Hemodextrin: a self-assembled cyclodextrin-porphyrin construct that binds dioxygen

Synthetic hemoprotein model compounds are of great interest due to the vital roles and complexities of hemoproteins. This study reports a novel, self-assembled hemoprotein model, hemodextrin. The synthesis and characterization of py-PPCD (2(A)-monopyridylmethyl-perPEGylated-beta-cyclodextrin) (2) is described. The molecular design is based on a pegylated cyclodextrin scaffold that bears both a heme-binding pocket and an axial ligand that binds an iron porphyrin. The binding constant for Fe(III)TPPS iron(III) meso-tetra(4-sulphonatophenyl)porphyrin] by py-PPCD (2) was determined to be 2 x 10(6) M(-1) at pH 6.0 by observing characteristic changes in the UV-Vis spectrum of the porphyrin. The pyridyl nitrogen of py-PPCD (2) was shown to ligate to the iron center by observing signal changes in the Fe(II)-porphyrin 1H-NMR spectrum. This hemodextrin ensemble was shown to bind dioxygen reversibly and to form a stable ferryl species.