ULTRAVIOLET ABSORPTION SPECTRA 



193 



The presence of this band has at times been mistaken as an indication of 

 the presence of nucleic acid (Strait et al., 1947). Confirmation of the 

 presence of ascorbic acid can be obtained by disappearance of the band 

 upon oxidation, which can be induced by simply raising the pH above 10. 



Vitamin E (a-tocopherol) has a distinct absorption maximum at 2940 A 

 (e = 3200). The 13- and 7-tocopherols have similar spectra (Smith, 1940) . 



Vitamin Ki has a strong, five-peaked absorption band in the region 

 2400-2800 A and a weaker broad secondary maximum at 320 m^ (Fig. 

 5-27). The peaks of the former band occur at 239, 243, 249, 260, and 

 270 m/x, and for the 249-m/x peak, e = 19,600 (Ewing et al., 1943). Vita- 



.«i 



240 



280 320 



WAVE LENGTH, m// 



Fig. 5-27. Absorption spectrum of vitamin Ki in hexane. 



360 



{Ewing et ah, 1943.) 



min K2 has a similar, but slightly weaker, absorption spectrum (Ewing 

 et al., 1939). 



PLANT PIGMENTS 



The common plant pigments such as the anthocyanins and flavones 

 have strong ultraviolet absorption bands. In acid solution, all antho- 

 cyanidins and anthocyanins have one or two strong absorption maxima 

 in the region 2650-2800 A (e = 10,000-20,000) (Fig. 5-28). Some have 

 additional bands at ~2450 and ~3300 A. In basic solution these ultra- 

 violet absorption bands, as Avell as the visible bands responsible for the 

 color of these pigments, are displaced a few hundred Angstroms toward 

 the longer wave lengths (Schou, 1927; Hayashi, 1934, 1936). 



The flavones have two ultraviolet absorption bands at 2500 and 3000 A 

 (e « 10,000). Hydrogenation of the chromene ring, as in the flavonones, 



