1. Department of Physical Chemistry, Uppsala Biomedical Centre, P.O. Box 579, SE-751 23 Uppsala, Sweden, and Department of Pharmacy, Uppsala Biomedical Centre, P.O. Box 580, SE-751 23 Uppsala, Sweden
2. Department of Chemistry, Surface Chemistry, Drottning Kristinas väg 51, Royal Institute of Technology, SE-100 44 Stockholm and YKI, Institute for Surface Chemistry, Box 5607, SE-114 86 Stockholm, Sweden
3. GKSS Research Centre, Max-Planck Strasse, 21502 Geesthacht, Germany