1. Department of Chemistry and Medicinal Chemistry Programme, National University of Singapore, and Singapore Bioimaging Consortium, Agency for Science, Technology and Research (A*STAR), Biopolis, Singapore
2. School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, U.K.
3. Department of Chemistry, University of Connecticut, Storrs, Connecticut 06269-3060, United States
4. Department of Chemistry, Pohang University of Science and Technology, Pohang 790-784, Republic of Korea