ESR Spectra and Ab Initio Calculations of the DMPO/*OH Adduct

Perkowski, A.J.I., M. Danilczuk, J.E. Stevens, and S. Schlick

Previous work by Bosnjakovic and Schlick examined the potential of the spin trap 5,5-dimethylpyrroline-N-oxide (DMPO) for the detection of short-lived radicals in Fenton media in a system of Nafion perfluorinated ionomers. Of interest to this work was a magnetic range of 94 G measured at 240 K, and a hyperfine splitting of 6.2 G from the Hγ of the DMPO/OH adduct measured at 160 K, which disappeared at higher temperatures, in the system Nafion/Fe(II)/H2O2/DMPO/H2O. The magnetic range of 94 G was attributed to a carbon-centered radical adduct derived from Nafion, and the 6.2 G hyperfine splitting was thought to be due to conformational differences at lower versus higher temperatures. Studies of the

DMPO/OH adduct in the absence of Nafion were carried out to either support or refute the previous conclusions. Ab initio moelcular orbital studies were performed to investigate the different conformations of the DMPO/OH adduct and to obtain magnetic parameters. The 94 G magnetic range was measured in the temperature range of 100 – 180 K in the absence of Nafion, and thus must be due to the DMPO/OH and not the capture of a carbon-centered adduct derived from Nafion. The magnetic parameters calculated for the two DMPO/OH adducts did not indicate a Hγ hyperfine splitting of 6.2 G. This hyperfine splitting may be due to a conformation of the DMPO/OH adduct found only in the presence of Nafion.