Mn(III)-Catalyzed Radical Cyclization for the Phosphorylation of Heteroarenes via the Reactions of Diphenylphosphine Oxide with Isocyanides/Heteroarenes.

Electron spin dynamics during microwave irradiation are of increasing interest in electron paramagnetic resonance (EPR) spectroscopy, as locking electron spins into a dressed state finds applications in EPR and dynamic nuclear polarization (DNP) experiments. Here, we show that these dynamics can be probed by modern pulsed EPR experiments that use arbitrary waveform generators to produce shaped microwave pulses. We employ phase-modulated pulses to measure Rabi nutations, echoes, and echo decays during spin locking of a BDPA (1,3-bisdiphenylene-2-phenylallyl) radical at 94 GHz EPR frequency. Depending on the initial state of magnetization, different types of echoes are observed. We analyze these distinct coherence transfer pathways and measure the decoherence time , which is a factor of 2–3 times longer than . Furthermore, we use chirped Fourier transform EPR to detect the evolution of magnetization profiles. Our experimental results are well reproduced using a simple density matrix model that accounts for relaxation in the spin lock (tilted) frame. The results provide a starting point for optimizing EPR experiments based on hole burning, such as electron–nuclear double resonance or ELectron–electron DOuble Resonance (ELDOR)-detected NMR.

Electron paramagnetic resonance (EPR) experiments in vitro; spin trapping of the reactive oxygen/nitrogen species (superoxide radicals and nitric oxide, NO); gel zymography measurements in the tumor tissues, in the healthy and tumor-affected bone marrow (BM) samples of rats are carried out. The superoxide and NO generation rates are derived; matrix metalloproteinases (MMP-2 and MMP-9) concentrations are measured. Their changes after the incubation of BM samples with Guerin carcinoma cells at 37 °C are defined. It is shown that the impact of tumor cells on BM manifests in the metabolic disorder, increased concentrations of active forms of MMP-2 and MMP-9, increased production of superoxide and NO radicals. Correlation between the appearance and intensity of the broad EPR signal at g = 2.2–2.4 with the concentrations of active forms of MMP-2 and MMP-9, NO and superoxide radicals’ rates is observed. The obtained spatial and temporal changes of the measured parameters demonstrate the usefulness of the potential application of EPR imaging to study the mechanisms of tumor invasion. The EPR signal may indicate the presence of distant metastases, may become a part of diagnostics and used for the estimation of the therapeutic treatments in the pre-clinical studies. It is proposed that labile iron pool is responsible for the appearance of the EPR signal in tumor and BM samples.

Properly Interpreting Lipid-Protein Specificities in Pulmonary Surfactant

Cellular studies have indicated that some Fe-S proteins, and the aconitases in particular, are targets for nitric oxide. Specifically, NO has been implicated in the intracellular process of the conversion of active cytosolic aconitase containing a [4Fe-4S] cluster, to its apo-form which functions as an iron-regulatory protein. We have undertaken the in vitro study of the reaction of NO with purified forms of both mitochondrial and cytosolic aconitases by following enzyme activity and by observing the formation of EPR signals not shown by the original reactants. Inactivation by either NO solutions or NO-producing NONOates under anaerobic conditions is seen for both enzyme isoforms. This inactivation, which occurs in the presence or absence of substrate, is accompanied by the appearance of the g = 2.02 signals of the [3Fe-4S] clusters and the g approximately 2.04 signal of a protein-bound dinitrosyl-iron-dithiol complex in the d7 state. In addition, in the reaction of cytosolic aconitase, the transient formation of a thiyl radical, g parallel = 2.11 and g perpendicular = 2.03, is observed. Disassembly of the [3Fe-4S] clusters of the inactive forms of the enzymes upon the anaerobic addition of NO is also accompanied by the formation of the g approximately 2.04 species and in the case of mitochondrial aconitase, a transient signal at g approximately 2. 032 appeared. This signal is tentatively assigned to the d9 form of an iron-nitrosyl-histidyl complex of the mitochondrial protein. Inactivation of the [4Fe-4S] forms of both aconitases by either superoxide anion or peroxynitrite produces the g = 2.02 [3Fe-4S] proteins.

Electron paramagnetic resonance investigation of photosynthetic reaction centers from Rhodobacter sphaeroides R-26 in which Fe2+ was replaced by Cu2+. Determination of hyperfine interactions and exchange and dipole-dipole interactions between Cu2+ and QA-

A series of electron spin resonance (ESR) experiments is done to quantitatively measure the concentrations of aqueous 1O2 and ̇OH produced by a surface micro-discharge air plasma device. 1O2 is tested to be existed in the plasma treated solution by using the spin trap of TEMP. However, the unexpected DMPOX spectrum is observed in measuring ̇OH by the spin trap of 5,5-Dimethyl-1-Pyrroline-N-Oxide (DMPO). With more chemical scavenger experiments, it is found that removal of aqueous 1O2 leads to the disappearance of DMPOX in ESR. Therefore, the generation of DMPOX is directly related to the oxidation of DMPO by plasma-produced aqueous 1O2. This oxidation process and interactions between DMPO and chemical scavengers used in experiments can all be well explained by a proposed reaction mechanism. The revelation of interactions between aqueous 1O2 and the spin trap DMPO shows that the observation of spectra of DMPOX in the ESR measurement can be regarded as a marker of high concentrations of plasma-produced 1O2 in liquid. These results also prove the existence of interactions between spin traps and non-targeted plasma-produced reactive species in ESR experiments. Also, these results have offered a better understanding of the use of spin traps such as DMPO in the plasma-induced highly oxidative aqueous environment.

The electrogenerated chemiluminescence (ECL) of semiconductor quantum dots (QDs) is generally believed to be independent of particle sizes or the capping agents used. Herein, we demonstrate that CdTe QDs with different sizes and stabilizers evidently exhibit different ECL behavior in aqueous solution. The ECL of CdTe QDs stabilized by 3-mercaptopropionic acid (MPA) displays two waves at potentials of about +1.17 V and +1.74 V vs. Ag/AgCl, respectively. ECL spectra confirm that the ECL of QDs is attributed to their band gap luminescence, in which the peak positions are changed with QD sizes. The ECL mechanism of CdTe QDs involves superoxide radical generation by reduction of dissolved oxygen at lower potential or water splitting at higher potential. Direct evidence for superoxide radicals in this medium was obtained via electron spin resonance (ESR) experiments. In comparison, the 2-mercaptoethylamine (MEA)-capped CdTe QDs did not exhibit any ECL in air-saturated pH 7.4 PBS. Both ESR and X-ray photon spectroscopy (XPS) experiments revealed that amine groups in MEA-capped QDs were responsible for the absence of ECL. The reaction of an amine group with a superoxide radical leads to the quenching of ECL. The ECL quenching of MPA-capped CdTe QDs was further used to detect melamine. Under the optimum conditions, the inhibited ECL was linear with the logarithm of concentration of melamine within the concentration range of 10⁻⁹ to 10⁻⁵ M and the detection limit was found to be 6.74 × 10⁻¹⁰ M, which was 100-100,000 times lower than that of the most previous methods.

EPR as a complementary tool for the analysis of low-temperature oxidation reactions of crude oils

Electrochemical Oxidative [4+2] Annulation of Different Styrenes toward the Synthesis of 1,2-Dihydronaphthalenes

ZnCl2 Enabled Synthesis of Highly Crystalline and Emissive Carbon Dots with Exceptional Capability to Generate O2⋅–

Chapter 13 - Electron Paramagnetic Resonance

Mate (MT) is a popular South American beverage that has been used as a traditional medicine for centuries, spurring recent interest in its nutraceutical properties. MT is prepared as an infusion of leaves from the Yerba Mate (llex paraguriensis) tree. MT has been reported to have antioxidant properties in vitro and in vivo, but these have not been fully characterized in terms of effects against specific radicals. Accordingly, we examined the antioxidant effects of an MT infusion against hydroxyl and superoxide radicals in both chemical and cell culture assays. MT infusions were prepared at 3.10 g/L in boiling water and diluted to experimental dilutions from this stock. Electron spin resonance (ESR) experiments indicated that MT scavenged hydroxyl radicals (produced via the Fenton reaction) and superoxide radicals (produced via the xanthine/xanthine oxidase enzymatic reaction) at all concentrations tested (P < 0.05). Further controls indicated that superoxide radical scavenging was not due to xanthine oxidase inhibition. MT scavenged hydroxyl radicals and decreased cellular oxygen consumption in a dose-dependent manner in Cr(VI)-stimulated RAW 264.7 cells, based on ESR and oxygraph measurements (P < 0.05). Similarly, MT also inhibited hydroxyl-radical-induced lipid peroxidation and DNA damage in a dose-dependent manner in RAW 264.7 cells, based on malondialdehyde and Comet assay data (P < 0.05). This study indicates that MT possesses potent antioxidant effects against hydroxyl and superoxide radicals in both chemical and cell culture systems, as well as DNA-protective properties. These data further clarify the reported antioxidant effects of Yerba Mate infusions.

Electron paramagnetic resonance imaging and Overhauser imaging are magnetic resonance techniques for detecting paramagnetic substances (i.e. molecules which have one or more unpaired electron(s) in their outer orbitals). The main impetus for developing these techniques is the intriguing possibility of detecting and imaging the distribution of free radicals in the body. Naturally occurring free radicals are widely believed to be involved in the early development of many diseases, so the ability to localize and quantify them in vivo would have profound implications for many areas of biomedical research. Stable free radicals can also be used as `contrast agents', and following their fate in the body can give useful insights into organ function. Some free radicals and paramagnetic solids have the ability to probe the chemical and physical nature of their surroundings, also offering a wide variety of potential applications, in particular the measurement of oxygen concentrations in tissues. Electron paramagnetic resonance (EPR) was first demonstrated in 1945, the same year that nuclear magnetic resonance (NMR) experiments were first carried out. EPR and NMR are very closely related at the fundamental level, differing mainly in the fact that EPR involves a magnetic resonance experiment on unpaired electrons in the sample, while NMR uses atomic nuclei with non-zero spin. On a practical level, the techniques are also closely related, despite the fact that most EPR experiments are continuous-wave, while virtually all NMR is carried out using pulsed, Fourier-transform methods. Overhauser-based techniques combine both flavours of magnetic resonance in EPR/NMR double-resonance experiments. While NMR has found a valuable place in clinical practice, in the form of magnetic resonance imaging (MRI), biomedical EPR is still in its relative infancy, with about twenty research groups world-wide having the capability to use EPR spectroscopy or imaging to study small animals in vivo. It may appear to the casual observer that progress in the field of EPR is much slower than in NMR, but this is not actually the case: EPR is technically much more demanding than NMR, due to the six orders-of-magnitude shorter relaxation times encountered in EPR. Indeed, considerable progress has been made in the technology and applications of EPR-based methods over the last five years, and the field has now developed sufficiently to enable useful biomedical applications to be investigated. The papers presented in this topical issue represent a broad cross-section of the work being carried out in developing and applying EPR and Overhauser techniques in biology and medicine. A number of papers describe recent advances in technology and methods, including continuous-wave, longitudinally detected and pulsed EPR, and Overhauser imaging. Others focus on applications including those using both endogenous and exogenous free radicals. Two of the most promising areas are in the detection of nitric oxide, a ubiquitous, naturally occurring free radical, and in the measurement of local oxygen concentrations by EPR. Both of these topics are covered in this issue. It is both timely and appropriate that Physics in Medicine and Biology, with its strong reputation in the field of physics applied to medicine and biology, should publish a topical issue on this subject, at a time when rapid improvements in technology are being made, and when useful applications are starting to emerge. The guest editors hope that this summary of the state-of-the-art will act as a comprehensive reference work for those in the field, and will encourage others to develop new applications for the techniques, which we believe have a valuable role to play in biomedical research. David J Lurie Antonello Sotgiu Guest Editors

Graphite carbon nitride (g-C3N4) photocatalyst was synthesized via thermal condensation at high temperatures using melamine as a starting material. The structure and properties of the catalyst was characterized by scanning electron microscopy (SEM),X-ray diffraction (XRD),UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), and attenuated total reflection infrared spectroscopy (ATR-IR).The results indicate that the as-synthesized g-C3N4 had a layered structure with a specific surface area of 15.34 m2·g-1 and possed strong visible light absorption capacity. Photocatalytic degradation of 2,4-dichlorophenol (2,4-DCP) using g-C3N4 under visible light irradiation (λ>420 nm) corresponds to the first order kinetics with a reaction rate constant of 0.0113 min-1.After 250 min,the mineralization rate of 2,4-DCP in the presence of 0.67 g·L-1g-C3N4 reached 60%. The degradation efficiency of 2,4-DCP was highly enhanced in weak acid. Trapping experiments and electron spin resonance (ESR) experiments show that superoxide radical (O2·-) was the main active species in the photocatalytic degradation of 2,4-DCP.The main degradation pathways of 2,4-DCP include dechlorination,aromatic ring opening and carbon chain rupture.

Introduction Ciclopirox olamine (CPO), a hydroxypyridone derivative, belongsto antifungal agents used for the treatment of superficial fungalinfections. Recently, it has been reported that CPO acts as apotential chelating agent and influences some cellular processesof the fungus by chelating metal irons.