1-Substituted 2-methylimidazoles included in α-cyclodextrin (CyD) were found to form stable penta-eoordinate complexes with iron(II) protoporphyrin K (Scheme 1). When an equivalent amount of CyD-included l-phenethyl-2-methylimidazole (PMI) was added to a hexa-coordinate complex of (imidazole) 2-heme, they were selectively transfered to the penta-coordinate CyD-included PMI-heme complex (Scheme 2). The apparent formation constants (Ky of the heme complexes with these CyD-included imidazoles were measured spectroscopi-cally (Fig. 1). The K values of the CyD-included imidazoles were 15~30 times larger than that of 2-methylimidazole—heme, due to the larger entropy change (Table 1). The fluores-cenece spectrum of the zinc(II) protoporphyrin K complex with CyD-included PMI suggested a hydrophobic interaction between CyD and the porphyrin. CyD-included PMI-heme complex formed a stable oxygen adduct in an aqueous N, N-dimethylformamide solution (1/9) at-30°C.
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