1. Biophysics Group, Department of Biochemistry and Molecular Biology I and Laboratory of Applied Photochemistry, Department of Organic Chemistry, Faculty of Chemistry, Universidad Complutense de Madrid, E-28040 Madrid, Spain, and Lehrstuhl für Umweltmesstechnik, Engler-Bunte-Institut, Universität Karlsruhe, D-76128 Karlsruhe, Germany