1. Department of Chemistry, Katholieke Universiteit Leuven, Celestijnenlaan 200 F, 3001 Heverlee, Belgium, Center for Microbial and Plant Genetics, Kasteelpark Arenberg 20, 3001 Heverlee, Belgium, and Unité CMAT, Université Catholique de Louvain, Bât. Lavoisier Place L. Pasteur 1, 1348 Louvain-la-Neuve, Belgium