Electron Spin Resonance Investigation Research Articles

Highly effective CNT-based magnetic pn-junction nanocomposite photocatalyst/solar-energy material for hazmat conversion to hydrogen fuel

Hazmat conversion to hydrogen using low-cost effective eco-friendly solar energy active materials is a sustainable strategy for environmental remediation and provision of future green fuel. In this paper, a novel magnetic pn-junction nanocomposite was rationally designed and synthesized through a facile hydrothermal route using affordable chemicals in the absence and presence of CNT (carbon nanotube). The easy recyclable/re-collectable CNT-based magnetic materials with the scaling up capability synthesized here were applied as effective nanoenergy materials for photocatalytic conversion of H2S feed to hydrogen fuel. The maximum hydrogen production was attained for the pn-junction nanocomposite photocatalyst at the molar ratio 1:2 of p to n (rate:5652μmolH2g.h) and boosted 60% by adding CNT. Transient photocurrent, impedance, fluorescence and electron paramagnetic resonance (EPR) investigations revealed that the charge recombination is reduced in the presence of CNT and hence the photogenerated e−/h+ pairs can more effectively be utilized in the hazmat-to-fuel conversion process. The junction formation was approved at an atomistic scale through HRTEM observation. Furthermore, the magnetic property of the synthesized nanocomposite photocatalyst was improved in the presence of CNT and discussed in detail from physicochemical standpoint using VSM (vibrating sample magnetometric) and XPS (X-ray photoelectron spectroscopic) evidence.

Selective oxidation of ammonia nitrogen to nitrogen gas by Fe2+/PMS/Cl−: The role of reactive chlorine species

Ammonia nitrogen (NH4+-N) can pose a threat to ecosystems and human health. Many methods have been used for the removal of NH4+-N. In particular, reactive chlorine species (RCS, including Cl·, Cl2·−, and ClO·) show superior performance for the selective oxidation of NH4+-N to nitrogen gas (N2). Herein, Fe2+/peroxymonosulfate (PMS)/Cl− process was proposed to generate RCS for the conversion of NH4+-N to N2, in which Fe2+ was used as the activator of PMS in the presence of Cl−. Fe2+, PMS, and Cl− concentrations could affect the removal of NH4+-N in Fe2+/PMS/Cl− process. Fe2+/PMS/Cl− exhibited good performance in removing NH4+-N at pH 3.5–8.0. At all investigated conditions, NH4+-N was mainly converted to N2, and N2 selectivity was more than 90 %. Under optimal conditions, 50 % of NH4+-N was removed in 5 min, and the removal efficiency reached the maximum of 96 % within 120 min with the high N2 selectivity of 100 %. The electron spin resonance tests, scavenging experiments, and probe experiments demonstrated the generation of RCS in Fe2+/PMS/Cl− reaction system. Experimental results and model analysis consistently proved that ClO· and Cl· were crucial radicals during the selective oxidation of NH4+-N, especially ClO·. Fe2+/PMS/Cl− system could remove NH4+-N and COD simultaneously in real wastewater. This study can provide an efficient strategy for the removal of NH4+-N.

Activation of peroxymonosulfate with natural pyrite-biochar composite for sulfamethoxazole degradation in soil: Organic matter effects and free radical conversion

Peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs) represent an effective method for the remediation of antibiotic-contaminated soils. In this study, a natural pyrite-biochar composite material (FBCx) was developed, demonstrating superior activation performance and achieving a 76% removal rate of SMX from soil within 120 min. There existed different degradation mechanisms for SMX in aqueous and soil solutions, respectively. The production of 1O2 and inherent active species produced by soil slurry played an important role in the degradation process. The combination of electron paramagnetic resonance (EPR) and free radical probe experiments confirmed the presence of free radical transformation processes in soil. Wherein, the·OH and SO4·− generated in soil slurry did not directly involve in the degradation process, but rather preferentially reacted with soil organic matter (SOM) to form alkyl-like radicals (R·), thereby maintaining a high concentration of reactive species in the system. Furthermore, germination and growth promotion of mung bean seeds observed in the toxicity test indicated the environmental compatibility of this remediation method. This study revealed the influence mechanism of SOM in the remediation process of contaminated soil comprehensively, which possessed enormous potential for application in practical environments.

Unraveling the generation mechanism of singlet oxygen in Bi2WxMo1-xO6 solid solution and roles in photocatalytic degradation of gaseous toluene under visible-light irradiation

Photocatalytic degradation volatile organic compounds (VOCs) represent an appealing strategy since the inexhaustible solar energy and facile reaction condition. In this work, a flower-like microsphere Bi2WxMo1-xO6 solid solution photocatalysts with abundant oxygen vacancies (OVs) were prepared via HTAB-assisted hydrothermal method. The mole ratio of W and Mo atoms were regulated by adjusting the stoichiometric ratio of their precursor. The optimized Bi2W0.25Mo0.75O6 presented outstanding photocatalytic performance with 96.8% of toluene degradation rate after 180 min of irradiation under visible light (>420 nm), which was 13.76 times higher than that of pure Bi2MoO6 and 10.32 times higher than that of pure Bi2WO6, respectively. The enhanced photocatalytic activity of Bi2W0.25Mo0.75O6 was attributed to the optimized band structure and efficient separation efficiency of carriers as well as the participation of singlet oxygen (1O2) radicals. Free radical trap experiments and electron spin resonance investigations revealed that 1O2, hydroxyl radical, and holes were the predominated reactive oxygen species (ROSs) in toluene degradation. Meanwhile, the generation of 1O2 was related to abundant OVs of Bi2W0.25Mo0.75O6 solid solution. This work suggested that solid solution with abundant OVs was an effective photocatalyst to improve the VOCs degradation activity under visible-light irradiation.

Catalytic ozonation with carbon-coated copper-based core-shell catalysts (C/Cu-Al2O3) for the treatment of high-salt petrochemical wastewater

High-salt petrochemical wastewater requires advanced treatment for water reuse due to its high salinity and the presence of refractory organic compounds. Heterogeneous catalytic ozonation is an effective advanced treatment method, with the key to its success lying in the preparation of catalysts. A novel carbon-coated copper-based core-shell catalyst (C/Cu-Al2O3) was successfully prepared. In this work, Al2O3 was used as a carrier and copper as an active component to construct a catalyst with levodopa (L-DOPA) shell and embedded copper sites through the self-polymerization of L-DOPA. The active groups in L-DOPA molecules such as amine and carboxyl groups can be introduced into catalyst and L-DOPA also served as carbon source to reduce Cu(II) to more reactive Cu(I) and Cu(0). Under optimal conditions, its chemical oxygen demand (COD) removal rate for high-salt petrochemical wastewater reached 62.5%. After 20 cycles, its COD removal rate was maintained at above 53%. Electron paramagnetic resonance (EPR) investigations, quenching tests, and degradation experiments of oxalic acid revealed that the generation of embedded copper sites (Cu-O, Cu-N) and the construction of the carbon shell provided the catalyst with rich surface hydroxyl groups and Lewis acid sites, which promoted the decomposition of ozone into hydroxyl radicals (•OH), superoxide radicals (•O2-), and singlet oxygen (1O2) and achieved efficient degradation of organic compounds.

Large dynamics of a phase separating arginine-glycine-rich domain revealed via nuclear and electron spins

Liquid-liquid phase separation is the key process underlying formation of membrane-less compartments in cells. A highly dynamic cellular body with rapid component exchange is Cajal body (CB), which supports the extensive compositional dynamics of the RNA splicing machinery, spliceosome. Here, we select an arginine-glycine (RG)-rich segment of coilin, the major component of CB, establish its RNA-induced phase separation, and through combined use of nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) probes, interrogate its dynamics within the crowded interior of formed droplets. Taking advantage of glycine-based singlet-states, we show that glycines retain a large level of sub-nanoseconds dynamics inside the coilin droplets. Furthermore, the continuous-wave (CW) and electron-electron dipolar (PELDOR) and electron-nucleus hyperfine coupling EPR data (HYSCORE) support the RNA-induced formation of dynamic coilin droplets with high coilin peptide concentrations. The combined NMR and EPR data reveal the high dynamics of the RG-rich coilin within droplets and suggest its potential role in the large dynamics of CBs.

In-depth insight into the structural properties of nanoparticulate NiO for CO sensing

The outstanding properties exhibited by the p-type NiO nanostructures can be greatly affected by morpho-structural and defect characteristics with constructive or competing effects. We have conducted an in-depth study on NiO nanoparticles obtained by hydrothermal synthesis and submitted to various thermal treatments, to monitor the evolution of their structural properties and the effect of the thermal history on their CO sensing. Correlated electron paramagnetic resonance and analytical transmission electron microscopy investigations evidenced an amount of up to 1 % metallic nickel clusters close to surface in the NiO nanoparticles calcined at 400 °C and 500 °C for 8 h. Subsequent annealing in vacuum and in air of the sample calcined at 400 °C resulted in different size distributions and morphology of the NiO nanoparticles and an increase/decrease of the nickel phase, respectively. Comparative CO sensing tests on the two pristine samples and on the sample calcined at 400 °C and further annealed in air at 500 °C for 2 h showed an increase in the baseline resistance of the later due to the decrease of free charge carriers induced by the dissolution of the nickel clusters. The overall CO sensing results show a strong dependence on the samples thermal history.

Single-molecule electron spin resonance by means of atomic force microscopy

Understanding and controlling decoherence in open quantum systems is of fundamental interest in science, whereas achieving long coherence times is critical for quantum information processing1. Although great progress was made for individual systems, and electron spin resonance (ESR) of single spins with nanoscale resolution has been demonstrated2–4, the understanding of decoherence in many complex solid-state quantum systems requires ultimately controlling the environment down to atomic scales, as potentially enabled by scanning probe microscopy with its atomic and molecular characterization and manipulation capabilities. Consequently, the recent implementation of ESR in scanning tunnelling microscopy5–8 represents a milestone towards this goal and was quickly followed by the demonstration of coherent oscillations9,10 and access to nuclear spins11 with real-space atomic resolution. Atomic manipulation even fuelled the ambition to realize the first artificial atomic-scale quantum devices12. However, the current-based sensing inherent to this method limits coherence times12,13. Here we demonstrate pump–probe ESR atomic force microscopy (AFM) detection of electron spin transitions between non-equilibrium triplet states of individual pentacene molecules. Spectra of these transitions exhibit sub-nanoelectronvolt spectral resolution, allowing local discrimination of molecules that only differ in their isotopic configuration. Furthermore, the electron spins can be coherently manipulated over tens of microseconds. We anticipate that single-molecule ESR-AFM can be combined with atomic manipulation and characterization and thereby paves the way to learn about the atomistic origins of decoherence in atomically well-defined quantum elements and for fundamental quantum-sensing experiments.

Electron Spin Resonance Probe Incorporation into Bioinks Permits Longitudinal Oxygen Imaging of Bioprinted Constructs

PurposeBioprinting is an additive manufacturing technology analogous to 3D printing. Instead of plastic or resin, cell-laden hydrogels are used to produce a construct of the intended biological structure. Over time, cells transform this construct into a functioning tissue or organ. The process of printing followed by tissue maturation is referred to as 4D bioprinting. The fourth dimension is temporal. Failure to provide living cells with sufficient amounts of oxygen at any point along the developmental timeline may jeopardize the bioprinting goals. Even transient hypoxia may alter cells' differentiation and proliferation or trigger apoptosis. Electron paramagnetic resonance (EPR) imaging modality is proposed to permit 4D monitoring of oxygen within bioprinted structures.ProceduresLithium octa-n-butoxy-phthalocyanine (LiNc-BuO) probes have been introduced into gelatin methacrylate (GelMA) bioink. GelMA is a cross-linkable hydrogel, and LiNc-BuO is an oxygen-sensitive compound that permits longitudinal oximetric measurements. The effects of the oxygen probe on printability have been evaluated. A digital light processing (DLP) bioprinter was built in the laboratory. Bioprinting protocols have been developed that consider the optical properties of the GelMA/LiNc-BuO composites. Acellular and cell-laden constructs have been printed and imaged. The post-printing effect of residual photoinitiator on oxygen depletion has been investigated.ResultsModels have been successfully printed using a lab-built bioprinter. Rapid scan EPR images reflective of the expected oxygen concentration levels have been acquired. An unreported problem of oxygen depletion in bioprinted constructs by the residual photoinitiator has been documented. EPR imaging is proposed as a control method for its removal. The oxygen consumption rates by HEK293T cells within a bioprinted cylinder have been imaged and quantified.ConclusionsThe feasibility of the cointegration of 4D EPR imaging and 4D bioprinting has been demonstrated. The proof-of-concept experiments, which were conducted using oxygen probes loaded into GelMA, lay the foundation for a broad range of applications, such as bioprinting with many types of bioinks loaded with diverse varieties of molecular spin probes.

Hydrothermal synthesis of Mn2+- and Cu2+-doped calcium hydroxyapatite: morphological features and importance of EPR insights

This study aims to explore the effects of various hydroxyapatite (HA) doping techniques in depth. For this purpose, two ions with comparable sizes, namely Mn2+ and Cu2+, were selected based on their suitability as dopants for HA in biomedical applications. Moreover, their paramagnetic properties enable sample characterization through electron paramagnetic resonance (EPR) spectroscopy. Two different approaches were employed: (I) ion-substituted α-TCP was used as starting material; (II) foreign ions presented in the solution during the transformation of undoped α-TCP to HA. The foreign ions influenced the hydrolysis process of α-TCP, altering the phase purity and morphology of the products. Doped α-TCP showed a weaker effect, while adding ions to the synthesis solution had substantial impact. Mn-doped α-TCP transformed into plate-like HA particles while Mn2+ ions present in the solution led to the formation of both plate- and rod-shaped particles. In contrast, Cu2+ ions induced the formation of rod-like particles independently of the doping process. Plate-like particles demonstrated higher Brunauer–Emmet–Teller surface area (SBET) than rod-like HA. Each sample exhibited a combination of mesopores and macropores, with mesopores in the range of 15–17 Å being dominant. EPR investigations revealed that Mn2+ and Cu2+ are excellent paramagnetic probes to monitor synthesis reactions of HA and determine the localisation of foreign ions in the material.

Pyrolysis Free Out-of-Plane Co-Single Atomic Sites in Porous Organic Photopolymer Stimulates Solar-Powered CO2 Fixation.

Herein, a facile strategy is illustrated to develop pyrolysis-free out-of-plane coordinated single atomic sites-based M-POP via a one-pot Friedel Craft acylation route followed by a post-synthetic metalation. The optimized geometry of the Co@BiPy-POP clearly reveals the presence of out-of-plane Co-single atomic sites in the porous backbone. This novel photopolymer Co@BiPy-POP shows extensive π-conjugations followed by impressive light harvesting ability and is utilized for photochemical CO2 fixation to value-added chemicals. A remarkable conversion of styrene epoxide (STE) to styrene carbonate (STC) (≈98%) is obtained under optimized photocatalytic conditions in the existence of promoter tert-butyl ammonium bromide (TBAB). Synchrotron-based X-ray adsorption spectroscopy (XAS) analysis reveals the single atom coordination sites along with the metal (Co) oxidation number of +2.16 in the porous network. Moreover, in situ diffuse reflectance spectroscopy (DRIFTS) and electron paramagnetic resonance (EPR) investigations provide valuable information on the evolution of key reaction intermediates. Comprehensivecomputational analysis also helps to understand the overall mechanistic pathway along with the interaction between the photocatalyst and reactants. Overall, this study presents a new concept of fabricating porous photopolymers based on a pyrolysis-free out-of-plane-coordination strategy and further explores the role of single atomic sites in carrying out feasible CO2 fixation reactions.

Synergistic removal of organic and inorganic composite pollutants from water by zero-valent iron activated calcium peroxide

Agricultural non-point source pollution has received widespread attention in recent years due to its characteristics of dispersion, uncertainty, extensiveness and high difficulty in control. Among them, components such as fertilizers, heavy metals and herbicides constitute complex inorganic–organic composite pollution, which poses great threat to agricultural water ecosystem. Therefore, in this study, phosphate (P), lead (Pb) and atrazine (ATZ) as typical pollutants from agricultural non-point sources were investigated to remove collaboratively by constructing an environmentally friendly zero-valent iron (ZVI)-activated calcium peroxide (CaO2) system. At unadjusted initial pH 2.86, with the mass ratio of ZVI/CaO2 1:1, the removal efficiencies of P, Pb and ATZ were 95.3%, 97.4%, and virtually 100%, respectively. The main active species in the ZVI/CaO2 system was identified as hydroxyl radicals (·OH) by quenching experiment, electron spin resonance test and probe experiment. The characterization results showed that P was mainly precipitated in the form of Ca-P and Fe-P species. Pb was mainly adsorbed and reduced by ZVI and precipitated in solution. ATZ was mainly degraded into ten by-products, and the overall toxicity showed a decrease. The influence of pH on the removal efficiencies of pollutants was reflected in the fact that high pH promoted the removal of P and Pb but inhibited the degradation of ATZ. The ZVI/CaO2 system performed well under the influence of humic acid and typical anions. Therefore, this work provides a promising technology for the organic–inorganic co-polluted water treatment.

Biocomposites Based on Electrospun Fibers of Poly(3-hydroxybutyrate) and Nanoplatelets of Graphene Oxide: Thermal Characteristics and Segmental Dynamics at Hydrothermal and Ozonation Impact.

In order to create new biodegradable nanocomposites for biomedicine, packaging, and environmentally effective adsorbents, ultra-thin composite fibers consisting of poly(3-hydroxybutyrate) (PHB) and graphene oxide (GO) were obtained by electrospinning. Comprehensive studies of ultrathin fibers combining thermal characteristics, dynamic electron paramagnetic resonance (ESR) probe measurements, and scanning electron microscopy (SEM) were carried out. It is shown that at the addition of 0.05, 0.1, 0.3, and 1% OG, the morphology and geometry of the fibers and their thermal and dynamic characteristics depend on the composite content. The features of the crystalline and amorphous structure of the PHB fibers were investigated by the ESR and DSC methods. For all compositions of PHB/GO, a nonlinear dependence of the correlation time of molecular mobility TEMPO probe (τ) and enthalpy of biopolyether melting (ΔH) is observed. The influence of external factors on the structural-dynamic properties of the composite fiber, such as hydrothermal exposure of samples in aqueous medium at 70 °C and ozonolysis, leads to extreme dependencies of τ and ΔH, which reflect two processes affecting the structure in opposite ways. The plasticizing effect of water leads to thermal destruction of the orientation of the pass-through chains in the amorphous regions of PHB and a subsequent decrease in the crystalline phase, and the aggregation of GO nanoplates into associates, reducing the number of GO-macromolecule contacts, thus increasing segmental mobility, as confirmed by decreasing τ values. The obtained PHB/GO fibrillar composites should find application in the future for the creation of new therapeutic and packaging systems with improved biocompatibility and high-barrier properties.

Identification of defect centers responsible for thermoluminescence emission in sol-gel synthesized calcium silicate phosphor

The thermoluminescence (TL) of calcium silicate phosphor (CSO) prepared by the sol-gel method and sintered at 1200 °C were investigated. From Tm-Tstop curve, TL emission spectrum and computer deconvolution using electron traps with discrete and continuous distributions, the glow curves were found to be composed of four TL peaks (117, 190, 250 and 275 °C) with a single emission band centered at 370 nm. Electron paramagnetic resonance (EPR) investigation has been carried out to identify the defect centers formed in the CSO phosphor by γ-irradiation and find the centers related to the TL process in the phosphor. At room temperature, three defect centers were observed. The first center, characterized by the principal g-values of 2.014, 2.011, and 2.0080 was assigned to an O− ion. The second center with g-values 2.015, 2.013, and 2.010 is also attributed to an O− ion and is associated with the TL peak at 280 °C. The third center, with an isotropic g-value of 2.0011 was identified as the F+ center (singly ionized oxygen vacancy) and relates to the TL peak at 280 °C.

Different peroxymonosulfate activation and utilization pathways of typical cobalt oxides, cobalt-carbon and carbonaceous composites derived from metal-organic frameworks for pollutant oxidation in wastewater

Cobalt-based persulfate activation system has attracted increasing interests in recent years. However, few studies have focused on the corresponding relationship between different types of catalysts and peroxymonosulfate (PMS) utilization pathway in PMS activation process. To unravel this, three typical cobalt-based catalysts derived from ZIF materials (metal oxides ZMs, metal–carbon composite ZMCs, and etching metal–carbon composite ZCs) were applied in PMS activation system, and acetaminophen (APAP) was used as target contaminant. Quenching experiments and electron paramagnetic resonance (EPR) investigation testified that SO4·− were considered as the dominant reactive oxygen species (ROS) in the ZMs/PMS system, whereas non-radical pathway was dominant in the ZMCs/PMS and ZCs/PMS system. More Co-N species in ZMCs promoted the adsorption of PMS molecules and the formation of metastable PMS-catalyst complex. Electrochemical analysis proved that the improved intrinsic redox potential of metastable PMS-catalyst complex was due to the strong combination of PMS with positively charged Co-N species, resulting in the mass consumption of PMS. In addition, the CoⅣ=O species were mainly generated from single atomic Co or encapsulated Co sites in ZMCs and ZCs. Major degradation intermediates of APAP were detected by liquid chromatograph mass spectrometer (LC-MS) and differences in degradation pathway in three reaction systems were proposed. This study provides new insight into the PMS utilization mechanism during PMS activation process and offered environmentally friendly catalytic process for the degradation of pharmaceutical contaminants in wastewater.

EPR investigation of gamma-irradiated FAMOSER drug for DOSIMETRIC purposes.

Exposure to ionizing radiation can also lead to the formation of stable or unstable radicals in the structures of drugs, as in many materials. The concentrations of these radicals may show a linear dependence on the radiation dose exposed. Since drugs are materials that can be found next to or on radiation victims during a possible nuclear or radiological accident, it is very meaningful to determine the Electron Paramagnetic Resonance (EPR) dosimetric properties of stable radicals in their structures. In this study, the dosimetric properties of Famoser, which is one of the stomach-relieving drugs that people often have with them in their daily life, in the dose range of 10-800Gy were investigated by EPR technique.

Applications of Boron Cluster Supramolecular Frameworks as Metal-Free Chemodynamic Therapy Agents for Melanoma.

Chemodynamic therapy (CDT) is a highly targeted approach to treat cancer since it converts hydrogen peroxide into harmful hydroxyl radicals (OH·) through Fenton or Fenton-like reactions. However, the systemic toxicity of metal-based CDT agents has limited their clinical applications. Herein, a metal-free CDT agent: 2,4,6-tri(4-pyridyl)-1,3,5-triazine (TPT)/ [closo-B12 H12 ]2- (TPT@ B12 H12 ) is reported. Compared to the traditional metal-based CDT agents, TPT@B12 H12 is free of metal avoiding cumulative toxicity during long-term therapy. Density functional theory (DFT) calculation revealed that TPT@B12 H12 decreased the activation barrier more than 3.5 times being a more effective catalyst than the Fe2+ ion (the Fenton reaction), which decreases the barrier about twice. Mechanismly, the theory calculation indicated that both [B12 H12 ]-· and [TPT-H]2+ have the capacity to decompose hydrogen into 1 O2 , OH·, and O2 -· . With electron paramagnetic resonance and fluorescent probes, it is confirmed that TPT@B12 H12 increases the levels of 1 O2 , OH·, and O2 -· . More importantly, TPT@B12 H12 effectively suppress the melanoma growth both in vitro and in vivo through 1 O2 , OH·, and O2 -· generation. This study specifically highlights the great clinical translational potential of TPT@B12 H12 as a CDT reagent.

Native and nonnative reactions in ethanolamine ammonia-lyase are actuated by different dynamics

We address the contribution of select classes of solvent-coupled configurational fluctuations to the complex choreography involved in configurational and chemical steps in an enzyme by comparing native and nonnative reactions conducted at different protein internal sites. The low temperature, first-order kinetics of covalent bond rearrangement of the cryotrapped substrate radical in coenzyme B12-dependent ethanolamine ammonia-lyase (EAL) from Salmonella enterica display a kink, or increase in slope, of the Arrhenius plot with decreasing temperature. The event is associated with quenching of a select class of reaction-actuating collective fluctuations in the protein hydration layer. For comparison, a nonnative, radical reaction of the protein interior cysteine sulfhydryl group with hydrogen peroxide (H2O2) is introduced by cryotrapping EAL in an aqueous H2O2 eutectic system. The low-temperature aqueous H2O2 protein hydration and mesodomain solvent phases surrounding cryotrapped EAL are characterized by using TEMPOL spin probe electron paramagnetic resonance spectroscopy, including a freezing transition of the eutectic phase that orders the protein hydration layer. Kinetics of the cysteine-H2O2 reaction in the EAL protein interior are monitored by DEPMPO spin trapping of hydroxyl radical product. In contrast to the native reaction, the linear Arrhenius relation for the nonnative cysteine-H2O2 reaction is maintained through the solvent-protein ordering transition. The nonnative reaction is coupled to the generic local, incremental fluctuations that are intrinsic to globular proteins. The comparative approach supports the proposal that select coupled solvent-protein configurational fluctuations actuate the native reaction, and suggests that select dynamical coupling contributes to the degree of catalysis in enzymes.

Tetrabromidocuprate(II) complexes with diprotonated 1-hydroxy-4methyl-2-(pyridin-2-yl)-5-phenylimidazole and 1-hydroxy-2-(pyridin-2-yl)-4,5,6,7-tetrahydrobenzimidazole ligands: Relationship between the structure and magnetic properties

Two new tetrabromidocuprate(II) complexes with diprotonated 1-hydroxy-2-(pyridin-2-yl)-4,5,6,7-tetrahydrobenzimidazole (1) and 1-hydroxy-4methyl-2-(pyridin-2-yl)-5-phenylimidazole (2) were synthesized and their structure established from single-crystal X-ray data. Compounds crystallized in the monoclinic space groups P21/n and P21/c, respectively, where tetrabromidocuprate anions formed magnetic chains as inferred from the distances between the halide ions of different [CuBr4]2− units. Magnetization measurements showed that both compounds behave as well-isolated uniform S = 1/2 antiferromagnetic chains described by the one-dimensional Heisenberg antiferromagnetic model with intra-chain exchange interaction 2 J = 23 K (1) and 2 J = 33 K (2) (the Hamiltonian Hˆ=2J∑SˆiSˆi+1). Electron paramagnetic resonance, optical absorption, and density functional theory investigations provided complementary results for 1 and 2. A calculation of exchange coupling constants gave values of 2 J = 24 K (1) and 2 J = 39 K (2), in good agreement with the experiment. The quantum theory of atoms in molecules and non-covalent interaction analyses showed that halogen bonding determined the exchange interaction between [CuBr4]2− units in magnetic chains of these cation–anion compounds.

4-Amino-TEMPO loaded liposomes as sensitive EPR and OMRI probes for the detection of phospholipase A2 activity

This work aims at developing a diagnostic method based on Electron Paramagnetic Resonance (EPR) measurements of stable nitroxide radicals released from “EPR silent” liposomes. The liposome destabilisation and consequent radical release is enzymatically triggered by the action of phospholipase A2 (PLA2) present in the biological sample of interest. PLA2 are involved in a broad range of processes, and changes in their activity may be considered as a unique valuable biomarker for early diagnoses. The minimum amount of PLA2 measured “in vitro” was 0.09 U/mL. Moreover, the liposomes were successfully used to perform Overhauser-enhanced Magnetic Resonance Imaging (OMRI) in vitro at 0.2 T. The amount of radicals released by PLA2 driven liposome destabilization was sufficient to generate a well detectable contrast enhancement in the corresponding OMRI image.