Computer controlled <i>in</i> <i>situ</i> radiolysis electron spin resonance spectrometer incorporating magnetic field-microwave frequency locking

Madden, Keith P.; McManus, Hugh J. D.; Fessenden, Richard W.

doi:10.1063/1.1144745

Cited by 23 publications

(18 citation statements)

References 19 publications

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“…The measured drift of the magnetic field of the permanent magnet is approximately 30 μT per hour, which could be problematic for studies with narrow EPR lines of, for example, oxygen sensitive lithium phthalocyanine (11). To avoid this drift and frequency drift of the RF oscillator, the magnetic field is locked to the frequency using a field to the frequency locking (FFL) device based on an auxiliary system for detection of the EPR (14). This device has an automatic search for locking, allowing even inexperienced users to operate it easily.…”

Section: Methodsmentioning

confidence: 99%

EPR spectrometer for clinical applications

Salikhov

Walczak

Lesniewski

et al. 2005

Magnetic Resonance in Med

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This article describes an EPR spectrometer specifically designed and constructed for EPR spectroscopy in humans. The spectrometer is based on a permanent magnet, suitable for measurements at 1200 MHz. The magnet has a full 50 cm gap between the poles, which facilitates accurate and comfortable placement of the subject for the EPR measurement at any location on the human body. The bridge includes features to facilitate clinical operations, including an indicator for phasing of the reference arm and a 2 level RF amplifier. Resonators with holders for each type and site of measurement have been developed that comfortably position the resonator and the patient and prevent artifacts due to motion. The initial applications for which the spectrometer has been designed are for oximetry using loops on the surface, oximetry using implanted resonators for measuring deep sites, and measurements in the teeth for determination of exposures to clinically significant doses of ionizing radiation. Magn Reson Med 54:1317-1320, 2005.

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Section: Methodsmentioning

confidence: 99%

EPR spectrometer for clinical applications

Salikhov

Walczak

Lesniewski

et al. 2005

Magnetic Resonance in Med

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“…Microwave power was sufficiently low such that power saturation effects were negligible. The ESR spectrometer and associated data acquisition system are described elsewhere . An ESR spectrum of irradiated water itself was recorded each day and was subtracted from that day's DMPO-spin adduct ESR spectra to correct the baseline arising from the color-center signal in the irradiated quartz ESR flat cell.…”

Section: Methodsmentioning

confidence: 99%

In Situ Radiolysis Steady-State ESR Study of Carboxyalkyl Radical Trapping by 5,5-Dimethyl-1-pyrroline-N-oxide: Spin Adduct Structure and Stability

Taniguchi

Madden

1998

J. Phys. Chem. A

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Short-lived carboxyalkyl radicals formed in the reaction of three mono- and two dicarboxylic acids with radiolytically produced hydroxyl radicals or hydrated electrons were trapped successfully with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) in dilute aqueous solution. The in situ radiolysis steady-state ESR spectra of the spin adducts were analyzed to determine accurate ESR parameters for these spin adducts in a uniform environment. DMPO spin adducts of the five carboxyalkyl radicals were identified for the first time. Parent radicals include carboxymethyl, dicarboxymethyl, 1,2-dicarboxyethyl, 1-amino-1-carboxymethyl (glycine radical), and 2-carboxyethyl radicals. ESR parameters for DMPO spin adducts of carboxyalkyl radicals are rather similar with nitrogen hyperfine coupling constants of approximately 16 G and with g values around 2.0054 except for glycine radical. Proton hyperfine coupling constants due to C2−H vary between 21 and 25 G. Nitrogen and C2-proton hyperfine coupling constants are smaller than those of alkyl radical adducts with larger g values. These changes are ascribed to the spread of the π-conjugation system to include the carboxyl groups. Moreover, the ESR spectrum of both the carboxymethyl and the 1,2-dicarboxyethyl radical is a superposition of spectra from adduct radicals with protonated and deprotonated carboxyl groups in the spin addend. The protonated radical adducts have small additional proton hyperfine couplings due to these carboxyl protons. These carboxyalkyl radicals exhibit intramolecular hydrogen bonding between the hydroxyl function and the aminoxyl oxygen in aqueous solution, which has a profound effect upon the stability of their DMPO spin adducts against spin adduct rearrangement and fragmentation. From carboxymethyl and dicarboxymethyl−DMPO adducts, (CH3)2C(CH2CHCH2)N(O·)CH2CO2H and (CH3)2C(CH2CHCH2)N(O·)CH(CO2 -)CO2H are proposed to form following the opening of the DMPO ring. A similar fragmentation reaction is proposed to occur from DMPO−dicarboxyhydroxymethyl adduct formed in γ-irradiated tartronic acid (hydroxymalonic acid) solution. DMPO spin adducts of glycine and 2-carboxyethyl radicals also show the small proton hyperfine splitting, revealing the intramolecular hydrogen bonding.

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“…The detection system has been previously described. 11 Some key results are shown in Fig. 1 which shows the kinetic profile of the line for H 2 N-ؒ CH-CO 2 Ϫ at 12.70 G above the center of the spectrum.…”

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Direct EPR observation of the aminomethyl radical during the radiolysis of glycine

Hug

Carmichael

Fessenden

2000

J. Chem. Soc., Perkin Trans. 2

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Aminomethyl ( ؒ CH 2 NH 2 ) and H 2 N-ؒ CH-CO 2Ϫ radicals were detected in time-resolved EPR experiments following the reaction of ؒ OH radicals with glycine anions.Oxidation of amino acid residues in proteins is a main focus of interest in oxidative stress. 1 Oxidation of glycine, the simplest amino acid, usefully models the degradation of key organic complexants in the strongly basic media of nuclear-waste storage tanks. 2 The mechanism of free-radical oxidation of glycine anions is the subject of this communication. In particular, we report here the detection and identification, by time-resolved electron paramagnetic resonance (EPR) spectroscopy, of two carbon-centered radicals recently suggested 3 to participate in the mechanism of the radiolytic oxidation of the glycine anion. The new observations provide direct evidence implicating these C-centered radicals in the primary radiolytic processes.In 1971 the H 2 N-ؒ CH-CO 2 Ϫ radical was detected by EPR in the steady-state electron irradiation of glycine in N 2 Osaturated aqueous solutions at high pH. 4 In highly basic solutions, no other radicals were seen on this time scale (estimated radical lifetimes were in the 100's of microseconds to be observable by this technique). However, in 1985, extensive CO 2 was detected 5 in gamma-irradiated basic aqueous solutions of glycine, and this large yield was rationalized as being accompanied by extensive amounts of ؒ CH 2 NH 2 . This observation and conclusion appeared to be in conflict with steady-state EPR experiments, using both radiolytic 4 and Ti 3ϩ -H 2 O 2 initiation, 6-10 in which no ؒ CH 2 NH 2 radicals were reported following the oxidation of glycine anions by ؒ OH. This conflict was resolved by postulating the participation of reaction (1), 5which converts the highly reactive aminomethyl radical ( ؒ CH 2 NH 2 ) into the less reactive H 2 N-ؒ CH-CO 2 Ϫ radical. Recently a comprehensive mechanism 3 was proposed that attempted to reconcile the observation of ؒ OH oxidation of glycine anions on the short-time scale (10's of nanoseconds) with steady-state observation of large CO 2 yields. The shorttime experiments used the optical detection of products generated by scavenging of the radicals formed following the direct ؒ OH attack on glycine anions. The behavior was comprehensively explained by a scheme that involved about 2 3 -of the ؒ OH yield generating ؒ CH 2 NH 2 and CO 2 , through an intermediate zwitterion radical H 2 N ϩ -CH 2 -CO 2 Ϫ . It was also proposed that the remaining 1 3 -of the ؒ OH radicals generated the oxidizing aminyl radical, HN ؒ -CH 2 -CO 2 Ϫ . Evidence for the oxidizing HN ؒ -CH 2 -CO 2Ϫ radical was seen in scavenging experiments that optically monitored the oxidation of hydroquinone in pulse radiolysis. 3 The relative yield of 2 3 -for reduced products (such as the methyl viologen radical cation) from the scavenging reactions matched within experimental error the steady-state CO 2 yields when the glycine anion concentrations were in the 1-5 mM range. 3 This strongly suggested that there...

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Computer controlled in situ radiolysis electron spin resonance spectrometer incorporating magnetic field-microwave frequency locking

Cited by 23 publications

References 19 publications

EPR spectrometer for clinical applications

EPR spectrometer for clinical applications

In Situ Radiolysis Steady-State ESR Study of Carboxyalkyl Radical Trapping by 5,5-Dimethyl-1-pyrroline-N-oxide: Spin Adduct Structure and Stability

Direct EPR observation of the aminomethyl radical during the radiolysis of glycine

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