236 CAROTENOIDS CONTAINING CARBONYL GROUPS XII 



formulation of the pigment, di-esters can be prepared (cf. p. 235). According 

 to KuHN and Sorensen, the deep blue potassium salt of astaxanthin may be 

 compared with the orange coloured potassium derivative of benzoin*, and the 

 corresponding salts of dihydrocrocetin dimethyl ester and dihydrobixin- 

 dimethyl ester*^^ ^nd may be formulated as follows: : 



CH3 CH3 CH3 CH3 



C CH3 CH3 CH3 CH3 C 



CHa C-CH=CH-C = CHCH=CH-C=CHCH=CHCH=C-CH=CHCH = C-CH=CH-C CH, 



KOC C-CH, HjC-C COK 



V \^ 



c c 



j Potassium Salt of Astaxanthin (deep blue) I 



OK (^K 



Constitution of Ovoverdin^^ 



Ovoverdin is the name given by Kuhn and Leuerer^i to the blue-green 

 chromoproteid which is the natural pigment of the lobster shell. According to 

 Kuhn and Sorensen*^, ovoverdin is an enol salt somewhat analogous to the 

 potassium derivatives of benzoin and astaxanthin. This formulation would 

 explain the blue-green colour of the compound. 



CH3 CH3 CH3 CH3 



\/ \V 



C CH3 CH3 CH3 CH3 c 



CH2 C-CH=CH-C=CHCH=CH-C=CHCH=CHCH=C-CH=CHCH=C-CH=CH-C CH^ 

 C C-CH3 BX-G C 



-0 c c 0- 



\ ' I / 



0- Ovoverdin (blue-green) 0- / 



Protein++ Prot"ein++ 



It is surprising, however, that ovoverdin is not autoxidisable, in contrast 

 to the potassium derivative of astaxanthin. This fact is explained by Kuhn 

 and Sorensen by assuming that the interaction with the protein component 

 is not simply ionic in nature, but that additional binding forces are involved 

 which result in a relatively stable combination of the pigment and the protein 

 in the form of a molecular complex. The nature of the additional binding 

 forces is not specified but a complex derived from one protein molecule with 

 two separate links, rather than from two independent protein molecules, appears 

 to be implied. 



* See note page 235. 

 References p. 253-255. 



