1. Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands, Bijvoet Center for Biomolecular Research, Utrecht University, Padualaan 8, 3584 CH, Utrecht, The Netherlands, Université Bordeaux 1, CNRS-CRPP UPR 8641, 115 Avenue Schweitzer 33600 Pessac, France, and ALS, Berkeley Laboratory, 1 Cyclotron Rd, MS2-400, Berkeley, California 94720