Ferrihaemoprotein Hydroxides 



131 



The simplest method by which the fractions of the high- and low-spin forms 

 can be calculated, throughout the temperature range, is to use the experi- 

 mental values of x^si for ^^'^ fluoride and cyanide derivatives at various 

 temperatures as the values appropriate to the high- and low-spin forms, and 

 substitute in the equation, 



yfM(hydroxide) "" °^XM(cyanide) + (^ ^)ZM(fluoride) 



(17) 



In practice, this is equivalent to taking // j = 2-34 B.M., i.e., the value for the 

 cyanide derivative, instead of 2-24 B.M., as in the majority of calculations in 



650 



600 



550 

 A(mjj) 



500 



Fig. 20. The visible spectra of the high- and low-spin hydroxides calculated from 

 the difference spectrum in Fig. 19, and the corresponding change in the fraction 

 of the low-spin form, 0055, as obtained from the variation of magnetic suscepti- 

 bility with temperature. 



Section IV. Such a slight change in Hi only affects the value of a to a negli- 

 gible extent, i.e., from 0-300 to 0-304. Values of a and (1 — a), obtained in 

 this way, are listed in Table 5 for temperatures from 0° to 30°, together with 

 values for K^, the equilibrium constant for the conversion reaction (12). 



Interpolation and extrapolation for the temperature interval 5° to 35° 

 gives 0-055 for the corresponding change in a. The spectra of the high- and 

 low-spin forms of ferrimyoglobin hydroxide were then obtained by calculating 

 Ey^ and £j throughout the wavelength range according to equations (15) 

 and (16). 



The similarity between these spectra, shown in Fig. 20, and those in 

 Figs. 13, 14 and 16 is very gratifying. But it must be remembered that the 

 previous spectra, calculated from data for pairs of haemoproteins, are 



