1. Institute of Medicinal Biotechnology; Peking Union Medical College and Chinese Academy of Medical Sciences; Beijing 100050 China
2. National Institutes for Food and Drug Control; Beijing 100050 China
3. Instituto de Química; Universidade de São Paulo; São Paulo 05599-970 Brazil
4. Laboratoire de Chimie Physique; Université Paris Sud; Orsay 91405 France