Heme Complex with the Imidazole Derivatives Included in Cyclodextrint

Abstract

1-Substituted 2-methylimidazoles included in ce-cyclodextrin (CyD) were found to form stable penta-coordinate complexes with iron( II) protoporphyrin IX (Scheme 1). When an equivalent amount of CyD-included 1-phenethyl-2-methylimidazole (PMI) was added to a hexa-coordinate complex of (imidazole), -heme, they were selectively transfered to the pentacoordinate CyD-included PMI-heme complex (Scheme 2). The apparent formation constants (K) of the heme complexes with these CyD-included imidazoles were measured spectroscopically (Fig.1). The K values of the CyD-included imidazoles were 15-30 times larger than that of 2-methylimidazoleheme, due to the larger entropy change (Table I). The fluorescenece spectrum of the zinc(II) protoporphyrin N 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.