1. Contribution from the Department of Chemistry, Nuclear Chemistry, Royal Institute of Technologyy, S-100 44 Stockholm, Sweden, Division of Biochemical Toxicology, Institute of Environmental Medicine, Karolinska Institute, Box 210, S-171 77 Stockholm, Sweden, Department of Physical Chemistry, Uppsala University, Box 532, S-751 21 Uppsala, Sweden, and Uppsala University, Institute of Chemistry, Department of Organic Chemistry, Box 531, S-751 21 Uppsala, Sweden