1. Department of Chemistry and Research Institute of Natural Sciences, Changwon National University, Changwon 641-773, Korea, Department of Chemistry and Research Institute of Natural Science, Gyeongsang National University, Chinju 660-701, Korea, Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas 75390, and Rigaku Corporation, 3-9-12 Matsubara-cho, Akishima-shi, Tokyo 196-8666, Japan %yjyoon@nongae.gsnu.ac.kr