30 



VITAMINS A AND CAROTENES 



as hydroquinone or a-tocopherol. The latter seems to be preferred, since 

 it is known to have, in addition to its antioxygenic effect, a synergistic 

 action on vitamins A. 



Since vitamin Ai^*^ is an alcohol, it forms esters and ethers, most of which 

 are more stable than the vitamin itself. The acetate has been adopted by 

 the World Health Organisation as the international standard .^^' ^^ The physi- 



220 30 40 50 60 70 80 90300 10 20 30 40 50 60 70 80 90 400 K) 20 



Wavelength, m/^ 



Fig. 4. Ultraviolet absorption spectra: A, all-<rans vitamin Ai; B, all-/mns vita- 

 min Ai acetate plotted from the data of Cama et al.f and C, vitamin Ai palmitate.** 



cal properties of some of these derivatives together with their spectroscopic 

 data and biopotencies are listed in Table X. Similar data for the all-f rans 

 vitamin Ai are also included for comparison. The calculated biopotencies 

 are based on the biopotencies of the all-^raws vitamin Ai and that of the 

 all-^rans vitamin Ai acetate.*^ Figure 4 shows the ultraviolet absorption 

 curves of the all-^raws vitamin Ai (curve A), the 2\\-tran8 ^dtamin Ai ace- 

 tate (curve B), plotted from data published by Cama el al.^'^ and vitamin 

 Ai palmitate (curve C).^^ The configuration of vitamin Ai palmitate was not 

 definitely known when the measurements were made for this curve. 



Vitamin Ai is also known to react with antimony trichloride in chloroform 



