1. Center for Molecular Modeling, Office of Intramural Research, Center for Information Technology; National Institutes of Health, Building 12A; Rm 2049 Bethesda MD 20892 USA
2. Molecular Imaging Branch, National Institute of Mental Health; National Institutes of Health, Rm. B3C346A; 10 Center Drive Bethesda MD 20892 USA
3. Present address: Department of Nuclear Medicine; Yonsei University College of Medicine; 50-1 Yonsei-ro Seodaemun-gu 03722 South Korea
4. National Heart, Lung and Blood Institute; National Institutes of Health; Bethesda MD 20892 USA
5. National Institute of Chemistry; Ljubljana Slovenia