Electron Spin Research Articles

Protein‐protein interaction and conformational change in the alpha‐helical membrane transporter BtuCD‐F in the native cellular envelope

Alpha‐helical membrane proteins perform numerous critical functions essential for the survival of living organisms. Traditionally, these proteins are extracted from membranes using detergent solubilization and reconstitution into liposomes or nanodiscs. However, these processes often obscure the effects of nanoconfinement and the native environment on the structure and conformational heterogeneity of the target protein. We demonstrate that pulsed dipolar electron spin resonance spectroscopy, combined with the Gd³⁺‐nitroxide spin pair, enables the selective observation of the vitamin B12 importer BtuCD‐F in its native cellular envelope. Despite the high levels of non‐specific labeling in the envelope, this orthogonal approach combined with the long phase‐memory time for the Gd³⁺ spin enables the observation of the target protein complex at a few micromolar concentrations with high resolution. In the native envelope, vitamin B12induces a distinct conformational shift at the BtuCD‐BtuF interface, which is not observed in the micelles. This approach offers a general strategy for investigating protein‐protein and protein‐ligand/drug interactions and conformational changes of the alpha‐helical membrane proteins in their native envelope context.

Spin injection from a magnetically near-compensated state in GdFeCo and inverse spin Hall effect in electron-hole compensated metal YH2.

Rare-earth-transition-metal (RE-TM) ferrimagnets are excellent materials for spin encode/decode operations via spin transport in nonmagnetic regions. This superior performance stems from two key factors. First, the antiferromagnetic coupling between RE4f and TM3d sublattices reduces both the spin-transfer-torque switching time and inter-device magnetic-coupling. Second, the RE-TM ferrimagnets function as spin injectors/ejectors, with the TM3d sublattice solely responsible for carrier spin polarization (p), similar to conventional ferromagnetic metals. We performed spin transport experiments using the sign change of p in RE-TM, which exhibits a positive value above the magnetization compensation temperature and a negative value below it. We measured temperature dependencies of the transverse resistances (RT) of electron-hole compensated metal YH2under out-of-plane spin-polarized current injection/ejection from GdFeCo (Gd:Fe:Co=25:66:9). The abrupt change in loop polarity of the out-of-plane field dependence of RT in YH2between 290 and 300 K, which aligns with the out-of-field curve of the polar Kerr rotation in GdFeCo electrodes, strongly suggests that the observed RT results from the inverse spin Hall effect (ISHE) in YH2. We analytically formulated ISHE in terms of the electron and hole spin currents injected from the spin sources, enabling regression analysis to assess the spin transport characteristics of a GdFeCo/YH2/GdFeCo magnetic double heterostructure. To explain the observed Hall voltages, enhancements in both the spin diffusion length of YH2and the spin injection efficiency are necessary.&#xD.

Design, Synthesis, ssDNA Binding Affinities, and Evaluation of Novel Metal‐Centered Ferrocene as an Effective Antimicrobial and DNA Cleavage Agent

ABSTRACTMetal (Co3+, Ni2+, and Pt2+)–centered and noncentered ferrocene–Schiff bases were prepared. They have been structurally characterized by spectroscopic methods, elemental analysis, conductivity, and magnetic moment. Electron spin resonance was used for the characterization of the Co3+‐centered complex. All synthesized compounds showed antibacterial activity against all tested Gram‐positive and Gram‐negative strains, as well as potent antifungal effect against Candida species. Remarkably, these compounds demonstrated greater efficacy against Gram‐positive bacteria than Gram‐negative. Without an additional oxidant or reductant, the compounds exhibited DNA cleavage capability in the dark. The development of synthesized novel chemical compounds having DNA cleavage and antimicrobial activity plays a profound role in the advancement of medical therapeutics.

Dual Signature of Chirality Induced Spin Selectivity through Spontaneous Resolution of 2D Metal–Organic Frameworks

AbstractThe Chiral‐Induced Spin Selectivity (CISS) effect has emerged as a fascinating phenomenon within the realm of electron's spin manipulation, showcasing a unique interplay between electron's spin and molecular chirality. Subsequent to its discovery, researchers have been actively involved in exploring the new chiral molecules as effective spin filters. In the realm of observing the CISS effect, the conventional approach has mandated the utilization of two distinct enantiomers of chiral molecules. However, this present study represents a significant advancement by demonstrating the ability to control both spin states of electrons in a single system. In this work, we have demonstrated the preparation of chiral metal–organic frameworks (MOFs) via a “spontaneous resolution” process, obviating the requirement for chiral sources. This resulted in the production of chiral crystals exhibiting opposite handedness (1P and 1M) and these crystals were subsequently employed as a new class of spin filters based on CISS effect. Remarkably, this work signifies the first instance of achieving dual signature of spin selectivity from a single and exclusively achiral system through a spontaneous resolution process. This holds immense potential as it facilitates the production of two distinct spin‐filtering materials from a unified system. Furthermore, we investigated the contact potential differences (CPD) of these chiral crystals and, for the first time, associated it with the preferential spin transport properties. Our findings revealed a correlation between the CPD and the chirality of the crystals, as well as the magnetization orientations of the ferromagnetic substrate, which can be elucidated by the CISS effect. In overall, the significant findings achieved using these robust and easily synthesized MOF crystals without the requirement for chiral medium represent a crucial advancement in enhancing the effectiveness of spin filtering materials to produce spintronic devices.

Evaluation of materials for developing a new individual dosemeter using electron spin resonance spectroscopy.

Alanine dosemeters are widely used as solid dosemeters; however, evaluating doses in the mGy order of radiation is difficult because of their lower sensitivity for low doses. We applied the electron spin resonance dosimetry technique to investigate whether hydroxyapatite, the main component of teeth, is a suitable material for a new dosemeter to detect radiation from mGy to Gy. Commercially available synthetic hydroxyapatite possesses the essential characteristics required for a dosemeter material and has been demonstrated to accurately measure doses in the mGy to Gy range.

ESR measurement of carbonated hydroxyapatite for dosemeter.

We have examined a dosimetry characteristic of carbonate hydroxyapatite (CO3HAp), which is a dental bone graft material. The purpose of this work is to investigate the reproducibility and stability of radiation-induced radicals on CO3HAp samples and assess the feasibility of using these materials as dosemeters. CO3HAp samples were exposed to gamma rays with dose range from 10 to 10000Gy. The electron spin resonance (ESR) spectra for irradiated samples were measured. Variation of peak-to-peak amplitude of the ESR signal intensity as a function of absorbed dose for CO3HAp was compared with that for alanine dosemeters, suggesting that the CO3HAp sample has a good linear dose response in the range from 10to 10000Gy as well as does the alanine dosemeters.

Amorphous Ni3B Promotes Electroreduction of Nitrate to Ammonia.

The electrocatalytic nitrate reduction to ammonia (NRA) can address nitrogen cycle imbalance and high carbon emissions; however, the intense competition of hydrogen evolution reaction (HER) restricts the rate of NH3 production. Herein, amorphous Ni3B (a-Ni3B) is designed to balance the NRA and HER. The NH3 yield of a-Ni3B surpasses those of pure Ni and NiO, which is attributed to the preferential adsorption of NO3- on the B and Ni sites of a-Ni3B for the NRA reaction, greatly inhibiting the HER. Furthermore, the a-Ni3B possesses advantages in NRA performance compared to crystalline Ni3B (c-Ni3B) due to more active hydrogen (*H) generated during the catalytic process. The *H in the NRA process on a-Ni3B is verified by the electron spin resonance technique. The NRA mechanism is comprehensively discussed based on the results of in situ characterization and density functional theory calculations. The a-Ni3B can enhance NH3 production by inhibiting HER, which provides ideas for sustainable NH3 synthesis.

Abstract 4124277: Resorcimoline, a Novel Free Radical Scavenger, Exhibits Cardioprotective Effects Following Coronary Ischemia-reperfusion Injury

Background: Ischemic heart disease remains the leading cause of death worldwide. Early coronary revascularization is the most important treatment. Recent findings have revealed that reactive oxygen species (ROS) can lead to tissue damage following coronary artery revascularization, known as ischemia-reperfusion injury. In this study, we focused on a novel free radical scavenger, resorcimoline (RML). Last year, we reported the scavenging activity of RML in vitro against multiple ROS, confirmed by the electron spin resonance spectrometry. Hypothesis: Resorcimoline might reduce ROS damage in cardiomyocytes, thereby exerting cardioprotective effects following coronary ischemia-reperfusion injury. Methods: Nine-to-eleven-week-old male Wistar rats were subjected to acute myocardial ischemia induced by ligation of the left anterior descending coronary artery for 30 minutes. Rats received intravenous injections of RML at 6 mg/kg before the ligation release or saline as a control. The heart sections were double-stained at 24-hour reperfusion with Evans blue and triphenyltetrazolium chloride to assess the infarct area. Cardiac function was evaluated at 2-day and 7-day reperfusion with echocardiography. Myocardial fibrosis was assessed at 7-day reperfusion by Masson’s trichrome staining. Primary cultured rat cardiomyocytes were treated with 10 μM angiotensin II for 3.5 hours and then exposed to RML for 30 minutes. Cellular ROS assay kits were used to assess the levels of ROS in the cardiomyocytes. Results: Infarct size in RML-treated animals was significantly smaller than in control animals (41.8±19.4% vs. 60.8±12.9%, p=0.03, Fig. 1A). Apoptotic cells in the border zone were significantly reduced in RML-treated animals (32.0±11.7% vs. 55.1±16.9%, p=0.01, Fig. 1B). Troponin I level in RML-treated animals was significantly lower than in control animals (p=0.04, Fig. 1C). Ejection fraction in RML-treated animals was significantly preserved at 2-day reperfusion and 7-day reperfusion when compared to control animals (p=0.001, p=0.003, Fig. 2A). Myocardial fibrosis area in RML-treated animals was significantly smaller than in control animals (23.9±11.7% vs. 40.6±15.6%, p=0.01, Fig. 2B). RML significantly reduced angiotensin II-induced ROS in cardiomyocytes in a concentration-dependent manner (Fig. 3A,B,C). Conclusion: Resorcimoline exhibits cardioprotective effects following coronary ischemia-reperfusion injury by reducing the infarct size and ROS damage in cardiomyocytes.

Pursuing high-fidelity control of spin qubits in natural Si/SiGe quantum dot

Electron spins in silicon quantum dots are a promising platform for fault-tolerant quantum computing. Low-frequency noise, including nuclear spin fluctuations and charge noise, is a primary factor limiting gate fidelities. Suppressing this noise is crucial for high-fidelity qubit operations. Here, we report on a two-qubit quantum device in natural silicon with universal qubit control, designed to investigate the upper limits of gate fidelities in a non-purified Si/SiGe quantum dot device. By employing advanced device structures, qubit manipulation techniques, and optimization methods, we have achieved single-qubit gate fidelities exceeding 99% and a two-qubit controlled-Z (CZ) gate fidelity of 91%. Decoupled CZ gates are used to prepare Bell states with an average fidelity of 91%, typically exceeding previously reported values in natural silicon devices. These results underscore that even natural silicon has the potential to achieve high-fidelity gate operations, particularly with further optimization methods to suppress low-frequency noise.

LDOS of electron pair and the role of the Pauli exclusion principle.

The local density of states (LDOS) for a pair of non-relativistic electrons, influenced by repulsive Coulomb forces, is expressed in term of one-dimensional integrals over Whittaker functions. The computation of the electron pair's LDOS relies on a two-particle Green's function (GF), a generalization of the one-particle GF applicable to a charged particle in an attractive Coulomb potential. By incorporating electron spins and considering the Pauli exclusion principle, the resulting LDOS consists of two components: one originating from an exchange-even two-particle GF and the other from an exchange-odd two-particle GF. The calculated LDOS reveals its dependence on both inter-electron distance and energy. The pseudo-LDOS, derived from the two-body contribution to the LDOS, is examined. This term ensures complete LDOS suppression at r = 0, exhibiting a limited spatial extent, and the reasons for its emergence are elucidated. It is shown that for energies exceeding the effective Hartree energy and inter-electron distances beyond the effective Bohr radius, the impact of manybody contributions to the LDOS can be disregarded. The induced LDOS for an electron pair subjected to an attractive contact potential in two dimensions is evaluated. At small distances a from the potential center, a predicted relative difference in LDOS between even and odd state pair reaches approximately 8%. The calculated LDOS is compared with available experimental findings from a two-dimensional electron gas (2DEG). Both exhibit similar oscillation periods; however, the LDOS of the electron pair decays as 1/a3, significantly faster than the 1/a decay observed for free electrons in a 2DEG.&#xD.

Van der Waals magnetic materials for current-induced control toward spintronic applications

AbstractSpintronics, leveraging electron spin for information processing, promises substantial advancements in energy-efficient computing. Van der Waals (vdW) magnetic materials, with their unique-layered structures and exceptional magnetic properties, have emerged as pivotal components in this field. This report explores the current-based control of vdW magnets, focusing on the spin–orbit torque (SOT) mechanism, which is crucial for spintronic applications. Key studies on Fe3GaTe2/Pt and Fe3GaTe2/WTe2 heterostructures are highlighted, demonstrating efficient SOT switching at room temperature. The advantages of vdW magnets for SOT switching, including high spin-torque efficiencies and superior interface quality, are discussed. The report also examines future directions, such as wafer-scale growth techniques, materials design for enhanced Curie temperatures (Tc), and the development of magneto tunnel junctions using all-vdW materials. These advancements underscore the potential of vdW magnetic materials in developing scalable, high-performance spintronic devices, paving the way for significant breakthroughs in energy-efficient computing. Graphical abstract

Spin-photon entanglement with direct photon emission in the telecom C-band.

Quantum networks, relying on the distribution of quantum entanglement between remote locations, have the potential to transform quantum computation and secure long-distance quantum communication. However, a fundamental ingredient for fibre-based implementations of such networks, namely entanglement between a single spin and a photon directly emitted at telecom wavelengths, has been unattainable so far. Here, we use a negatively charged exciton in an InAs/InP quantum dot to implement an optically active spin qubit taking advantage of the lowest-loss transmission window, the telecom C-band. We investigate the coherent interactions of the spin-qubit system under resonant excitation, demonstrating high fidelity spin initialisation and coherent control using picosecond pulses. We further use these tools to measure the coherence of a single, undisturbed electron spin in our system. Finally, we demonstrate spin-photon entanglement in a solid-state system with entanglement fidelity F = 80.07 ± 2.9%, more than 10 standard deviations above the classical limit.

Unlocking the potential of photoexcited molecular electron spins for room temperature quantum information processing

Abstract Future information processing technologies like quantum memory devices have the potential to store and transfer quantum states to enable quantum computing and networking. A central consideration in practical applications for such devices is the nature of the light-matter interface which determines the storage state density and efficiency. Here, we employ an organic radical, α,γ-bisdiphenylene-β-phenylallyl doped into an o-terphenyl host to explore the potential for using tuneable and high-performance molecular media in microwave-based quantum applications. We demonstrate that this radical system exhibits millisecond-long spin-lattice relaxation and microsecond-long phase memory times at room temperature, while also having the capability to generate an oscillating spin-polarized state using a co-dissolved photo-activated tetraphenylporphyrin moiety, all enabled by using a viscous liquid host. This latest system builds upon collective wisdom from previous molecules-for-quantum literature by combining careful host matrix selection, with dynamical decoupling, and photoexcited triplet-radical spin polarisation to realise a versatile and robust quantum spin medium.

Efficient Preparation of S-Scheme Ag/AgBr/BiOBr Heterojunction Photocatalysts and Implications for Degradation of Carbendazim: Mechanism, Pathway, and Toxicology.

Carbendazim (CBZ), as a highly effective benzimidazole fungicide, has a good control effect on various crops caused by fungi. However, excessive use of CBZ in water, atmosphere, soil, and crops has serious effects. The efficient degradation of CBZ is an effective way to reduce its toxic effect. In this work, the type of S-scheme Ag/AgBr/BiOBr heterojunction photocatalyst was effectively prepared by a simple one-step solvothermal in situ method and first applied to the mineralization and degradation of CBZ. The effects of the molar ratio of AgBr to BiOBr, catalyst dosage, CBZ concentration, pH value of the original solution, and inorganic salt ions on the photocatalytic degradation performance of CBZ were comprehensively studied. The results showed that, under visible light irradiation, 0.9-Ag/AgBr/BiOBr (0.9-AAB) exhibited the best photocatalytic degradation performance (88.9%) against the concentration at 10 mg/L of CBZ in original solutions with pH of 10. However, the degradation effect was also good at pH 7. After 90 min, the degradation efficiency reached 86.0%, corresponding to a TOC removal efficiency of 84.0%. The results indicate that the main active species are 1O2 and •O2- free radicals according to the free radical quenching experiments and electron spin resonance spectra. Combined with the XPS characterization results, the electron transfer mechanism of the S-scheme heterojunction was deeply revealed. Additionally, the degradation pathway of CBZ was proposed through both the intermediate identification and the theoretical calculation derived from the DFT Fukui index. Finally, the toxicity of CBZ and the degradation intermediates were predicted based on the T.E.S.T.

Characterization of low sodium type II silicon clathrate film spin dynamics

Type II Si clathrate is a Si-based, crystalline alternative to diamond silicon with interesting optoelectronic properties. Here, a pulsed electron paramagnetic resonance study of the spin dynamics of sodium-doped, type II NaxSi136 silicon clathrate films is reported. Focusing on the hyperfine lines of isolated Na atoms, the temperature dependence of the electron spin dynamics is examined from 6 to 25 K. The measurements exhibit multi-exponential decay, indicating multiple spin relaxation rates in the system. As expected, spin relaxation time (T1) increases rapidly with decreasing temperature, reaching ∼300 μs at 6.4 K. The phase memory (TM) shows less temperature dependence with a value of ∼3 μs at the same temperature. The temperature dependence of T1 exhibits Arrhenius behavior in the measurement range consistent with an Orbach pathway. There are strong similarities to the spin behavior of other defect donors in diamond silicon. The results provide insights into the potential of Si clathrates for spin-based applications.

Understanding the Spin of Metal Complexes from a Single-Molecule Perspective.

Compared with aggregate spin behavior, single-molecule spin behavior can be accurately understood, controlled, and applied at the level of basic building blocks. The potential of single-molecule electronic and nuclear spins for monitoring and control represents a beacon of promise for the advancement of molecular spin devices, which are fabricated by connecting a single molecule between two electrodes. Metal complexes, celebrated for their superior magnetic attributes, are widely used in the devices to explore spin effects. Moreover, single-molecule electrical techniques with high signal-to-noise ratio, temporal resolution, and reliability help to understand the spin characteristics. In this review, the focus is on the devices with metal complexes, especially single-molecule magnets, and systematically present experimental and theoretical state of the art of this field at the single-molecule level, including the fundamental concepts of the electronic and nuclear spin and their basic spin effects. Then, several experimental methods developed to regulate the spin characteristics of metal complexes at single-molecule level are introduced, as well as the corresponding intrinsic mechanisms. A brief discussion is provided on the comprehensive applications and the considerable challenges of single-molecule spin devices in detail, along with a prospect on the potential future directions of this field.

Efficient Near-Infrared to Blue Photon Upconversion by Ultrafast Spin Flip and Triplet Energy Transfer at Organic/2D Semiconductor Interface.

Solid state photon upconversion by triplet-triplet annihilation (TTA), particularly near-infrared (NIR)-to-blue upconversion, holds instant promise for enhancing optoelectronic and photochemical applications. Despite extensive studies, NIR-to-blue upconversion has remained particularly challenging and elusive due to inherent multiple energy-downhill processes in TTA upconversion. In this study, using atomically thin two dimensional (2D) monolayer semiconductor as a triplet sensitizer, we demonstrate an efficient and robust solid-state NIR-to-blue photon upconversion system. The ultrathin and flexible organic/2D bilayer heterostructure exhibits a NIR-to-blue upconversion with high quantum yield (ΦUC = 1.2%, out of 50%), low threshold power density (Ith = 110 mW/cm2) and a record-high apparent anti-Stokes shift of 1.12 eV. Further spin- and time-resolved spectroscopy reveals an ultrafast (< 500 fs) electron spin flip to triplet-like excitons in semiconductor sensitizer and subsequent picosecond (~ 6×1010 s-1) interfacial dexter energy transfer to annihilator molecules. The triplet energy transfer rate and efficiency depend strongly on driving force, exhibiting Marcus normal region behavior. This work demonstrates 2D monolayer semiconductor as a superior ultrathin light harvesting and triplet sensitization layer and reveals the key knob to overcome the compromise between upconversion efficiency and energy loss, offering a viable pathway to efficient solid state NIR-to-blue photon upconversion and implementation.

Efficient Near‐Infrared to Blue Photon Upconversion by Ultrafast Spin Flip and Triplet Energy Transfer at Organic/2D Semiconductor Interface

Solid state photon upconversion by triplet‐triplet annihilation (TTA), particularly near‐infrared (NIR)‐to‐blue upconversion, holds instant promise for enhancing optoelectronic and photochemical applications. Despite extensive studies, NIR‐to‐blue upconversion has remained particularly challenging and elusive due to inherent multiple energy‐downhill processes in TTA upconversion. In this study, using atomically thin two dimensional (2D) monolayer semiconductor as a triplet sensitizer, we demonstrate an efficient and robust solid‐state NIR‐to‐blue photon upconversion system. The ultrathin and flexible organic/2D bilayer heterostructure exhibits a NIR‐to‐blue upconversion with high quantum yield (ΦUC = 1.2%, out of 50%), low threshold power density (Ith = 110 mW/cm2) and a record‐high apparent anti‐Stokes shift of 1.12 eV. Further spin‐ and time‐resolved spectroscopy reveals an ultrafast (&lt; 500 fs) electron spin flip to triplet‐like excitons in semiconductor sensitizer and subsequent picosecond (~ 6×1010 s‐1) interfacial dexter energy transfer to annihilator molecules. The triplet energy transfer rate and efficiency depend strongly on driving force, exhibiting Marcus normal region behavior. This work demonstrates 2D monolayer semiconductor as a superior ultrathin light harvesting and triplet sensitization layer and reveals the key knob to overcome the compromise between upconversion efficiency and energy loss, offering a viable pathway to efficient solid state NIR‐to‐blue photon upconversion and implementation.

Continuous-Flow Electron Spin Resonance Measurements of Hydroxyl Radicals Produced during Photocatalytic Water Oxidation

Continuous-Flow Electron Spin Resonance Measurements of Hydroxyl Radicals Produced during Photocatalytic Water Oxidation

The contribution of methyl groups to electron spin decoherence of nitroxides in glassy matrices.

Long electron spin coherence lifetimes are crucial for high sensitivity and resolution in many pulse electron paramagnetic resonance (EPR) experiments aimed at measuring hyperfine and dipolar couplings, as well as in potential quantum sensing applications of molecular spin qubits. In immobilized systems, methyl groups contribute significantly to electron spin decoherence as a result of methyl torsional quantum tunneling. We examine the electron spin decoherence dynamics of the nitroxide radical 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) in both a methyl-free solvent and a methyl-containing solvent at cryogenic temperature. We model nitroxide and solvent methyl effects on decoherence using cluster correlation expansion (CCE) simulations extended to include methyl tunneling and compare the calculations to experimental data. We show that by using the methyl tunneling frequency as a fit parameter, experimental Hahn echo decays can be reproduced fairly well, allowing structural properties to be investigated in silico. In addition, we examine the Hahn echo of a hypothetical system with an unpaired electron and a single methyl to determine the effect of geometric configuration on methyl-driven electron spin decoherence. The simulations show that a methyl group contributes the most to electron spin decoherence if it is located between 2.5 and 6-7Å from the electron spin, with its orientation being of secondary importance.