Structural Differentiation of CO and O2 Binding to Iron Porphyrins: Polar Pocket Effects

Article abstract of DOI:10.1021/ja00309a014

A new iron porphyrin, 3,5-pyridine-5,5-hemecyclophane, has been prepared, and its dioxygen and carbon monoxide binding studied.In contrast to other "strapped" pyridines with larger cyclophane links, this compound shows no tendency to bind its attached pyridine.With use of 1,5-dicyclohexylimidazole as proximal base, a five-coordinated heme is obtained.This heme shows severe steric hindrance toward both dioxygen and carbon monoxide binding.It displays a ratio of carbon monoxide to dioxygen affinities as low as 5, a much lower binding ratio than those shown by any other model systems, by hemoglobin, or by myoglobin.This suggests ways of preparing artificial dioxygen-binding materials which preferentially bind dioxygen.