Spin Trapping and Electron Transfer

Eberson, Lennart

doi:10.1016/s0065-3160(08)60193-8

Cited by 16 publications

(16 citation statements)

References 128 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This is due to the oxidation of the TOAC nitroxide radical to the oxoammonium cation. 36 The DPV curves of Figure 4 show that nitroxide oxidation in 1+ is considerably easier than that of 1− by 80 mV. Therefore, the E°shift is, once again, consistent with the direction expected on the basis of the dipole moment effect: the nitroxide group of 1+ is on the negative side of the peptide dipole, which makes its oxidation easier.…”

Section: ■ Results and Discussionsupporting

confidence: 76%

Effect of Orientation of the Peptide-Bridge Dipole Moment on the Properties of Fullerene–Peptide–Radical Systems

et al. 2012

View full text Add to dashboard Cite

We synthesized two series of compounds in which a nitroxide radical and a fullerene C 60 moiety were kept separated by a 3 10 -helical peptide bridge containing two intramolecular CO···H−N hydrogen bonds. The direction of the resulting molecular dipole moment could be reversed by switching the position of fullerene and nitroxide with respect to the peptide nitrogen and carbon termini. The resulting fullerene−peptide−radical systems were compared to the behaviors of otherwise identical peptides but lacking either C 60 or the free radical moiety. Electrochemical analysis and chemical nitroxide reduction experiments show that the dipole moment of the helix significantly affects the redox properties of both electroactive groups. Besides providing evidence of a folded helical conformation for the peptide bridge, IR and NMR results highlight a strong effect of peptide orientation on the spectral patterns, pointing to a specific interaction of one of the helical orientations with the C 60 moiety. Time-resolved EPR spectra show not only that for both systems triplet quenching by nitroxide induces spin polarization of the radical spin sublevels, but also that the coupling interaction can be either weak or strong depending on the orientation of the peptide dipole. As opposed to the concept of dyads, the molecules investigated are thus better described as fullerene−peptide−radical systems to stress the active role of the bridge as an important ingredient capable of tuning the system's physicochemical properties. ■ INTRODUCTIONSince its discovery in 1985, 1 the properties of the C 60 fullerene have been extensively investigated. Thorough understanding of its chemical reactivity has led to the synthesis of a large number of fullerene derivatives whose properties and applications have been studied from many viewpoints.2 Among them, interesting molecular systems are featured by fullerene−radical dyads where C 60 is covalently linked, through formation of fulleropyrrolidines, 3 either directly or via a molecular spacer to a free radical function. 4,5 Besides interest in synthesis and properties of C 60 and its derivatives, endohedral fullerenes 6 in which atom or small molecule is encapsulated in the C 60 nano cavity have become a field that attracts more attention due to their potential applications in medicine and biology. 7,8 In particular, the recently successful synthesis 9 of H 2 @C 60 by the molecular surgery method makes the material available in quantities from tens to hundreds of milligrams. Therefore, to probe the interactions of the motion of the endohedral molecule with the outside environment, 10 a series of H 2 @C 60 derivatives covalently linked to a nitroxide radical has been synthesized in which the nitroxide moiety acts as a relaxation agent, and the effect of the nitroxide radical on proton nuclear spin relaxation of the endohedral molecule has been investigated. 11In this Article, we describe properties and compare the behavior of compounds in which a free radical and a fullerene C 60 moiety are...

show abstract

Section: ■ Results and Discussionsupporting

confidence: 76%

Effect of Orientation of the Peptide-Bridge Dipole Moment on the Properties of Fullerene–Peptide–Radical Systems

et al. 2012

View full text Add to dashboard Cite

show abstract

“…Another secondary mechanism might be oxidation of DMPO through it's cation radical, by addition of water (and elimination of a proton) with ultimate formation of DMPO-OH adduct 48 . This, as well as all other possible conversions of DMPO in aqueous solution (oxidation by dissolved oxygen, dimerization, reduction/oxidation, etc.…”

Section: Resultsmentioning

confidence: 99%

Environmentally Persistent Free Radicals (EPFRs)-2. Are Free Hydroxyl Radicals Generated in Aqueous Solutions?

Khachatryan

Dellinger

2011

Environ. Sci. Technol.

144

120

View full text Add to dashboard Cite

A chemical spin trap, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), in conjunction with electron paramagnetic resonance (EPR) spectroscopy was employed to measure the production of hydroxyl radical (.OH) in aqueous suspensions of 5% Cu(II)O/silica (3.9% Cu) particles containing environmentally persistent free radicals (EPFRs) of 2-monochlorophenol (2-MCP). The results indicate: 1) a significant differences in accumulated DMPO-OH adducts between EPFR containing particles and non-EPFR control samples, 2) a strong correlation between the concentration of DMPO-OH adducts and EPFRs per gram of particles, and 3) a slow, constant growth of DMPO-OH concentration over a period of days in solution containing 50 μg/ml EPFRs particles + DMPO (150 mM) + reagent balanced by 200 μl phosphate buffered (pH = 7.4) saline. However, failure to form secondary radicals using standard scavengers, such as ethanol, dimethylsulfoxide, sodium formate, and sodium azide, suggests free hydroxyl radicals may not have been generated in solution. This suggests surface-bound, rather than free, hydroxyl radicals were generated by a surface catalyzed-redox cycle involving both the EPFRs and Cu(II)O. Toxicological studies clearly indicate these bound free radicals promote various types of cardiovascular and pulmonary disease normally attributed to unbound free radicals; however, the exact chemical mechanism deserves further study in light of the implication of formation of bound, rather than free, hydroxyl radicals.

show abstract

“…Spectra were recorded at a scan rate of 2400 nm/min, and difference spectra were generated using Origin 3.0 software. sumed that the E°DBNBS ⅐ ϩ /DBNBS is comparable with E°M NP ⅐ ϩ /MNP (2.06 V) (23), which is beyond the reach of the high oxidation states of heme proteins under non-forcing conditions. Hence, "inverted spin trapping" is ruled out in the cyt c/H 2 O 2 /DBNBS reaction, since (i) the reaction time was only 10 min and (ii) the Fe IV ϭ O center is rapidly converted to Fe III by endogenous electron transfer to heme (data not shown).…”

Section: Analysis Of Dbnbs Mass Adduct Formation With Ferricytochromementioning

confidence: 88%

“…Inverted spin trapping of DBNBS ⅐ ϩ by an amino acid residue could lead to a DBNBS-cyt c adduct identical to that formed by "normal" spin trapping of X ⅐ by DBNBS (reviewed in Ref. 23 Reactions were carried out in 50 mM ammonium acetate (pH 7.5) containing 200 M DTPA. The HPLC-purified reaction products (see "Experimental Procedures") were collected, lyophilized, and suspended in 1:1 methanol/water with 0.5% acetic acid.…”

Section: Analysis Of Dbnbs Mass Adduct Formation With Ferricytochromementioning

confidence: 99%

Mass Spectral Analysis of Protein-based Radicals Using DBNBS

Filosa

English

2001

Journal of Biological Chemistry

View full text Add to dashboard Cite

Protein-based radicals generated in the reaction of ferricytochrome c (cyt c) with H 2 O 2 were investigated by electrospray mass spectrometry (ESI-MS) using 3,5-dibromo-4-nitrosobenzenesulfonate (DBNBS). Up to four DBNBS-cyt c adducts were observed in the mass spectra. However, by varying the reaction conditions (0 -5 molar equivalents of H 2 O 2 and substituting cyt c with its cyanide adduct which is resistant to peroxidation), noncovalent DBNBS adduct formation was inferred. Nonetheless, optical difference spectra revealed the presence of a small fraction of covalently trapped DBNBS. To probe the nature of the noncovalent DBNBS adducts, the less basic proteins, metmyoglobin (Mb) and ␣-lactalbumin, were substituted for cyt c in the cyt c/H 2 O 2 /DBNBS reaction. A maximum of two DBNBS adducts were observed in the mass spectra of the products of the Mb/ H 2 O 2 /DBNBS reactions, whereas no adducts were detected following ␣-lactalbumin/H 2 O 2 /DBNBS incubation, which is consistent with adduct formation via spin trapping only. Titration with DBNBS at pH 2.0 yielded noncovalent DBNBS-cyt c adducts and induced folding of acid-denatured cyt c, as monitored by ESI-MS and optical spectroscopy, respectively. Thus, the noncovalent DBNBS-cyt c mass adducts observed are assigned to ion pair formation occurring between the negatively charged sulfonate group on DBNBS and positively charged surface residues on cyt c. The results reveal the pitfalls inherent in using mass spectral data with negatively charged spin traps such as DBNBS to identify sites of radical formation on basic proteins such as cyt c.Reactive oxygen species, such as H 2 O 2 and superoxide, are generated by all aerobic cells as by-products of a number of metabolic reactions and in response to various stimuli. Oxidative damage can occur when H 2 O 2 reacts with heme proteins, such as ferricytochrome c (cyt c), 1 to form highly reactive oxyferryl-heme and transient protein-based radical species (X ⅐ ) that are linked to the initiation of lipid peroxidation (1, 2). Detection of X ⅐ in biological systems is often difficult because they are short-lived and highly reactive. Spin traps, which are diamagnetic compounds containing a functional group that reacts with X ⅐ to form a more stable paramagnetic adduct (XST ⅐ ), are frequently used in electron paramagnetic resonance (EPR) investigations (3). Although EPR signals can provide information about a radical center and its environment, the specific sites of radical formation in biomolecules are not identified. Coupling of high performance liquid chromatography (HPLC) and mass spectrometry (MS) has been used to identify spin adducts of various small molecules (4 -6). Our research group has extended the use of LC/MS of spin adducts to proteins to overcome the inherent limitations of EPR. We have found that conversion of the spin adduct XST ⅐ to a stable diamagnetic mass adduct (XMA) via ascorbate reduction permits the assignment of XMA to a specific amino acid residue when spin trapping and peptide mass mapping by ...

show abstract

Spin Trapping and Electron Transfer

Cited by 16 publications

References 128 publications

Effect of Orientation of the Peptide-Bridge Dipole Moment on the Properties of Fullerene–Peptide–Radical Systems

Effect of Orientation of the Peptide-Bridge Dipole Moment on the Properties of Fullerene–Peptide–Radical Systems

Environmentally Persistent Free Radicals (EPFRs)-2. Are Free Hydroxyl Radicals Generated in Aqueous Solutions?

Mass Spectral Analysis of Protein-based Radicals Using DBNBS

Contact Info

Product

Resources

About