1. Institute of Physics, N. Copernicus University, Grudzia̧dzka 5/7, 87-100 Toruń, Poland; Department of Biophysics, Warsaw University, Zwirki i Wigury 93, 02-089 Warsaw, Poland; Interdisciplinary Centre for Mathematical and Computational Modelling, Warsaw University, Banacha 2, 02-097 Warsaw, Poland; and Department of Chemistry and Biochemistry, and Department of Pharmacology, University of California at San Diego, La Jolla, California 92093-0365