Electron Paramagnetic Resonance Spin Trapping Research Articles

EPR Investigations of G-C3N4/TiO2 Nanocomposites

The g-C3N4/TiO2 nanopowders prepared by the annealing of melamine and TiO2 P25 at 550 °C were investigated under dark and upon UV or visible-light photoactivation using X- and Q-band electron paramagnetic resonance (EPR) spectroscopy. The EPR spectra of powders monitored at room temperature and 100 K showed the impact of the initial loading ratio of melamine/TiO2 on the character of paramagnetic centers observed. For the photocatalysts synthesized using a lower titania content, the paramagnetic signals characteristic for the g-C3N4/TiO2 nanocomposites were already found before exposure. The samples annealed using the higher TiO2 loading revealed the photoinduced generation of paramagnetic nitrogen bulk centers (g-tensor components g1 = 2.005, g2 = 2.004, g3 = 2.003 and hyperfine couplings from the nitrogen A1 = 0.23 mT, A2 = 0.44 mT, A3 = 3.23 mT) typical for N-doped TiO2. The ability of photocatalysts to generate reactive oxygen species (ROS) upon in situ UV or visible-light photoexcitation was tested in water or dimethyl sulfoxide by EPR spin trapping using 5,5-dimethyl 1-pyrroline N-oxide. The results obtained reflect the differences in photocatalyst nanostructures caused by the differing initial ratio of melamine/TiO2; the photocatalyst prepared by the high-temperature treatment of melamine/TiO2 wt. ratio of 1:3 revealed an adequate photoactivity in both spectral regions.

Detection of the formyl radical by EPR spin-trapping and mass spectrometry.

For the first time we here present the unambiguous identification of the formyl radical (•CHO) by EPR (Electron Paramagnetic Resonance) spectroscopy and mass spectrometry (MS) using DMPO (5,5-dimethyl-1-pyrroline N-oxide) as spin trap at ambient temperature without using any catalyst(s). The •CHO was continuously generated by UV photolysis in closed anoxic environment from pure formaldehyde (HCHO) in aqueous solution. The isotropic hyperfine structure constants of •CHO were determined as aN = 15.72G and aH = 21.27G. The signals were deconvoluted and split by simulation in their single adduct components: DMPO-CHO, DMPO-H and DMPO-OH. We verified our results at first using MNP (2-methyl-2-nitroso-propane) as spin trap with known literature data and then mass spectrometry. Similarly the MNP adduct components MNP-CHO, MNP-H as well as its own adduct, the MNP-2-methyl-2-propyl (MNP-MP) were deconvoluted. Due to the low signal intensities, we had to accumulate single measurements for both spin traps. Using MS we got the exact mass of the reduced •CHO adduct independently confirming the result of EPR detection of formyl radical.

Continuous generation of hydroxyl radicals for highly efficient elimination of chlorophenols and phenols catalyzed by heterogeneous Fenton-like catalysts yolk/shell Pd@Fe3O4@metal organic frameworks

Core/shell Fe3O4-decorated Pd nanoparticles (NPs) hybrids (Pd@Fe3O4) are prepared through a “green”, and one-pot chemical process. The Pd@Fe3O4 hybrids consisted of faceted quasi-spherical Pd nanoparticles (NPs) cores (∼20 nm) surrounded by close-packed Fe3O4 NPs (∼7 nm). To improve the stability and avoid aggregation of Pd@Fe3O4 hybrids in water, hollow Fe-metal organic frameworks (Fe-MOFs) were applied to enwrap Pd@Fe3O4 to obtain yolk/shell structured composites. Sub-10 nm Fe3O4 and Pd NPs close to each other were distributed evenly in the MOFs shell of Pd@Fe3O4@MOFs. The yolk/shell Pd@Fe3O4@MOFs can catalyze the oxidative degradation of chlorophenols and phenols by hydroxyl radicals (OH) decomposed from H2O2. With low molar ratio of H2O2/pollutants, the pollutants are degraded and mineralized efficiently and rapidly. The outstanding catalytic efficiency of Pd@Fe3O4@MOFs is contributed by the fast and continuous generation of OH radicals in Pd@Fe3O4@MOFs suspension which is detected with the electron spin resonance spin-trap technique and a continuous-flow chemiluminescence system. Lack of consumption of hydroperoxyl radicals/superoxide radicals (HO2/O2−) in the Pd@Fe3O4@MOFs-H2O2 system might suggest that the production of OH radicals results from the electron transferring from Pd to Fe3O4 component both in the inner Pd@Fe3O4 and MOF shell, which facilitates fast Fe(III)/Fe(II) redox cycle.

A plasma/liquid microreactor for radical reaction chemistry: An experimental and numerical investigation by EPR spin trapping

In this paper, a novel plasma/liquid microreactor has been developed to generate and inject radical species with the aim to perform chemical synthesis reactions in liquid phase. Plasma has always been considered as a source of reactive species, such as radicals, atoms, electrons, etc., with applications mostly dedicated to surface modifications of materials. By injecting reactive species created by the plasma to the liquid phase, it is possible to initiate liquid phase synthesis reactions. In addition, gas/liquid interactions can be enhanced with a high surface‐area‐to‐volume ratio by confining the plasma and the liquid in diphasic micro‐structured systems. Herein is reported a novel plasma/liquid microreactor for liquid phase radical reactions. Radicals are generated in the gas phase in a steady flow microreactor and then transported to the liquid phase. The spin trapping reaction and the electron paramagnetic resonance (EPR) spectroscopy have been used to identify and quantify the radical species generated in the microreactor. Hydroxyl radicals and hydrogen atoms have been detected and measured in the liquid phase, indicating the huge potential of the microreactor as a handful tool for chemical synthesis.

Oxidative removal of sulfa antibiotics by introduction of activated carbon fiber to enhance the catalytic activity of iron phthalocyanine

Supported metallophthalocyanine catalysts were synthesized by immobilizing covalently amino-containing iron trinitro phthalocyanine (FeMATNPc) on activated carbon fibers (ACF) by deamination to produce ACF-FeTNPc. The introduction of ACF enhanced the decomposition of sulfamethoxazole by FeMATNPc significantly with an obvious improvement in pH tolerance and stability. The oxidative removal of sulfamethoxazole(SMX) in the ACFs-FeTNPc/H2O2 system, based on phase-transfer catalytic oxidation, was investigated in aqueous solution by ultra-performance liquid chromatography. Repetitive tests showed that ACF-FeTNPc could maintain a high adsorption capacity and degradation activity over several cycles. The resulting hybrid structure was confirmed and characterized by X-ray photoelectron and ultraviolet–visible spectroscopy. ACF are rich in free electrons, and the π-conjugated macrocyclic structure of FeMATNPc may present convenient channels for the transfer of free electrons from the ACF, and promote the generation of hydroxyl radicals and high-valence iron species. Electron paramagnetic resonance spin-trap experiments and inhibition and probe studies indicated that free radicals and high-valence iron species reacted in our system.

N1, N14-diferuloylspermine as an antioxidative phytochemical contained in leaves of Cardamine fauriei.

Most Brassicaceae vegetables are ideal dietary sources of antioxidants beneficial for human health. Cardamine fauriei (Ezo-wasabi in Japanese) is a wild, edible Brassicaceae herb native to Hokkaido, Japan. To clarify the main antioxidative phytochemical, an 80% methanol extraction from the leaves was fractionated with Diaion® HP-20, Sephadex® LH-20, and Sep-Pak® C18 cartridges, and the fraction with strong antioxidant activity depending on DPPH method was purified by HPLC. Based on the analyses using HRESIMS and MS/MS, the compound might be N1, N14-diferuloylspermine. This rare phenol compound was chemically synthesized, whose data on HPLC, MS and 1H NMR were compared with those of naturally derived compound from C. fauriei. All results indicated they were the same compound. The radical-scavenging properties of diferuloylspermine were evaluated by ORAC and ESR spin trapping methods, with the diferuloylspermine showing high scavenging activities of the ROO·, O2·-, and HO· radicals as was those of conventional antioxidants.

An Electron Paramagnetic Resonance (EPR) spectroscopy study on the γ-irradiation sterilization of the pharmaceutical excipient l-histidine: Regeneration of the radicals in solution

The effects of γ-radiation sterilization on the parenteral excipient l-histidine were analysed by means of EPR spectroscopy. The irradiation process was found to induce the formation of a deamination radical which was persistent in the solid state. The nature and reactivity of the radicals following dissolution in water was evaluated using spin-trapping EPR experiments. The deamination radical was found to regenerate in solution in the presence of trace metals, potentially leading to radical induced degradation reactions occurring up to an hour after the dissolution process. Understanding this process is significant for the improved design of parental pharmaceutical formulations in which unwanted radical reactions after γ‐radiation sterilization could lead to degradation of active ingredients.

Polysulfides and products of H2S/S-nitrosoglutathione in comparison to H2S, glutathione and antioxidant Trolox are potent scavengers of superoxide anion radical and produce hydroxyl radical by decomposition of H2O2

Exogenous and endogenously produced sulfide derivatives, such as H2S/HS−/S2−, polysulfides and products of the H2S/S-nitrosoglutathione interaction (S/GSNO), affect numerous biological processes in which superoxide anion (O2−) and hydroxyl (OH) radicals play an important role. Their cytoprotective-antioxidant and contrasting pro-oxidant-toxic effects have been reported. Therefore, the aim of our work was to contribute to resolving this apparent inconsistency by studying sulfide derivatives/free radical interactions and their consequent biological effects compared to the antioxidants glutathione (GSH) and Trolox. Using the electron paramagnetic resonance (EPR) spin trapping technique and O2−, we found that a polysulfide (Na2S4) and S/GSNO were potent scavengers of O2− and cPTIO radicals compared to H2S (Na2S), GSH and Trolox, and S/GSNO scavenged the DEPMPO-OH radical. As detected by the EPR spectra of DEPMPO-OH, the formation of OH in physiological solution by S/GSNO was suggested. All the studied sulfide derivatives, but not Trolox or GSH, had a bell-shaped potency to decompose H2O2 and produced OH in the following order: S/GSNO > Na2S4 ≥ Na2S > GSH = Trolox = 0, but they scavenged OH at higher concentrations. In studies of the biological consequences of these sulfide derivatives/H2O2 properties, we found the following: (i) S/GSNO alone and all sulfide derivatives in the presence of H2O2 cleaved plasmid DNA; (ii) S/GSNO interfered with viral replication and consequently decreased the infectivity of viruses; (iii) the sulfide derivatives induced apoptosis in A2780 cells but inhibited apoptosis induced by H2O2; and (iv) Na2S4 modulated intracellular calcium in A87MG cells, which depended on the order of Na2S4/H2O2 application. We suggest that the apparent inconsistency of the cytoprotective-antioxidant and contrasting pro-oxidant-toxic biological effects of sulfide derivatives results from their time- and concentration-dependent radical production/scavenging properties and their interactions with O2−, OH and H2O2. The results imply a direct involvement of sulfide derivatives in O2− and H2O2/OH free radical pathways modulating antioxidant/toxic biological processes.

Antimicrobial Intervention by Photoirradiation of Grape Pomace Extracts via Hydroxyl Radical Generation.

The annual production of grape worldwide amounts to almost 70 million tons, and around 80% is used for winemaking. The two major wastes from winemaking process, pomace and lees account for 20 and 7% of the grapes, respectively. They have been expected as a valuable resource to be recycled because they are rich in polyphenols. Polyphenols possess prooxidatve activity as well as antioxidative one just like a two sides of a coin. A typical example of the prooxidative activity is antibacterial activity of catechins. The activity is exerted through oxidation of phenolic hydroxyl moiety coulpled with reduction of dissolved oxygen leading to hydrogen peroxide (H2O2) generation. In addition, once the oxidation of phenolic hydroxyl moiety is augmented by photoirradiation, highly reactive hydroxyl radical (·OH) is generated. Accordingly, there have been several reports showing that photoirardiation of polyphenols exerts bactericidal activity via ·OH generation. This review focuses mainly on antimicrobial intervention by photoirradiation of grape pomace extract in relation to ·OH generation analyzed by an electron spin resonance-spin trapping method.

Rapid-Flow and Spin-Trapping ESR Study on Carbonyl-Conjugated Radicals of Modified Poly(vinyl alcohol) Bearing 1,2-Propanediol Pendant Moiety as Intermediates of Graft Copolymerization

Abstract Based on the results of rapid-flow electron spin resonance (RF-ESR) and spin-trapping (ST-ESR) measurements, carbonyl-conjugated radicals derived from the vicinal diol moiety (2, i.e., the head-to-head structure) of poly(vinyl alcohol) (PVA) have been proposed to be the most probable intermediate species involved in the initial stages of the graft reaction of PVA with methyl methacrylate (MMA). A modified poly(vinyl alcohol) (PPVA) bearing a 1,2-propanediol pendant moiety (3) with a molar ratio of 8% (based on the monomer unit) was prepared to clarify the role of the carbonyl-conjugated radicals of PPVA in the graft reaction with MMA. The RF-ESR spectra observed for the mixtures composed of PPVA, hydrogen peroxide (HPO) or ammonium persulfate (APS), and Ti2(SO4)3 (pH ca. 2) revealed the formation of four radical species (A, B1, B2, and C) derived from PPVA. By comparison of the RF-ESR spectra observed for PPVA and PVA, species A (g = 2.0041) was confirmed to be the pendant derived radical of PPVA, and species B1 and B2 (g = 2.0023) and C (g = 2.0032) were assigned to be the PVA main-chain derived radicals. Species B1 and B2 were deduced to be a pair of carbonyl-conjugated radicals (4, 5, R1–CH2–CO–•CH–CH2–R2) derived from the vicinal diol (2), and species C was assigned to be the secondary alcohol (1) derived radicals (6, R1–CH2–•COH–CH2–R2). In terms of g value and proton hyperfine coupling constants (hfcc), the molecular structure of species A was ascribed to be the carbonyl-conjugated radical of the pendant moiety (7, •CH2–CO–CHR1R2). The results of ST-ESR measurements using the sodium salt of 3,5-dibromo-4-nitroso-benzene-sulfonate (DBNBS) show that a pair of pendant radicals (7) and (8, O=CH–•CH–CHR1R2) was formed in the graft polymerization reaction solutions containing APS or HPO as an oxidant (80 °C, pH ca. 2). The grafted copolymers of PPVA and PVA (PPVA-g-MMA and PVA-g-MMA) were separated from similar graft reaction solutions composed of APS and MMA after heating at 70 °C for 1 h (pH ca. 2), and the grafting efficiencies of PPVA (PPVAge%) and PVA (PVAge%) were, respectively, estimated to be 4% and 2%. The molecular and electronic structure of the carbonyl-conjugated radicals derived from the main-chain (4, 5) and from the pendant moiety (7, 8) of PPVA will be discussed in relation to the reaction mechanisms of the initial reaction stage of the graft copolymerization with MMA.

Ultrahigh efficient degradation activity of single- and few-layered MoSe2 nanoflowers in dark by piezo-catalyst effect

We have demonstrated an ultrahigh degradation activity of the single-layer and few-layered MoSe2 nanoflowers for decomposing the Rhodamine (RhB) dye by the piezo-catalyst effect. The MoSe2 nanoflowers can successfully decompose the RhB dye by 90% in 30s through the application of the mechanical force (e.g., ultrasonic vibration) in dark. The size of the MoSe2 nanoflowers has a diameter of less than 3µm, which exhibits a great number of the single- and few-layers with a plentiful amount of active surface sites. The interlayer spacing between each single-layer MoSe2 is ~ 0.67nm. The piezoresponse force microscopy (PFM), and the tunneling atomic force microscopy (TUNA), further evidence that the MoSe2 nanoflowers exhibit a significantly piezoelectric potential as created by the internal electric fields in different polarization domains of the single- and few-layered MoSe2. The observed kobs rate constant is 0.3 (ppms−1) with an ultra-fast degradation rate of ~ 69,889ppmL mole−1s−1. This is the fastest degradation rate in the dark among all reported catalysts. A redox process of the MoSe2 nanoflowers as induced by mechanical force in dark have been evidenced by XPS spectra. The electron paramagnetic resonance (EPR) spin trapping with 5,5-dimethylpyrroline-1-oxide (DMPO) spectra indeed demonstrated the formation of the hydroxyl radical from the MoSe2 nanoflowers during the ultrasonic vibration in dark, which is the major reactive oxygen species (ROS) for destroying the dye molecules. This is first work to demonstrate the very efficient catalyst and redox processes by piezo-catalyst effect using the MoSe2 nanoflowers.

Improvement of the method to estimate the relative reaction rate constants of hydroxyl radical with polyphenols using ESR spin trap: X-ray irradiation of water with a flowing system

UV-photolysis of hydrogen peroxide is a useful technique to produce hydroxyl radical. However, it is not an appropriate method to estimate the reactivity of polyphenols with hydroxyl radicals because many of the polyphenol derivatives also absorb the UV-light to generate hydroxyl radicals. In this study, X-ray irradiation of water with a flowing system was applied to estimate the reactivity of hydroxyl radicals with polyphenols using electron spin resonance (ESR) spin trap. The obtained relative reaction rates reasonably agreed with previous data by pulse radiolysis. This method will be a useful technique to estimate the reactivity of antioxidants including polyphenols with hydroxyl radicals.

Formation of artifactual DMPO-OH spin adduct in acid solutions containing nitrite ions

We investigated aqueous solutions containing nitrite ions and DMPO (5,5-dimethyl-1-pyrroline-N-oxide) by electron spin resonance (ESR) in the pH range from 1 to 6. A DMPO-OH signal was observed below pH 3.0 in the presence of nitrite ions, whereas in the absence of nitrite ion, an extremely weak signal was observed below pH 1.5. Addition of methanol, a hydroxyl radical scavenger, to this system did not lead to the appearance of a detectable DMPO-CH2OH signal. The possibility of this DMPO-OH signal being due to a genuine spin trapping process with hydroxyl radical was, therefore, ruled out. The reactivities of reactive nitrogen species (RNS) in this system with DMPO have also been investigated by density functional theory (DFT) at the IEFPCM (water)/B3LYP/6–311 + G ** level of theory. On the basis of the pH dependence of the signal intensity and the redox potential E° (versus SHE) calculated by DFT theory, we propose that the origin of this signal is “inverted spin trapping” via one-electron oxidation of DMPO by H2ONO+, followed by the nucleophilic addition of water. Prevention of these false-positive results when detecting hydroxyl radical using ESR spin trapping requires an awareness of both the presence of nitrite ions in the solution and the solution pH.

Real-time monitoring of superoxide anion radical generation in response to wounding: electrochemical study.

BackgroundThe growth and development of plants is deleteriously affected by various biotic and abiotic stress factors. Wounding in plants is caused by exposure to environmental stress, mechanical stress, and via herbivory. Typically, oxidative burst in response to wounding is associated with the formation of reactive oxygen species, such as the superoxide anion radical (O2•−), hydrogen peroxide (H2O2) and singlet oxygen; however, few experimental studies have provided direct evidence of their detection in plants. Detection of O2•− formation in plant tissues have been performed using various techniques including electron paramagnetic resonance spin-trap spectroscopy, epinephrine-adrenochrome acceptor methods, staining with dyes such as tetrazolium dye and nitro blue tetrazolium (NBT); however, kinetic measurements have not been performed. In the current study, we provide evidence of O2•− generation and its kinetics in the leaves of spinach (Spinacia oleracea) subjected to wounding.MethodsReal-time monitoring of O2•− generation was performed using catalytic amperometry. Changes in oxidation current for O2•− was monitored using polymeric iron-porphyrin-based modified carbon electrodes (φ = 1 mm) as working electrode with Ag/AgCl as the reference electrode.ResultThe results obtained show continuous generation of O2•− for minutes after wounding, followed by a decline. The exogenous addition of superoxide dismutase, which is known to dismutate O2•− to H2O2, significantly suppressed the oxidation current.ConclusionCatalytic amperometric measurements were performed using polymeric iron-porphyrin based modified carbon electrode. We claim it to be a useful tool and a direct method for real-time monitoring and precise detection of O2•− in biological samples, with the potential for wide application in plant research for specific and sensitive detection of O2•−.

Cold atmospheric plasma enhances osteoblast differentiation.

This study was designed to assess the effects of cold atmospheric plasma on osteoblastic differentiation in pre-osteoblastic MC3T3-E1 cells. Plasma was irradiated directly to a culture medium containing plated cells for 5 s or 10 s. Alkaline phosphatase (ALP) activity assay and alizarin red staining were applied to assess osteoblastic differentiation. The plasma-generated radicals were detected directly using an electron spin resonance-spin trapping technique. Results show that plasma irradiation under specific conditions increased ALP activity and enhanced mineralization, and demonstrated that the yield of radicals was increased in an irradiation-time-dependent manner. Appropriate plasma irradiation stimulated the osteoblastic differentiation of the cells. This process offers the potential of promoting bone regeneration.

Antidiabetic, antioxidant and anti inflammatory properties of water and n-butanol soluble extracts from Saharian Anvillea radiata in high-fat-diet fed mice

Ethnopharmacological relevanceAccording to Saharian traditional medicine, Anvillea radiata Coss. & Dur. (Asteraceae) has been valued for treating a variety of ailments such as gastro-intestinal, liver and pulmonary diseases, and has gained awareness for its beneficial effect on postprandial hyperglycemia. However, to best of our knowledge, no detailed study of the antidiabetic curative effects of this plant has been conducted yet. Aim of the studyTo determine the hypoglycemic and antidiabetic effect of dietary supplementation with Anvillea radiata extracts on high-fat-diet (HFD)-induced obesity and insulin resistance in C57BL/6J mice in relation with antioxidant, anti-inflammatory, pancreatic beta-cells and skeletal muscle protection, and digestive enzyme inhibiting properties. Materials and methodsSix extracts (water soluble and organic) from aerial parts of the plant were analyzed phytochemically (total phenolic and flavonoid content) and screened for in vitro superoxide (by chemiluminescence) and hydroxyl radical (by electron paramagnetic resonance spin-trapping) scavenging, antioxidant (DPPH, TRAP and ORAC assays), xanthine oxidase, metal chelating, α-amylase and α-glucosidase inhibitory property, and protective effects on copper-induced lipoprotein oxidation. Then selected hydroalcoholic and aqueous extracts were assessed for toxicity in normal human lung fibroblasts and A549 cancer cells using FMCA and MTT assays. Two water-soluble extracts having the best overall properties were assessed for their (i) protective effect at 1−15µg/mL on metabolic activity of rat insulinoma-derived INS-1 cells exposed to hyperglycemic medium, and (ii) acute hypoglycemic effect on 16-weeks HFD-induced diabetic mice. Then diabetic mice were administered HFD supplemented by extracts (up to 150mg/kg/day) for 12 additional weeks using standard diet as control and the antidiabetic drug, metformin (150mg/kg), as positive control. Then the antidiabetic, anti-inflammatory and antioxidant activity of extracts were determined. ResultsOf the highly efficient polyphenolics-enriched hydroalcoholic and ethyl acetate extracts, the lyophilized aqueous (AQL) and butanol extracts were not toxic in cells (≤ 400µg/mL) or when given orally in normal mice (≤ 2000mg/kg), exerted a dose-dependent hypoglycemic action in diabetic mice, which was maximal at the dose of 150mg/kg. Upon administering this dose for 12 weeks, both extracts significantly ameliorated body weight control capacity, recovery of plasma glucose and insulin level, reduced oxidative stress in blood, myocardial and skeletal muscles, and improved hyperlipidemic and inflammatory status. Moreover, diabetes-related complications were optimally ameliorated by oral therapy based on halved doses (75mg/kg) of a mixture of AQL and metformin. ConclusionsCurrent investigation supports the traditional medicinal usage of Anvillea radiata and suggests that both readily accessible and low-cost bio-extracts have the potency to develop an antihyperglycemic, antihyperlipidemic and protective agent against beta-cells and muscle dysfunction at doses compatible with the common practices of indigenous people for the management of metabolic disorders.

Evaluation of Hydroxyl Radical and Alkyl-oxy Radical Scavenging Activity of Coffee by ESR Spin Trapping Method

Evaluation of Hydroxyl Radical and Alkyl-oxy Radical Scavenging Activity of Coffee by ESR Spin Trapping Method

P 045 - The activation of the endoperoxide ascaridole in Leishmania

Endoperoxides (EP) are successfully used in malaria therapy. It was shown in a mouse model that the EP ascaridole (Asc) is useful for the treatment of cutaneous leishmaniasis. The current study explored the activation of Asc and artemisinin (Art) in biomimetic systems and inside Leishmania tarentolae promastigotes (LtP) as model for pathogenic Leishmania in comparison to J774 macrophages. Using ESR spin-trapping we identified isopropyl radicals arising from reduction by Fe 2+ in cell-free systems. Combined GC/NMR analysis confirmed the loss of isopropyl residues from Asc. In LtP carbon-centered radicals were identified in the presence of Asc and Art by ESR spin-trapping. Both Asc and Art inhibited the viability in LtP with IC50 values in the low µM range, while IC50 values for J774 macrophages were considerably higher. A similar structure without EP bridge (1,4-cineole) resulted in no detectable radicals and less cytotoxicity in LtP. The IC50 values for LtP viability in the presence of Asc or Art were increased by the spin trap DMPO. ICP-OES measurements revealed that in LtP the total iron concentration was twice as high as values in J774 macrophages. Studies of the labile iron pool (LIP) in LtP by low temperature ESR revealed an oxidation of the LIP by Asc. These data demonstrate that radical formation from Asc/Art in LtP is an essential part of their antileishmanial mechanism.

Investigation of the Halogenate-Hydrogen Peroxide Reactions Using the Electron Paramagnetic Resonance Spin Trapping Technique.

The differences in the mechanism of the halogenate reactions with the same oxidizing/reducing agent, such as H2O2 contribute to the better understanding of versatile halogen chemistry. The reaction between iodate, bromate, and chlorate with hydrogen peroxide in acidic medium at 60 °C is investigated by using the electron paramagnetic resonance (EPR) spin trapping technique. Essential differences in the chemistry of iodate, bromate, and chlorate in their reactions with hydrogen peroxide have been evidenced by finding different radicals as governing intermediates. The reaction between KIO3 and H2O2 is supposed to be the source of IO2• radicals. The KBrO3 and H2O2 reaction did not produce any EPR signal, whereas the KClO3-H2O2 system was found to be a source of HO• radical. Moreover, KClO3 dissolved in sulfuric acid without hydrogen peroxide produced HO• radical as well. The minimal-core models explaining the origin of obtained EPR signals are proposed. Current findings suggested the inclusion of IO2• and HOO• radicals, and ClO2• and HO• radicals in the particular kinetic models of iodate-hydrogen peroxide and chlorate-hydrogen peroxide systems, as well as possible exclusion of BrO2• radical from the kinetic scheme of the bromate-hydrogen peroxide system. Obtained results may pave the way for understanding more complex, nonlinear reactions of these halogen-containing species.

Simultaneous estimation of scavenging capacities of peach extract for multiple reactive oxygen species by fluorescence fingerprint method

In this study, the potential of using fluorescence fingerprint, also known as fluorescence excitation–emission matrix, for estimating the scavenging capacity of peach extract on reactive oxygen species (ROS) was investigated. Samples from each of the five cultivars (Asama Hakuto, Hakuho, Kawanakajima Hakuto, Natsukko and Ougonto) were freeze-dried and crushed. The scavenging capacities of peach extracts for the target ROS (hydroxyl, superoxide, alkoxyl radicals and singlet oxygen) were measured by electron paramagnetic resonance spin trapping method. Fluorescence fingerprints of the same samples were obtained. Partial least squares regression analysis was carried out to develop prediction models for ROS scavenging capacity. The models were assessed by external validation. Fluorescence fingerprint was found to accurately estimate the scavenging capacity for the alkoxyl and superoxide radicals with the prediction error of 0.06mmoltroloxeq./mL and 0.31mmolα-lipoicacideq./mL with a coefficient of determination of prediction (R2P) of 0.78 and 0.91, respectively.