Analytical Sciences

DMPO-OH Radical Formation from 5,5-Dimethyl-1-pyrroline N-Oxide (DMPO) in Hot Water

Tomoko SHOJI,*¹ Linxiang LI,*¹ Yoshihiro ABE,*¹ Masahiro OGATA,*² Yoshihisa ISHIMOTO,*¹ Ryoko GONDA,*¹ Tadahiko MASHINO,*¹ Masataka MOCHIZUKI,*¹ Michihisa UEMOTO,*³ and Naoki MIYATA*⁴

*1 Kyoritsu University of Pharmacy, 1-5-30 Shibakoen, Minato, Tokyo 105-8512, Japan
*2 Faculty of Pharmaceutical Sciences, Aomori University, 2-3-1 Koubata, Aomori 030-0943, Japan
*3 Tokyo Metropolitan Industrial Technology Research Institute, 3-13-10 Nishigaoka, Itabashi, Tokyo 115-8586, Japan
*4 Faculty of Pharmaceutical Sciences, Nagoya City University, 3-1 Tanabe-dori, Mizuho, Nagoya 467-8603, Japan

When an aqueous solution of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) was heated at 70°C for 30 min, formation of DMPO-OH was observed by ESR. This DMPO-OH radical formation was suppressed under an argon atmosphere. When water was replaced with ultra-pure water for ICP-MS experiments, DMPO-OH radical formation was also diminished. Under an argon atmosphere in ultra-pure water, the intensity of the DMPO-OH signal decreased to about 1/20 of that observed under aerobic conditions with regular purified water. The addition of hydroxyl radical scavengers such as mannitol did not affect the formation of DMPO-OH, but the signal turned faint in the presence of EDTA. We suggest that DMPO reacted with dissolved oxygen to form DMPO-OH.

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