1. Department
of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
2. Bruker BioSpin, 15 Fortune Drive, Billerica, Massachusetts 01821, United States
3. Brookhaven National Laboratory, 50 Bell Avenue, Building 463, Upton, New York 11973-5000, United States
4. Department
of Biochemistry and Structural Biology, Lund University, SE22100 Lund, Sweden