72 



III. PORPHYRIN CHEMISTRY 



for their estimation, and for the differentiation of some porphyrins 

 from one another. The bands are sharp and thus the position of the 

 maxima can be readily estabhshed, particularly with the Hartridge 

 Reversion Spectroscope. 



600 550 



WAVELENGTH, ran 



600 



Fig. 13. Absorption curves of porphyrin esters in dioxane (after Stern and 

 Wenderlein, 26 W) ■ 



Porphyrins dissolved in organic solvents have a typical four- 

 banded absorption spectrum in the visible region, although a number 

 of finer bands can be observed in addition to the four main bands. 

 The strength of the main bands increases toward shorter wavelengths. 

 In addition there is a still stronger band at about 400 m/x, which 

 was first observed by Soret in hemoglobin and found by Gamgee 

 {979) in porphyrins. It is usually called the Soret band. The visible 

 absorption curve of coproporphyrin tetramethyl ester in dioxane is 

 given in Figure 13. The absorption spectra of porphyrins dissolved 

 in dilute alkali are similar to this "neutral spectrum"; the carboxyl 

 groups of the propionic acid side chains are separated from the 



