312 CAROTENOIDS OF UNCERTAIN STRUCTURE XIV 



Solubility: Fucoxanthin is readily soluble in ethanol, somewhat less soluble 

 in carbon disulphide, sparingly soluble in ether, and quite insoluble in petroleum 

 ether. lOO g of hot methanol will dissolve 1.66 g of the pigment. 



Spectral properties: Fucoxanthin exhibits an absorption spectrum similar 

 to that of xanthophyll, but the bands are less sharp. 



In carbon disulphide 510 477 445 m/n (diffuse) 



In chloroform . . . 492 457 m/t (cell thickness 2 mm)*^ 



(cf. Fig. 9, p. 351) 



A solution of fucoxanthin in ether is orange-yellow, a solution in ethanol is 

 reddish, and a solution in carbon disulphide is red. 



Colour reactions: On shaking an ethereal solution of fucoxanthin with 25 % 

 aqueous hydrochloric acid, the latter is coloured deep-blue. 



Optical rotation: According to Karrer and co-workeis*^ fucoxanthin has a 

 specific rotation of [a]p = + 72.5° ± 9° (in chloroform). Heilbron and 

 Phipers*", on the other hand, find that the pigment does not rotate the plane 

 of polarised hght. 



Chromatographic behaviour: Hardly any data are available regarding the 

 chromatographic adsorption of fucoxanthin*^. In order to estabhsh whether 

 the pigments investigated by different workers were identical or mixtures 

 of different substances, a renewed detailed chromatographic investigation of 

 fucoxanthin would be desirable. 



Detection and estimation: As far as is known at the present time, the pigment 

 occurs mainly in brown algae. It is accompanied by j8-carotene, zeaxanthin and 

 xanthophyll from which it can be easily distinguished by means of its absorption 

 maxima and its colour reaction with hydrochloric acid. 



Chemical properties: Although fucoxanthin has no acidic properties, it is 

 not indifferent towards alcoholic alkah since methanolic potassium hydroxide 

 dissolves the pigment much more quickly than methanol alone. On acidification, 

 no fucoxanthin can be regenerated from this solution, but new compounds are 

 obtained which Heilbron and Phipers*" termed isofucoxanthins. Nothing 

 definite is yet known concerning the nature of these compounds. Heilbron 

 suggests that isofucoxanthins are formed by an aldol condensation but this 

 suggestion has not been proved. Isofucoxanthins are much more strongly 

 basic than fucoxanthin. Even 0.001 % hydrochloric acid removes the blue 

 colour of an ethereal solution of these new pigments. The absorption maxima 

 of isofucoxanthin are displaced towaids shorter wavelengths with respect to 

 fucoxanthin. 

 References p. 341-343. 



