Interaction of chlorine dioxide with nitroxyl radicals

The formation of charge transfer complexes between chlorine dioxide and nitroxyl radicals (2,2,6,6-tetramethylpiperidin-1-oxyl, 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl, 4-oxo-2,2,6,6-tetramethylpiperidin-1-oxyl, 4-methoxy-2,2,6,6-tetramethylpiperidin-1-oxyl, 4-acetylamido-2,2,6,6-tetramethylpiperidin-1-oxyl, 2,2,5,5-tetramethyl-4-phenyl-3-imidazolin-1-oxyl, and bis(4-methoxyphenyl) nitroxide) in acetone, acetonitrile, n-heptane, diethyl ether, carbon tetrachloride, toluene, and dichloromethane was found by spectrophotometry at –60—+20 °C. The thermodynamic parameters of complex formation were determined. The radical structure affects its complex formation ability. The charge transfer complex is transformed into the corresponding oxoammonium salt.     

Characterization of titanium dioxide photoactivity following the formation of radicals by EPR spectroscopy

In order to find ways to characterize oxygen-saturated aqueous TiO₂ suspensions, the formation of photo-induced free radicals was followed by EPR spectroscopy, using as indicators N-oxide and nitrone spin trapping agents, 5,5-dimethyl-1-pyrroline N-oxide (DMPO), 3,3,5,5-tetramethyl-1-pyrroline N-oxide (TMPO), α-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POB N), 4-(N-methylpyridyl)-N-tert-butylnitrone (MePyBN), as well as semi-stable free radicals, 4-hydroxy-2,2,6,6-tetramethylpiperidine N-oxyl (TEMPOL), cation radical of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), diammonium salt (ABTS) and 1,1-diphenyl-2-picrylhydrazyl (DPPH). DMPO and TMPO are efficiently oxidized to the EPR-silent products via radical in termediates. Conversely, the nitrone spin traps (POBN and MePyBN) showed selective formation of hydroxyl radical spin adducts upon continuous irradiation of oxygenated TiO₂ suspensions. Their concentrations increased proportionally with the amount of photocatalyst and irradiation time. The EPR spectrum of the semi-stable free radicals TEMPOL, ABTS^·+ or DPPH is gradually eliminated during irradiation, and this system represents a simple technique for the evaluation of TiO₂ activity.     

Electron spin resonance studies on the oxidation mechanism of sterically hindered cyclic amines in TiO2 photocatalytic systems

A sterically hindered cyclic amine, 4-hydroxy-2,2,6,6-tetramethylpiperidine (HTMP), is converted to the corresponding aminoxyl radical (nitroxide radical), 4-hydroxy-2,2,6,6-tetramethyl piperidine 1-oxyl (TEMPOL radical) as a result of a photocatalytic reaction in TiO2 aqueous suspension. The time profile of the radical formation and the effect of additives, such as SCN-, I-, methanol, and H2O2, on the initial formation rate were measured in order to elucidate the reaction mechanism. The experimental observations indicated that the direct photocatalytic oxidation of HTMP followed by reaction with O2 is the dominant process in the formation of TEMPOL radicals. Electrochemical measurements showed that HTMP is oxidized at 0.7 V (vs NHE), which is consistent with the proposed mechanism. The possibility of other processes, involving reactions with singlet molecular oxygen, superoxide radical, and hydroxyl radical, were excluded from the reaction mechanism.     

Polymers having stable radicals. I. Synthesis of nitroxyl polymers from 4-methacryloyl derivatives of 2,2,6,6-tetramethylpiperidine

Polymers having stable nitroxyl free radicals, poly-4-methacryloylamino- and poly-4-methacryloyloxy-2,2,6,6-tetramethylpiperidine-1-oxyls, were synthesized from their precursor polymers by oxidizing them in a methanolic solution of hydrogen peroxide. The precursor polymers were prepared by radical polymerization of 4-methacryloyl-amino/oxy-2,2,6,6-tetramethylpiperidines in various solvents. These polymerizations in acetic acid were found to yield polymers of high molecular weight. The copolymers of the precursor monomers with styrene and methyl methacrylate were also prepared as precursor copolymers. These precursor polymers of a piperidine type were converted to the polymers having stable nitroxyl free radicals by the hydrogen peroxide method. In this report, it was assumed that the post-oxidation reaction introduced a nitroxyl group smoothly and quantitatively at room temperature. Elucidations of the stable radical formation and the electron spin behavior of the stable radical polymers were made in terms of elemental analyses, infrared, ultraviolet, and ESR spectroscopy.     

The Synthesis of New Type Diazo Compounds by 4-hydroxy-2,2,6,6-Tertramethyl-1-Piperidinyloxy 1 as The Phases Transfer Dehydrogenation Catalyst

It is well known that 4-hydroxy-2,2,6,6-tertramethyl-1-piperidinyloxyl is a stable nitroxyl radical. It can be used as antioxidants¹ and spin labeled compounds to mark protein, biomembrance and nucleic acid etc. Furthermore, as an efficient inhibitor, it can prevent olefin polymerizing by free radical. However, using 4-hydroxy-2,2,6,6-tertramethyl-1-piperidinyloxyl as the phase transfer catalyst has not been reported so far.     

Photoexcitation of aqueous suspensions of titanium dioxide nanoparticles: an electron spin resonance spin trapping study of potentially oxidative reactions

It is well‐established that exposure of aqueous suspensions of titanium dioxide (TiO₂) nanoparticles to ultraviolet A (UVA) light produces reactive oxygen species which leads to biological damage. However, there is disagreement in the literature as to the exact nature of these species and how they are formed. Using a number of different spin traps (i.e. PBN, POBN, DMPO, DEPMPO), we have shown that the primary damaging species produced on irradiation of an aqueous suspension of TiO₂ is the hydroxyl radical, which is formed at the valence band hole under both aerobic and hypoxic conditions. Hydroxyl radical production is enhanced by the presence of oxygen which probably reacts with the conduction band electrons or resultant Ti³⁺, inhibiting hole‐electron recombination, although we find no evidence of reaction of oxygen to form free superoxide radical anions or of the formation of any other radical at that site. The present results suggest that the resulting O₂ ^?? species may not be as labile as previously thought and may possibly undergo further reduction to the O ₂ ^2? dianion. Hydroxyl radicals formed at the surface of the TiO ₂ readily react with substrates containing an abstractable hydrogen to produce secondary radicals that, in biological systems, could lead to cell damage.     

Synthesis and properties of 3,5-dibromo-4-oxo-2,2,6,6-tetramethylpiperidine-1-oxyl radical

Bromination of 1-hydroxy-4-oxo-2,2,6,6-tetramethylpiperidine gives 3,5-dibromo-1-hydroxy-4-oxo-2,2,6,6-tetramethylpiperidine hydrobromide. Oxidation of the latter generates 3,5-dibromo-4-oxo-2,2,6,6-tetramethylpiperdine-1-oxyl radical, which represents a convenient acylating spin trap.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 73–74, January, 1992.     

Reactions of hydrated electron with various radicals: spin factor in diffusion-controlled reactions

The reactions of hydrated electron (eaq-) with various radicals have been studied in pulse radiolysis experiments. These radicals are hydroxyl radical (*OH), sulfite radical anion (*SO3-), carbonate radical anion (CO3*-), carbon dioxide radical anion (*CO2-), azidyl radical (*N3), dibromine radical anion (Br2*-), diiodine radical anion (I2*-), 2-hydroxy-2-propyl radical (*C(CH3)2OH), 2-hydroxy-2-methyl-1-propyl radical ((*CH2)(CH3)2COH), hydroxycyclohexadienyl radical (*C6H6OH), phenoxyl radical (C6H5O*), p-methylphenoxyl radical (p-(H3C)C6H4O*), p-benzosemiquinone radical anion (p-OC6H4O*-), and phenylthiyl radical (C6H5S*). The kinetics of eaq- was followed in the presence of the counter radicals in transient optical absorption measurements. The rate constants of the eaq- reactions with radicals have been determined over a temperature range of 5-75 degrees C from the kinetic analysis of systems of multiple second-order reactions. The observed high rate constants for all the eaq- + radical reactions have been analyzed with the Smoluchowski equation. This analysis suggests that many of the eaq- + radical reactions are diffusion-controlled with a spin factor of 1/4, while other reactions with *OH, *N3, Br2*-, I2*-, and C6H5S* have spin factors significantly larger than 1/4. Spin dynamics for the eaq-/radical pairs is discussed to explain the different spin factors. The reactions with *OH, *N3, Br2*-, and I2*- have also been found to have apparent activation energies less than that for diffusion control, and it is suggested that the spin factors for these reactions decrease with increasing temperature. Such a decrease in spin factor may reflect a changing competition between spin relaxation/conversion and diffusive escape from the radical pairs.     

ESR spin probes in ionic liquids.

The spin probes 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL), and 2,2,6,6-tetramethyl-4-trimethylammoniumpiperidine-1-oxylIodide (CAT-1) are examined in a number of ionic liquids based on substituted imidazolium cations and tetrafluoroborate and hexafluorophosphate anions, respectively. The reorientation correlation times tau(R) of the spin probes in these systems have been determined by complete spectra simulation and, for rapid reortientation, by analysis of the intensities of the hyperfine lines of the electron spin resonance (ESR) spectra. A comparison of the results with those from the model system glycerol/water and selected organic solvents is made. Additions of diamagnetic and paramagnetic ions allow the conclusion that salt effects and spin exchange are present, and that both are superimposed by motional effects. Specific interactions in the ionic liquids, as well as between the spin-probe molecules and the constituents of the ionic liquids are reflected in the spectra of the spin probes, depending on their molecular structure.     

Oxidation of 4-substituted TEMPO derivatives reveals modifications at the 1- and 4-positions

Potenital pathways for the deactivation of hindered amine light stabilisers (HALS) have been investigated by observing reactions of model compounds--based on 4-substituted derivatives of 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO)--with hydroxyl radicals. In these reactions, dilute aqueous suspensions of photocatalytic nanoparticulate titanium dioxide were irradiated with UV light in the presence of water-soluble TEMPO derivatives. Electron spin resonance (ESR) and electrospray ionisation mass-spectrometry (ESI-MS) data were acquired to provide complementary structural elucidation of the odd- and even-electron products of these reactions and both techniques show evidence for the formation of 4-oxo-TEMPO (TEMPONE). TEMPONE formation from the 4-substituted TEMPO compounds is proposed to be initiated by hydrogen abstraction at the 4-position by hydroxyl radical. High-level ab initio calculations reveal a thermodynamic preference for abstraction of this hydrogen but computed activation barriers indicate that, although viable, it is less favoured than hydrogen abstraction from elsewhere on the TEMPO scaffold. If a radical is formed at the 4-position however, calculations elucidate two reaction pathways leading to TEMPONE following combination with either a second hydroxyl radical or dioxygen. An alternate mechanism for conversion of TEMPOL to TEMPONE via an alkoxyl radical intermediate is also considered and found to be competitive with the other pathways. ESI-MS analysis also shows an increased abundance of analogous 4-substituted piperidines during the course of irradiation, suggesting competitive modification at the 1-position to produce a secondary amine. This modification is confirmed by characteristic fragmentation patterns of the ionised piperidines obtained by tandem mass spectrometry. The conclusions describe how reaction at the 4-position could be responsible for the gradual depletion of HALS in pigmented surface coatings and secondly, that modification at nitrogen to form the corresponding secondary amine species may play a greater role in the stabilisation mechanisms of HALS than previously considered.     

Simultaneous production of superoxide radical and singlet oxygen by sulphonated chloroaluminum phthalocyanine incorporated in human low-density lipoproteins: implications for photodynamic therapy

Sulfonated chloroaluminum phthalocyanines have been studied for their use in the photodynamic therapy (PDT) of tumors. Plasma low-density lipoproteins (LDL) are important carriers of phthalocyanines in the blood, but on exposure to visible light, phthalocyanine-loaded LDL undergo an oxidation process that propagates to erythrocytes. We attempted to identify the reactive species involved in LDL and erythrocyte oxidation by means of electron paramagnetic resonance (EPR) spectroscopy in the presence of 2,2,6,6-tetramethyl-4-piperidone (TEMP) and the spin trap 5,5'-dimethyl-1-pyrroline-N-oxide (DMPO). Irradiation of phthalocyanine-loaded LDL in the presence of DMPO resulted in the formation of a four-line EPR spectrum with relative intensity of 1:2:2:1 (a(N) = a(H) = 14.8 G), characteristic of DMPO-hydroxyl radical spin adduct. This signal was sensitive to superoxide dismutase and slightly sensitive to catalase, but a mixture of the two enzymatic activities was the most efficient in promoting a decrease in the intensity of the EPR signal. In the presence of erythrocytes, an increase in the quartet intensity for a hematocrit of 1% and 4% was observed, decreasing for higher erythrocyte concentrations. The irradiation of phthalocyanine-loaded LDL in the presence of TEMP resulted in the formation of a nitroxide radical, 2,2,6,6-tetramethyl-4-piperidone-N-oxyl radical, intensity of which was sensitive to histidine, a singlet oxygen ((1)O(2)) quencher. Under both incubation conditions, with DMPO and TEMP, the formation of the respective EPR signals required the sensitizer (phthalocyanine), light and oxygen. Overall, the results are compatible with the simultaneous formation of superoxide anion and (1)O(2), implying that Type-I and Type-II mechanisms of photochemistry are simultaneously operative in phthalocyanine-loaded LDL. However, for a constant LDL/phthalocyanine ratio, the formation of oxygen free radicals shows a biphasic behavior with the concentration of LDL increasing and reaching a plateau, whereas the formation of (1)O(2) increases linearly with LDL concentration. Erythrocytes at high (physiological) concentrations induced a decrease in the intensity of both EPR signals. The physiological relevance of these findings in the framework of PDT is briefly discussed.     

Generation of Aryl Radicals through Reduction of Hypervalent Iodine(III) Compounds with TEMPONa: Radical Alkene Oxyarylation

A novel method for selective generation of aryl radicals from diaryliodonium salts and iodanylidene malonates with sodium 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPONa) as a single‐electron transfer (SET) reducing reagent is described. In the presence of various alkenes, aryl radicals formed after SET‐reduction of hypervalent iodine compounds undergo alkene addition and the adduct radicals that are thus generated are efficiently trapped by the concomitantly generated TEMPO radical to eventually afford oxyarylated products in moderate to very good yields. The efficiency of aryl radical generation of various iodine(III) reagents is studied and the generation of an iodanylidene malonate aryl radical is also investigated by computational methods.     

Spin exchange of nitroxyl radicals in H2O and D2O

By means of continuous wave electron spin resonance (cw ESR) in the X and L bands, the spin exchange of series of different concentrations of the spin probes 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL), and 4-(trimethylamino)-2,2,6,6-tetramethylpiperidine-1-oxyl iodide (CAT-1) in H(2)O and D(2)O have been examined. The rate constants k(e) of the spin exchange have been determined by complete spectra simulations, as well as directly from hyperfine line broadenings and concentration depending line shifts. The obtained results showed a good agreement. Their respective differences {k(e)(H(2)O) - k(e)(D(2)O)} could be determined for the first time. They reflect the different influence of the solvents on the spin dynamics but confirm the decrease of the reaction rate in D(2)O, caused by the higher degree of order in this liquid. The spectroscopic and kinetic results presented in this paper establish a further kind of isotopic effect.     

TWO NEW METHODS OF ACTINOMETRY FOR EPR-MEASUREMENTS

Abstract— Two methods to perform actinometry in an EPR-cavity are described. One method is based on the observation that photoproduced anion radicals of hematoporphyrin react with the stable free radical 2,2,6,6-tetramethyl-4-piperidone-N-oxyl to eliminate the spin. The other method is based on the dye sensitized photoproduction of nitroxyl radicals resulting from the reaction of singlet oxygen with sterically hindered amines.     

UV-generated free radicals (FR) in skin: their prevention by sunscreens and their induction by self-tanning agents

In the past few years, the cellular effects of ultraviolet (UV) irradiation induced in skin have become increasingly recognized. Indeed, it is now well known that UV irradiation induces structural and cellular changes in all the compartments of skin tissue. The generation of reactive oxygen species (ROS) is the first and immediate consequence of UV exposure and therefore the quantitative determination of free radical reactions in the skin during UV radiation is of primary importance for the understanding of dermatological photodamage. The RSF method (radical sun protection factor) herein presented, based on electron spin resonance spectroscopy (ESR), enables the measurement of free radical reactions in skin biopsies directly during UV radiation. The amount of free radicals varies with UV doses and can be standardized by varying UV irradiance or exposure time. The RSF method allows the determination of the protective effect of UV filters and sunscreens as well as the radical induction capacity of self-tanning agents as dihydroxyacetone (DHA). The reaction of the reducing sugars used in self-tanning products and amino acids in the skin layer (Maillard reaction) leads to the formation of Amadori products that generate free radicals during UV irradiation. Using the RSF method three different self-tanning agents were analyzed and it was found, that in DHA-treated skin more than 180% additional radicals were generated during sun exposure with respect to untreated skin. For this reason the exposure duration in the sun must be shortened when self-tanners are used and photoaging processes are accelerated.     

Photochemical and phototoxic properties of ethyl 1,4-dihydro-8-nitro-4-oxoquinoline-3-carboxylate, a new quinoline derivative

The present study demonstrates photoinduced generation of superoxide radical anion and singlet oxygen upon UVA irradiation of ethyl 1,4-dihydro-8-nitro-4-oxoquinoline-3-carboxylate (DNQC), and its cytotoxic/phototoxic effects on murine leukemia L1210 cells. The formation of reactive oxygen species (ROS) was investigated by EPR spectroscopy using in situ spin trapping technique and 4-hydroxy-2,2,6,6-piperidine (TMP) for singlet oxygen ((1)O(2)) detection. The EPR spectra monitored upon photoexcitation of aerated solutions of DNQC in dimethylsulfoxide evidenced the efficient activation of molecular oxygen via Types I and II mechanisms. The cytotoxic/phototoxic effects of DNQC, analysis of cell cycle, induction of apoptosis/necrosis, DNA damage and molecular mechanism of apoptotic death of L1210 cells in dark and in the presence of UVA irradiation were compared. DNQC induced a different cytotoxic/phototoxic effect, which was concentration- and time-dependent. The four highest tested concentrations of non-photoactivated and photoactivated DNQC induced immediate cytotoxic/phototoxic effect after 24h cultivation of L1210 cells. This effect decreased with the time of treatment. The irradiation increased the sensitivity of leukemia cell line on DNQC, but the cell sensitivity decreased with time of processing. Quinolone derivative DNQC significantly induced direct DNA strand breaks in L1210 cells, which were increased with the irradiation of cells. The DNA damage generated by DNQC alone/with combination of UVA irradiation induced cell arrest in G(0)/G(1) and G(2)/M phases, decrease in the number of L1210 cells in Sphase and apoptotic cell death of certain part of cell population after 24 h of influence. DNQC alone/with combination of UVA irradiation induced apoptosis in L1210 cells through ROS-dependent mitochondrial pathway.     

Active oxygen species generated from photoexcited fullerene (C60) as potential medicines: O2-* versus 1O2

To characterize fullerenes (C(60) and C(70)) as photosensitizers in biological systems, the generation of active oxygen species, through energy transfer (singlet oxygen (1)O(2)) and electron transfer (reduced active oxygen radicals such as superoxide anion radical O(2)(-)* and hydroxyl radical *OH), was studied by a combination of methods, including biochemical (DNA-cleavage assay in the presence of various scavengers of active oxygen species), physicochemical (EPR radical trapping and near-infrared spectrometry), and chemical methods (nitro blue tetrazolium (NBT) method). Whereas (1)O(2) was generated effectively by photoexcited C(60) in nonpolar solvents such as benzene and benzonitrile, we found that O(2)(-)* and *OH were produced instead of (1)O(2) in polar solvents such as water, especially in the presence of a physiological concentration of reductants including NADH. The above results, together with those of a DNA cleavage assay in the presence of various scavengers of specific active oxygen species, indicate that the active oxygen species primarily responsible for photoinduced DNA cleavage by C(60) under physiological conditions are reduced species such as O(2)(-)* and *OH.     

Zeolite encapsulation decreases TiO2-photosensitized ROS generation in cultured human skin fibroblasts

Sunscreens protect skin against sunburn. However, studies have demonstrated that UV-irradiated sunscreen components such as titanium dioxide (TiO2) promote the photogeneration of reactive oxygen species (ROS). Because encapsulation of TiO2 within zeolites alters its photocatalytic activity, supramolecular composites based on NaY zeolite hosts containing TiO2 guests were prepared, and the effects on ROS formation in cells under UVA-irradiation evaluated. DCFH-DA (2',7'-dichlorofluorescein diacetate) was used as a profluorescent probe to monitor intracellular ROS. The detection of intracellular 2',7'-dichlorofluorescein (DCF) fluorescence by confocal microscopy revealed that DCFH-DA was taken up, hydrolyzed and oxidized by yeast cells and cultured human skin fibroblasts within 20 and 6 min, respectively. Higher DCF fluorescence was observed in fibroblasts following UVA irradiation in the absence but not in the presence of the radical nitroxide, TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperydine-1-oxyl), which exhibits superoxide dismutase-mimetic and catalase-mimetic activity. UVA-induced fluorescence increased by approximately 50% in the presence of 32-nm anatase TiO2 particles and decreased by essentially an equal amount in the presence of TiO2 encapsulated within NaY zeolites (TiO2@NaY). Addition of the uncomplexed NaY host also decreased (by approximately 30%) the amount of UVA-induced fluorescence but, unexpectedly, the combination of the free guest and host (TiO2+NaY) caused a doubling of the fluorescence. Protection of cells against TiO2-induced intracellular ROS by encapsulation suggests that supramolecular species may be beneficial in photoprotection of the skin. In contrast, the potentiation of TiO2-induced ROS by uncomplexed NaY points to a critical role for formulation when free TiO2 is used as a sun screen ingredient.     

Scavenging with TEMPO* to identify peptide- and protein-based radicals by mass spectrometry: advantages of spin scavenging over spin trapping

The detection and characterization of radicals in biomolecules are challenging due to their high reactivity and low concentration. Mass spectrometry (MS) provides a tool for the unambiguous identification of protein-based radicals by exploiting their reactivity with suitable reagents. To date, protein-radical detection by MS has been modeled after electron paramagnetic resonance experiments, in which diamagnetic spin traps, such as 3,5-dibromo-4-nitrosobenzene sulfonic acid, convert unstable radicals to more stable spin adducts. Since MS detects mass changes, and not unpaired spins, conversion of radicals to stable diamagnetic adducts is more desirable. The use of 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO(*)) in the MS identification of protein-based radicals was explored here to establish whether scavenging via radical combination would give rise to TEMPO adducts that were stable to MS analysis. The horseradish peroxidase/H(2)O(2) reaction was used to generate radicals in derivatives of tyrosine, tryptophan, and phenylalanine as models of protein-based radicals. TEMPO(*) was added as a radical scavenger, and the products were analyzed by electrospray ionization (ESI) MS. Dramatically higher mass-adduct yields were obtained using radical scavenging vs radical trapping, which greatly enhanced the sensitivity of radical detection. The efficiency of TEMPO(*) in protein radical scavenging was examined in horse heart myoglobin and cytochrome c peroxidase (CCP) from Saccharomyces cerevisiae. On H(2)O(2) binding to their ferric hemes, two oxidizing equivalents are transferred to the proteins as an Fe(IV)=O species and a polypeptide-based radical. In addition, CCP has been shown to reduce up to 10 equiv of H(2)O(2) using endogenous donors, thereby generating as many as 20 radicals on its polypeptide. Following myoglobin and CCP incubation with a 10-fold molar excess of H(2)O(2) and TEMPO(*), matrix-assisted laser desorption ionization (MALDI) time-of-flight analysis of the tryptic peptides derived from the proteins revealed 1 and 9 TEMPO adducts of myoglobin and CCP, respectively. Given the high scavenging efficiency of TEMPO(*) and the stability of TEMPO-labeled peptides in ESI and MALDI sources, scavenging by stable nitroxide radicals coupled with MS analysis should provide sensitive and powerful technology for the characterization of protein-based radicals.     

超氧负离基研究: 无水乙腈中超氧负离子基的稳定性及其捕获

考察了影响无水乙腈中超氧负离子基(O2^-)稳定性的因素,发现氧促使乙腈中O2^-浓度迅速减小,通过产物鉴定和UV动力学分析提出氧促O2^-与乙腈反应的可能机理。研究了O2^-与2,2,6,6-四甲基-4-羟基-N-溴哌啶(NB)的反应,表明NB可望成为非水溶剂中O2^-的专一捕获剂。