1. Department of Pharmacology and Center for Biomedical EPR Spectroscopy and Imaging, The Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University, Columbus, Ohio 43210, and Laboratoire Chimie Provence, UMR 6264, Equipe Spectrométries Appliquées à la Chimie Structurale, Case 512, Université de Provence-CNRS, Campus de Saint Jérôme, 13397 Marseille Cedex 20, France