1. Department of Chemistry, Graduate School of Science, Hiroshima University, Kagamiyama, Higashi-Hiroshima 739-8526, Japan, Department of Chemistry, University of Peshawar, NWFP, Peshawar, Pakistan, and Department of Life Science, Yasuda Women's Junior College, Yasuhigashi, Asaminami-ku, Hiroshima 731-0153, Japan