyzed desulfinative coupling reaction between C(sp2) and C(sp3) carbon atoms. In the crystal structure, [16]PCP encapsulated cyclohexane and formed a 1D columnar structure

Conversion of Nitrate to Ammonia by Amidinothiourea-Coordinated Metal Molecular Electrocatalysts with d-π Conjugation.

The electrochemical reduction of nitrate to ammonia (NO3RR) provides a desired alternative of the traditional Haber-Bosch route for ammonia production, igniting a research boom in the development of electrocatalysts with high activity. Among them, molecular electrocatalysts hold considerable promise for the NO3RR, suppressing the competing hydrogen evolution reaction. However, the complicated synthesis procedure, usage of environmentally unfriendly organic solvents, and poor stability of Cu-based molecular electrocatalysts greatly limit their employment in NO3RR, and the development of desired Cu-based molecular catalysts remains challenging. Herein, a simple nonorganic solvent involving a one-step strategy was proposed to synthesize d-π-conjugated molecular electrocatalysts metal-amidinothiourea (M-ATU). Cu-ATU is composed of Cu coordinated with two S and two N atoms, whereas Ni-ATU is formed by Ni with four N atoms from two ATU ligands. Remarkably, Cu-ATU with a Cu-N2S2 coordination configuration exhibits superior NO3RR activity with a NH3 yield rate of 159.8 mg h-1 mgcat-1 (-1.54 V) and Faradaic efficiency of 91.7% (-1.34 V), outperforming previously reported molecular catalysts. Compared to Ni-ATU, Cu-ATU transfers more electrons to the *NO intermediate, effectively breaking the strong sp2 hybridization system and weakening the energy of N═O bonds. The increase in free energy of *NO reduced the energy barriers of the rate-determining step, facilitating the further hydrogenation process over Cu-ATU. Our work opened up a new horizon for exploring molecular electrocatalysts for nitrate activation and paved a way for the in-depth understanding of catalytic behaviors, aligning more closely with industrial demands.

Synergistic Pd(OAc)2/CuI-catalyzed alkynylation of β-lactam derivative via Sonogashira coupling

Herein, a novel approach of bimetallic Pd(OAc)2/CuI-catalyzed alkynylation of 3-chloroazetidin-2-one (β-lactam derivative) with terminal alkyne via tandem C–C bond activation/Sonogashira-type cross-coupling reaction is developed. This synthesis encompasses a sequence of inert Csp3–X/Csp–H functionalization processes involving the coupling of the C(sp3) adjacent to the 3-chloroazetidin-2-one with the C(sp) of a terminal alkyne. The final analogs are synthesized by means of the indole-benzothiazole Schiff base formation, cyclization of the Schiff base to generate the β-lactam derivative, and Sonogashira coupling to afford a C(sp3)–C(sp) bond. In addition, indole, benzothiazole, and azetidine-2-one have been identified to be highly efficient heterocyclic scaffolds with a range of pharmacological benefits. It encouraged us to discover a hybrid compound that had each of these moieties. Cooperation between two different metals is essential for the successful implementation of this approach. Specifically, the interaction between the Pd and Cu centers in the transmetallation step is depicted through a plausible mechanistic route. The reaction conditions have been optimized by varying catalyst and ligand loadings, bases, temperatures, and solvents. The reaction is highly efficient, yielding alkynylated products in up to 84 % yield with a wide range of substrates and functional group tolerance, thereby serving as a functional model for the Sonogashira coupling reaction.

A DFT study of the second-order nonlinear optical properties of [22]smaragdyrin-BF2-NiII porphyrin fused hybrids

Nonlinear optical response of four [22]smaragdyrin-BF2 (S)-NiII porphyrin (P) fused hybrids were explored by using DFT at CAM-B3LYP/6–31 + G(d)/SDD level of theory. We choose two types of hybrids, SP and PSP fused hybrids, for our study. Calculations indicate that these fused hybrids might be promising candidates for NLO materials based on considerable static and dynamic hyper-Rayleigh scattering (HRS) hyperpolarizability. The PSP fused hybrids possess larger first hyperpolarizabilities values compared to SP hybrids. Further analysis of hyperpolarizability density reveals the nature of the large first hyperpolarizability of the PSP fused hybrids. For all compounds, HRS hyperpolarizability at λ = 1907 nm is higher than the static value. After the interpretation of dipolar and octupolar character of βHRS, these hybrids show the high dipolar character.

Size and chemistry of 1–2 layer graphene nanosheets at the transition into photoluminescence and assembly with large shifts from blue to red emission

Synthetic refinement of graphene photoluminescence remains challenging because underlying characteristics have not been well understood from polydisperse mixtures of different sizes and surface chemistries. Here, we isolate and characterise different populations of 1–2 layer graphene (1-2LG) each with narrow size range. Small 1-2LG nanosheets down to 25 nm size remained black and non-luminescent with N. and O. additions at their edges, whereas 15 nm nanosheets transitioned into photoluminescence, while retaining substantial sp2 carbon of graphene. Positively-charged amine modifications overcame the repulsion between nanosheets from the negative zeta potential of sp2 graphene faces in water and allowed assembly of similarly-sized nanosheets with large red shifts (>150 nm) taking blue emission into the red. However, more extensive edge modification into carboxyl groups and neutral amides built negative charge at the edges. Together with smaller nanosheet size and reduced sp2 carbon, red shifts were weakened by half in these isolates, which were most modified and more like graphene oxide and carbon quantum dots. N addition to form amines at nanosheet edges, while avoiding O atom addition and carboxyl groups, presents as a simple refinement for synthesis of self-assembling graphene quantum dots with multi-colour emission, which also retain sp2 carbon properties of graphene.

Investigation of thermal transport mechanism of silicone-modified phenolic matrix nanocomposites with different pyrolysis degrees

Polymeric nanocomposites with low thermal conductivity show promising applications for next-generation thermal protection materials used in re-entry vehicles due to their lightweight, high char yield, and excellent ablation-oxidation resistance. However, the thermal conductivity of polymeric nanocomposites varies with the pyrolysis degree of the polymer matrix in aerodynamic environments, which significantly affects thermal protection and structural applications but is challenging to identify experimentally. Herein, non-equilibrium molecular dynamics simulations combined with experiments were implemented to determine the dependence of thermal conductivities on pyrolysis degree and microstructures for polymeric nanocomposites. We further explore the thermal transport mechanism through various contributions to the morphology. The results show that the thermal conductivity of the polymer matrix can be increased by a factor of 4.44 (from 0.27 W/m/K to 1.47 W/m/K) as the pyrolysis degree increases from 0 to 100%, and the thermal conductivity depends nonlinearly on the pyrolysis degree and temperature. Molecular dynamics simulations found that the side chains of the polymer matrix are rapidly scissored with the increasing pyrolysis degrees, and the structural ordering of the residual solids containing sp2 hybridization is enhanced, exhibiting graphene-like microtopological features, which reduces phonon scattering and makes thermal transport more efficient. This work provides insight into the linkage between the thermal transport properties and the pyrolysis degree of polymeric nanocomposites, which is valuable for improving the thermal transport performance and modeling ablation response for polymeric nanocomposites.

Investigating Layered Topological Magnetic Materials as Efficient Electrocatalysts for the Hydrogen Evolution Reaction under High Current Densities

Despite considerable progress, high-performing durable catalysts operating under large current densities (i.e., >1000 mA/cm2) are still lacking. To discover platinum group metal-free (PGM-free) electrocatalysts for sustainable energy, our research involves investigating layered topological magnetic materials (semiconducting ferromagnets) as highly efficient electrocatalysts for the hydrogen evolution reaction under high current densities and establishes the novel relations between structure and electrochemical property mechanisms. The materials of interest include transition metal trihalides, i.e., CrCl3, VCl3, and VI3, wherein a structural unit, the layered structure, is formed by Cr (or V) atoms sandwiched between two halides (Cl or I), forming a tri-layer. A few layers of quantum crystals were exfoliated (~50−60 nm), encapsulated with graphene, and electrocatalytic HER tests were conducted in acid (0.5M H2SO4) and alkaline (1M KOH) electrolytes. We find a reasonable HER activity evolved requiring overpotentials in a range of 30–50 mV under 10 mA cm−2 and 400−510 mV (0.5M H2SO4) and 280−500 mV (1M KOH) under −1000 mA cm−2. Likewise, the Tafel slopes range from 27 to 36 mV dec−1 (Volmer–Tafel) and 110 to 190 mV dec−1 (Volmer–Herovsky), implying that these mechanisms work at low and high current densities, respectively. Weak interlayer coupling, spontaneous surface oxidation, the presence of a semi-oxide subsurface (e.g., O–CrCl3), intrinsic Cl (or I) vacancy defects giving rise to in-gap states, electron redistribution (orbital hybridization) affecting the covalency, and sufficiently conductive support interaction lowering the charge transfer resistance endow the optimized adsorption/desorption strength of H* on active sites and favorable electrocatalytic properties. Such behavior is expedited for bi-/tri-layers while exemplifying the critical role of quantum nature electrocatalysts with defect sites for industrial-relevant conditions.

Electrocatalytic properties of transition metal vanadates (T = Ti, Cr, Mn, & Fe) for overall water splitting

In this work, first row transition metal vanadates (TMVs), including titanium vanadate (TiV), chromium vanadate (CrV), manganese vanadate (MnV), and iron vanadate (FeV), were synthesized and investigated their electrocatalytic performance for the alkaline water splitting. The prepared TMVs showed easy electron transfer characteristics and tunable band structures, and among these TMVs, the synthesized FeV demonstrated the best electrocatalytic bifunctional activities for both HER (η100 = 375 mV) and OER (η100 = 260 mV) with a significant electronic and morphological stability over 100 h operation. The examination of electronic structure revealed that the balanced catalyst-intermediate interaction through optimum d-p orbital hybridization in FeV, adhering to the Sabater principle, vouched for such facile redox reaction. The structural stability might be attributed to the synergism between iron and vanadate as the multivalent Fe adjusted the shift in vanadium coordination when the oxidation state of Vn+ (n = 3–5) changed. Moreover, the two-electrode system of FeV || FeV in a single electrolyzer demonstrated superior cell voltage100 of 1.86 V in comparison to commercial Pt/C || IrO2 electrodes (1.91 V). This work offers facile perspective to produce TMVs as the efficient electrocatalysts for green synthesis of fuel gases.

Chemo- and diastereoselective four-component reactions with Rh carbynoids

Multi-component reactions (MCRs) provide an efficient method for constructing multiple chemical bonds by combining three or more starting materials in a single operational step, enabling rapid and cost-effective synthesis of structurally diverse compounds. Although carbynoids (R-C:+) have shown potential for the development of selective MCRs due to their unique carbene and carbocation characteristics, their application in four-component reactions (4CRs) has been constrained by challenges in chemoselectivity. Herein, we provide a general solution to the challenges of chemoselective 4CR, using halo diazo reagents as carbynoid precursors, followed by reacting with pyrazoles, alcohols and imines sequentially. This approach allows the simultaneous construction of three different C(sp3)-N, C(sp3)-O, and C(sp3)-C(sp3) bonds on the same carbon. The success of this protocol mainly depends on precise control of chemical kinetics. Detailed experimental studies elucidate that the generation rate of aza-Rh(II)-carbene is faster than oxy-Rh(II)-carbene.

Enhanced electrochemical performance of flexible carbon substrates via carbonized layer of oxidant-induced polydopamine for high-performance supercapacitors

Flexible substrates are essential for advancing energy storage materials in portable and wearable devices. Carbon cloth is a promising option due to its flexibility and lightweight properties, but its high electrical resistance and hydrophobic surface present challenges for solution-based electrolytes. To overcome these issues, a surface modification technique was developed that coats carbon cloth with dopamine and subsequently carbonizes it. This process enhances hydrophilicity while preserving the sp2 carbon structure, significantly improving electrical conductivity. The chemical bath deposition of Ni(OH)2 onto the carbonized polydopamine-coated carbon cloth produced a uniform layer that increased specific capacitance dramatically. At a current density of 1 A/g, the specific capacitance reached 1100F/g, compared to 919F/g for Ni(OH)2 on unmodified carbon cloth. Furthermore, the electrodes maintained high specific capacitance at higher current densities, showcasing superior rate capability. Overall, carbonized polydopamine layers effectively reduce electrical resistivity and hydrophobicity, enhancing the performance of carbon-based materials for energy storage applications.

The origin of ferroelectricity in HfO2 from orbital hybridization and covalency

Fluorite-structured HfO2 ferroelectrics exhibit remarkable ferroelectricity owing to the robust thickness scalability, rendering them promising for next-generation ferroelectric memories. Unlike the well-understood perovskite structured ferroelectrics, such as Pb(Zr,Ti)O3, the origin of ferroelectricity in HfO2 remains elusive, which impedes the experimental fabrication of pure and stable ferroelectric orthorhombic phase in films. This study seeks to elucidate its origin by analyzing the covalent nature of local chemical bonding and changes in orbital hybridization and by catching the typical feather of the half-unit-cell spacer/polar layer in the orthorhombic phase. Notably, we find that the differences in the hybridization intensity of the 2s orbitals of two types of O atoms (OI and OII) and 5d orbitals of Hf atoms play a crucial role in inducing ferroelectric distortion. Furthermore, we demonstrate that the intrinsic mechanisms of stress in enhancing the ferroelectricity of HfO2 originate from the modulation of orbital hybridization intensity of the Hf–O bonds. These insights provide a vital theoretical foundation for further exploration of ferroelectric phase transitions and property modulation in HfO2 and similar fluorite-structured ferroelectrics.

Potassium tert-Butoxide Promoted α-Keto Ester Synthesis through C(O)–N Bond Cleavage of Isatins

AbstractWe present a novel and cost-effective method for synthesizing biologically important α-keto esters in a single-step reaction. This approach involves a sequential cascade process within a single reaction vessel facilitated by t-BuOK, which promoted the cleavage of the sp2 C(O)–N bond of an isatin and the formation of a new N–C(sp2)(O) bond with benzoyl chloride. To the best of our knowledge, this is the first instance of the construction of an α-keto ester scaffold adjacent to an amide group through a one-pot process. In comparison to existing methods, our protocol offers several advantages: readily available starting materials, mild reaction conditions, a concise synthetic pathway, high sustainability, and excellent tolerance towards various functional groups. Given these strengths, we anticipate widespread use of this method in the synthesis of related α-keto ester scaffolds.

Effect of edge dual-hydrogenation on electronic and magnetic properties of armchair silicon carbide nanoribbons

Using the first-principles calculations, we investigate the electronic and magnetic properties of armchair silicon carbide nanoribbon (aSiCNR) with different combinations of edge dual-hydrogenation. The dual-hydrogenation on the boundary Si or C atom changes it from sp2 hybridization to sp3 hybridization, which will have an important role on the stability of aSiCNR. Only the full dual-hydrogenation on the one edge or two edges don't change the band structure and magnetic moment of aSiCNR. However, the other different combinations of edge dual-hydrogenation can result in aSiCNR exhibiting metallic, semiconductor, and half-metallic properties under non-magnetism state, ferromagnetic and anti-ferromagnetic states. These results may present a new avenue for band engineering of aSiCNR, as well as valuable suggestions for the practical application of SiC based nanomaterials in spintronics and multifunctional nanodevices.

Proximity-induced ferromagnetism of platinum thin film on magnetic insulating CrI3 nanoflakes

The induced magnetization of Pt holds significant promise for the development of spintronic devices. In this study, we constructed a two-dimensional heterostructure consisting of a ferromagnetic insulating CrI3 nanoflake and metallic Pt thin films. The observation of anomalous Hall effect suggests the emergence of a ferromagnetic long-range order in the Pt thin film induced by the magnetic proximity effect. Density functional theory calculations were performed to investigate the underlying mechanisms. We propose that the spontaneous magnetization of Pt in Pt/CrI3 stems from an intensified exchange interaction between Pt 5d and Cr 3d electrons, which is facilitated by the interface coupling and the formation of interfacial hybrid orbitals. These results contribute to a deeper understanding of spin-based phenomena and have potential implications for advancements in the field of spintronics.

Decision threshold models in medical decision making: a scoping literature review

BackgroundDecision thresholds play important role in medical decision-making. Individual decision-making differences may be attributable to differences in subjective judgments or cognitive processes that are captured through the decision thresholds. This systematic scoping review sought to characterize the literature on non-expected utility decision thresholds in medical decision-making by identifying commonly used theoretical paradigms and contextual and subjective factors that inform decision thresholds.MethodsA structured search designed around three concepts—individual decision-maker, decision threshold, and medical decision—was conducted in MEDLINE (Ovid) and Scopus databases from inception to July 2023. ProQuest (Dissertations and Theses) database was searched to August 2023. The protocol, developed a priori, was registered on Open Science Framework and PRISMA-ScR guidelines were followed for reporting on this study. Titles and abstracts of 1,618 articles and the full texts for the 228 included articles were reviewed by two independent reviewers. 95 articles were included in the analysis. A single reviewer used a pilot-tested data collection tool to extract study and author characteristics, article type, objectives, theoretical paradigm, contextual or subjective factors, decision-maker, and type of medical decision.ResultsOf the 95 included articles, 68 identified a theoretical paradigm in their approach to decision thresholds. The most common paradigms included regret theory, hybrid theory, and dual processing theory. Contextual and subjective factors that influence decision thresholds were identified in 44 articles.ConclusionsOur scoping review is the first to systematically characterizes the available literature on decision thresholds within medical decision-making. This study offers an important characterization of the literature through the identification of the theoretical paradigms for non-expected utility decision thresholds. Moreover, this study provides insight into the various contextual and subjective factors that have been documented within the literature to influence decision thresholds, as well as these factors juxtapose theoretical paradigms.

Modular alkene synthesis from carboxylic acids, alcohols and alkanes via integrated photocatalysis.

Alkenes serve as versatile building blocks in diverse organic transformations. Despite notable advancements in olefination methods, a general strategy for the direct conversion of carboxylic acids, alcohols and alkanes into alkenes remains a formidable challenge owing to their inherent reactivity disparities. Here we demonstrate an integrated photochemical strategy that facilitates a one-pot conversion of these fundamental building blocks into alkenes through a sequential C(sp3)-C(sp3) bond formation-fragmentation process, utilizing an easily accessible and recyclable phenyl vinyl ketone as the 'olefination reagent'. This practical method not only offers an unparalleled paradigm for accessing value-added alkenes from abundant and inexpensive starting materials but also showcases its versatility through various complex scenarios, including late-stage on-demand olefination of multifunctional molecules, chain homologation of acids and concise syntheses of bioactive molecules. Moreover, initiating from carboxylic acids, alcohols and alkanes, this protocol presents a complementary approach to traditional olefination methods, making it a highly valuable addition to the research toolkit for alkene synthesis.

Nickel-Catalyzed Stereoconvergent C(sp2)-F Alkenylation of Monofluoroalkenes.

The stereoconvergent synthesis of a single stereoisomer from E/Z-olefin mixtures remains one of the foremost challenges in organic synthesis. Herein, we describe a nickel-catalyzed stereoconvergent cross-coupling between E- and Z-mixed monofluoroalkenes and alkenyl electrophiles, which allows the construction of C(sp2)-C(sp2) bonds. This defluorinative transformation offers facile access to various 1,3-dienes with E-selectivity and good functional group tolerance. Preliminary mechanistic studies indicate that the reaction most likely proceeds through a migratory insertion/β-F elimination/isomerization process.

Asymmetric Alkyl-Alkyl Cross-Coupling Enabled by Ni-Catalyzed Cross-Hydrodimerization of Enamides with Unactivated Alkenes

AbstractSaturated stereogenic centers containing C(sp3)–C(sp3) bonds comprise a major portion of organic molecules. Over the past decades, transition-metal-catalyzed asymmetric C(sp3)–C(sp3) cross-coupling has evolved into an efficient strategy for constructing such stereogenic centers. However, reaction modes to build asymmetric C(sp3)–C(sp3) bonds remain limited. Herein, a nickel-catalyzed enantioselective cross-hydrodimerization between distinct alkenes to enable the enantioselective construction of alkyl–alkyl bonds has been developed. In this reaction mode, N-acyl enamines (enamides) and unactivated alkenes undergo oxidative enantioselective cross-hydrodimerization with excellent levels of chemo- and head-to-tail regioselectivity to give enantioenriched N-acyl α-branched amines by forging the C(sp3)–C(sp3) bond with control of the enantioselectivity. The presence of both reducing and oxidizing reagents in the reaction allows the use of alkenes as sole precursors to forge enantioselective C(sp3)–C(sp3) bonds, representing a new reaction mode for asymmetric alkyl–alkyl cross-coupling. The asymmetric cross-hydrodimerization between distinct alkenes provides a new strategy for constructing saturated stereogenic centers containing C(sp3)–C(sp3) bonds.

Uncovering an Interfacial Band Resulting from Orbital Hybridization in Nickelate Heterostructures.

The interaction of atomic orbitals at the interface of perovskite oxide heterostructures has been investigated for its profound impact on the band structures and electronic properties, giving rise to unique electronic states and a variety of tunable functionalities. In this study, we conducted an extensive investigation of the optical and electronic properties of epitaxial NdNiO3 synthesized on a series of single-crystal substrates. Unlike nanofilms synthesized on other substrates, NdNiO3 on SrTiO3 (NNO/STO) gives rise to a unique band structure featuring an additional unoccupied band situated above the Fermi level. Our comprehensive investigation, which incorporated a wide array of experimental techniques and density functional theory calculations, revealed that the emergence of the interfacial band structure is primarily driven by orbital hybridization between the Ti 3d orbitals of the STO substrate and the O 2p orbitals of the NNO thin film. Furthermore, exciton peaks have been detected in the optical spectra of the NNO/STO film, attributable to the pronounced electron-electron (e-e) and electron-hole (e-h) interactions propagating from the STO substrate into the NNO film. These findings underscore the substantial influence of interfacial orbital hybridization on the electronic structure of oxide thin films, thereby offering key insights into tuning their interfacial properties.

Spin-dependent electronic phenomena in heavily-doped monolayer graphene

The controlled manipulation of doping levels in graphene is crucial for advancing next-generation low-power electronics. Owing to its peculiar band structure, graphene's electronic functionalities can be easily tuned by electron doping, resulting in the bandgap openings, orbital hybridization, and induced spin-polarization. Here, we unveil the substantial doping of the graphene layer and the emergence of a significant bandgap by sandwiching a monolayer graphene, supported on ferromagnetic cobalt, between two europium layers. Our angle- and spin-resolved photoemission spectroscopy experiments, accompanied by dedicated density functional theory calculations, demonstrate that single-spin electron pockets form as a result of the hybridization of the topmost europium majority bands with graphene, while hybridization gaps are induced in the graphene π∗ bands by the Eu minority bands. Spin-resolved measurements further emphasize a single-spin dispersionless contribution proximal to the Fermi level, possibly arising from the coupling of single-spin polarized graphene bands to optical phonons. This work provides crucial insights into the phase diagram of heavily doped graphene, with significant potential for the design and development of novel 2D systems.