1. Eberhard-Karls-Universität Tübingen, Postfach 35, 72076 Tübingen, Germany
2. University of Wollongong, Department of Chemistry, Wollongong NSW 2522, Australia
3. Gunma University, Department of Nuclear Medicine, Marbashi 317, Japan
4. Japan Atomic Energy Research Institute, Department of Radioisotopes, Takasaki 370-12, Japan