On the application of electron paramagnetic resonance in the study of naturally occurring quinones and quinols.

From electron paramagnetic resonance (EPR) spectra of numerous semiquinone anion radicals we propose that the spin density distributions in benzo-, naphtho- and anthrasemiquinones are changed under the influence of various substituent in a comparable fashion, electron donating substituents having the opposite effect of withdrawing ones. These findings facilitate the work in obtaining correct assignments, further leading to safe identification of new radicals. Semiquinone anion radicals of para- and ortho-hydroquinones are demonstrated to exist at physiological pH in buffered solutions under continuous access to molecular oxygen.

Polyphenol oxidase and herbivore defense in trembling aspen (Populus tremuloides): cDNA cloning, expression, and potential substrates.

The biochemical anti-herbivore defense of trembling aspen (Populus tremuloides Michx.) was investigated in a molecular analysis of polyphenol oxidase (PPO; EC 1.10.