| Institution: | 1. Graduate School of Science and Engineering, Ibaraki University, Mito, Ibaraki, 310-8512 Japan
Present address: Department of Chemistry of Functional Molecules, Konan University, Higashinada-ku, Kobe, 658-8501 Japan;2. Graduate School of Science and Engineering, Ibaraki University, Mito, Ibaraki, 310-8512 Japan;3. Photon Factory, Institute of Materials Structure Science, High Energy Accelerator Research Organization, Tsukuba, Ibaraki, 305-0801 Japan;4. Institute for Material Chemistry and Engineering, Kyushu University, Nishi-ku, Fukuoka, 819-0395 Japan;5. Faculty of Chemistry, Materials and Bioengineering, Kansai University, Suita, Osaka, 564-8680 Japan |
| Abstract: | In order to gain new insights into the effect of the π–π stacking interaction of the indole ring with the CuII–phenoxyl radical as seen in the active form of galactose oxidase, we have prepared a CuII complex of a methoxy-substituted salen-type ligand, containing a pendent indole ring on the dinitrogen chelate backbone, and characterized its one-electron-oxidized forms. The X-ray crystal structures of the oxidized CuII complex exhibited the π–π stacking interaction of the indole ring mainly with one of the two phenolate moieties. The phenolate moiety in close contact with the indole moiety showed the characteristic phenoxyl radical structural features, indicating that the indole ring favors the π–π stacking interaction with the phenoxyl radical. The UV/Vis/NIR spectra of the oxidized CuII complex with the pendent indole ring was significantly different from those of the complex without the side-chain indole ring, and the absorption and CD spectra exhibited a solvent dependence, which is in line with the phenoxyl radical–indole stacking interaction in solution. The other physicochemical results and theoretical calculations strongly support that the indole ring, as an electron donor, stabilizes the phenoxyl radical by the π–π stacking interaction. |
