166 David L. Drabkin 



Enlargement of this assumption involves the inference that the internal 

 energy of the atom or molecule is increased by the absorption of light, and 

 transfers from lower to higher quantized energy states occur, which give rise 

 to absorption bands. In the ultra-violet and visible spectral regions the bands 

 may represent either transitions of optical or valence electrons (as distin- 

 guished from core electrons) through different quantized energy levels, or 

 internal vibrational phenomena set up in the molecule by the absorption of 

 hght energy. Henri (1919, 1923a and b) and Lifschitz (1920) were among the 

 first to recognize that orderliness exists in the distribution of bands in simple 

 molecules, which is expressed by the spacing of the bands at constant fre- 

 quency distances from each other. Such integrally related bands, forming a 

 spectral series, were early demonstrated in the spectra of KMn04 and C0CI2 

 (see Fig. 4), and have been interpreted as vibrational fine structure in a broad 

 band of electronic origin (Harrison et al, 1948). The important implication 

 lies in the inference that all bands which are members of a single series 

 probably originate from a common configuration in the molecule, or from the 

 same fundamental molecular disturbance incident to the absorption of light 

 energy. 



The Spectra of the Haemin Chromoproteins. The finding — extended and 

 supported by a graphic-mathematical analysis — that most of the bands 

 (exclusive of a and (i) in the spectra of haemin chromoproteins and their 

 derivatives are spaced at equal frequency distances allows the interpretation 

 that they originate (as in the simple molecules above) in a common molecular 

 structure and from fundamentally the same dynamic source. This enormously 

 simplifies the interpretation of the complex spectra of these complex molecules. 

 In effect, spectrally they behave like much simpler molecules. The location of 

 the bands in the ultra-violet and visible regions permits the deduction that 

 they represent electron transitions. Furthermore, the total iron-porphyrin 

 structure as a unit is held responsible for the bands in the spectral series. In 

 the resonating conjugated double bond system of the porphyrins, each atom 

 contributes an optical electron to the molecule's collection, but the electrons 

 belong collectively to all the atoms in the complex, not to a particular atom. 

 Such electrons, belonging to several atoms, are characterized by relatively 

 low energy (hence the spectral bands in the near infra-red, visible and ultra- 

 violet regions), and the energy levels associated with them are regarded as 

 closely and regularly spaced (cf. Harrison et al, 1948; Braude, 1945). The 

 iron may be thought of as either facilitating or modifying the movement of the 

 electrons over the atoms of the porphyrin ring. At any rate, the over-all 

 spectrum is viewed as an expression of the spectrum of iron in a hexa- 

 co-ordinated Werner type structure. Supporting evidence for the common 

 origin of the bands in the spectral series may be drawn from Warburg's 

 classical deduction of the photochemical spectrum of cytochrome c oxidase 

 (Warburg and Negelein, 1928; Warburg, 1929). The photochemical spectrum, 



