1. Department of Chemistry, National Research Laboratory for Polymer Synthesis and Physics, Pohang Accelerator Laboratory, Center for Integrated Molecular Systems, Polymer Research Institute, and BK School of Molecular Science, Pohang University of Science and Technology (Postech), Pohang 790-784, Republic of Korea, and Department of Microbiology, Dongguk Medical Institute, Dongguk University College of Medicine, Gyeongju 780-714, Republic of Korea