1. Center for Fluorescence Spectroscopy, Department of Biological Chemistry, and Medical Biotechnology Center, University of Maryland at Baltimore, School of Medicine, 108 N. Greene Street, Baltimore, Maryland 21201, Department of Pharmacology, Box 448, Jordan Hall, Room 561, University of Virginia, Charlottesville, Virginia 22908, and Faculty of Applied Physics and Mathematics, Technical University of Gdańsk, ul. Narutowicza 11/12, 80-952 Gdańsk, Poland