1. Computational Laboratory, Institute of Pharmaceutical Innovation, University of Bradford, Bradford, West Yorkshire BD7 1DP, U.K., Institute of Physics, Tampere University of Technology, P.O. Box 692, FI-33101 Tampere, Finland, Helsinki University of Technology, P.O. Box 1100, FI-02015 HUT, Finland, and MEMPHYS-Center for Biomembrane Physics, University of Southern Denmark, Odense, Denmark