ESR spin-trapping analysis of radical type (superoxide or hydroxyl radical) scavenged by stout. ESR spectra of DMPO-spin-trapped free radicals in the reaction mixture containing xanthine oxidase, in 57% DMSO or aqueous media. All spectra were run on a Bruker ESP 300 with the following parameters: centerfield, 348.005 mT (3480.05 G); sweep width, 8.0 mT (80 G); scan time, 10.49 s; number of scans, 10; microwave frequency, 9.74 GHz; microwave power, 20 mW; modulation amplitude, 0.68 G; gain, 3.2 × 10
4. The parameters of the spectra shown in the figure are as follows: DMPO/OH:
aN =
= 15.0 G; DMPO/OOH:
aN = 14.2 G,
= 11.2 G,
= 1.3 G; DMPO/(C?):
aN = 16.4 G,
= 23.6 G. The DMPO/(C?) is an unknown carbon-centered radical, which approximately fits the parameters described by Buettner (1987) for CH
3 or CH
2C
6H
4. The reaction mixtures were as follows, with a description of the spectrum in brackets: (A) xanthine oxidase 0.1 dilution from 25 units per 1.2 ml (0.02 ml), hypoxanthine, 0.5 mM (0.28 ml), DMPO (5 Φl), DMSO 1.2 ml (superoxide), phosphate-buffered saline (0.3 ml), water (0.3 ml), final volume 2.1 ml; (B) same ingredients as A, with the addition of ethanol (0.3 ml of stout, replacing the water in A (superoxide signal strongly reduced); (C) xanthine oxidase, 0.1 dilution from 25 units per 1.2 ml (0.02 ml), hypoxanthine, 0.5 mM (0.28 ml), DMPO (5 Φl), phosphate-buffered saline (0.3 ml), water to 2.1 ml. After 7 min the superoxide radical dismutation had produced peroxide which combined with superoxide to give a typical hydroxyl radical spin-trapped spectrum; (D) same ingredients as C, with the substitution of stout (0.3 ml) for 0.3 ml of the water (hydroxyl radical signal strongly reduced from C).