1. Department of Chemistry, University of Leuven, Leuven 3001, Belgium.
2. National Research Institute of Chinese Medicine, Ministry of Health and Welfare, Taipei 11221, Taiwan.
3. Electron Microscopy Unit, Veterinary and Agrochemical Research Centre (CODA-CERVA), Brussels 1180, Belgium.
4. Groningen Biotechnology Institute, University of Groningen, Groningen 9747AG, Netherlands.