1. Department of Physics, The Royal Veterinary and Agricultural University, DK 1871 Frederiksberg C, Denmark, Department of Chemistry, Technical University of Denmark, 2800 Denmark, Center for Biochemical and Biophysical Sciences and Medicine and Department of Pathology, Harvard Medical School and Brigham and Women's Hospital, Boston, Massachusetts 02115, and Department of Chemistry, The Royal Veterinary and Agricultural University, DK 1871 Frederiksberg C, Denmark