1. Theoretical and Physical Chemistry Institute; National Hellenic Research Foundation, 48 Vassileos Constantinou Ave.; Athens 116 35 Greece
2. Karoliska Institutet; Dept of Physiology and Pharmacology; Karolinska Institutet, Solnavägen 9; 17165 Stockholm Sweden
3. Dept of Pharmacy; School of Life & Medical Sciences; University of Hertfordshire, Hatfield, Hertfordshire; AL10 9AB, U K
4. National Council for Scientific and Technological Development (CNPq); Brazil
5. Department of Biochemistry; Hellenic Pasteur Institute, 127 Vas.Sofias Ave., Athens; GR-11521 Greece