Free Radical Signal Research Articles

P-nitrophenol degradation by pine-wood derived biochar: The role of redox-active moieties and pore structures

Biochar can both adsorb and degrade p-nitrophenol (PNP); however, the PNP degradation mechanism has not been well investigated. We prepared two biochars at pyrolysis temperatures of 500 °C (B500) and 700 °C (B700). Although B500 showed much stronger free radical signals (which are associated with organic degradation, according to previous studies), the apparent PNP degradation was approximately 3 times higher in the B700 system. The degradation increased significantly after the biochars were washed with water. According to a quantitative analysis of the sorption and degradation and two-compartment first-order kinetics modeling of the apparent removal kinetics, sorption occurred mainly in the initial period, whereas degradation continued throughout the removal process. The PNP degradation rate constant depended mainly on the external surface area at a relatively low concentration (200 mg/L) and was controlled by the microporous surface area at a relatively high concentration (800 mg/L). In addition, the apparent degradation did not depend on the biochar particle size. Therefore, PNP degradation may be related to the three-dimensional structure of the biochar in addition to the exposed external surface. The well-developed pore structure, more accessible surface, and larger electron exchange capacity of B700 may promote electron transfer between the biochar and PNP, and thus accelerate PNP degradation. This study demonstrates that various properties of the biochar may contribute to PNP degradation.

Magnetic field effect on the free induction decay of hydroxyl radicals (OH) in the terahertz region.

The effect of an external longitudinal magnetic field on the optical free induction decay from a free radical is observed for the first time. The experiments were performed on a rotational transition of the hydroxyl radical, OH (2Π3/2(J = 1) ← 2Π3/2(J = 0) at 83.8 cm-1), using a terahertz free electron laser. In contrast to the results of the experiments with a stable paramagnetic molecule, NO, the observed effect of an external magnetic field on the free induction decay from hydroxyl radicals is more complicated. A longitudinal magnetic field leads to the rotation of the polarization plane of the FID radiation and to an additional modulation of the signal intensity. The angle of the rotation of the plane of polarization is large, in agreement with the theoretical predictions. The observed FID kinetics in the time domain are in semi-quantitative agreement with the modeling. This observation opens an opportunity for the selective detection of weak signals of short-lived reactive paramagnetic free radicals from overwhelming signals that originate from stable non-paramagnetic species by polarization discrimination.

Synergistic Reinforcing and Stabilizing Effect of Carbon Black–Zinc Dimethacrylate on the Ethylene Propylene Diene Monomer and Improving Mechanism of Sealing Resilience

EPDM/Carbon black (CB)-Zinc dimethacrylate (ZDMA) vulcanizate was prepared. Compared with EPDM, addition of CB-ZDMA resulted in remarkable raise in tensile/compressive properties, storage/loss modulus and glass transition temperature, superior to that of vulcanizates with CB or ZDMA. Moreover, the increase in compression set and decrease in stress relaxation coefficient were inhibited during stress-thermal oxidation aging, resulting in enhancement of durable sealing resilience performance of vulcanizate. Combination of CB-ZDMA facilitated dispersion of CB in matrix, and improved interfacial interaction and dispersion of ZDMA with matrix. A multiple covalent/ionic crosslinking network structure with increasing crosslinking density formed in composite during vulcanization. It maintained stable free radical signal and crosslinking density, presented minimum degradation rate and carbonyl index growth rate, and surface damage was inhibited during aging, leading to retardation of crosslinking, degradation and o...

Radiation-induced free radicals from different milk powders and its possible use as radiation dosimeters

Abstract Electron paramagnetic resonance spectroscopy (EPR) has been used to assess the free radical signal in different kinds of milk powder. Buffalos, colostrum’s, butter, milk cows, goat, camel and commercial milk before and after γ-ray irradiation. Moreover, un-irradiated milk samples exhibited weak signals, but upon increasing the absorbed doses EPR signal intensities were increased. The useful dose range was from 0.1 to 11 kGy. The results show that the stability of the signal of milk powder in relation to gamma irradiation was in order as follows: buffalo’s buttermilk; camel; cows; commercial milk; goat; buffalo’s; and colostrum milk. This study was recommended to use EPR as a new technique in an evaluation, quality control of dairy products and food irradiation applications. These milk powders undergo the influence of γ-rays can be applied as radiation dosimeters. Moreover, it can be used in food preservation, food irradiation processing, medical sterilization and water treating.

Effect of Decabromodiphenyl Ether on Free Radicals in the Degradation of P-nitrophenol under Ultraviolet Light

Polybrominated diphenyl ether as an additive bromine flame retardant is widely used in industrial products, due to its strong fat-soluble and biological accumulating, it is a new type of ecological risk of environmental organic pollutants, and thus, resulted in more and more serious and widespread pollution. In view of the increasingly severe environmental conditions, this paper selected decabromodiphenyl ether(Deca-BDE) as the research object, based on the limited research data, taking its flame retardant mechanism as the starting point, and preliminarily discussed how the photodegradation of organic pollutants when Deca-BDE coexisted with other organic pollutants was affected by Deca-BDE. The experimental results show that, when ten Deca-BDE coexist with organic pollutants, the signal strength of organic pollutants photodegradation produce free radicals decreases, the preliminary judgment is Deca-BDE have a shielding effect on free radical signal, or Deca-BDE curbed the photodegradation of organic pollutants, lead to degradation of intermediate reduction, to detect the radical signal intensity weaken. Of course, there are still many areas for improvement and improvement in this study, which need to be proved by further research methods. This study is expected to provide guidance for the scientific classification and treatment of organic pollutants.

γ-Irradiation Induced Decomposition of Polydopamine Nanoparticles under Ambient Condition

Polydopamine nanoparticles (PDAPs) with an average particle size of about 180 nm were irradiated with a 60Co source. The morphology, thermal stability and free radical signal of γ-irradiated PADPs ...

Radiochromic and radiofluorogenic solid state polymer dosimeter; a third signal: Electron Paramagnetic Resonance (EPR)

A solid-state polymeric dosimeter has been developed. The solid-state dye-doped polymeric dosimeter comprises the photo-curable polymer materials Poly(ethylene glycol)-diacrylate (PEGDA) and 2-Hydroxyethyl-methacrylate (HEMA) and the radiochromic leuco-dye 4,4′,4″- Triamino-triphenyl –acetonitrile. Using a photo-curable polymer blend facilitates a tight control of the polymerization process and hence the properties of the solid-state dosimeter. The radiation sensitive leuco-dye responds to ionising radiation by forming a stable free radical – a triphenylmethyl dye. This free radical has strong colour, and is fluorescent because it is dissolved in the solid polymeric material. Both physical properties can be measured optically. The free radical, however, provides a third signal as it is paramagnetic and hence can be detected by means of Electron Paramagnetic Resonance (EPR) spectroscopy. The EPR signal makes it possible to measure the radiation-induced free radical signal free from optical artefacts of the polymer material. Results from irradiations using a low-dose-rate cobalt-60 gamma irradiator shows an EPR signal measured using a Bruker EMX EPR spectrometer for the solid polymeric dosimeter, whose peak-to-peak amplitude is linear with the dose in the medical dose range and saturates for higher doses (100 Gy).

Characterization of eNOS ser‐600 Phosphorylation: A Link to the Cell Cycle

Nitric oxide (NO) is a gaseous, free‐radical signaling molecule produced by nitric oxide synthases (NOS). NO has a variety of cellular and physiological functions ranging from maintaining cardiovascular homeostasis to neurotransmission. In low concentrations NO is deemed physiologically crucial and in high concentrations NO is understood to be pathophysiological. The role of NO in the cell cycle is less understood, it is likely cell type specific and concentration dependent, in many cases low levels of NO promote proliferation and prevent apoptosis; at high levels NO has been shown to arrest cells and cause apoptosis. Endothelial nitric oxide synthase (eNOS) is one of three isoforms in the NOS family, it is the most regulated of the isoforms. Regulations include protein‐protein interactions and posttranslational modifications. The most commonly studied and well understood posttranslational modification of eNOS is phosphorylation. This work builds on our laboratories discovery of the ser‐600 phosphorylation site in the auto‐inhibitory loop of eNOS. Our work confirms this site is modulated in cells and links it to the cell cycle using immunofluorescence, flow cytometry, western blot analysis, in vitro kinase assays, and in vitro eNOS activity assays.Support or Funding InformationThis work was supported by NIH grant # R15 GM110634‐01A1 to Dr. Carol Chrestensen.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Observation of Free Induction Decay Signals of OH Radicals Excited by Terahertz Free-Electron Laser Pulses

The first experimental observation of free induction decay signals of free radicals is reported. The signals were observed on the line of the rotational transition of OH radicals in the terahertz region. OH radicals were generated by the chemical reaction of excited oxygen atoms with water molecules. Radicals were excited by free-electron laser radiation pulses. Free induction decay radiation was detected in real time using ultra fast terahertz radiation detectors. The possibility of using free induction decay signals of radicals as a new method for detection of free radicals in combustion processes is discussed.

Fire Detection Algorithm Combined with Image Processing and Flame Emission Spectroscopy

Fire poses a significant risk to the safety, health, and property of people around the world. However, traditional ‘‘point sensor’’ fire detection techniques for indoor buildings based on air particles, air temperatures, and smoke have a low sensitivity, long response time, and poor stability. Therefore, video-based fire detection has become a particularly efficient and important method for detecting the early signs of a fire. Due to image blur, low illumination, flame-like interference and other factors, there is a certain error rate of fire recognition using video flame recognition methods. According to our previous study of a multi-feature flame recognition algorithm, a novel flame recognition algorithm based on free radical emission spectroscopy during combustion is investigated in this paper. First, multiple features are extracted from the video images by employing our proposed processing scheme. Then, the features are post-processed by a temporal smoothing algorithm to eliminate the error recognition rate, which is caused by the similar characteristics of objects between flame-like and real flame areas. In the temporal smoothing experiments, the proposed method achieves the true positive rates of 0.965 and 0.937 for butane flames and forest fire, respectively. Additionally, the spectral signals of OH, CH, C2 and other free radicals in the combustion objects were acquired by the spectrometer. The vibrational temperature and rotational temperature are calculated after identification of the A2Δ → X2Π transition of the CH (410–440 nm). The flames-like are completely rejected by the proposed method in the validation experiment. In the subsequent butane combustion experiment, the vibrational temperature of the butane was 4896 K, and the rotational temperature was 2290 K. The experimental results show that real fires can be precisely recognized and that the combustion temperature can be determined from the CH emission spectroscopy. This novel method provides a new viewpoint for fire detection and recognition.

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

Air injection is a promising method for enhanced oil recovery (EOR) in both conventional and unconventional oil sources. It is widely accepted that oxidation reactions between oil and injected air determine the success of an air injection process. In this study, electron paramagnetic resonance (EPR) was introduced as a new route to investigate the occurrence of low-temperature oxidation (LTO) and its behavior by monitoring the signals of free radicals. The EPR experiments were conducted for the different crude oil samples (light, medium and heavy) heated in both static air and flow air (air-bubbling) conditions under different temperatures from 25 °C to 180 °C. The results showed that the free-radical concentrations exhibited a good correspondence on the heating temperature. Furthermore, nuclear magnetic resonance (NMR), Fourier-transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) experiments were carried out to help to analyze the oxidation process and verify the EPR results. It turned out that the EPR results can be well supported by NMR, FTIR and DSC data, which indicates that proposed EPR monitoring method can be applied as a fast and low-cost technique to investigate LTO under mild reaction conditions. Simultaneously, the combination of EPR, NMR, FTIR and DSC can help to better understand the LTO mechanism and to monitor the application of in-situ combustion technique in the field.

Mechanisms for ·[Formula: see text] and ·OH Production on Flowerlike BiVO4 Photocatalysis Based on Electron Spin Resonance.

Many studies have focused on the use of BiVO4 as a photocatalyst, but few have investigated the production of free radicals during the photocatalytic process. Following synthesis of flowerlike BiVO4 and characterization by X-ray diffraction (XRD), Raman spectroscopy, Scanning electron microscopy (SEM) Scanning electron microscopy (EDX), UV-Vis and XPS, we successfully prepared BiVO4. Then we used electron spin resonance (ESR) to determine the production and degradation of individual active free radicals, including the superoxide radical (·) and the hydroxyl radical (·OH). In the first experiment, we used ESR to detect the signals of free radicals (· and ·OH) under varying oxygen conditions. The results shown that in addition to production by ·, ·OH could also be produced by oxidation of h+ to OH−. In the next experiment, we detected ·OH under varying pH to identify the result of the first experiment, and found that signal intensities increased with increasing pH, indicating the mechanism for ·OH production. Finally, we conducted a trapping experiment to examine free radical degradation mechanisms. We identified ·OH and h+ as the main active free radicals and showed the complete production about ·OH. These results improve current knowledge of free radical production mechanisms, which can be used to enhance the photocatalytic performance of BiVO4.

Nitric oxide reduces oxidative stress in cancer cells by forming dinitrosyliron complexes

The chelatable iron pool (CIP) is a small but chemically significant fraction of total cellular iron. While this dynamic population of iron is limited, it is redox active and capable of generating reactive oxygen species (ROS) that can lead to oxidative stress which is associated with various pathologies. Nitric oxide (•NO), is a free radical signalling molecule that regulates numerous physiological and pathological conditions. We have previously shown that macrophages exposed to endogenously generated or exogenously administered nitric oxide (•NO) results in its interaction with CIP to form dinitrosyliron complexes with thiol containing ligands (DNICs). In this study we assessed the consequences of DNIC formation in cancer cells as •NO is known to be associated with numerous malignancies. Incubation of cancer cells with •NO led to a time and dose dependent increase in formation of DNICs. The formation of DNICs results in the sequestration of the CIP which is a major source of iron for redox reactions and reactive oxygen species (ROS) generation. Therefore, we set out to test the antioxidant effect of •NO by measuring the ability of DNICs to protect cells against oxidative stress. We observed that cancer cells treated with •NO were partially protected against H2O2 mediated cytotoxicity. This correlated to a concomitant decrease in the formation of oxidants when •NO was present during H2O2 treatment. Similar protective effects were achieved by treating cells with iron chelators in the presence of H2O2. Interestingly, •NO decreased the rate of cellular metabolism of H2O2 suggesting that a proportion of H2O2 is consumed via reactions with cellular iron. When the CIP was artificially increased by supplementation of cells with iron, a significant decrease in the cytoprotective effect of •NO was observed. Notably, •NO concentrations, at which cytoprotective and antioxidant effects were observed, correlated with concentration-dependent increases in DNIC formation. Collectively, these results demonstrate that •NO has antioxidant properties by its ability to sequester cellular iron. This could play a significant role in variety of diseases involving ROS mediated toxicity like cancer and neurodegenerative disorders where •NO has been shown to be an important etiologic factor.

Evidences of extracellular abiotic degradation of hexadecane through free radical mechanism induced by the secreted phenazine compounds of P. aeruginosa NY3

The aim of this work was to investigate the effects of secreted extracellular phenazine compounds (PHCs) on the degradation efficiency of alkanes by P. aeruginosa NY3. Under aerobic conditions, the PHCs secreted by P. aeruginosa NY3 initiate the oxidation of alkanes outside cells, in coupling with some reducing agents, such as β-Nicotinamide adenine dinucleotide, reduced disodium salt (NADH) or reduced glutathione (GSH). This reaction might be via free radical reactions similar to Fenton Oxidation Reaction (FOR). P. aeruginosa NY3 secretes pyocyanin (Pyo), 1-hydroxyphenazine (HPE), phenazine-1-carboxylic acid (PCA), and phenazine-1-amide (PCN) simultaneously. The cell-free extracellular fluid containing these four PHCs degrades hexadecane effectively. The observation of Electron Spin Resonance (EPR) signals of superoxide anion radical (O2−), hydroxyl radical (OH) and/or carbon free radicals (R) both in vivo and in vitro suggested the degradation of hexadecane could be via a free radical pathway. Secretion of PHCs has been found to be characteristic of Pseudomonas which is often involved in or related to the degradation of organic pollutants. Our work suggested that certain organic contaminants may be oxidized through ubiquitously extracellular abiotic degradation by the free radicals produced during bio-remediation and bio-treatment.

Age-dependent redox status in the brain stem of NO-deficient hypertensive rats

BackgroundThe brain stem contains important nuclei that control cardiovascular function via the sympathetic nervous system (SNS), which is strongly influenced by nitric oxide. Its biological activity is also largely determined by oxygen free radicals. Despite many experimental studies, the role of AT1R-NAD(P)H oxidase-superoxide pathway in NO-deficiency is not yet sufficiently clarified. We determined changes in free radical signaling and antioxidant and detoxification response in the brain stem of young and adult Wistar rats during chronic administration of exogenous NO inhibitors.MethodsYoung (4 weeks) and adult (10 weeks) Wistar rats were treated with 7-nitroindazole (7-NI group, 10 mg/kg/day), a specific nNOS inhibitor, with NG-nitro-L-arginine-methyl ester (L-NAME group, 50 mg/kg/day), a nonspecific NOS inhibitor, and with drinking water (Control group) during 6 weeks. Systolic blood pressure was measured by non-invasive plethysmography. Expression of genes (AT1R, AT2R, p22phox, SOD and NOS isoforms, HO-1, MDR1a, housekeeper GAPDH) was identified by real-time PCR. NOS activity was detected by conversion of [3H]-L-arginine to [3H]-L-citrulline and SOD activity was measured using UV VIS spectroscopy.ResultsWe observed a blood pressure elevation and decrease in NOS activity only after L-NAME application in both age groups. Gene expression of nNOS (youngs) and eNOS (adults) in the brain stem decreased after both inhibitors. The radical signaling pathway triggered by AT1R and p22phox was elevated in L-NAME adults, but not in young rats. Moreover, L-NAME-induced NOS inhibition increased antioxidant response, as indicated by the observed elevation of mRNA SOD3, HO-1, AT2R and MDR1a in adult rats. 7-NI did not have a significant effect on AT1R-NADPH oxidase-superoxide pathway, yet it affected antioxidant response of mRNA expression of SOD1 and stimulated total activity of SOD in young rats and mRNA expression of AT2R in adult rats.ConclusionOur results show that chronic NOS inhibition by two different NOS inhibitors has age-dependent effect on radical signaling and antioxidant/detoxificant response in Wistar rats. While 7-NI had neuroprotective effect in the brain stem of young Wistar rats, L-NAME- induced NOS inhibition evoked activation of AT1R-NAD(P)H oxidase pathway in adult Wistar rats. Triggering of the radical pathway was followed by activation of protective compensation mechanism at the gene expression level.

Degradation of p-Nitrophenol by Lignin and Cellulose Chars: H2O2-Mediated Reaction and Direct Reaction with the Char.

Chars and other black carbons are reactive toward certain compounds. Such reactivity has been attributed to reduction of O2 by persistent free radicals in the solid to H2O2, which then back-reacts with the solid to generate reactive oxygen species (ROS; especially HO•). We studied the decomposition of p-nitrophenol (PNP) by pure lignin and cellulose chars aged in moist air or a vacuum at room temperature for up to a month. In air, the chars chemisorbed oxygen, a portion of which was liberated as H2O2 when the char was submerged in water. The evolved H2O2 was simultaneously decomposed by the char. PNP reacted predominantly in the sorbed state and only reduction products (phenol, catechol) were identified. Aging the char in air sharply (within hours) reduced H2O2-producing capacity and free radical concentration, but more gradually reduced PNP decay rate over the month-long period. PNP decay was only modestly suppressed (12-30%) by H2O2 removal (catalase), and had little effect on the free radical signal (<6 radicals annihilated per 1000 PNP reacted). Contrasting with previous studies, the results show that direct reaction of PNP with char predominates over H2O2-dependent reactions, and the vast majority of direct-reacting sites are nonradical in character. Nonradical sites are also responsible in part for H2O2 decomposition; in fact, H2O2 pretreatment depleted PNP reactive sites. Lignin char was generally more reactive than cellulose char. The Fe impurity in lignin played no role. The results are relevant to the fate of pollutants in black carbon-rich environments and the use of carbons in remediation.

Peptide-Functionalized Fluorescent Particles for In Situ Detection of Nitric Oxide via Peroxynitrite-Mediated Nitration.

Nitric oxide (NO) is a free radical signaling molecule that plays a crucial role in modulating physiological homeostasis across multiple biological systems. NO dysregulation is linked to the pathogenesis of multiple diseases; therefore, its quantification is important for understanding pathophysiological processes. The detection of NO is challenging, typically limited by its reactive nature and short half‐life. Additionally, the presence of interfering analytes and accessibility to biological fluids in the native tissues make the measurement technically challenging and often unreliable. Here, a bio‐inspired peptide‐based NO sensor is developed, which detects NO‐derived oxidants, predominately peroxynitrite‐mediated nitration of tyrosine residues. It is demonstrated that these peptide‐based NO sensors can detect peroxynitrite‐mediated nitration in response to physiological shear stress by endothelial cells in vitro. Using the peptide‐conjugated fluorescent particle immunoassay, peroxynitrite‐mediated nitration activity with a detection limit of ≈100 × 10−9 m is detected. This study envisions that the NO detection platform can be applied to a multitude of applications including monitoring of NO activity in healthy and diseased tissues, localized detection of NO production of specific cells, and cell‐based/therapeutic screening of peroxynitrite levels to monitor pronitroxidative stress in biological samples.

Physi-chemical and sorption properties of biochars prepared from peanut shell using thermal pyrolysis and microwave irradiation

Microwave irradiation (MW) is an effective technique in heating and pyrolysis. This study compared the properties of peanut shell-biochars produced using MW and muffle furnace (FN). At the same pyrolysis temperature, MW biochars preserved more biomass (as indicated by their higher yields and higher abundance of functional groups) and possessed larger surface areas due to the high abundance of micropores. MW biochars generally exhibited higher adsorption of carbamazepine (CBZ) and bisphenol A (BPA) than FN biochars. However, their surface area-normalized sorption was lower, suggesting that the inner pores may not be fully available to CBZ and BPA sorption. We observed significant free radical signals in both types of biochars. Although CBZ and BPA did not degrade in the biochar sorption systems, the potential role of stronger free radical signals in MW biochars for organic contaminant control may not be overlooked in studies with other chemicals.

Effects of the components in rice flour on thermal radical generation under microwave irradiation

The relationships between radical generation under microwave irradiation and the components of various types of rice flour were investigated. Electron paramagnetic resonance (EPR) spectroscopy was used to characterize the radicals found in rice flour samples. The EPR spectra revealed that several types of radical (carbon-centered, tyrosyl and semiquinone) were localized in the starch and protein fractions of the rice flour. The signal intensity of the free radicals was observed to increase exponentially with increasing microwave power and residence time. The rice bran samples exhibited the greatest free radical signal intensity, followed by the brown rice samples and the white rice samples. This finding was consistent for both the native and the microwaved samples. The ratio of rice starch to rice protein also played an important role in the generation of radicals.

Catechol degradation on hematite/silica-gas interface as affected by gas composition and the formation of environmentally persistent free radicals.

Environmentally persistent free radicals (EPFRs) formed on a solid particle surface have received increasing attention because of their toxic effects. However, organic chemical fate regulated by EPFRs has rarely been investigated, and this information may provide the missing link in understanding their environmental behavior. Previous studies have suggested that the reduction of transition metals is involved in EPFRs formation. We thus hypothesize that an oxidative environment may inhibit EPFRs formation in particle-gas interface, which will consequently release free radicals and accelerate organic chemical degradation. Our result indicates that a 1% hematite coating on a silica surface inhibited catechol degradation in N2, especially at low catechol loadings on solid particles (SCT). However, under an O2 environment, catechol degradation decreased when SCT was <1 μg/mg but increased when SCT was >1 μg/mg. Stable organic free radicals were observed in the N2 system with g factors in the 2.0035–2.0050 range, suggesting the dominance of oxygen-centered free radicals. The introduction of O2 into the catechol degradation system substantially decreased the free radical signals and decreased the Fe(II) content. These results were observed in both dark and light irradiation systems, indicating the ubiquitous presence of EPFRs in regulating the fate of organic chemicals.