1. Division of Chemistry, Luleå University of Technology, Luleå, Sweden S-97187, Division of Bioengineering and Physical Science, Office of Research Services, National Institutes of Health, Bethesda, Maryland 20892-5766, and Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0520