1. Contribution from the Frontier Research Program, The Institute of Physical and Chemical Research (RIKEN), Wako, Saitama 351-01, Japan, Department of Chemistry, Columbia University, New York, New York 10027, Department of Information System Engineering, Faculty of Engineering, Osaka Sangyo University, Daito-shi, Osaka 574, Japan, and Department of Biophysics, Faculty of Science, Kyoto University, Sakyo-ku, Kyoto 606-01, Japan