ULTRAVIOLET ABSORPTION SPECTRA 



189 



5.70 



5.50 



5,00 - 



Steroids with diene and triene chains, such as ergosterol (Fig. 5-18) and 

 calciferol, will have strong absorption maxima in the region 2200 2900 A 

 (for calciferol, \,„^^. = 2650 A, and e = 18,200). Steroids that contain 

 aromatic rings, such as the estrogens, will, in general, have strong absorp- 

 tion bands in the region 2400-2800 A and may have absorption intensity- 

 well above 3000 A if the aromatic grouping includes more than one ring, 

 as in equilenin (Fig. 5-19) (Morton, 1942; Jones, 1948). 



CAROTENOIDS 



The long conjugated double-bond chains of the carotenoid compounds 

 give rise to from one to three ultraviolet absorption bands at varying posi- 

 tions (Karrer and Jucker, 1948). 

 One band is usually found in the 

 region 260-320 m^u. Absorption 

 in the region 320-380 m/x has 

 been demonstrated to be depend- 

 ent on the number and position 

 of cts-configurations in the chain 

 (Fig. 5-20) (Zechmeister, 1944). 

 These ultraviolet bands 



(e = 10,000 50,000) 



are considerably weaker than the 

 intense set of three bands com- 

 monly found in the visible absorp- 

 tion spectra of these compounds 

 (e = 50,000-200,000). 



PORPHYRINS 



The intense Soret absorption 

 band of the porphyrins is found 

 in the near ultraviolet in the 

 simpler members of the group, 

 such as porphyrin itself (Fig. 

 5-21). With increasing substitu- 

 tion of the tetrapyrrole ring, this 

 band moves into the visible-spec- 

 trum region. A number of shoul- 

 ders or weak maxima are usually 

 to be found on the descending short wave limb of this peak. Porphyrins 

 usually show a minimum of absorption in the region 2500-3000 A and 

 then increasing absorption again at wave lengths <2500 A (Pruckner 

 and Stern, 1937; Theorell, 1947; Holden, 1941). 



The Soret band of the dihydroporphyrines, such as the chlorophylls, is 



o 

 o 



4 50 - 



4 00 - 



3,50 



450 



250 300 350 400 

 WAVE LENGTH, m/i 



Fig. 5-21. Ultraviolet absorption spectra 

 of several porphyrins in dioxane. I, 

 porphyrin; II, aetioporphyrin; III, copro- 

 porphyrin-II-tetramethyl ester; IV, rhodo- 

 porphyrin-XV-dimethyl ester. {Pruckner 

 and Stern, 1937.) 



