1. Department of Polymer Science and Engineering, Hannam University, 133 Ojeong Dong, Daedeog Ku, Taejeon, Korea 306-791, School of Life Sciences and Biotechnology, Korea University, 1, 5-ka, Anam Dong, Sungbuk Ku, Seoul, Korea, 136-701, and Nanobiomaterials Laboratories, Korea Research Institute of Chemical Technology, P.O. Box 107, Yusung, Taejeon, Korea 305−600