7 APHANICIN 305 



aphanin*. Reduction of the pigment with aluminium isopropoxide and iso- 

 propyl alcohol yields a product, aphanicol, the absorption maxima of which are 

 displaced by about 10 m/^ towards shorter wavelength as compared with 

 aphanicin (in petrol). From this fact and from the identical location of the 

 absorption maxima in petrol and methanol it may be concluded that the carbo- 

 nyl group is not in conjugation with the system of conjugated double bonds. 



Properties 



Crystalline form: Aphanicin crystallises from a mixture of benzene and 

 methanol with a little more difficulty than aphanin and forms red-violet 

 prismatic needles with a strong metallic lustre. 



Melting point: 190° (corr., crystallised from benzene-methanol) . 195° (corr., 

 crystallised from benzene-petrol). 



Solubility: The pigment is even less soluble in methanol than aphanin. In 

 other solvents the solubility of the two pigments is about equal. 



Spectral properties: 



Solvent Absorption range Absorption maxima 



Carbon disulphide . 475-555 533 494 m^ 



Chloroform .... 455-520 504 474 ra/x 



Benzene 455-520 505 474 m/f 



Petrol, b.p. 70-80° . 445-510 494 462 m^ 



Pyridine 460-525 507.5 478 m^ 



Methanol 445-505 491.5 457 m^i 



The colours of solutions of aphanicin in organic solvents are the same as 

 those of aphanin, see p. 303. 



Optical activity: No data have been recorded. 



Partition test: On partition of aphanicin between petroleum ether and 95 % 

 methanol, a somewhat higher proportion of the pigment is found in the alcoholic 

 layer than in the case of aphanin. Even with 90 % methanol the lower layer is 

 slightly coloured. 



Chromatographic behaviour: Aphanicin is more strongly adsorbed than 

 aphanin on alumina from a mixture of benzene and petrol (1:1) and can thus 

 be readily separated from the lattei. The two zones are also distinguished by 

 the depth of their colours, the lower zone being a darker bordeaux-red than the 

 upper zone. 



It has recently been shown that steric differences have a great influence on vitamin 

 A activity, cf. L. Zechmeister and co-workers. Arch. Biochem. 5 (1944) 107; 7 (1945) 247; 

 7 (1945) 157- 

 References p. 341-343. 



Carotenoids 20 



