Using ESR spectroscopy to study radical intermediates in proton-exchange membranes exposed to oxygen radicals

Bosnjakovic, Admira; Kadirov, Marsil K.; Schlick, Shulamith

doi:10.1163/156856707782169372

Cited by 29 publications

(32 citation statements)

References 32 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…While DECPO may offer opportunities for bi-conjugation via amide bond, we have not been successful in hydrolyzing DECPO to dicarboxylic acid nitrone due to the decarboxylation reaction that occurs during base hydrolysis. In order to resolve this problem, compound 2 (see Figure 3 and Scheme 1) was designed to have an extra methylene group on one of the substituents at the C-5 position which could be hydrolyzed successfully to dicarboxylic acid cyclic nitrone (Scheme 1). …”

Section: Resultsmentioning

confidence: 99%

“…Michael addition of acrolein to the nitro-diester 7 led to compound 8 which was immediately used without further purification. Reductive cyclization of 8 using Zn/NH 4 C1 41 gave the nitrone 2 after purification. Compound 2 was then subjected to base hydrolysis of the ester bond then followed by ion exchange column chromatography to give 1 as a slightly yellowish solid.…”

Section: Resultsmentioning

confidence: 99%

“…The use of spin trapping has been gaining popularity in the investigation of reactive intermediates in the areas of fuel cell research,2 nanotechnology,3 catalysis,4 environmental remediation,5 and photodynamic therapy 6. Moreover, the ability of nitrones to trap radicals make them suitable as antioxidants in the treatment of reactive oxygen species-mediated pathophysiological disorders such as neurodegenerative disease,7 acute stroke,8,9 cancer9 and ischemia-reperfusion injury 10.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Lipophilic β-Cyclodextrin Cyclic−Nitrone Conjugate: Synthesis and Spin Trapping Studies

Han¹,

Liu²,

Rockenbauer

et al. 2009

J. Org. Chem.

View full text Add to dashboard Cite

Nitrone spin traps are commonly employed as probes for the identification of transient radicals in chemical and biological systems using electron paramagnetic resonance (EPR) spectroscopy. Nitrones have also found applications as therapeutic agent in the treatment of radical-mediated diseases. Therefore, spin trap that incorporates high reactivity to superoxide radical anion (O 2•− ), more persistent superoxide adduct, enhanced bioavailability and selective targeting in one molecular design is desirable. In this work, the synthesis of a nitrone spin trap, 4, that is tethered via amide bonds to a β-cyclodextrin (β-CD) and a dodecyl chain was achieved with the expectation that the β-cyclodextrin would lead to persistent spin adduct while the lipophilic chain would impart membrane targeting property. The two constitutional racemic isomers, 4a and 4b, were separated using preparative HPLC and structural analysis as well as self-aggregations properties were carried out using NMR, induced circular dichroism, dynamic light scattering, transmission electron microscopy, and computational approach. EPR spin trapping of 0 2•− by 4a and 4b was only successful in DMSO and not in aqueous system due most likely to the amphiphilic character of 4 that can favor conformations (or aggregation) hindering radical addition to nitrone. Kinetics of formation and decay of 4a-O 2 H adduct in polar aprotic solvents show faster reactivity to O 2•− and more persistent O 2•− adduct compared to nitrones not conjugated to β-CD. Computational analysis of 4a and 4b as well as 4a-OOH and 4b-OOH adducts were carried out and results show that isomerism, both constitutional and stereochemical, affects the orientations of aminoxyl-NO and/or hydroperoxyl groups relative to the β-CD annulus for optimal H-bond interaction and stability.

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Lipophilic β-Cyclodextrin Cyclic−Nitrone Conjugate: Synthesis and Spin Trapping Studies

Han¹,

Liu²,

Rockenbauer

et al. 2009

J. Org. Chem.

View full text Add to dashboard Cite

show abstract

“…It was therefore difficult to extract a strong causal relationship between fuel cell operating parameters, ROS generation rates, and ROS-induced chemical degradation. The presence of ROS in PEM fuel cells has been directly identified by electron paramagnetic resonance (EPR) measurements (21)(22)(23)(24). However, these measurements are limited to cells that fit within the EPR probe and cannot be translated to subscale or larger scale cells operating under realistic conditions.…”

mentioning

confidence: 99%

Investigation of polymer electrolyte membrane chemical degradation and degradation mitigation using in situ fluorescence spectroscopy

Prabhakaran

Arges

Ramani

2012

Proc. Natl. Acad. Sci. U.S.A.

139

126

View full text Add to dashboard Cite

A fluorescent molecular probe, 6-carboxy fluorescein, was used in conjunction with in situ fluorescence spectroscopy to facilitate realtime monitoring of degradation inducing reactive oxygen species within the polymer electrolyte membrane (PEM) of an operating PEM fuel cell. The key requirements of suitable molecular probes for in situ monitoring of ROS are presented. The utility of using free radical scavengers such as CeO 2 nanoparticles to mitigate reactive oxygen species induced PEM degradation was demonstrated. The addition of CeO 2 to uncatalyzed membranes resulted in close to 100% capture of ROS generated in situ within the PEM for a period of about 7 h and the incorporation of CeO 2 into the catalyzed membrane provided an eightfold reduction in ROS generation rate.fuel cells | Nafion® degradation | hydroxyl radicals | hydroperoxyl radicals | miniature fluorescence probe H ydrogen/air (H 2 ∕air) polymer electrolyte membrane (PEM) fuel cells possess high efficiency and modularity. However, significant technical advances are required to facilitate fuel cells' commercialization and widespread use in targeted applications in the automotive, portable power, and military sectors. A key technological issue that remains to be addressed is component durability under an array of adverse operating conditions. The ionexchange membrane in a PEM fuel cell is one of the components whose limited long-term durability is of concern. The PEM undergoes mechanical, thermal, and chemical degradation during fuel cell operation (1-8). The chemical degradation process that takes place in a H 2 ∕O 2 PEM fuel cell is attributed to reactive oxygen species (ROS) that are generated in situ through both chemical and electrochemical pathways during fuel cell operation. Hydrogen peroxide (H 2 O 2 ) is an ROS and is often an intermediate formed in both pathways and is known to form free radical ROS in the presence of transition metal ions via the Fenton mechanism (9-12). These free radical ROS, namely hydroxyl and hydroperoxyl radicals, are amongst the strongest oxidizing agents known. ROS initiate oxidative degradation of both the PEM backbone and the side chains that contain ionic groups that are essential for ion conduction (13-16). The adverse consequences of these degradation modes (e.g., membrane thinning, pin-hole formation, and loss of ionic conductivity) eventually contribute to catastrophic cell and stack failure. Complete elimination of ROS generation and PEM chemical degradation, while a worthy goal, is difficult due to constraints in terms of membrane materials, choice of fuel and oxidant, and fuel cell operating conditions. Therefore, it is imperative to develop effective mitigation strategies that minimize the rate and extent of PEM degradation.Prior to proposing an effective mitigation strategy, it is essential to quantify the rate of ROS generation within the PEM during fuel cell operation. However, detecting the presence of ROS within the PEM of an operating fuel cell is an extremely difficult proposition because free ra...

show abstract

“…Spin trapping has found enormous application in the field of biomedical research, particularly in the study of the toxicology of free radicals2 and the crucial role they play in regulating cell function 3. Moreover, the use of spin trapping has been gaining popularity in the investigation of reactive intermediates in the areas of fuel cell research,4 nanotechnology,5 catalysis,6 environmental remediation,7 and photodynamic therapy 8. Among the most commonly studied radicals are the hydroxyl radical (HO · ) and superoxide radical anion (O 2 ·- ), using the cyclic nitrones, 5,5-dimethyl-1-pyrroline N -oxide (DMPO),9 5-ethoxycarbonyl-5-methyl-1-pyrroline N -oxide (EMPO),10 and 5-diethoxyphosphoryl-5-methyl-1-pyrroline N -oxide (DEPMPO)11 (Scheme 1), even though the use of these spin traps is still confronted by some limitations such as slow reactivity to O 2 ·- and generally less persistent O 2 ·- adducts.…”

Section: Introductionmentioning

confidence: 99%

Superoxide Radical Anion Adduct of 5,5-Dimethyl-1-pyrroline N-Oxide. 4. Conformational Effects on the EPR Hyperfine Splitting Constants

2008

View full text Add to dashboard Cite

Spin trapping has been commonly employed in the detection of superoxide radical anion in chemical and biological systems; hence, accurate interpretation of the hyperfine splitting constants (hfsc's) arising from the O 2 ·-adducts (also referred to as hydroperoxyl (HO 2 · ) radical adducts) of various nitrones is important. In this work, the nature of the relevant hfsc's was investigated by examining the effect of conformational changes in the hydroperoxyl moiety of the O 2 ·-adducts of 5,5-dimethyl-1-pyrroline N-oxide (DMPO), 5-ethoxycarbonyl-5-methyl-1-pyrroline N-oxide (EMPO), 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide (DEPMPO), 5-carbamoyl-5-methyl-1-pyrroline N-oxide (AMPO), and 7-oxa-1-azaspiro[4.4]non-1-en-6-one N-oxide, (CPCOMPO) on the magnitude of a N , a β-H , and a γ-H . Conformational change around the substituents and their effect on the hfsc's were also explored. Results indicate that a β-H is most sensitive to conformational changes of the hydroperoxyl and substituent groups relative to hfsc's of other nuclei. The orbital overlap between the C-H σ-orbital and the SOMO of the nitroxyl nitrogen plays a crucial factor in determining the magnitude of the a β-H . The hfsc values for the O 2 ·-adducts were predicted with high accuracy by using a low-cost computational method at the PCM(water)/BHandHLYP/EPR-III//B3LYP/ 6-31G* level of theory without taking into account the explicit water interaction.

show abstract

Using ESR spectroscopy to study radical intermediates in proton-exchange membranes exposed to oxygen radicals

Cited by 29 publications

References 32 publications

Lipophilic β-Cyclodextrin Cyclic−Nitrone Conjugate: Synthesis and Spin Trapping Studies

Lipophilic β-Cyclodextrin Cyclic−Nitrone Conjugate: Synthesis and Spin Trapping Studies

Investigation of polymer electrolyte membrane chemical degradation and degradation mitigation using in situ fluorescence spectroscopy

Superoxide Radical Anion Adduct of 5,5-Dimethyl-1-pyrroline N-Oxide. 4. Conformational Effects on the EPR Hyperfine Splitting Constants

Contact Info

Product

Resources

About