1 Department of Chemistry, University of Oslo, NO-0315 Oslo, Norway. ute.krengel@kjemi.uio.no susanna.horsefield@biochemistry.lu.se.
2 Department of Biochemistry and Structural Biology, University of Lund, SE-22100 Lund, Sweden. ute.krengel@kjemi.uio.no susanna.horsefield@biochemistry.lu.se.