1. a Graduate School of Natural Science and Technology , Kumamoto University , Kurokami , Kumamoto , 860 , Japan
2. b Chemicals Research Laboratory , Showa Denko Co. Ltd. , 5–1 Ohgi-machi, Kawasaki-ku , Kawasaki , 210 , Japan
3. c Department of Chemistry, Faculty of Science , Kumamoto University , Kurokami , Kumamoto , 860 , Japan