3637-10-3Relevant articles and documents
Nitroxide destruction and flavin-photosensitized damage in inner mitochondrial membranes
Mehlhorn, Rolf Joachim,Packer, Lester
, p. 1452 - 1462 (1982)
Nitroxide free radicals lost their paramagnetic absorption spectrum when they were illuminated with visible light in aged but not freshly isolated inner mitochondrial membranes (SMP's).The action spectrum of spin loss rates coincided with a flavin absorption spectrum.Spin loss consisted of one-electron reduction and "destruction", the latter being defined as spin loss that cannot be reversed by ferricyanide oxidation.By placing SMP's in gas permeable tubing and illuminating alternately under nitrogen and air, it was possible to discriminate qualitatively betweenspin reduction and destruction.Aerobic spin loss consisted entirely of destruction.When aged SMP's were centrifuged, spin loss was observed in supernatants but not pellets.Flavin fluorescence was observed in the supernatants, suggesting that free flavins catalyzed spin loss.However, addition of exogenous flavins to fresh SMP's did not cause spin loss; hence some other factor was required to cause nitroxide destruction.This factor accumulates during either aerobic or anaerobic aging of SMP's and may be present in mitochondria.Supernatants of aged SMP's, when added to freshly isolated SMP's, induced rapid nitroxide destruction, slightly accelerated photodamage to succinate oxidase, and considerably increased photo-induced lipid peroxidation.
Sterically shielded spin labels for in-cell EPR spectroscopy: Analysis of stability in reducing environment
Jagtap,Krstic,Kunjir,H?nsel,Prisner,Sigurdsson, Snorri Th.
, p. 78 - 85 (2015)
Electron paramagnetic resonance (EPR) spectroscopy is a powerful and widely used technique for studying structure and dynamics of biomolecules under bio-orthogonal conditions. In-cell EPR is an emerging area in this field; however, it is hampered by the reducing environment present in cells, which reduces most nitroxide spin labels to their corresponding diamagnetic N-hydroxyl derivatives. To determine which radicals are best suited for in-cell EPR studies, we systematically studied the effects of substitution on radical stability using five different classes of radicals, specifically piperidine-, imidazolidine-, pyrrolidine-, and isoindoline-based nitroxides as well as the Finland trityl radical. Thermodynamic parameters of nitroxide reduction were determined by cyclic voltammetry; the rate of reduction in the presence of ascorbate, cellular extracts, and after injection into oocytes was measured by continuous-wave EPR spectroscopy. Our study revealed that tetraethyl-substituted nitroxides are good candidates for in-cell EPR studies, in particular pyrrolidine derivatives, which are slightly more stable than the trityl radical.
A Stopped-Flow ESR Study on the Reactivity of Some Nitroxide Radicals with Ascorbic Acid in the Presence of β-Cyclodextrin
Okazaki, M.,Kuwata, K.
, p. 4437 - 4440 (1985)
Reaction rates between ascorbic acid and three aminoxyl radicals, di-tert-butylnitroxide (DTBN), 2,2,5,5-tetramethyl-piperidine-1-oxyl (Tempo), and 2,2,5,5-tetramethylpiperidine-1-oxyl-4-ol (Tempol), were determined by the stopped-flow ESR technique in the presence of β-cyclodextrin (β-CDX) in aqueous solution.The reaction was found to be first order with respect to both ascorbic acid and the aminoxyl radicals.The reaction rates of both the free aminoxyl radicals and those included in the cavity of β-CDX were estimated by assuming a reaction mechanism.For DTBN and Tempol, the reaction rates decrease to 2/3 to 1/2 of the original value when these radicals are included in the cavity of β-CDX.In contrast to these cases, Tempo reacts with ascorbic acid just the same whether it is included in the cavity or not.These results could be explained by the effect of inclusion of these nitroxide radicals in the cyclodextrin cavity and are consistent with the molecular dispositions of these complexes which have been shown previously.
Scavenging free radicals to preserve enhancement and extend relaxation times in NMR using dynamic nuclear polarization
Mieville, Pascal,Ahuja, Puneet,Sarkar, Riddhiman,Jannin, Sami,Vasos, Paul R.,Gerber-Lemaire, Sandrine,Mishkovsky, Mor,Comment, Arnaud,Gruetter, Rolf,Ouari, Olivier,Tordo, Paul,Bodenhausen, Geoffrey
, p. 6182 - 6185 (2010)
Vitamin C for longer lifetimes: N-oxide radicals that are widely used for dynamic nuclear polarization can be reduced by scavengers such as sodium ascorbate (vitamin C) during the dissolution process, thus diminishing losses of polarization during the transfer and extending transverse and longitudinal relaxation times in NMR spectroscopy (see picture).
The use of cyclic nitroxide radicals as HNO scavengers
Samuni, Yuval,Samuni, Uri,Goldstein, Sara
, p. 155 - 161 (2013)
Reduction of cyclic stable nitroxides (RNO) by HNO to the respective hydroxylamines (RNO-H) has been demonstrated using EPR spectrometry. HNO shows low reactivity toward piperidine, pyrrolidine and nitronyl nitroxides with rate constants below 1.4 × 105 M- 1 s- 1 at pH 7.0, despite the high driving force for these reactions. The rate constants can be predicted assuming that the reactions take place via a concerted proton-electron transfer pathway and significantly low self-exchange rate constants for HNO/NO and RNO-H/RNO. NO does not react with piperidine and pyrrolidine nitroxides, but does add to HNO forming the highly oxidizing and moderately reducing hyponitrite radicals. In this work, the radicals are produced by pulse radiolysis and the rate constants of their reactions with 2,2,6,6,-tetramethylpiperidine-1-oxyl (TEMPO), 4-hydroxy-2,2,6,6-tetramethyl piperidine-1-oxyl (TEMPOL) and 3-carbamoyl-PROXYL have been determined at pH 6.8 to be (2.4 ± 0.2) × 106, (9.8 ± 0.2) × 105, (5.9 ± 0.5) × 105 M- 1 s - 1, respectively. This low reactivity implies that NO competes efficiently with these nitroxides for the hyponitrite radical. The ability of TEMPOL and 2-(4-carboxyphenyl)-4,4,5,5,-tetramethyl-imidazoline-1-oxyl-3-oxide (C-PTIO) to oxidize HNO and their different reactivity toward NO are used to quantify HNO formed via acetohydroxamic acid oxidation. The extent of TEMPOL or C-PTIO reduction was similar to the yield of HNO formed upon oxidation by OH under anoxia, but not by the metmyoglobin and H2O2 reaction system where both nitroxides catalytically facilitate H 2O2 depletion and nitrite accumulation. In this system the conversion of C-PTIO into 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1- oxyl (C-PTI) is a minor reaction, which does not provide any mechanistic insight.
Antioxidant and antiradical activities of resorcinarene tetranitroxides
Vovk, Andriy I.,Shivanyuk, Alexander M.,Bugas, Roman V.,Muzychka, Oxana V.,Melnyk, Andriy K.
, p. 1314 - 1317 (2009)
Resorcinarene oxazines bearing four TEMPO fragments at the wide rim of the macrocycle were prepared through the aminomethylation of resorcinarene octols with 4-amino-TEMPO and formaldehyde. Tetra-TEMPO resorcinarenes are efficient scavengers of 1,1-diphen
2′-Alkynylnucleotides: A Sequence- and Spin Label-Flexible Strategy for EPR Spectroscopy in DNA
Haugland, Marius M.,El-Sagheer, Afaf H.,Porter, Rachel J.,Pe?a, Javier,Brown, Tom,Anderson, Edward A.,Lovett, Janet E.
, p. 9069 - 9072 (2016/08/05)
Electron paramagnetic resonance (EPR) spectroscopy is a powerful method to elucidate molecular structure through the measurement of distances between conformationally well-defined spin labels. Here we report a sequence-flexible approach to the synthesis of double spin-labeled DNA duplexes, where 2′-alkynylnucleosides are incorporated at terminal and internal positions on complementary strands. Post-DNA synthesis copper-catalyzed azide-alkyne cycloaddition (CuAAC) reactions with a variety of spin labels enable the use of double electron-electron resonance experiments to measure a number of distances on the duplex, affording a high level of detailed structural information.
Synthesis and reduction kinetics of sterically shielded pyrrolidine nitroxides
Paletta, Joseph T.,Pink, Maren,Foley, Bridget,Rajca, Suchada,Rajca, Andrzej
supporting information, p. 5322 - 5325 (2013/01/15)
A series of sterically shielded pyrrolidine nitroxides were synthesized, and their reduction by ascorbate (vitamin C) indicate that nitroxide 3, a tetraethyl derivative of 3-carboxy-PROXYL, is reduced at the slowest rate among known nitroxides, i.e., at a 60-fold slower rate than that for 3-carboxy-PROXYL.
POLYMERISATION INITIATOR
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Page/Page column 38, (2010/08/04)
The invention relates to novel O-dialkylamino-isoureas and polymerizable compositions comprising these O-dialkylamino-isoureas of compounds of the general formula (I). The invention further relates to the use of O-dialkylamino-isoureas as polymerization initiators, especially to prepare coatings or for controlled degradation of polyolefins.
Synthetic studies on N-alkoxyamines: A mild and broadly applicable route starting from nitroxide radicals and aldehydes
Schoening, Kai-Uwe,Fischer, Walter,Hauck, Stefan,Dichtl, Alexander,Kuepfert, Michael
supporting information; experimental part, p. 1567 - 1573 (2009/07/01)
A broad variety of 2,2,6,6-tetramethylpiperidine-based N-alkoxyamines were prepared in a newly found reaction. By means of a copper-catalyzed fragmentation reaction of aldehyde peroxides in the presence of TEMPO or TEMPO derivatives, N-alkoxyamines were o
