Organic Free Radicals Research Articles

A Mechanistic Study on the Oxidative Degradation of Dibenzazepine Derivatives by Manganese(III) Complexes in Acidic Sulfate Media

ABSTRACTThe oxidative degradation of tricyclic antidepressants (TCA) was studied in the presence of a large excess of the oxidizing agent manganese(III) and its reduced form manganese(II) sulfate in acidic media. The products were detected and identified using UV–vis, ESI‐MS, IR, and EPR methods. The mechanism of the reaction was studied for the following two classes of TCA: 10,11‐dihydro‐5H‐dibenz[b, f]azepines and dibenz[b, f]azepines. The oxidative degradation between dibenz[b, f]azepines and the manganese(III) ions resulted in the formation of substituted acridine with the same substituent as in the origin dibenz[b, f]azepine derivative. The pseudo–first‐order rate constants (kobs) were determined for the degradation process. The dependences of the observed rate constants on the [MnIII] with a zero intercept were linear. The reaction between 10,11‐dihydro‐5H‐dibenz[b, f]azepines, and the manganese(III) sulfate ion resulted in oxidative dehydrogenation, which proceeded via the formation of the following two intermediates: a free organic radical and a dimer. Further oxidation of the second intermediate led to a positively charged radical dimer as the single final product. Linear dependences of the pseudo–first‐order rate constants (kobs) on the [MnIII] with a zero intercept were established for the degradation of 10,11‐dihydro‐5H‐dibenz[b, f]azepines. The observed rate constants were dependent on the [H+] and independent of the [TCA] within the excess concentration range of the manganese(III) complexes used in the isolation method. The radical product of the degradation of 10,11‐dihydro‐5H‐dibenz[b, f]azepines was not stable in the aqueous solution and was subsequently transformed to a nonradical dimer in the next slower step. The observed rate constants were independent of the [MnIII], independent of the [H+] and increased slightly with increasing TCA concentrations when TCA was used in excess. The mechanistic consequences of all of these results are discussed.

High field electron paramagnetic resonance characterization of electronic and structural environments for paramagnetic metal ions and organic free radicals in Deepwater Horizon oil spill tar balls.

In the first use of high-field electron paramagnetic resonance (EPR) spectroscopy to characterize paramagnetic metal-organic and free radical species from tar balls and weathered crude oil samples from the Gulf of Mexico (collected after the Deepwater Horizon oil spill) and an asphalt volcano sample collected off the coast of Santa Barbara, CA, we are able to identify for the first time the various paramagnetic species present in the native state of these samples and understand their molecular structures and bonding. The two tar ball and one asphalt volcano samples contain three distinct paramagnetic species: (i) an organic free radical, (ii) a [VO](2+) containing porphyrin, and (iii) a Mn(2+) containing complex. The organic free radical was found to have a disc-shaped or flat structure, based on its axially symmetric spectrum. The characteristic spectral features of the vanadyl species closely resemble those of pure vanadyl porphyrin; hence, its nuclear framework around the vanadyl ion must be similar to that of vanadyl octaethyl porphyrin (VOOEP). The Mn(2+) ion, essentially undetected by low-field EPR, yields a high-field EPR spectrum with well-resolved hyperfine features devoid of zero-field splitting, characteristic of tetrahedral or octahedral Mn-O bonding. Although the lower-field EPR signals from the organic free radicals in fossil fuel samples have been investigated over the last 5 decades, the observed signal was featureless. In contrast, high-field EPR (up to 240 GHz) reveals that the species is a disc-shaped hydrocarbon molecule in which the unpaired electron is extensively delocalized. We envisage that the measured g-value components will serve as a sensitive basis for electronic structure calculations. High-field electron nuclear double resonance experiments should provide an accurate picture of the spin density distribution for both the vanadyl-porphyrin and Mn(2+) complexes, as well as the organic free radical, and will be the focus of follow-up studies.

Synthesis and in vitro phantom NMR and MRI studies of fully organic free radicals, TEEPO-glucose and TEMPO-glucose, potential contrast agents for MRI

Two organic radical contrast agents, TEMPO-Glc and TEEPO-Glc, were synthesized and their stabilities and contrast enhancing properties were tested with in vitro NMR and MRI experiments.

Physicochemical characteristics, oxidative capacities and cytotoxicities of sulfate-coated, 1,4-NQ-coated and ozone-aged black carbon particles

Black carbon (BC) particles play important roles in climate change, visibility impairment, atmospheric reaction process, and health effect. The aging processes of BC alter not only atmospheric composition, but also the physicochemical characteristics of BC itself, thus impacting the environment and health effects. Here, three types of BC including sulfate-coated, 1,4-naphthoquinone (1,4-NQ)-coated, and O3-aged BC are presented. The morphologies, structures, extraction components, the amount of water-soluble organic carbon (WSOC) and free radical intensities of the three types of BC particles are examined by transmission electron microscopy, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), ultraviolet–visible spectrophotometry, total organic carbon detector and electron paramagnetic resonance, respectively. Dithiothreitol (DTT) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide assays are utilized to assess the changes in oxidative capacity and cytotoxicity towards murine alveolar macrophage cells. The orders of DTT activities and cytotoxicities of the particles are both arranged as follows: BC/1,4-NQ>BC/O3>BC>BC/sulfate, mainly because 1,4-NQ owned high oxidative potential and cytotoxicity, while sulfate did not exhibit oxidative capacity and cytotoxicity. The insoluble components of particles contribute most of the total DTT activity, whereas either water or methanol extract is minor contributor. DTT activity was positively correlated with both WSOC content and free radical intensity, with the correlation between DTT activity and WSOC content was stronger than that between DTT activity and free radical intensity.

High-Energy and High-Power Electrochemical Energy Storage Based on Dual Intercalation/Radical Electrodes

Li-ion and related battery technologies will be important for years to come. However, society needs energy storage that exceeds the energy and power of common Li-ion batteries.1,2 Many prospective applications of batteries require improving both energy density and rate capability. The simultaneous improvement of these two parameters is not sufficiently addressed by state-of-the-art approaches. High capacity lithium intercalation materials often exhibit poor ionic and electronic conductivity which limit rate capability. Battery electrodes based on polymers bearing organic free radicals allow for exceptionally high rates but fall short in meeting energy density requirements.3,4 Here, we combine the advantages of both storage principles, to form battery electrodes capable of delivering the capacity of the high-energy intercalation material and intermittently the high rate capability of the radical material. First, we must understand the processes that occur in the cell on discharge and charge to fully take advantage of the potential of the concept.We will discuss recent results on the detailed elucidation of the charge transfer mechanism in the so formed dual radical/intercalation electrodes, materials aspects, thermodynamic and kinetic considerations. We combine synthetic, spectroscopic and advanced electroanalytical methods to gain insight into the governing processes.1. B. Scrosati, J. Hassoun, Y.-K. Sun, Energy Environ. Sci., 4, 3287 (2011).2. M.M. Thackeray, C. Wolverton, E.D. Isaacs, Energy Environ. Sci., 5, 7854 (2012).3. K. Oyaizu, H. Nishide, Adv. Mat., 21, 2339 (2009).4. T. Janoschka, M.D. Hager, U.S. Schubert, Adv. Mat., 24, 6397 (2012).

ChemInform Abstract: Streamlining Organic Free Radical Synthesis Through Modern Molecular Technology. From Polymer Supported Synthesis to Microreactors and Molecular Reactors

AbstractReview: 88 refs.

Chemical Characterization and Antioxidant Activities of Different Sulfate Content of λ-Carrageenan Fractions from Edible Red Seaweed Chondrus ocellatus

In recent years, sulfated polysaccharides from marine algae have been demonstrated to have many activities including antioxidant activities. But whether degraded sulfated polysaccharides from Chondrus ocellatus have antioxidant activities, and what effects their sulfate content may have on those activities has not been reported. The aim of this study is to explore the antioxidant activities of λ-carrageenan fractions from edible red seaweed Chondrus ocellatus. In the present study, λ-carrageenan from Chondrus ocellatus was degraded by microwave, yielding five products of different molecular weights. Three sulfated polysaccharide fractions (CF1, CF2, and CF3) were isolated from one of the degraded λ-carrageenans (PC2) by anion-exchange column chromatography. In this study, the effects of the three polysaccharide fractions on hydroxyl radicals, superoxide radicals, organic free radical DPPH, H2O2 induced hemolysis of rat erythrocytes and lipid peroxidation in rat liver microsome were investigated. The results indicated that IR spectrum results indicated that these sulfated polysaccharide fractions had similar structures, but differed in their sulfate content. Chemical analysis indicated that CF1 had the lowest sulfate content (2.9%), while sulfate content in CF2 and CF3 was 7.8% and 37.5% respectively. CF3 had stronger scavenging activity on superoxide radical and hydroxyl radical than the other fractions (P<0.05). CF3 had the strongest scavenging activity on DPPH. the highest inhibitor of lipid peroxidation was CF3, with an IC50 of 0.087 mg/mL, and inhibitory rate reaching 90% at 1 mg/mL. All of the three fractions exhibited stronger scavenging activity at high concentration. In conclusion, sulfate group content of polysaccharides also effect on their biological activities, and which is important for antioxidant activities.

Formation of environmentally persistent free radicals as the mechanism for reduced catechol degradation on hematite-silica surface under UV irradiation

Iron is rich in soils, and is recently reported to form stable complexes with organic free radicals, generating environmentally persistent free radicals (EPFRs). The observation may challenge the common viewpoint that iron is an effective catalyst to facilitate the degradation of various organic chemicals. But no study was specifically designed to investigate the possible inhibited degradation of organic chemicals because of the formation of EPFRs in dry environment. We observed that catechol degradation under UV irradiation was decreased over 20% in silica particles coated with 1% hematite in comparison to uncoated silica particles. Stabilized semiquinone or quinine and phenol radicals were involved in HMT-silica system. EPFR formation was thus the reason for the reduced catechol degradation on HMT-silica surface under UV irradiation at ambient temperature. EPFRs should be incorporated in the studies of organic contaminants geochemical behavior, and will be a new input in their environmental fate modeling.

Organic Free Radicals in Clathrate Hydrates Investigated by Muon Spin Spectroscopy

Very little is known about the behavior of free H atoms and small organic radicals inside clathrate hydrate structures despite the relevance of such species to combustion of hydrocarbon hydrates. Muonium is an H atom analog, essentially a light isotope of hydrogen, and can be used to probe the chemistry of H atoms and transient free radicals. We demonstrate the first application of muon spin spectroscopy to characterize radicals in clathrate hydrates. Atomic muonium was detected in hydrates of cyclopentane and tetrahydrofuran, and muoniated free radicals were detected in the hydrates of cyclopentene and 2,5-dihydrofuran, indicating rapid addition of muonium to the organic guest. Muon avoided level-crossing spectra of the radicals in hydrates are markedly different to those of the same radicals in pure organic liquids at the same temperature, and this can be explained by limited mobility of the enclathrated radicals, leading to anisotropy in the hyperfine interactions.

Modification of Carbon Electrodes by Anodic Oxidation of Organic Anions

Functionalization of carbon surfaces was first carried out in electrode pre-treatments under drastic electrolysis conditions. As a result of these treatments, the electrode carbon surfaces were modified without selectivity with a wide variety of oxygenated functional groups. However, this lack of selectivity was partially overshot with some electrochemical strategies of covalent immobilization, such as the reduction of aryldiazonium, arylsulfonium and iodonium salts, the oxidation of amines, alkynes and arylacetates. In a variant of these direct methods, the oxidation of the carbon surfaces in presence of alcohols and alkyltrimethylsilanes has also been developed. This sort of derivatization has opened the possibility to incorporate a wide variety of functional groups according to the desired applications. In the majority of these methods, reactive intermediates such as organic free radicals and carbocations are generated, which react with the sp2 carbon atoms of the surface to produce covalently modified electrodes. In the particular case of the oxidation process of carboxylates, the loss of carbon dioxide is accompanied with the formation of free radicals and by analogy, it is proposed in this work that other organic anions are also susceptible to be oxidized to yield free radicals that could be covalently attached to carbon electrodes.

Determination of Organic Acid Composition and Free Radical Scavenging Capacity of Kefir

Determination of Organic Acid Composition and Free Radical Scavenging Capacity of Kefir

Rapid in situ synthesis of silver nanoparticles on the distal facet of a fiber by laser-induced photo-reduction

We explore a novel and rapid route for fabricating silver nanoparticles on the distal facet of an optical fiber. The reduction of neutral silver particles relies on the reaction between silver ions and organic free radicals initiated by the photolysis of photoinitiators. A similar approach has been extended to the fabrication of a silver nanoparticle array at the extremity of a fiber bundle. The size and number of silver nanoparticles can be tuned by controlling the laser exposure doses. The results of the synthesis can be envisaged via in situ measurement of their optical transmission rate after the photosynthesis process.

Application of termite nest for adsorption of Cr(VI)

This work proposes the use of tree termite nest as an adsorbent for the reduction/removal of Cr(VI) present in aqueous solution. In laboratory experiments, adsorption of Cr(VI) was sensitive to pH in the range investigated (2–5), with maximum adsorption capacity achieved at pH 2 (3.70 ± 0.04 mg g−1, representing 93.2% removal of Cr). The termite nest was characterized by off-line pyrolysis GC/MS (py-GC/MS), infrared spectroscopy (FTIR), and electron paramagnetic resonance spectroscopy (EPR). Pyrolysis of the adsorbent produced a complex mixture of aromatic compounds, including the guaiacyl and syringilic derivatives that are characteristic of lignocellulosic materials. Infrared spectroscopy revealed deprotonation of the carboxylic acid group of the biomass with increasing pH, which was associated with a decrease in the capacity for adsorption of Cr(VI). The EPR g-factor for the termite nest samples varied between 2.0037 and 2.0038, indicating the presence of organic free radicals that were responsible for the redox reaction. A second line with g-factor values of 1.9790, only observed for the samples after contact with Cr(VI) solutions at different pH values, was assigned to Cr(III)-Cr(III) exchange coupled pairs, which explained the capacity of the adsorbent to retain a large portion of the Cr(III) ions produced after reduction of Cr(VI) to Cr(III). Fixed-bed column experiments showed that the termite nest had a maximum adsorption capacity of 18.60 mg Cr g−1, an adsorption efficiency varying between 60.8 and 97.4%, and a desorption efficiency varying between 54.5 and 91.4%, for three successive cycles. The adsorbent presented excellent performance in the removal of chromium under acidic conditions, with the advantage that it could be regenerated and reused.

Modulating Crystal Packing and Magnetic Properties of Nitroxide Free Radicals by Halogen Bonding

By combining a halogen bonding donor of 1,4-diiodotetrafluorobenzene (1,4-DITFB) or 1,2-diiodotetrafluorobenzene (1,2-DITFB) with 4-benzoyloxy-2,2,6,6-tetramethyl-piperidine-1-oxy free radical (BTEMPO, 1), two novel cocrystals, BTEMPO·1,4-DITFB (2) and BTEMPO·2(1,2-DITFB) (3), featuring a one-dimensional (1D) zigzag chain and a cyclic tetrameric structure, respectively, were constructed via halogen bonding. Furthermore, by tuning the halogen bonding between BTEMPO and halogen bonding donors, the packing modes of organic free radicals in both 2 and 3 are successfully modulated to result in side-by-side 1D mode in 2 and head-to-head dimer manner in 3. Magnetic studies reveal that in all compounds the organic radicals are antiferromagnetically coupled; however, the magnetic coupling in 2 and 3 is stronger than that in 1, indicating the modulating effect of halogen bonding on magnetic properties that are further confirmed by quantum chemistry calculations.

Interaction of S-Nitrosoglutathione with Methemoglobin Under Conditions of Modeling Carbonyl Stress

The Maillard reaction is the key process in protein modification during pathologies connected with carbonyl stress. It was shown in system modeling that Maillard reaction interaction of L-lysine (L-lys) with methylglyoxal (MG) led to the formation of compounds reducing methemoglobin (metHb). Under the above conditions and in the presence of S-nitrosoglutathione (GSNO), metHb nitrosylation took place. Processes of metHb reduction and nitrosylation had the lag phase that was dependent on the presence of oxygen (O2) in the reaction mixture. Oxygen interacting with organic free radicals of the Maillard reaction inhibited hemoglobin (Hb) reduction and hence Hb nitrosylation during the first minutes of the reaction. It was also shown that the yield of organic free-radical intermediates of the L-lys with MG was increased in the presence of GSNO and metHb. All effects described could be a result of the formation of active red-ox GSNO derivates in the Maillard reaction. These derivates are probably mediators of one-electron oxidation of dialkylimine by MG. Anion radicals of S-nitrosothiols can function as such mediators.

An unexpected copper catalyzed ‘reduction’ of an arylazide to amine through the formation of a nitrene intermediate

Azido nitrobenzoxadiazole (NBD) was observed to undergo a ‘reduction’ reaction in the absence of an obvious reducing agent, leading to amine formation. In the presence of an excess amount of DMSO, a sulfoxide conjugate was also formed. The ratio of these two products was both temperature- and solvent-dependent, with the addition of water significantly enhancing the ratio of the ‘reduction’ product. Two intermediates of the azido-NBD reaction in DMSO were trapped and characterized by low-temperature EPR spectroscopy. One was an organic free radical (S=1/2) and another was a triplet nitrene (S=1) species. A mechanism was proposed based on the characterized free radical and triplet intermediates.

Tar Balls from Deep Water Horizon Oil Spill: Environmentally Persistent Free Radicals (EPFR) Formation During Crude Weathering

Tar balls collected from the Gulf of Mexico shores of Louisiana and Florida after the BP oil spill have shown the presence of electron paramagnetic resonance (EPR) spectra characteristic of organic free radicals as well as transition metal ions, predominantly iron(III) and manganese(II). Two types of organic radicals were distinguished: an asphaltene radical species typically found in crude oil (g = 2.0035) and a new type of radical resulting from the environmental transformations of crude (g = 2.0041-47). Pure asphaltene radicals are resonance stabilized over a polyaromatic structure and are stable in air and unreactive. The new radicals were identified as products of partial oxidation of crude components and result from the interaction of the oxidized aromatics with metal ion centers. These radicals are similar to semiquinone-type, environmentally persistent free radicals (EPFRs) previously observed in combustion-generated particulate and contaminated soils.

13C NMR and EPR spectroscopic evaluation of oil shale mined soil recuperation

In this work, native forest soil (NFS) organic matter (SOM) sample and SOM samples from a neighboring forest soil area of an oil shale mine which is being rehabilitated for thirty years (RFS) were analyzed. X-band electron paramagnetic resonance (EPR) and solid-state 13C nuclear magnetic resonance (NMR) spectroscopies were used to evaluate the soil reclamation of the Brazilian oil shale mining process. Two-dimensional heterospectral correlation studies of the results obtained from EPR and 13C NMR were used to obtain information about SOM structures and their interactions with residual paramagnetic metal ion. The signal of the residual metallic oxycation, VO2+ correlated positively with uronic acid-type hydrophilic organic structures, determined from the 13C NMR spectra, and correlated negatively with the organic free radical (OFR) signal associated with oxygen atoms (g = 2.0042). The hydrophobic aromatic structures correlate positively with the EPR OFR signal associated with carbon atoms (g = 2.0022). The data from the two spectroscopic magnetic techniques show that the used recuperation process is effective.

A New Horizon of DNP technology: Application to In-vivo 13C Magnetic Resonance Spectroscopy and Imaging.

Dynamic nuclear polarization (DNP) is an emerging technique for increasing the sensitivity (>10,000-fold) of magnetic resonance spectroscopy and imaging (MRSI), in particularly for low-γ nuclei. DNP methodology is based on polarizing nuclear spins in an amorphous solid state at low temperature (ca. 1 K) through coupling of the nuclear spins with unpaired electron spins that are added to the sample via an organic free radical. In an amorphous solid state, the high electron spin polarization can be transferred to the nuclear spins by microwave irradiation. While this technique has been utilized in solid-state research for many years, it is only recently that dissolution methods and the required hardware have been developed to produce the high nuclear polarization provided by DNP to produce injectable hyperpolarized solutions suitable for in vivo studies. It has been applied to a number of 13C-labeled cell metabolites in biological systems and their real-time metabolic conversion has been imaged. This review focuses the DNP methodology briefly and the significant molecules investigated to date in preclinical cancer models, in terms of their downstream metabolism in vivo or the biological processes that they can probe. In particular, conversion between hyperpolarized 13C-labeled pyruvate and lactate, catalyzed by lactate dehydrogenase, has been shown to have a number of potential applications such as diagnosis, staging tumor grade and monitoring therapy response. Strategies for making this technique more viable to use in clinical settings has been discussed.

Spin labeling ESR investigation of the molecular environment of soil interacting with chemical organic contaminants

This manuscript elucidates the influence of special functional groups of organic xenobiotic chemicals on partly simultaneous molecular binding mechanisms. Organic xenobiotics are released as contaminants into the environment and are partially bound to soil constituents, such as humic substances (HS) and the mineral phase. The interaction of chemical contaminants with HS of soil was investigated using a labeling technique of soil samples with stable nitroxide radicals as model contaminants. These nitroxide radicals only differed in one functionality, a hydroxy or an amino functional group. Electron spin resonance (ESR) analyses of contaminated soil samples showed that the interaction was a multistage process that comprised an initial increase in the concentration of free organic radicals of soil influenced by contaminants with hydroxy or amino functionality, a decrease in the polarity of the molecular environment of soil, and a change in mobility of contaminant molecules. Towards the end of interaction, the concentration of free organic radicals usually decreased. Binding of contaminants to soil constituents via specific functionality was revealed detecting a change in their ESR spectra. Basing on the ESR analyses, a two-way exchange of protons' electron pairs between contaminants and HS was hypothesized to interpret the beginning of interaction.