1. Department of Chemistry, University of Arizona, Tucson, Arizona 85721
2. K. U. Leuven - Department of Chemistry, Celestijnenlaan 200F, B-3001 Heverlee-Leuven, Belgium
3. Department of Bioengineering, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8501, Japan