Formation and stabilization of persistent free radicals

Dellinger, Barry; Lomnicki, Slawo; Khachatryan, Lavrent; Maskos, Zofia; Hall, Randall W.; Adounkpè, Julien; McFerrin, Cheri A.; Truong, Hieu

doi:10.1016/j.proci.2006.07.172

Cited by 323 publications

(319 citation statements)

References 28 publications

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“…in particles in the accumulation mode is consistent with mass size distributions of combustion-generated particles, such as soot or black carbon, which typically have peak concentrations around 100-200 nm (Bond et al, 2013). This observation is in line with the fact that EPFR may often be associated with soot particles (Dellinger et al, 2007). Figure 3 shows the temporal evolution of EPFR concentrations contained in particles with lower cut-off diameters of 100 and 180 nm.…”

Section: Methodssupporting

confidence: 80%

“…Paramagnetic species are characterized based on their g factor values. Free electrons have a g factor value of 2.0023 and organic radicals have higher g factor values (2.0030-2.0060), depending on the number of oxygen atoms in the molecule (Dellinger et al, 2007).…”

Section: Methodsmentioning

confidence: 99%

“…Fine particles, with lower cut-off diameters of 56-320 nm, show a single and unstructured peak with a g factor of ∼ 2.003 and with a peak to peak distance ( H p-p ) ranging from 3 to 8 G. Such spectra are characteristic for EPFR, which have been attributed to semiquinone radicals (Dellinger et al, , 2007Vejerano et al, 2011;Bahrle et al, 2015). Particles with a diameter smaller than 56 nm and larger than 560 nm did not show significant signals, indicating the reduced amount of EPFR in these size ranges.…”

Section: Methodsmentioning

confidence: 99%

“…The chemical nature of EPFR is remarkably similar to semiquinone radicals, which can be stabilized via electron transfer with transition metals in the particle phase (Truong et al, 2010;Vejerano et al, 2011;Gehling and Dellinger, 2013). EPFR are formed upon combustion and pyrolysis of organic matter (Dellinger et al, , 2007. The formation of stable radicals can also be induced by heterogeneous and multiphase chemistry of organic aerosols.…”

Section: Introductionmentioning

confidence: 99%

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Quantification of environmentally persistent free radicals and reactive oxygen species in atmospheric aerosol particles

et al. 2016

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Abstract. Fine particulate matter plays a central role in the adverse health effects of air pollution. Inhalation and deposition of aerosol particles in the respiratory tract can lead to the release of reactive oxygen species (ROS), which may cause oxidative stress. In this study, we have detected and quantified a wide range of particle-associated radicals using electron paramagnetic resonance (EPR) spectroscopy. Ambient particle samples were collected using a cascade impactor at a semi-urban site in central Europe, Mainz, Germany, in May-June 2015. Concentrations of environmentally persistent free radicals (EPFR), most likely semiquinone radicals, were found to be in the range of (1-7) × 10 11 spins µg −1 for particles in the accumulation mode, whereas coarse particles with a diameter larger than 1 µm did not contain substantial amounts of EPFR. Using a spin trapping technique followed by deconvolution of EPR spectra, we have also characterized and quantified ROS, including OH, superoxide (O − 2 ) and carbon-and oxygen-centered organic radicals, which were formed upon extraction of the particle samples in water. Total ROS amounts of (0.1-3) ×10 11 spins µg −1 were released by submicron particle samples and the relative contributions of OH, O − 2 , C-centered and O-centered organic radicals were ∼ 11-31, ∼ 2-8, ∼ 41-72 and ∼ 0-25 %, respectively, depending on particle sizes. OH was the dominant species for coarse particles. Based on comparisons of the EPR spectra of ambient particulate matter with those of mixtures of organic hydroperoxides, quinones and iron ions followed by chemical analysis using liquid chromatography mass spectrometry (LC-MS), we suggest that the particle-associated ROS were formed by decomposition of organic hydroperoxides interacting with transition metal ions and quinones contained in atmospheric humic-like substances (HULIS).

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Section: Methodssupporting

confidence: 80%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Quantification of environmentally persistent free radicals and reactive oxygen species in atmospheric aerosol particles

et al. 2016

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“…Carbon-centered radicals with an adjacent oxygen atom have higher g-values in the range of 2.003-2.004, while oxygen centered radicals have g-values that are >2.004. The g-value of 2.0034-2.0039 is characteristic for carbon-centered radicals in a nearby oxygen heteroatom that results in increased g-values over that of purely carbon-centered radicals [11][12][13][14][15] . Line-width is governed by the spin-lattice relaxation process.…”

Section: Introductionmentioning

confidence: 99%

Exploring the Radical Nature of a Carbon Surface by Electron Paramagnetic Resonance and a Calibrated Gas Flow

Green

Shenberger

Aizenshtat

et al. 2014

JoVE

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While the first Electron Paramagnetic Resonance (EPR) studies regarding the effects of oxidation on the structure and stability of carbon radicals date back to the early 1980s the focus of these early papers primarily characterized the changes to the structures under extremely harsh conditions (pH or temperature) [1][2][3] . It is also known that paramagnetic molecular oxygen undergoes a Heisenberg spin exchange interaction with stable radicals that extremely broadens the EPR signal [4][5][6] . Recently, we reported interesting results where this interaction of molecular oxygen with a certain part of the existing stable radical structure can be reversibly affected simply by flowing a diamagnetic gas through the carbon samples at STP 7 . As flows of He, CO 2 , and N 2 had a similar effect these interactions occur at the surface area of the macropore system. This manuscript highlights the experimental techniques, work-up, and analysis towards affecting the existing stable radical nature in the carbon structures. It is hoped that it will help towards further development and understanding of these interactions in the community at large. Video LinkThe video component of this article can be found at

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Azaquinoid‐Based High Spin Open‐Shell Conjugated Polymer for n‐Type Organic Field‐Effect Transistors

Kim

Yang

Kim

et al. 2022

Adv Materials Inter

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such as optically low bandgaps and electrically semiconducting properties. [1] These systems have been extensively investigated for promising applications in organic photovoltaics, photodetectors, thermoelectrics, and organic field-effect transistors (OFETs). [2] Most π-conjugated platforms, quinoidal compounds, have attracted attention from researchers because of their structural specificity and unique and noteworthy characteristics such as high electrical charge transport, non-linear optical and magnetic properties, which are uncommon in organic materials. [3] The quinoid structure is well known for its resonance form of a general aromatic structure, which has a planar structure linked by double bonds between each cyclic ring. [4] In terms of electronic state, the quinoid structure has a closed-shell form. When the closed-shell quinoid structure is extended, it can be converted into an openshell diradical structure due to the tendency to recover aromaticity. [5] These open-shell diradical characteristics of quinoidal compounds could promote interesting spin-induced magnetic behaviors and singlet fission processes. [6] Isatin-terminated quinoids have been used to incorporate quinoidal platforms in the conjugated polymer backbone. [7] Isatin may contain halogen atoms at the 6-position, which allows Pdcatalyzed carbon-carbon cross coupling polymerization (Stille and Suzuki coupling) resulting in para-connected conjugation pathway in the entire polymer backbone. Moreover, isatin-terminated quinoids have crucial advantages because they are easily synthesized via indophenine reactions under ambient conditions and allow easy structural modification. To date, a few isatinbased quinoidal conjugated polymers have been developed by researchers, including our group. [8] Whereas most quinoidal small molecules have demonstrated n-type field-effect transistor behaviors with strong electron-withdrawing terminal units such as dicyanomethylene groups, conjugated polymers composed of isatin-terminated quinoids rarely exhibit n-type behaviors because of the relatively weak electron-withdrawing nature of the isatin unit. [9] A conjugated polymer that contained S,S-dioxidized thienoquinoids demonstrated unipolar n-type semiconducting behaviors because of its strong electron withdrawing SO groups. [8a,10] To achieve n-type semiconducting behaviors, azaaromatic compounds may be incorporated into the conjugated building An open-shell quinoidal conjugated polymer exhibiting n-type semiconducting behavior is successfully synthesized and characterized. An electron-deficient azaaromatic unit is proven to reduce the energy levels of frontier orbitals via the electronegative nitrogen atom and steric hindrance within the polymer backbone. A synthesized azaquinoidal bithiophene (azaQuBT) is a quinoidal bithiophene that is end-functionalized with a pyridine ring. The open-shell quinodial conjugated polymer, poly(azaquinoidal bithiophene-thiophene), PazaQuBT-T, is synthesized using azaQuBT and thiophene. The extended quinoidal building ...

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Formation and stabilization of persistent free radicals

Cited by 323 publications

References 28 publications

Quantification of environmentally persistent free radicals and reactive oxygen species in atmospheric aerosol particles

Quantification of environmentally persistent free radicals and reactive oxygen species in atmospheric aerosol particles

Exploring the Radical Nature of a Carbon Surface by Electron Paramagnetic Resonance and a Calibrated Gas Flow

Azaquinoid‐Based High Spin Open‐Shell Conjugated Polymer for n‐Type Organic Field‐Effect Transistors

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