Electron Spin Resonance Technique Research Articles

Exploring the conformational landscapes of protein kinases: perspectives from FRET and DEER.

Conformational changes of catalytically-important structural elements are a key feature of the regulation mechanisms of protein kinases and are important for dictating inhibitor binding modes and affinities. The lack of widely applicable methods for tracking kinase conformational changes in solution has hindered our understanding of kinase regulation and our ability to design conformationally selective inhibitors. Here we provide an overview of two recently developed methods that detect conformational changes of the regulatory activation loop and αC-helix of kinases and that yield complementary information about allosteric mechanisms. An intramolecular Förster resonance energy transfer-based approach provides a scalable platform for detecting and classifying structural changes in high-throughput, as well as quantifying ligand binding cooperativity, shedding light on the energetics governing allostery. The pulsed electron paramagnetic resonance technique double electron-electron resonance provides lower throughput but higher resolution information on structural changes that allows for unambiguous assignment of conformational states and quantification of population shifts. Together, these methods are shedding new light on kinase regulation and drug interactions and providing new routes for the identification of novel kinase inhibitors and allosteric modulators.

The Use of Spectroscopic Methods to Study Organic Matter in Virgin and Arable Soils: A Scoping Review

The use of modern spectroscopic methods of analysis, which provide extensive information on the chemical nature of substances, significantly expands our understanding of the molecular composition and properties of soil organic matter (SOM) and its transformation and stabilization processes in various ecosystems and geochemical conditions. The aim of this review is to identify and analyze studies related to the application of nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopy techniques to study the molecular composition and transformation of organic matter in virgin and arable soils. This article is mainly based on three research questions: (1) Which NMR spectroscopy techniques are used to study SOM, and what are their disadvantages and advantages? (2) How is the NMR spectroscopy technique used to study the molecular structure of different pools of SOM? (3) How is ESR spectroscopy used in SOM chemistry, and what are its advantages and limitations? Relevant studies published between 1996 and 2024 were searched in four databases: eLIBRARY, MDPI, ScienceDirect and Springer. We excluded non-English-language articles, review articles, non-peer-reviewed articles and other non-article publications, as well as publications that were not available according to the search protocols. Exclusion criteria for articles were studies that used NMR and EPR techniques to study non-SOM and where these techniques were not the primary methods. Our scoping review found that both solid-state and solution-state NMR spectroscopy are commonly used to study the structure of soil organic matter (SOM). Solution-phase NMR is particularly useful for studying soluble SOM components of a low molecular weight, whereas solid-phase NMR offers advantages such as higher 13C atom concentration for stronger signals and faster analysis time. However, solution-phase NMR has limitations including sample insolubility, potential signal aggregation and reduced sensitivity and resolution. Solid-state NMR is better at detecting non-protonated carbon atoms and identifying heterogeneous regions within structures. EPR spectroscopy, on the other hand, offers significant advantages in experimental biochemistry due to its high sensitivity and ability to provide detailed information about substances containing free radicals (FRs), aiding in the assessment of their reactivity and transformations. Understanding the FR structure in biopolymers can help to study the formation and transformation of SOM. The integration of two- and three-dimensional NMR spectroscopy with other analytical methods, such as chromatography, mass spectrometry, etc., provides a more comprehensive approach to deciphering the complex composition of SOM than one-dimensional techniques alone.

SYNTHESIS OF Ag-MODIFIED TiO2 SOL-GEL FILMS AND ITS APPLICATION AS PHOTOCATALYSTS FOR METHYLENE BLUE DEGRADATION

In the study, the photocatalytic activity of TiO2 films that are created by dip-coating from a sol that contained titanium (IV) isopropoxide, monoethanolamine, and 2-methoxyethanol is demonstrated. Through photo-fixation of Ag (I) ions with varied concentration (10-2 - 10-4 M) in the water phase under UV illumination, the films are subsequently surface-modified with Ag co-catalyst layers. Scanning Electron Microscopy (SEM), X-Ray Photoelectron Spectroscopy (XPS), Ultraviolet-Visible (UV) Spectroscopy, and Electron Paramagnetic Resonance (EPR) techniques are used to physically characterize the samples. Results reveal that the modification of the co-catalyst had no impact on the thickness and porosity of the films. In addition, the study show that the modified TiO2 films had increased photocatalytic activity. All the characterization methods used have shown the formationof surface - bound Ag (I) species and metallic silver nanoclusters. By measuring the Methylene Blue (MB) dye degradation under UV light illumination, as - prepared and Ag -modified TiO2 films are evaluated for their photocatalytic activity, and the impact of the silver precursor concentration during photo-fixation is investigated.The highest catalytic activity is seen for films that have been modified at a concentration of Ag (I) of 10-2 M. Ordered from highest to lowest, the MB photodegradation rate constants are TiO2 < TiO2 /Ag, 10-4 < TiO2 /Ag, 10-3 < TiO2 / Ag, 10-2.

2D MoS2 nanosheets supported CoFe2O4 nanoparticles mediated persulfate activation for antibiotic removal

Advanced oxidation technology based on persulfate activation has caused extensive concern in the field of wastewater treatment. Nevertheless, this new technology is limited to the low catalytic efficiency and poor recovery of powder catalysts. Herein, we successfully synthesized MoS2 surface-supported CoFe2O4 nanoparticles composite catalyst employing a simple hydrothermal method. Compared with other systems, the performance of TC degradation was significantly improved by CoFe2O4/MoS2/PS system. Additionally, the influence of solution pH, catalyst dosage, PS dosage, and co-existing ions on the degradation process were studied. Both free radical (O2•−, •OH, SO4•−) and non-free radical (1O2) pathways coexisted in the catalytic degradation of TC on the account of radicals quenching experiments and electron spin resonance (ESR) technique. Additionally, the degradation pollutants were confirmed to display obvious decrease in toxicity based on microbial toxicology tests. Besides, CoFe2O4/MoS2 nanocomposite displays good magnetic recovery performance due to the introduction of CoFe2O4. In summary, this research provides a solid foundation for the application of magnetic CoFe2O4/MoS2 nanocomposite in the treatment of antibiotic wastewater.

Electron Paramagnetic Resonance (EPR) Spectroscopy to Measure Oxidative Stress (OS) in Ulcerative Colitis Mouse

Background: Inflammatory bowel disease (IBD) refers to a group of chronic, complex, relapsing and remitting inflammatory disorders that affect the gastrointestinal (GI) tract. Crohn’s disease (CD) and ulcerative colitis (UC) are the two commonly diagnosed forms of IBD that affect over 3 million Americans, or 1.3% of the US population. In CD, patchy inflammation penetrating through multiple epithelial layers is present in any part of the GI tract, whereas UC is characterized by uniform inflammation restricted to the colon and rectum. Studies have shown increased oxidative stress (OS) as one of the major mechanisms involved in the pathogenesis of UC. Increased OS has thus far been measured using Biochemical assay-kits. In recent studies, electron paramagnetic resonance (EPR) spectroscopy has been extensively used to quantitatively characterize OS level in various tissues. Hypothesis: We hypothesize that EPR technique could be used to characterize OS in epithelia of colon. Aim: We aimed to develop EPR spectroscopy technique to quantify the level of OS in epithelia of normal and UC mouse colon. Methods: Normal mice (C57BL/6 male; 6 – 7 weeks old; Charles River, Wilmington, MA) were given regular water, while acute UC mice were given 5% Dextran-Sulfate-Sodium (DSS) water ad libitum for 7-days. EPR spectroscopy measurements were performed using the redox sensitive hydroxylamine spin probe, 1-hydroxy-3-carboxymethyl-2,2,5,5-tetramethyl-pyrrolidine (CMH; EPR silent). CMH is oxidized by reactive species/oxidants to 3-carboxymethyl-2,2,5,5- tetramethyl-pyrrolidinyloxy radical (CM•; EPR active). We used EPR detected CM• level as a quantitative marker of OS level. OS levels were measured both in serum and distal colon collected from euthanized mice. OS levels were presented as arbitrary units of EPR intensity. Results: OS levels were increased by 41% in serum from UC mice (normal vs UC: 33.6 ± 2.2 vs 47.0 ± 2.0 units; p < 0.011). OS levels were also significantly (60%) increased in UC mice colon compared to normal colon (normal vs UC: 3.5 ± 0.1 vs 5.6 ± 0.7 EPR units; p < 0.02). OS levels were approximately 9-fold higher in serum compared to colon in both normal and UC mice (normal: 3.5 ± 0.1 vs 33.6 ± 2.2; UC: 5.6 ± 0.7 vs 47.0 ± 2.0 EPR signals). Conclusions: We conclude that: 1) EPR spectroscopy technique could successfully be used for the precise measurement of OS levels in serum and colon; 2) OS levels were significantly increased in both serum and colon of UC mice; and 3) increased tissue oxidants were continuously released into the blood. Speculation: Increased serum oxidants may eventually affect other tissues in the body. This study was supported by the West Virginia Clinical and Translational Science Institute (WVCTSI) pilot grant (JTK), and Transition Grant Support, Offce of Research and Graduate Education, WVU Health Sciences Center (VMR). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Investigations on single and multi-grain optically stimulated luminescence (OSL) sensitivity and electron spin resonance (ESR) signals in quartz derived from sandstones: Insights on provenance of quartz in ancient depositional systems

Trapped charge techniques of luminescence and electron spin resonance (ESR) are classic tools for dating Quaternary deposits. Over the past decade, these techniques have been routinely applied to investigate provenance and/or the sedimentary history of quartz grains based on their different luminescence and ESR characteristics. Of these, optically stimulated luminescence (OSL) sensitivity is one of the most widely investigated parameter for luminescence-based provenance approach. A majority of studies on this parameter are based on evaluation of multi-grain quartz OSL sensitivity of the samples. This is particularly concerning because single-grain quartz luminescence studies have shown that the luminescence signal of a multi-grain aliquot is contributed by less than ∼1–10% of the total grains. Since the sole criteria for discrimination of sources based on luminescence sensitivity relies on its intensity, therefore the results based on multi-grain analysis will most likely be skewed depending on the ‘proportion’ and ‘brightness’ of a few grains. This demands a need to evaluate the potential of single-grain quartz OSL sensitivity in provenance studies. In this study, we investigate single and multi-grain quartz OSL sensitivity from compositionally different sandstones with well-characterised sources based on U–Pb zircon ages. We further complement this analysis with characterisation of ESR centres commonly used in quartz provenance, namely E′1 and [AlO4]0 centres. Our study shows that single-grain quartz OSL sensitivity can help distinguish between sediments that have a predominant input from a single source as compared to those with contribution from multiple sources, which otherwise cannot be inferred from multi-grain studies. Moreover, our results on characterisation of quartz-based ESR intensity of E′1 and saturated [AlO4]0 centres successfully differentiates between sandstones and further complements the luminescence-based characterisation.

Periodate activation by MnFe2O4 spinel for sulfamethoxazole degradation: Iodate radical dominance, degradation pathway, DFT calculation and toxicity assessment

This study synthesized spinel MnFe2O4 at different temperatures, which was applied to activate periodate (PI) for sulfamethoxazole (SMX) degradation. It was found that the 500-MFO (MnFe2O4 calcined at 500 ℃) demonstrated superior activity in PI activation, with notable sustainability but strong substrate selectivity. Furthermore, a comprehensive analysis, including quenching experiment, electron paramagnetic resonance (EPR) technique, X-ray photoelectron spectroscopy (XPS) analysis, metal ions leaching detection, homogeneous PI activation, and methyl phenyl sulfoxide (PMSO) probe test, revealed that homo- and heterogeneous pathways as well as free and non-free radical routes coexisted in the 500-MFO/PI system. Multiple active species, including iodate radical (IO3•), hydroxyl radical (•OH), superoxide radical (O2•-), singlet oxygen (1O2), and Mn(IV) were identified, with IO3• from heterogeneous activation being the primary species. When PMSO and SMX coexisted, PMSO could react with Mn(IV), promoting the regeneration of Mn reaction sites and the production of IO3•, thereby being beneficial for the degradation of SMX. The degradation pathways of SMX were elucidated through high-performance liquid chromatography-mass spectrometry (HPLC-MS) and density functional theory (DFT) calculation. The acute and chronic toxicity of thirteen by-products to aquatic organisms were predicted using the Ecological Structure Activity Relationships (ECOSAR) software, with the corresponding results revealing that although the toxicity of intermediates fluctuated, the final products were environmentally benign. Therefore, this investigation provides a viable method for SMX degradation in wastewater treatment.

Elucidating Singlet-Fission-Born Multiexciton Dynamics via Molecular Engineering: A Dilution Principle Extended to Quintet Triplet Pair.

Multiexciton in singlet exciton fission represents a critical quantum state with significant implications for both solar cell applications and quantum information science. Two distinct fields of interest explore contrasting phenomena associated with the geminate triplet pair: one focusing on the persistence of long-lived correlation and the other emphasizing efficient decorrelation. Despite the pivotal nature of multiexciton processes, a comprehensive understanding of their dependence on the structural and spin properties of materials is currently lacking in experimental realizations. To address this gap in knowledge, molecular engineering was employed to modify the TIPS-tetracene structures, enabling an investigation of the structure-property relationships in spin-related multiexciton processes. In lieu of the time-resolved electron paramagnetic resonance technique, two time-resolved magneto-optical spectroscopies were implemented for quantitative analysis of spin-dependent multiexciton dynamics. The utilization of absorption and fluorescence signals as complementary optical readouts, in the presence of a magnetic field, provided crucial insights into geminate triplet pair dynamics. These insights encompassed the duration of multiexciton correlation and the involvement of the spin state in multiexciton decorrelation. Furthermore, simulations based on our kinetic models suggested a role for quintet dilution in multiexciton dynamics, surpassing the singlet dilution principle established by the Merrifield model. The integration of intricate model structures and time-resolved magneto-optical spectroscopies served to explicitly elucidate the interplay between structural and spin properties in multiexciton processes. This comprehensive approach not only contributes to the fundamental understanding of these processes but also aligns with and reinforces previous experimental studies of solid states and theoretical assessments.

HYSCORE and QM/MM Studies of Second Sphere Variants of the Type 1 Copper Site in Azurin: Influence of Mutations on the Hyperfine Couplings of Remote Nitrogens.

Secondary coordination sphere (SCS) interactions have been shown to play important roles in tuning reduction potentials and electron transfer (ET) properties of the Type 1 copper proteins, but the precise roles of these interactions are not fully understood. In this work, we examined the influence of F114P, F114N, and N47S mutations in the SCS on the electronic structure of the T1 copper center in azurin (Az) by studying the hyperfine couplings of (i) histidine remote Nε nitrogens and (ii) the amide Np using the two-dimensional (2D) pulsed electron paramagnetic resonance (EPR) technique HYSCORE (hyperfine sublevel correlation) combined with quantum mechanics/molecular mechanics (QM/MM) and DLPNO-CCSD calculations. Our data show that some components of hyperfine tensor and isotropic coupling in N47SAz and F114PAz (but not F114NAz) deviate by up to ∼±20% from WTAz, indicating that these mutations significantly influence the spin density distribution between the CuII site and coordinating ligands. Furthermore, our calculations support the assignment of Np to the backbone amide of residue 47 (both in Asn and Ser variants). Since the spin density distributions play an important role in tuning the covalency of the Cu-Scys bond of Type 1 copper center that has been shown to be crucial in controlling the reduction potentials, this study provides additional insights into the electron spin factor in tuning the reduction potentials and ET properties.

The different structure and properties of protic ionic liquid in alcohol from acid and base: butylammonium butyrate mixing with butanol, butyric acid, and butylamine respectively

Solvents are commonly added into protic ionic liquids (PILs) to reduce viscosity in practical applications. Understanding the relationship between the structure and properties of PILs mixed with solvents is also essential for tailoring specific applications, however, such research is limited. In this study, we measured and compared the density, viscosity, and conductivity of three mixed systems: n-butylammonium butyrate ionic liquid (PIL) mixing with N-butyric acid (PrCOOH), PIL-N-butylamine (BuNH2), and PIL-N-butanol (BuOH). Small- and wide-angle X-ray scattering (S/WAXS), molecular dynamics (MD) simulation, and electron paramagnetic resonance (EPR) techniques were used to explore their inherent structural differences. The results indicate that the properties of the PIL-BuOH and PIL-PrCOOH systems exhibit more overall similarity in trends compared to the PIL-BuNH2 system. However, when the molar fraction of alcohol or acid exceeds 0.8, structural differences between the two systems lead to the differences in properties. The hydrogen bond network between the BuOH molecules outside the ion cluster leads to higher viscosity and conductivity than the PIL-PrCOOH system. However, the strong hydrogen bond between PrCOOH and anions will replace the position of cations and form spherical clusters. This research highlights how distinct structures influence diverse properties, providing deeper insights into the structure-property relationship.

Direct Observation of All Open-Shell Intermediates in a Photocatalytic Cycle.

Molecular photocatalysis has shown tremendous success in sustainable energy and chemical synthesis. However, visualizing the transient open-shell intermediates in photocatalysis is a significant and long-standing challenge. By employing our recently developed innovative time-resolved electron paramagnetic resonance technique, we directly observed all radicals and radical ions involved in the photocatalytic addition of pempidine to tert-butyl acrylate. The full picture of the photocatalytic cycle is vividly illustrated by the fine structures, chemical kinetics, and dynamic spin polarization of all open-shell intermediates directly observed in this prototypical system. Given the universality of this methodology, we believe it greatly empowers the research paradigm of direct observation in both photocatalysis and radical chemistry.

Thermoluminescence (TL) and electron paramagnetic resonance (EPR) of dumortierite sensitized by heat treatments

The present study presents the effect of heat treatment on TL and EPR of dumortierite. It was found that applying a heat treatment at 1200 °C for 1h, followed by slow cooling to room temperature, is optimal for improving its TL sensitivity. The glow curves of the sensitized dumortierite sample show TL emission bands centered at 350, 475, and 580 nm. The kinetic parameters of the TL peaks were obtained using the Tm-Tstop and deconvolution methods. In addition, sensitized dumortierite exhibits a linear response with γ-radiation dose and low fading in its TL response. Studies using the technique of EPR were carried out to investigate the defect center EPR signals observed after γ-irradiation. A single defect center with an axially symmetric g-tensor was observed with principal values g∥ = 2.0009 and g⊥ = 2.0017. The center was attributed to an F+ center and appears to correlate with the TL peak at 200 °C.

Construction of functional direct Z-scheme PCN-224@MoS2 heterojunction with high photocatalytic performance by simple solvothermal method

Organic contamination due to overuse of antibiotics and microbial contamination caused by various bacteria not only damage the ecological environment, but also threaten people's health. In this work, the photocatalytic material PCN-224@MoS2 was synthesized using a simple solvothermal method. The successfully synthesized photocatalytic material possesses a direct Z-scheme heterojunction, which effectively separated the photogenerated electrons and holes and suppressed their rapid complexation, leading to an increase in reactive oxygen species (ROS) yield. The degradation experiments showed that PCN-224@MoS2 with a mass ratio of 5:16 exhibited the best degradation ability for the tetracycline hydrochloride (TCH), achieving 96.41% degradation rate in 60 min, which was 5.4 and 4.7 times higher than that of pure PCN-224 and pure MoS2. In addition, the photocatalytic material achieved antibacterial ratios of 99.98% and 99.86% against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), respectively, under suitable light time and concentration. Subsequently, free radical scavenging experiments and the electron-spin resonance (ESR) techniques were used to confirm the types of free radicals and the possible photocatalytic mechanism in the photocatalytic process. The development of PCN-224@MoS2 heterojunction provides a new insight to solve the environmental problems caused by organic pollutants and microbial contamination.

Efficient peroxymonosulfate activation by iron-cobalt bimetallic biochar for rapid removal of antibiotic resistant bacteria, antibiotic resistance genes, and ampicillin: The coexisting of free-radical and non-radical pathways

As a typical “One Health” issue, antibiotic resistance has been considered as a worldwide threat to public health. And its spread can be restricted by antibiotics degradation, inactivation of antibiotic resistant bacteria (ARB), and removal of antibiotic resistance genes (ARGs). In this study, iron-cobalt bimetallic biochar (Fe-Co@BC) activated peroxymonosulfate (PMS) system was applied to degrade ampicillin (AMP), inactivate ARB (E. coli DH5α), and remove ARGs (plasmid-encoded blaTEM-1). AMP was degraded efficiently (about 99 %) in the Fe-Co@BC/PMS system within 40 min, and the catalyst still showed good stability after four cycles. Similarly, the Fe-Co@BC/PMS system achieved complete inactivation of ARB (about 107 CFU/mL) within 5 min, and the oxidative damages of ARB were further verified in terms of cell viability, cell membrane integrity, and enzyme activity. The removal efficiency of blaTEM-1 was 3.47 log within 60 min, and the catalyst dose, PMS concentration, initial ARB concentration, pH, and inorganic anions had significant effects on blaTEM-1 removal. The coexistence of non-radical (1O2, electron transfer) and free-radical (SO4−, O2−, and OH) pathways in the Fe-Co@BC/PMS system was demonstrated by electron paramagnetic resonance techniques and free radical quenching experiments, with SO4− and 1O2 being the main reactive species. XPS results showed that redox cycles between Co (III)/Co (II) and Fe (III)/Fe (II) were important to the efficient catalytic performance of Fe-Co@BC. Moreover, possible degradation pathway of AMP was proposed according to LC-MS results and density functional theory analysis. The results obtained in this study provide a novel sight on preventing the propagation of antibiotic resistance in aquatic settings.

Synthesis, molecular modeling, DFT studies, and EPR analysis of 1,4-dihydropyridines as potential calcium channel blockers

1,4-Dihydropyridines (DHPs) are widely recognized as a highly effective class of L-type calcium channel blockers that offer significant therapeutic potential in managing cardiovascular conditions. Furthermore, their ability to target other types of calcium channels makes DHPs attractive candidates for therapeutic applications in neurological and psychiatric disorders. Close examination of the chemical structures of approved DHP-based antihypertensive drugs with a history of over forty years in the market reveals that the C-4 position is the least altered part of this privileged ring system. In the present study, we focused on this position and synthesized two novel compounds (DB1 and DB2) by carrying out chemical modifications on suitable positions of the main scaffold of DA1 (isobutyl 4-(benzo[d][1,3]dioxol-5-yl)-2,6,6-trimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate) that was previously identified as a DHP-based effective and selective inhibitor of T-type (Cav3.2) over L-type (Cav1.2) calcium channel. Based on whole-cell patch-clamp analysis on Cav1.2 and Cav3.2, DB1 with bromine group on the benzodioxole ring appeared to be a more effective and selective inhibitor of Cav3.2 compared to DB2 with nitro at the same locus. Molecular docking and molecular dynamics (MD) simulations were performed to investigate the binding mode of both DB1 isomers to Cav3.2. Furthermore, density functional theory (DFT) methods were employed to obtain information regarding the stability of the molecules by computing various parameters, such as electric dipole moment, band gap, electronegativity, and global chemical hardness-softness, related to their charge-transfer characteristics. According to DFT studies, DB1 also appeared to be chemically more stable than DB2. Finally, ionizing radiation-induced free radicals of gamma-irradiated DB1 and DB2 in powder form were examined utilizing the electron paramagnetic resonance (EPR) technique and the obtained data demonstrated that radiation sterilization is suitable for the dosage forms including DB1 and DB2.

Layered perovskite piezoelectric Bi3TiNbO9 as a piezo-photocatalyst: Synergistically enhanced catalytic activity and mechanism

Photocatalysis is considered as a green and efficient technology for dealing with water pollution problems, but there exists serious carrier recombination in photocatalysis. Introducing a piezoelectric electric field to reduce carrier recombination and accelerate carrier separation and migration is a recognized as an effective approach, while it remains testing for exploitation for high-performance catalysts with light and stress dual response as well as the coupling catalytic mechanism. In this work, we report a novel layered perovskite structure piezo-photocatalyst Bi3TiNbO9 and conducted an analysis of potential piezo-photocatalytic mechanisms. The piezoelectric force microscopy (PFM) and COMSOL finite element analysis prove that the Bi3TiNbO9 is a piezoelectric with strong piezoelectricity. In the degradation of tetracycline hydrochloride, Bi3TiNbO9 exhibits significantly better piezo-photocatalysis performance compared to piezocatalysis and photocatalysis. It is owing to that the ultrasound results in piezoelectric polarization accompanied by the generation of piezo-potential, which can induce piezocatalysis and facilitate the separation and transfer of photo-generated carriers. Electron paramagnetic resonance (EPR) technique and electrochemical tests are carried out under different excitation sources to identify the dominant active species involved in the reaction and to disclose the origin for the high performance of piezo-photocatalysis from the perspective of carriers. This study adds a new member to the family of piezo-photocatalytic material system, and provides further understanding on the synergistic piezo-photocatalysis mechanism.

Exploring the dynamics and structure of PpiB in living Escherichiacoli cells using electron paramagnetic resonance spectroscopy.

The combined effects of the cellular environment on proteins led to the definition of a fifth level of protein structural organization termed quinary structure. To explore the implication of potential quinary structure for globular proteins, we studied the dynamics and conformations of Escherichia coli (E. coli) peptidyl-prolyl cis/trans isomerase B (PpiB) in E. coli cells. PpiB plays a major role in maturation and regulation of folded proteins by catalyzing the cis/trans isomerization of the proline imidic peptide bond. We applied electron paramagnetic resonance (EPR) techniques, utilizing both Gadolinium (Gd(III)) and nitroxide spin labels. In addition to using standard spin labeling approaches with genetically engineered cysteines, we incorporated an unnatural amino acid to achieve Gd(III)-nitroxide orthogonal labeling. We probed PpiB's residue-specific dynamics by X-band continuous wave EPR at ambient temperatures and its structure by double electron-electron resonance (DEER) on frozen samples. PpiB was delivered to E. coli cells by electroporation. We report a significant decrease in the dynamics induced by the cellular environment for two chosen labeling positions. These changes could not be reproduced by adding crowding agents and cell extracts. Concomitantly, we report a broadening of the distance distribution in E. coli, determined by Gd(III)-Gd(III) DEER measurements, as compared with solution and human HeLa cells. This suggests an increase in the number of PpiB conformations present in E. coli cells, possibly due to interactions with other cell components, which also contributes to the reduction in mobility and suggests the presence of a quinary structure.

Photocatalytic degradation of sulfonamides in suspensions of coral-like graphene carbon nitride with nitrogen vacancies

Sulfonamides (SNs) belong to a category of broad-spectrum antibiotics, which have attracted growing concerns owing to the adverse effects on ecosystem. In this paper, coral-like graphitic carbon nitrides with nitrogen vacancies were prepared by polymerization of melamine in the presence of NH4Cl, and the effect of NH4Cl amount on the structure and photocatalytic performance of g-C3N4 in degradation of sulfonamide antibiotics such as sulfamethoxazole (SMX), sulfadiazine (SDZ) and sulfathiazole (STZ) was systematically studied. It was found that the addition of NH4Cl results in the formation of coral-like g-C3N4 with nitrogen vacancies, and optimal photocatalyst (PCN-1 sample) prepared with a melamine to NH4Cl mass ratio of 1:1 showed the highest photocatalytic activity towards SNs degradation due to the quick electron-hole migration, efficient separation capacity and excellent photoelectric properties. The electron paramagnetic resonance (EPR) technique was used to determine the reactive oxygen species (ROSs) that are responsible for the degradation of SNs, and the detailed degradation pathway of STZ was proposed according to the identification of the intermediates by liguid chromatography-high resolution mass spectrometry (LC-HRMS).

The role of ligand in the activation of peroxymonosulfate by Fe3O4 for the degradation of organic pollutants

Advanced oxidation processes based on peroxymonosulfate (PMS) hold remarkable promise for addressing emerging organic pollutants (EOPs) and are worthy of systematic investigation. However, the existing technology has not been widely applied due to bottlenecks such as reaction efficiency. Herein, we proposed a novel system incorporating nitrilotriacetic acid (NTA) as a functional ligand to enhance the activation of PMS by Fe3O4, thereby facilitating a better efficiency for the degradation of EOPs. Results indicated that the system can achieve an optimal removal rate of 99.6% for atrazine (ATZ) in the presence of NTA. Quenching experiments and electron paramagnetic resonance techniques were employed for mechanism exploration. The results revealed that the enhanced Fe(II)/Fe(III) cycling on the surface of Fe3O4, triggered by the addition of NTA, accelerates the reduction of trivalent iron and continuously activates PMS to generate radicals, particularly SO4−. The mechanistic analysis showed that in the first stage, the lower degradation efficiency could due to the self-quenching of the free radicals, with the uncomplexed Fe(II) and Fe(III) on the surface, the free NTA in the solution, or with the PMS, in addition to reacting with the pollutants. In the second stage, the ATZ achieved rapid degradation as the concentration of substances competing for free radicals decreased. Our work elucidates the key role of NTA functional ligand in the Fe3O4/PMS advanced oxidation processes, which may provide new approach for the efficient degradation of EOPs.

Room temperature coherence properties and 14N nuclear spin readout of NV centers in 4H–SiC

We have investigated the room temperature spin coherence properties of the axial NVkk center in 4H–SiC by pulsed high-frequency electron spin resonance and electron-nuclear double resonance techniques. Our results show a remarkable phase coherence time (TCoherence) of 25.3 μs at room temperature for ensembles of NV centers. We demonstrate precise control over NV defect spins through Rabi oscillations, which exhibit a linear response to microwave power. Additionally, the demonstrated room temperature readout of the intrinsic 14N nuclear spin (I = 1) underscores its potential as a robust nuclear spin memory resource, further positioning NV defects in 4H–SiC as an advanced platform for implementing cutting-edge quantum technologies in semiconductor systems.