Flow Esr Detection for Liquid Chromatography of Radicals

Detection of the reduced forms of radical adducts on the ESR trace using HPLC-electrochemical detector-ultraviolet absorption detector-electron spin resonance-MS

To detect and identify the electron spin resonance (ESR) silent forms of the alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (4-POBN) radical adducts, an electrochemical detector (ECD) was employed as a reactor in the HPLC-ECD-UV absorption detector-ESR-MS (HPLC-ECD-UV-ESR-MS). The ECD was employed to regenerate the radical forms from the reduced forms. The reduced forms of the 4-POBN/pentyl radical adducts were analyzed using the HPLC-ECD-UV-ESR-MS. On addition of the ECD applied potential of +0.3 V, a peak appeared on the ESR trace of the HPLC-ECD-UV-ESR-MS analyses, indicating that the radical forms are regenerated from the reduced forms. The HPLC-ECD-UV-ESR-MS analyses were also performed for the reaction mixtures of phenylhydrazine with CuCl(2). Two peaks (peaks I and II) were detected on the UV trace (300 nm) of the HPLC-ECD-UV-ESR-MS. The mass spectra showed that the peak I and peak II compounds are radical and reduced forms of the 4-POBN/phenyl radical adducts under the ECD applied potential of 0.0 V. Peak I was only detected on the ESR trace under the ECD applied potential of 0.0 V. In addition to peak I, peak II appeared on the ESR trace under the ECD applied potential of +0.3 V, indicating that the reduced forms are oxidized to the corresponding radical forms.

Identification of a radical formed in the reaction mixtures of ram seminal vesicle microsomes with arachidonic Acid using high performance liquid chromatography-electron spin resonance spectrometry and high performance liquid chromatography-electron spin resonance-mass spectrometry

The reaction of ram seminal vesicle (RSV) microsomes with arachidonic acid (AA) was examined using electron spin resonance (ESR), high performance liquid chromatography-electron spin resonance spectrometry (HPLC-ESR), and high performance liquid chromatography-electron spin resonance-mass spectrometry (HPLC-ESR-MS) combined use of spin trapping technique. A prominent ESR spectrum (alpha(N) = 1.58 mT and alpha(H)beta = 0.26 mT) was observed in the complete reaction mixture of ram seminal vesicle microsomes with arachidonic acid containing 2.0 mg protein/ml ram seminal vesicle (RSV) microsomal suspension, 0.8 mM arachidonic acid, 0.1 M 4-POBN, and 24 mM tris/HCl buffer (pH 7.4). The ESR spectrum was hardly observed for the complete reaction mixture without the RSV microsomes. The formation of the radical appears to be catalyzed by the microsomal components. In the absence of AA, the intensity of the ESR signal decreased to 16 +/- 15% of the complete reaction mixture, suggesting that the radical is derived from AA. For the complete reaction mixture with boiled microsomes, the intensity of the ESR signal decreased to 49 +/- 4% of the complete reaction mixture. The intensity of the ESR signal of the complete reaction mixture with indomethacin decreased to 74 +/- 20% of the complete reaction mixture, suggesting that cyclooxygenese partly participates in the reaction. A peak was detected on the elution profile of HPLC-ESR analysis of the complete reaction mixture. To determine the structure of the peak, an HPLC-ESR-MS analysis was performed. The HPLC-ESR-MS analysis of the peak showed two prominent ions, m/z 266 and m/z 179, suggesting that the peak is a 4-POBN/pentyl radical adduct. An HPLC-ESR analysis of the authentic 4-POBN/pentyl radical adduct comfirmed the identification.

Identification of the Several New Radicals Formed in the Reaction Mixture of Oxidized Linoleic Acid with Ferrous Ions using HPLC-ESR and HPLC-ESR-MS

ESR, HPLC-ESR and HPLC-ESR-MS analyses were performed for the reaction mixtures of oxidized linoleic acid with ferrous ions combined use of spin trapping technique. More than 14 peaks were detected on the HPLC-ESR elution profile. In addition to 7-carboxyheptyl and pentyl radicals, several new radicals such as 7-carboxyldihydroxyheptyl, 1,5-dihydroxypentyl, 8-carboxy-1-hydroxyoctyl, 7-carboxy-1-hydroxyheptyl, 1-hydroxypentyl and 1-hydroxyhexyl were identified using HPLC-ESR and HPLC-ESR-MS.

High performance liquid chromatography/electron spin resonance/mass spectrometry analyses of lipid-derived radicals

High performance liquid chromatography/electron spin resonance/mass spectrometry (HPLC/ EPR/MS) analyses of radicals is performed for the reaction mixture of 13-hydroperoxy-(9Z,11E)-octadeca-9,11-dienoic acid (13ZE-OOH) with ferrous ions under an aerobic condition, or an anaerobic condition. Radicals are identified from 13ZE-OOH by using high performance liquid chromatography/electron spin resonance spectrometry (HPLC/EPR) and HPLC/EPR/MS. The pentyl radical and isomers of epoxylinoleic acid radicals from 13ZE-OOH are identified under an anaerobic condition and the 7-carboxyheptyl radical and pentyl radical from 13ZE-OOH under an aerobic condition. These results suggest that the formation of the respective radical species depends to a great extent on oxygen concentration in the reaction mixtures.

Identification of 1-ethoxyethyl radicals in the reaction of ferrous ions with serums from rats exposed to diethyl ether

Using alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (4-POBN) as a spin trap reagent, an electron paramagnetic resonance (EPR) spectrum was observed for the complete reaction mixture of ferrous ions with serums from rats exposed to diethyl ether. The EPR spectrum was not observed for the complete reaction mixture without the serums (or ferrous ions) or with a serum from a rat not exposed to diethyl ether. In order to identify the 4-POBN radical adducts, HPLC-EPR and HPLC-EPR-MS analyses were employed. The HPLC-EPR analysis of the complete reaction mixture showed a prominent peak with a retention time of 25.2 min. The HPLC-EPR-MS analysis of the peak gave ions at m/z 181 and m/z 268. The ions m/z 268 correspond to the protonated molecular ions of 4-POBN/1-ethoxyethyl radical adducts, (M + H)+. The fragment ions at m/z 181 correspond to the loss of [(CH3)3C(O)N] from the protonated molecular ions. The HPLC-EPR analysis of the Fenton reaction mixture with diethyl ether gave a peak with the same retention time as the one in the reaction of the rat serums with ferrous ions. Thus, the radicals detected in the reaction mixture of ferrous ions with the serums from rats exposed to diethyl ether are identified as 1-ethoxyethyl radicals.

High-performance liquid chromatographic determination of linoleic acid peroxide-derived radicals using electrochemical detection

High-performance liquid chromatography-electrochemical detection (HPLC-ED) was applied to detect 13-hydroperoxide octadecadienoic acid (13-HPODE)-derived radicals such as the pentyl radical and octanoic acid radical. The 13-HPODE-derived radicals were successfully detected using HPLC-ED by the combined use of the spin-trapping technique with alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (4-POBN). The 4-POBN-pentyl radical adduct was detected at the retention time of 18.2 +/- 0.3 min on the elution profile of HPLC-ED with an ODS column (15 cm x 4.6 mm I.D.) using a flow-rate of 1.0 ml/min with 50 mM ammonium acetate in 29% (v/v) aqueous acetonitrile. The 4-POBN-octanoic acid radical adduct was also detected at the retention time of 13.7 +/- 0.7 min using a flow-rate of 1.0 ml/min with 50 mM ammonium acetate in 14% (v/v) aqueous acetonitrile. The concentrations of the 4-POBN radical adducts were determined using HPLC-ED without an internal standard. HPLC-ED is 100 times as sensitive as HPLC-electron spin resonance (ESR) under the ESR and ED conditions employed here. Even 1.8 pmol of the 4-POBN-pentyl (or octanoic acid) radical adduct was detectable using

Studies of short-lived radicals in the gamma-irradiated aqueous solution of uridine-5'-monophosphate by the spin-trapping method and the liquid chromatography

An aerated aqueous solution of uridine-5'-monophosphate was gamma-irradiated with 2-methyl-2-nitrosopropane as a spin-trapping reagent. Liquid chromatography was applied to separate the stable nitroxide radicals in the irradiated solution. The radicals were detected by U.V. and e.s.r. spectrometry. The e.s.r. detection showed four peaks in the chromatogram. The orcinol method for detection of the residual sugar moieties was applied before and after reduction of the base to determine the existence of the 5,6-double bond for the molecules in each fraction. From the combined results of the e.s.r. and orcinol methods, the short-lived radicals which were trapped by 2-methyl-2-nitrosopropane were identified as radicals of N-1 and C-6 positions of the base moiety and t-butyl radical which was the radiolytic product of the trapping reagent.