@misc{oai:repo.qst.go.jp:00072905,
 author = {Matsumoto, Ken-ichiro and Nakanishi, Ikuo and 松本 謙一郎 and 中西 郁夫},
 month = {Aug},
 note = {ABSTRACT
Radiation exposure to an aqueous solution containing a nitroxyl radical and glutathione (GSH) or other hydrogen donors, such as NAD(P)H, produces a dose-dependent EPR signal loss of the nitroxyl radical [1, 2]. Radiation induced EPR signal loss of TEMPOL in water without coexisting hydrogen-donor, such as GSH or NAD(P)H, observed by relatively high dose has been also reported [3]. This hydrogen-donor-independent reduction of TEMPOL is partly depend on the generation of hydrogen peroxide (H2O2), since the reaction was partly suppressed by catalase. However, TEMPOL does not react with H2O2 directly. The detail mechanism of this hydrogen-donor-independent reduction of TEMPOL was in progress.
A water solution of TEMPOL or Carbamoyl-PROXYL (0.1 mM) was irradiated by several doses (0, 16, 32, 64, 128 Gy) of X-ray, and the reduction of the X-band EPR signal of the nitorxyl radical was measured. A reaction mixture containing 0.1 mM TEMPOL or Carbamoyl-PROXYL and several concentration (1.0 mM‒9.8 M) of H2O2 was prepared, and then time course of X-band EPR signal intensity of the nitorxyl radical at room temperature was measured. A reaction mixture containing 0.1 mM TEMPOL or Carbamoyl-PROXYL and several concentration (1.0 mM‒9.8 M) of H2O2 was irradiated by 128 Gy of X-ray, and the reduction of the EPR signal of the nitorxyl radical was measured. An aliquot (2 µL) of 200 mM K3Fe(CN)6 solution was added to 200 µL of the reaction mixture containing 0.1 mM TEMPOL or Carbamoyl-PROXYL and several concentration (1.0 mM‒9.8 M) of H2O2, and the time course of the EPR signal of the nitorxyl radical was measured.
When a water solution of a nitorxyl radical was irradiated by X-ray, EPR signal loss of the nitorxyl radical in the sample was decreased dose dependently. This X-ray induced EPR signal loss of the nitorxyl radical could be suppressed partly by adding catalase. On the other hand, nitorxyl radicals were quite stable in the solution containing H2O2. The X-ray induced EPR signal loss of the nitorxyl radical was slightly increased with H2O2 existing in the reaction mixture H2O2-concentration-dependently. The EPR signal of nitorxyl radicals were decreased in the solution containing quite high concentration (M level) of H2O2, when Fe3+ was added to the reaction mixture. However, in the solution containing lower H2O2 concentration (< mM level), the EPR signal intensity of the nitorxyl radical was stable even when the Fe3+ was added. Oxidative stimulation by X-ray irradiation or addition of Fe3+ could cause nitorxyl radical reduction in a very high concentration H2O2 environment.
\nREFERENCES
[1] K. Matsumoto, A. Okajo, K. Nagata, et al., Biol. Pharm. Bull. 32 (2009) 542
[2] K. Matsumoto, K. Nagata, H. Yamamoto, et al., Magn. Reson. Med. 61 (2009) 1033
[3] K. Matsumoto, I. Aoki, I. Nakanishi, et al., Magn. Reson. Med. Sci. 9 (2010) 131, International Conference 2018 Modern Trends in Natural Sciences and Advanced Technologies in Science Education},
 title = {Reduction of TEMPOL in Highly Concentrated Hydrogen Peroxide caused by Oxidative Stimulation},
 year = {2018}
}