1. Department of Physical Chemistry, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden, Substance Analysis, Pharmaceutical R&D, AstraZeneca R&D Mölndal, SE-431 83 Mölndal, Sweden, and Department of Biochemistry B, Center for Biomolecular Recognition, The Panum Institute, Blegdamsvej 3c, DK-2200 N Copenhagen, Denmark