Evidence for dimer formation of nitrosyl(meso-2,3,7,8,12,13,17,18-octaethyl-5-nitroporphyrinato)iron(II) and its implication in the interpretation of the electron spin resonance spectrum of the nitrosyl-haemoglobin–salicylate system

Abstract

Dimer formation of the title complex in toluene has been demonstrated by an electron spin resonance study of this complex at a high concentration at 9 K, and the approximate dimer structure has been determined by spectral simulation. The observation enables us to interpret the hitherto unexplained four resonance absorptions which are known to appear in nitric oxide ligated haemoglobin (NO-haem) as a result of interaction with salicylate, on the basis of similar dimer formation of the NO-haem prosthetic groups. The event appears to take place intramolecularly by association of NO-haem molecules coming out of the haem pockets, and the complex is stabilized by the globin structure.