1. The Graduate School, University of Santo Tomas, Manila, Philippines;
2. Department of Chemistry, Chung Yuan Christian University, Chung-Li, Taiwan;
3. Natural Science Department, College of Science, University of Santo Tomas, Manila, Philippines;
4. Research Center for Natural and Applied Sciences, University of Santo Tomas, Manila, Philippines;
5. Department of Chemistry, College of Science, University of Santo Tomas, Manila, Philippines;
6. Faculty of Pharmacy, University of Santo Tomas, Manila, Philippines