Three types of per-O-methylated â-cyclodextrin dimers, Im2CD, Im3NHCD and Py3NHCD, were prepared as globin models. Im2CD was synthesized by the condensation reaction of mono(2(A)-amino)-per-O-methylated â-cyclodextrin with 3-(1H-imidazol-1-yl)pentanedioic acid. Im3NHCD and Py3NHCD were obtained through the S(N)2 reactions of mono(2(A),3(A)-epoxy)-per-O-methylated â-cyclodextrin with 3-(1H-imidazol-1-yl)pentane-1,5-diamine and 3,5-bis(aminomethyl)pyridine, respectively. These cyclodextrin dimers formed 1:1 supramolecular inclusion complexes of tetrakis(4-sulfonatophenyl)porphinatoiron(II) (Fe(II)TPPS) in aqueous solution. The supramolecular complexes bound dioxygen (O(2)), with the O(2) affinity of the Fe(II)TPPS/Im3NHCD complex (P(1/2)(O2) = 1.5 ± 0.1 Torr) being much higher than those of the Fe(II)TPPS/Im2CD (36 ± 2 Torr) and Fe(II)TPPS/Py3NHCD complexes (70 ± 5 Torr). On the basis of the results of the present study and previous results, it is concluded that the imidazole axial ligand at the linker attached at the 3- and 3'-positions of the cyclodextrin units causes higher O(2) affinity as compared with the imidazole ligand at the 2- and 2'-positions and the pyridine ligand at the 2,2'- or 3,3'-positions. The electron donating ability and orientation of the axial ligand may control the O(2) affinity of a supramolecular receptor.
Coordination Complexes Crystallography, X-Ray