On the magnetic properties of some haemoglobin complexes

Abstract

Most haemoglobin compounds fall satisfactorily into Pauling’s classification of ‘ionic’ and ‘covalent’ complexes. A few, however, have surprising magnetic properties. In this paper interpretations of these properties are offered which enable all the compounds to be fitted into a theoretical scheme of the type which is adequate for an approximate understanding of simple inorganic complexes. In particular, it is suggested that: the oxygen molecule in oxyhaemoglobin is not at right angles to the haem but probably parallel to it; all ferrihaemoglobin derivatives have a spin of either S = ½ or S = 5/2 at each iron atom or, in the case of ferrihaemoglobin hydroxide, are a thermal equilibrium of the two; ferrihaemoglobin derivatives with S = 5/2 have usually or always a large zero-field splitting, the lowest states being characterized by S ᴟ = ± ½ perpendicular to the haem.