5 ASTACENE AND ASTAXANTHIN 237 



A number of investigations have been made regarding the nature of the 

 protein component. Thus, Wyckoff^* determined a molecular weight of about 

 300.000 for ovoverdin. Kuhn and Sorensen*^ worked out a procedure for the 

 purification of ovoverdin which involves the fractional adsorption of the 

 chromoproteid on aluminium hydroxide and the fractional elution with 

 disodium phosphate or ammonium sulphate. The molecular weight of ovoverdin 

 purified in this manner was 144,000. According to Stern and Salomon*® the 

 protein component of ovoverdin has albumin character. 



Properties and Derivatives of Astacene 



Crystalline form: The pigment crystallises from a mixture of pyridine and 

 water in violet needles with a metallic lustre. Sometimes the needles are sickle- 

 shaped. 



Melting point: 240-243° (corr., in vacuum, slow heating)^!; 241°*', 228°^. 



Solubility: Astacene is insoluble in water, very sparingly soluble in ether, 

 petroleum ether and methanol, sparingly soluble in benzene, ethyl acetate and 

 acetic acid, fairly soluble in carbon disulphide, and easily soluble in chloroform, 

 pyridine and dioxan. 



Optical activity: Astacene is optically inactive. 



Partition test: On partition between petroleum ether and 90% methanol, 

 astacene is found almost entirely in the lower layer. On addition of a little more 

 water, the pigment is easily transferred to the petroleum ether layer, but 

 remains in the lower layer in the presence of alkali*^. 



Chromatographic behaviour: Astacene is hardly adsorbed on calcium carbonate 

 from a mixture of benzene and petrol. It is found in the top zone of the chroma- 

 togram on adsorption on alumina from the same solvent mixture. It cannot 

 be eluted from alumina either with a mixture of benzene and methanol or a 

 mixture of pyridine and methanol. 



Spectral properties (cf. Fig. 16, p. 354) : 



Solvent Absorption ynaxitna 



Pyridine about 500 m/i (wide band) 



Carbon disulphide about 510 m/<*' 



Colours of solutions: Concentrated solutions of the pigment in pyridine are 

 blood-red, dilute solutions orange-red. 



Colour reactions: Astacene dissolves in concentrated sulphuric acid with a 

 deep blue colour. Treatment of the solution of the pigment in chloroform with 

 antimony trichloride results in a blue-green colouration. 

 References p. 253—255. /^ 





