Electron Spin Resonance Spin-trapping Technique Research Articles

Effect of Dental Local Anesthetics on Reactive Oxygen Species: An In Vitro Study.

Introduction Oxidative stress, an imbalance between reactive oxygen species (ROS) production and antioxidant defenses, plays an important role in various dental diseases. Local anesthetics are frequently used in dentistry. The potential antioxidant activity of dental local anesthetics can contribute to dental practice. Therefore, this study aimed to investigate the ROS-scavenging activities of three commonly used dental local anesthetics, lidocaine, prilocaine, and articaine, focusing on their effects on hydroxyl radicals (HO•) and superoxide anions (O2 •-). Materials and methods The electron spin resonance (ESR) spin-trapping technique was employed to specifically measure the ROS-scavenging activities of these local anesthetics at varying concentrations. Results Lidocaine, prilocaine, and articaine exhibited concentration-dependent HO•-scavenging activities, with IC50 values of 0.029%, 0.019%, and 0.014%, respectively. Lidocaine and prilocaine showed concentration-dependent O2 •--scavenging activity, with IC50 values of 0.033% and 0.057%, respectively. However, articaine did not scavenge O2 •-. Conclusions The proactive use of dental local anesthetics may mitigate oxidative injury and inflammatory damage through direct ROS scavenging. However, further research is needed to elucidate the specific mechanisms underlying the antioxidant effects of these dental local anesthetics and their potential impact on the dental diseases associated with oxidative stress.

(Invited) Operando EPR Study on Radicals in Anion-Exchange Membrane Fuel Cells

In the rapidly developing modern society, there is an urgent need for the wide-ranging availability of advanced and eco-friendly energy sources. One of the possible alternatives is the application of anion exchange membrane fuel cells (AEMFCs) with a catalyst reducing dioxygen efficiently. These promising devices can revolutionize the energy sector since they practically produce no pollution. However, to make them more widely used, several obstacles must be overcome. As a result, vast-ranging investigations focus on improving the properties of conductive polymer membranes [1] and catalysts for the oxygen reduction reaction (ORR) [2]. The durability of the membrane electrode assembly (MEA) is one of the critical requirements for the successful commercialization of anion exchange membrane fuel cells (AEMFCs). Despite significant impacts of nucleophilic degradation on ion-exchange capability and the anionic conductivity of investigated membranes, it is believed to affect only cationic sites of membrane polymers and thus cannot explain the reported loss in the mechanical strength of degraded AEMs. Such a phenomenon might be related to polymer backbone degradation caused by free radicals. This was widely described in the literature in the case of fuel cells using proton-conducting membranes [3] but barely mentioned for AEMFCs [4]. Since the oxidative degradation of hydrocarbon polymers is very well known, we aimed to comprehensively investigate the formation of the short-lived species generated during the operation of AEMFCs as well as stable radicals present in the polymer membranes.We investigated the LDPE-base membranes with Pt black, Pd black, PdAg, and Ag as the ORR catalysts, whereas for HOR the Pt black, Pd black, and NiFe catalysts were used. The in-situ measurements are performed with a micro-AEMFC inserted into a resonator of an electron paramagnetic resonance (EPR) spectrometer, which enables separate monitoring of radicals formed on the anode and cathode sides. The creation of radicals was monitored by the EPR spin trapping technique. In Figure 1 the EPR spectra of DMPO spin adducts trapped during operation of micro-fuel cell placed in EPR spectrometer cavity are presented. In this experiment, the LDPE-base membrane with platinum catalysts on both sides was used. The main detected adducts during the operation of the micro-AEMFC were DMPO-OOH and DMPO-OH on the cathode side and DMPO-H on the anode side. Additionally, we clearly show the formation and presence of stable radicals in AEMs during and after long-term AEMFC operation [5]. Preliminary results suggest that the creation of the short-living radicals during AEMFCs operation is independent of the used membrane. However, the applied catalysts determine the number of detected radicals. The EPR investigations indicate that, in addition to the known chemical degradation mechanisms of the cationic ammonium groups of the membrane, oxidative degradation, including radical reactions, has to be taken into account when the stability of an anion conductive polymer for AEMFCs is investigated. The formation of stable radicals in AEMs was proven for the first time in this study. All short-living radicals formed during the AEMFC operation were fully identified. The presence of radicals in the AEM after AEMFC testing indicates that reactive oxygen species may play a very important role in the degradation mechanism of the anion conducting polymers. Results from this study shed light on the understanding of radical formation and presence in the membranes during AEMFC tests, which in turn may help to solve the challenge of anion exchange membrane stability. Acknowledgments. This work was supported by the Polish National Science Centre (NCN) project OPUS-14, No. 2017/27/B/ST5/01004.

Symmetrically-substituted Thiazolo[5,4-d]thiazole derivatives as both photoinitiators and dyes for 3D printing under violet LED

The outstanding photochemical properties of thiazolothiazole and its derivatives make them attractive as potential photoinitiators. Two homosubstituted thiazolo[5,4-d]thiazole derivatives, 2,5-di(furan-2-yl)thiazolo[5,4-d]thiazole and 2,5-di(thiophen-2-yl)thiazolo[5,4-d]thiazole, were investigated as photoinitiators for both the free radical and the cationic polymerization upon the light irradiation from LED@410 nm. In particular, steady-state photolysis, fluorescence quenching experiments, and electron paramagnetic resonance spin-trapping techniques were used to study their photochemical mechanisms in generating active species. When coupled with one or two additives, these thiazolothiazole-based photoinitiating systems showed effective photoinitiation abilities on both the free radical and the cationic photopolymerization. Specifically, 2,5-di(furan-2-yl)thiazolo[5,4-d]thiazole- and 2,5-di(thiophen-2-yl)thiazolo[5,4-d]thiazole-based photoinitiating systems were found to be of similar efficiency on the free radical photopolymerization of trimethylolpropane triacrylate and the dental resin (the blend of bisphenol A glycidyl methacrylate and triethylene glycol dimethacrylate) with minor shrinkage but presented different performance in cationic photopolymerization of 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate. Moreover, the curing depth of the samples and 3D printing capability were also investigated to determine their potential applications.

Effects of Acidity on Reactive Oxygen Species Formation from Secondary Organic Aerosols.

Reactive oxygen species (ROS) play a critical role in the chemical transformation of atmospheric secondary organic aerosols (SOA) and aerosol health effects by causing oxidative stress in vivo. Acidity is an important physicochemical property of atmospheric aerosols, but its effects on the ROS formation from SOA have been poorly characterized. By applying the electron paramagnetic resonance spin-trapping technique and the Diogenes chemiluminescence assay, we find highly distinct radical yields and composition at different pH values in the range of 1–7.4 from SOA generated by oxidation of isoprene, α-terpineol, α-pinene, β-pinene, toluene, and naphthalene. We observe that isoprene SOA has substantial hydroxyl radical (•OH) and organic radical yields at neutral pH, which are 1.5–2 times higher compared to acidic conditions in total radical yields. Superoxide (O2•–) is found to be the dominant species generated by all types of SOAs at lower pH. At neutral pH, α-terpineol SOA exhibits a substantial yield of carbon-centered organic radicals, while no radical formation is observed by aromatic SOA. Further experiments with model compounds show that the decomposition of organic peroxide leading to radical formation may be suppressed at lower pH due to acid-catalyzed rearrangement of peroxides. We also observe 1.5–3 times higher molar yields of hydrogen peroxide (H2O2) in acidic conditions compared to neutral pH by biogenic and aromatic SOA, likely due to enhanced decomposition of α-hydroxyhydroperoxides and quinone redox cycling, respectively. These findings are critical to bridge the gap in understanding ROS formation mechanisms and kinetics in atmospheric and physiological environments.

Spin trapping analysis of the thermal degradation of polypropylene

The thermal degradation mechanism of poly(propylene) (PP) fabric from room temperature to 220 °C was analyzed using the electron spin resonance (ESR) spin-trapping technique. This method was adopted to prolong the lifetime of the short-lived radical intermediates generated by thermal degradation with the object of inspecting their molecular structure. A spin-trapping reagent, 2,4,6-tri‑tert-butylnitrosobenzene (TTBNB), was impregnated into the PP fabric using supercritical CO2 (scCO2) treatment in the presence of a co-solvent. The impregnation efficiency and effect were evaluated using proton nuclear magnetic resonance (1H NMR) spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, and scanning electron microscopy (SEM). ESR analysis showed that the degradation of PP is initiated from the tertiary carbon positions via two pathways: homolysis to generate ·CH3 and −CH2−·CH−CH2− radicals, and hydrogen abstraction to generate −CH2−·C(CH3)−CH2− radicals. These radicals are also attacked by oxygen to form hydroperoxides, which then decompose to form the alkoxy radicals −CH2−CH(O·)−CH2− and −CH2−C(CH3)(O·)−CH2−. These radicals are involved in the subsequent β-scission reactions that produce primary and secondary carbon radicals. Alkoxy radicals also take part in the β-scission reactions involving the main chain carbon radicals, which have a hydroxyl group in the β-position, and in hydrogen abstraction from a five-membered ring at temperatures higher than the melting-point to produce an α‑hydroxyl carbon radical, ·CH(OH)−. These inferred processes involved in the thermal degradation of PP fabric were supported by other methods of analysis, including differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA).

EPR Spin-Trapping Study of Free Radical Intermediates in Polyalphaolefin Base Oil Autoxidation

Autoxidation is a set of spontaneous oxygen-mediated radical reactions common to degradation processes of all hydrocarbon-based materials. In this work, EPR (electron paramagnetic resonance) spin-trapping technique was used to study radical species involved in the autoxidation of a sample of synthetic base oil. A sample of polyalphaolefin base oil was aged at 140°C in the presence of oxygen and the difference in the tendency to generate radical species between the aged and non-aged samples of the same base oil was investigated using DMPO (5,5-dimethyl-1-pyrroline N-oxide) spin-trap. The ageing was performed in such a way that a small amount of hydroperoxides, the primary and key intermediate in autoxidation reactions, accumulated in the sample. Subsequently, the degradation of hydroperoxides was triggered by three different means: thermal treatment, introduction of soluble transition metal ions, and UV irradiation. Radical intermediates were monitored by EPR spin trapping; mixtures of peroxyl, alkoxyl, and carbon-centered radicals were detected and their origin was discussed.

Terthiophene Derivative-Based Photoinitiating Systems for Free Radical and Cationic Polymerization under Blue LEDs

Terthiophene derivatives were prepared and utilized as photoinitiators of photopolymerization reactions upon exposure to LEDs (410 and 445 nm). The photochemical mechanisms of the terthiophene-based photoinitiating systems were investigated and confirmed by steady-state photolysis, fluorescence quenching, and electron paramagnetic resonance spin-trapping techniques. The photoinitiation ability of terthiophene derivatives in combination with the iodonium salt and optionally with a tertiary amine in the free radical polymerization of multifunctional acrylates and cationic polymerization of epoxides under mild light irradiation was investigated. Exceptionally, a sodium salt form of a terthiophene derivative presented exceeding water solubility and admirable efficiency in rapid hydrogel formation from the 2-hydroxy ethyl acrylate and water blend. The storage stability of the effective photoinitiating systems in the formulations was also studied under moderate conditions.

Are Radicals Formed During Anion-Exchange Membrane Fuel Cell Operation?

In this paper we present a study on stable radicals and short-lived species generated in anion-exchange membrane (AEM) fuel cells (AEMFCs) during operation. The in situ measurements are performed with a micro-AEMFC inserted into a resonator of an electron paramagnetic resonance (EPR) spectrometer, which enables separate monitoring of radicals formed on the anode and cathode sides. The creation of radicals is monitored by the EPR spin trapping technique. For the first time, we clearly show the formation and presence of stable radicals in AEMs during and after long-term AEMFC operation. The main detected adducts during the operation of the micro-AEMFC are DMPO-OOH and DMPO-OH on the cathode side, and DMPO-H on the anode side. These results indicate that oxidative degradation involving radical reactions has to be taken into account when stability of AEMFCs is investigated.

Different non-radical oxidation processes of persulfate and peroxymonosulfate activation by nitrogen-doped mesoporous carbon

Activated persulfate oxidation is an emerging advanced oxidation process for organic pollutant degradation. Own to different molecular structures and oxidation potentials, persulfate (PDS) and peroxymonosulfate (PMS) may show different degradation performances due to various catalytic mechanisms even by the same catalysts. In this study, the nitrogen-doped mesoporous carbon (N-OMC) was applied to activate PDS and PMS for degrading a model organic pollutant phenol to reveal their activation mechanisms. Results show that both PDS and PMS could be efficiently activated by N-OMC. The degradation of phenol fitted well with pseudo-first-order kinetics, whose kinetic constants increased with the increase of pH, PDS/PMS dosage, and N-OMC dosage. Based on quenching experiments and electron spin resonance spin-trapping technique, the N-OMC was found to activate PDS and PMS via non-radical process of electron transfer and singlet oxygen formation, respectively, instead of the commonly observed radical process. This work will be useful to understand the activation processes of PDS and PMS, and benefit for the development of catalysts for pollutant degradation.

Fabrication of Z-scheme γ-Bi2MoO6/Bi12GeO20 heterostructure for visible-light-driven photocatalytic degradation of organic pollutants

In this study, an efficient and durable photocatalyst composed of Bi12GeO20 and γ-Bi2MoO6 through like Z-scheme mechanism was successfully obtained by heat treatment. The as-prepared Z-scheme 40γ-Bi2MoO6/Bi12GeO20 heterostructure presents the superior photocatalytic performance for degrading MBT, which is nearly 46 and 4.95 times higher than that of the pure Bi12GeO20 (kapp = 0.0007 min−1) and Bi2MoO6 (kapp = 0.0065 min−1), respectively. Meanwhile, the 40γ-Bi2MoO6/Bi12GeO20 heterostructure also shows the quite high photocatalytic performance for degrading TC, which is approximately 5.48 and 1.89 times higher than that of the pure Bi12GeO20 (kapp = 0.0021 min−1) and Bi2MoO6 (kapp = 0.0061 min−1), respectively. The enhancement of photocatalytic performance originates from not only the strong interface between Bi12GeO20 and γ-Bi2MoO6, but also the unique Z-scheme system which can effectively promote the separation of photogenerated electron-hole pairs and sufficiently utilize the photogenerated carriers for generating more active radicals. In addition, based on the active species trapping experiments and electron spin resonance (ESR) spin-trap technique, the photocatalytic mechanism over the Z-scheme γ-Bi2MoO6/Bi12GeO20 heterostructure is discussed in detail. The research may provide theoretical basis and significant guiding for future development of fabricating other Z-scheme heterostructure with superior photocatalytic performance and high stability.

Enhanced photoelectric conversion efficiency: A novel h-BN based self-powered photoelectrochemical aptasensor for ultrasensitive detection of diazinon

This work presents a novel hexagonal boron nitride (h-BN) based self-powered photoelectrochemical (PEC) aptasensor for ultrasensitive detection of diazinon (DZN) with excellent photoelectric conversion efficiency. It was the first time that h-BN based materials were applied to PEC aptasensor, in which the construction of Z-scheme heterojunction of h-BN and graphitic carbon nitride (CN) via doping sulfur into h-BN was innovatively proposed. Meanwhile, Au nanoparticles (AuNPs) were utilized for the surface plasmon resonance (SPR) effect and the formation of new recombination centers. The charge transfer mechanism was expounded and verified by the electron spin resonance (ESR) spin-trap technique. The proposed PEC aptasensor for determination of DZN exhibited a wide linear range from 0.01 to 10000 nM and a low detection limit of 6.8 pM with superb selectivity and remarkable stability. Moreover, the constructed PEC aptasensor performed well with excellent recoveries in three different real samples. This work illustrated that PEC aptasensor is a promising alternative to conventional analytical technologies for the detection of DZN and other organophosphorus (OP) pesticides. The designing ideas of the proposed h-BN based material can provide a foothold for the innovative construction of photoactive materials for PEC bioanalysis.

Photoinitiation Mechanism and Ability of Monoamino-Substituted Anthraquinone Derivatives as Cationic Photoinitiators of Polymerization under LEDs.

The design and development of photoinitiating systems applicable to UV or even visible light delivered from light-emitting diodes (LEDs) has been attracting increasing attention due to their great potential applications in various fields. Compared to the strategy of synthesizing novel compounds, the exploration of existing chemicals with interesting photochemical/photophysical properties for their usage as photoinitiators is more appealing and easily commercialized. Nevertheless, a number of compounds such as monoamino-substituted anthraquinone derivatives, which are intensively investigated for their photophysical and photochemical properties, have seldom been studied for their roles as photoinitiators under LED irradiation. Herein, three monoamino-substituted anthraquinone derivatives, that is, 1-aminoanthraquinone, 1-(methylamino)anthraquinone and 1-(benzamido)anthraquinone, are studied for their potential as photoinitiators. The photoinitiation mechanism of these monoamino-substituted anthraquinone derivatives, when combined with iodonium salt, is first clarified using computational quantum chemistry, fluorescence, steady-state photolysis, and electron spin resonance spin-trapping techniques. Then, their photoinitiation ability for the cationic photopolymerization of epoxide and divinyl ether monomers is also investigated.

Systematic diagnostics of the electrical, optical, and physicochemical characteristics of low-temperature atmospheric-pressure helium plasma sources

The performance characteristics of two plasma sources, based on different types of discharge, were assessed. Three primary aspects of these sources were examined. These were electrical parameters (voltage and current flowing through a target), plasma parameters (gas temperature and electron density, determined using optical emission spectroscopy), and levels of gas-phase oxygen atoms (measured by vacuum ultraviolet absorption spectroscopy) and liquid-phase ▪OH radicals (generated by plasma treatment of water and detected using an electron spin resonance spin-trapping technique). As a result, there were few significant differences such as electron density, oxygen atom density, and gas temperature between the two plasma sources. However, the time-averaged electrical currents flowing to the target and the amount of liquid-phase ▪OH radicals showed a large difference, especially when the plume made contact with the target. Thus, many points of similarity but some differences in the two devices were found by the benchmarking study. These shall contribute to our understanding of the mechanisms for each consequence in medical applications.

Activation of peroxymonosulfate by a novel EGCE@Fe3O4 nanocomposite: Free radical reactions and implication for the degradation of sulfadiazine

A novel magnetic epigallocatechin-3-gallate-modified Fe3O4 nano-catalyst (EGCG@Fe3O4) was fabricated, characterized, and tested to active peroxymonosulfate (PMS) for the degradation of sulfadiazine (SD) in solution. The results illustrate that EGCG@Fe3O4 exhibits a higher catalytic ability than unmodified Fe3O4 toward SD degradation. Both SD removal and PMS decomposition clearly follow the pseudo-first-order kinetic pattern in the EGCG@Fe3O4/PMS system. When the catalyst and PMS dosages were 0.8 g/L and 0.3 mM, respectively, the pseudo-first-order rate constants (kobs) were 5.41 × 10−2 and 1.05 × 10−2 min−1 for the EGCG@Fe3O4/PMS and Fe3O4/PMS systems, accompanied by 97.9% and 51.4% utilizations of initial PMS, respectively. Numerous hydroxyl radicals (*OH) and few sulfate radicals (SO4*−) were measured in the EGCG@Fe3O4/PMS system by in situ electron spin resonance (ESR) spin-trapping techniques. The production of reactive radicals most likely involved the activation of PMS by the cycle of Fe2+-Fe3+ on the EGCG@Fe3O4 catalyst surface, with EGCG enhancing the redox of Fe3+ to Fe2+ significantly. The EGCG@Fe3O4/PMS system may provide new insights for the decomposition of organic pollutants dissolved in water.

Facile fabrication of g-C3N4 QDs/BiVO4 Z-scheme heterojunction towards enhancing photodegradation activity under visible light

Abstract In this study, we report a facile and green strategy to produce graphitic carbon nitride quantum dots (g-C3N4 QDs)/BiVO4 Z-scheme nanoheterostructure, which is composed by g-C3N4 QDs assembled on the surface of mesh-like BiVO4 crystals. As compared with pure BiVO4, the g-C3N4 QDs/BiVO4 composite showed significantly enhanced photocatalytic performance towards degradation of rhodamine B (RhB) and Tetracycline (TC) under visible light irradiation, which is attributed to the increased surface area, (increased number of photocatalytically active sites) and the improved efficiency of separation of photogenerated electron-hole pairs through an efficient charge transfer Z-scheme system. The stability and durability of photocatalyst are also discussed in detail. Moreover, the possible enhanced photocatalytic mechanism was put forwarded and explained by the electron spin resonance (ESR) spin-trap technique and active species trapping experiments. The successful implementation of this work will have guiding significance for the preparation of photocatalysts, and provide theoretical basis and experimental guidance for future development of Z-scheme photocatalytic mechanism of the hybrid photocatalysts with better performance.

Photopolymerization under various monochromatic UV/visible LEDs and IR lamp: Diamino-anthraquinone derivatives as versatile multicolor photoinitiators

Diamino-anthraquinone derivatives [1,4-bis(isopropylamino)anthraquinone (SB36), 1-amino-4-anilinoanthraquinone (SB68), and 1,4-bis(p-tolylamino)anthraquinone (SG3)] exhibit absorption maxima in red light wavelength range and demonstrate broad ground state light absorption from ultraviolet to infrared light. When combined with coinitiators (e.g. iodonium salt), SB36-based photoinitiating systems exhibit the highest photoinitiation efficiency among all the studied diamino-anthraquinone derivative-based combinations for both cationic and free radical photopolymerization upon exposure to a red LED bulb. And SB36-based systems even demonstrate higher photoinitiating ability for free radical photopolymerization than that of previously studied 1,4-bis(pentylamino)anthraquinone (i.e. oil blue N)-based systems. In contrast, SG3-based photoinitiating systems show the lowest photoinitiation efficiency especially for free radical photopolymerization. Interestingly, the SB36/iodonium salt/N-vinylcarbazole system is a capable multicolor photoinitiating system able to initiate both cationic and free radical photopolymerization under the irradiation of UV to red LED bulbs and IR lamp. The photochemical mechanism associated with the production of cations and radicals from the diamino-anthraquinone derivative-based photoinitiating systems are investigated using steady state photolysis, fluorescence, laser flash photolysis, and electron spin resonance spin-trapping techniques.

Construction of novel CNT/LaVO4 nanostructures for efficient antibiotic photodegradation

It is an urgent matter to eliminate antibiotics in waste water, due to the rapid emergence of antibiotic resistance. The search for low cost, high activity and stable novel photocatalysts has attracted great interest. Herein, we demonstrated the rational construction of CNT/LaVO4 nanostructures for efficient antibiotic photodegradation by a one-step hydrothermal method. The phase structures, chemical compositions, morphologies, and optical properties of the prepared samples were investigated via various characterization techniques. The optimized CNT/LaVO4 nanostructures exhibited efficient photodegradation activity with remarkable stability. The 0.1% CNT/LaVO4 showed the highest tetracycline degradation rate, which is 2 times that of pure LaVO4. Photoluminescence (PL), transient photocurrent response and electrochemical impedance spectroscopy (EIS) together verified that this design successfully expedites the separation and transfer of photogenerated charge carriers. Subsequently, by the electron spin resonance (ESR) spin-trap technique, free radical trapping experiments and mass spectrometry analysis (MS), the active species, intermediate product, photodegradation pathway and reaction mechanism during the photocatalytic process were identified. The antibacterial results showed that the degrading products have lower toxicity. The CNT/LaVO4 composite is a potential photocatalyst for improving the water quality.

Multihydroxy-Anthraquinone Derivatives as Free Radical and Cationic Photoinitiators of Various Photopolymerizations under Green LED.

Multihydroxy-anthraquinone derivatives [i.e., 1,2,4-trihydroxyanthraquinone (124-THAQ), 1,2,7-trihydroxyanthraquinone (127-THAQ), and 1,2,5,8-tetrahydroxyanthraquinone (1258-THAQ)] can interact with various additives [e.g., iodonium salt, tertiary amine, N-vinylcarbazole, and 2-(4-methoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine] under household green LED irradiation to generate active species (cations and radicals). The relevant photochemical mechanism is investigated using quantum chemistry, fluorescence, cyclic voltammetry, laser flash photolysis, steady state photolysis, and electron spin resonance spin-trapping techniques. Furthermore, the multihydroxy-anthraquinone derivative-based photoinitiating systems are capable of initiating cationic photopolymerization of epoxides or divinyl ethers under green LED, and the relevant photoinitiation ability is consistent with the photochemical reactivity (i.e., 124-THAQ-based photoinitiating system exhibits highest reactivity and photoinitiation ability). More interestingly, multihydroxy-anthraquinone derivative-based photoinitiating systems can initiate free radical crosslinking or controlled (i.e., reversible addition-fragmentation chain transfer) photopolymerization of methacrylates under green LED. It reveals that multihydroxy-anthraquinone derivatives can be used as versatile photoinitiators for various types of photopolymerization reactions.

Copper(II) Thiosemicarbazone Complexes and Their Proligands upon UVA Irradiation: An EPR and Spectrophotometric Steady-State Study.

X- and Q-band electron paramagnetic resonance (EPR) spectroscopy was used to characterize polycrystalline Cu(II) complexes that contained sodium 5-sulfonate salicylaldehyde thiosemicarbazones possessing a hydrogen, methyl, ethyl, or phenyl substituent at the terminal nitrogen. The ability of thiosemicarbazone proligands to generate superoxide radical anions and hydroxyl radicals upon their exposure to UVA irradiation in aerated aqueous solutions was evidenced by the EPR spin trapping technique. The UVA irradiation of proligands in neutral or alkaline solutions and dimethylsulfoxide (DMSO) caused a significant decrease in the absorption bands of aldimine and phenolic chromophores. Mixing of proligand solutions with the equimolar amount of copper(II) ions resulted in the formation of 1:1 Cu(II)-to-ligand complex, with the EPR and UV-Vis spectra fully compatible with those obtained for the dissolved Cu(II) thiosemicarbazone complexes. The formation of the complexes fully inhibited the photoinduced generation of reactive oxygen species, and only subtle changes were found in the electronic absorption spectra of the complexes in aqueous and DMSO solutions upon UVA steady-state irradiation. The dark redox activity of copper(II) complexes and proligand/Cu(II) aqueous solutions towards hydrogen peroxide which resulted in the generation of hydroxyl radicals, was confirmed by spin trapping experiments.

Free radical generation by non-equilibrium atmospheric pressure plasma in alcohol–water mixtures: an EPR-spin trapping study

Free radical species in aqueous solution—various alcohol–water reaction mixtures—by exposure to non-equilibrium cold atmospheric pressure Ar plasma (CAP), were monitored using electron paramagnetic resonance spin-trapping techniques with 3, 5-dibromo-4-nitrosobenzene sulfonate as a water soluble nitroso spin trap. The major radical species were formed by H-abstraction from alcohol molecules due to ·OH radicals. In the ethanol–water mixture ·CH2CH2OH produced by H abstraction from CH3 group of the ethanol and ·CH3 radicals were detected. The latter was due to the decomposition of unstable CH3·CHOH to form the ·CH3 radicals and the stable formaldehyde by C–C bond fission. These intermediates are similar to those observed by reaction with ·OH radicals generation in the H2O2–UV photolysis of the reaction mixtures. The evidence of ·CH3 radical formation in the pyrolytic decomposition of the reaction mixtures by exposure to ultrasound or in methane irradiated with microwave plasma have been reported previously. However, the pyrolytic ·CH3 radicals were not found in both plasma and H2O2–UV photolysis condition. These results suggests that free radicals produced by Ar-CAP are most likely due to the reaction between abundant ·OH radicals and alcohol molecules.