74 Discussion 



longer wavelengths than that of the low-spin pyridine protoferrohaemochrome, but 

 that of high-spin protohaem lies at still shorter wavelengths. Nor does there seem a 

 clear relationship between bond-type and autoxidizability. We find autoxidizable 

 haem compounds both with high-spin (haem) and low-spin (pyridine and imidazole 

 haemochromes), and compounds slowly or not at all autoxidizable also both with 

 high-spin (haemoglobin) and low-spin (cytochrome c). 

 Williams: I have discussed above the shift in Soret band with ligand (Fig. 1, p. 43). 

 Only for haemoproteins will the Soret band shift to shorter wavelengths (with change 

 of spin-type) as ligand basicity increases. For the change haem to haemoprotein 

 (haemoglobin) there is no change of spin-type and the Soret band moves to longer 

 wavelength with basicity. This is also likely to be true for all low-spin complexes. 



I believe bond-type and autoxidizability to be clearly related. I wonder whether 

 the compounds (pyridine and imidazole haemochromes), which Lemberg speaks of 

 as low-spin, are in equilibrium with amounts of dissociated complexes (high-spin). 

 It does seem that imidazole and pyridine reduce the rate of autoxidation of haems; 

 thus imidazole and pyridine complexes of haems in strong solution pick up oxygen 

 reversibly without being autoxidized (Corwin and Bruck, /. Amer. chem. Soc. 80, 

 4736, 1958). I think oxidation occurs only on addition of water in this case. 



Models for Haemoproteins 



Some New Compounds of Haems with Bases 

 By J. E. Falk (Canberra) 



Falk : The properties of some new complexes of meso-, proto- and 2 : 4-diformyldeutero- 

 haems are indicated in Figs. 1 and 2 and Table 1. These complexes were made in 

 0-01 N NaOH. The ligands hydrazine (pA'a8-l), ethanolamine (9-5), n-propylamine 

 (10-5) and dimethylamine (10-6) form an interesting series of compounds with these 

 haems. As shown in Fig. 1 both Amax and cmax of the meso- and proto-haem com- 

 plexes increase with pKa of the ligand, and the effects are very similar for both haems. 



With the diformyl haem, the e of the dimethylamine complex is sim.ilar to that 

 found with meso- and proto-haems. It was not possible to measure A values with the 

 other amines because of spectral shifts associated with Schiff's base formation between 

 the ligands and the formyl side-chains. This reaction was slow enough, however, to 

 permit measurement with the reversion spectroscope of the position of the absorption 

 bands of the initial complexes, and as shown in Table 1, the a-bands of all these 

 complexes, from hydrazine to dimethylamine, were at the same wavelength as the 

 a-band of the pyridine haemochrome. This lack of influence of the ligands upon the 

 spectrum, as com.pared with meso- and proto-haems, is apparently related to the 

 much greater electron-attraction in the side-chains of diformyldeuterohaem. 



We were able to obtain interesting complexes of protohaem and the diformylhaem 

 with 2-mercaptoethanol (Table 1 and Fig. 2) ; the a-band of the protohaem complex 

 is displaced 17 m/« to longer wavelength than that of pyridine protohaemochrome — 

 the greatest shift we have yet encountered. Ethanol did not react in the same way 

 under these conditions, so that as a first presumption, it appears that the thiol-group 

 of mercaptoethanol is complexing with the haem iron. The electrophilic side-chains 

 of proto- and diformyl haems appear to have some influence, since mercaptoethanol 

 reacted poorly with mesohaem (Fig. 2). 



The Srnu of the pyridine haemochrome of 2 : 4-diformyldeuterohaem at the a maxi- 

 mum was assumed to be the same as that of protohaem. 



As shown in Table 1 , the a-bands of these compounds of meso- and proto-haems 

 more than cover the ranges of a-band positions (cf. Morton, Rev. pure appl. Chem. 

 8, 161, 1958) of the known cytochromes of types c and b respectively. 



Absorption spectra were determined with a Beckman DU Spectrophotometer, except 

 compounds marked *, which were measured with a Beck-Hartridge reversion spectro- 

 scope (see text). The fmM=31 for the pyridine haemochrome of 2: 4-diformyl- 

 deuterohaem is assumed, and the £niM for the other ligands calculated on this basis. 



