Bonding of nitrosobenzene and phenyl isocyanide to chelated mesoheme, hemoglobin and ferrous phthalocyanine.

Reactions of nitrosobenzene, phenyl isocyanide and their ring-substituted analogues with hemoglobin, ferrous phthalocyanine and a synthetic model compound of hemoglobin were investigated by optical, 1H-NMR and infrared spectroscopy. Complexes of chelated ferromesoheme, the model compound, with 2-methyl-, 2-ethyl, 2-isopropyl- or 2,6-disubstituted nitrosobenzene were less stable than its complex with nitrosobenzene. Formation of a complex of the model compound with 2-tert-butylnitrosobenzene was incomplete. Previous studies showed that 2,6-disubstituted nitrosobenzenes are not ligands of ferrohemoglobin. In the present work 2,6-dimethylphenyl isocyanide was found to be a ligand of ferrohemoglobin. These results are consistent with binding of the nitrogen of the nitroso group of nitrosobenzene and of the carbon of the isocyanide group of phenyl isocyanide to ferroheme. The same bonding modes of these ligands to ferrous phthalocyanine were inferred from ring-current-induced shifts in the 1H-NMR spectra of the respective complexes.