1. Department of Chemistry, Nucleoside Research and Mass Spectrometry Unit and Center for Proteomics and Mass Spectrometry, University of Antwerp, Antwerp, Belgium, Flemish Institute for Technological Research, Boeretang 200, B-2400 Mol, Belgium, and Biochemistry Group, Department of Biological Sciences, SOTEAS and Biomolecular Analysis Mass Spectrometry Facility, Swansea University, United Kingdom