The visible spectra of sperm-whale metmyoglobin and its fluoride, hydroxide, cyanide, azide, cyanate, formate, acetate, thiocyanate and nitrite derivatives were measured and resolved into Gaussian components. A linear correlation between the intensity of the band at 18500cm.−1 and the magnetic susceptibility is found, suggesting that the band is the β-band of the low-spin form. The analysed intensity of this band can be used to determine the relative proportions of the two spin states present. The spectra of the pure high-spin and low-spin components of each derivative can be reconstructed. Correlations between the energy of the near-infrared band and the visible bands of the high-spin form, and between the position and intensity of the 16000cm.−1 band, are demonstrated. The relationship between the position of the Soret band and the magnetic susceptibility can be explained in terms of the equilibrium between spin states.
