Properties of Carotenoid Sulphates

Chromatographic properties of carotenoid sulphates are described in Vol. lA, Worked Example 11, which also describes chemical conversion into the free hydrogen sulphates by ion exchange and removal of sulphate groups by acid hydrolysis to provide the parent carotenol, as well as enzymic hydrolysis. 

The characteristic infrared absorption of the sulphates is treated in Vol. IB, Chapter 4 and MS data in Vol. IB, Chapter 7. Recently, field desorption MS for carotenoid sulphates has been discussed [18]. It should be noted that molecular ions are not observed upon ordinary electron impact MS. NMR data are given in the original literature [2,5-7,11,14]. 

In aqueous solution a hypsochromic effect on the electronic spectrum has been observed [12]. Like other substituents a secondary sulphate substituent in cyclohexene rings appears to influence the CD spectrum by determining the preferred conformation of the ring [11,12]. 

The water solubility of carotenoid sulphates is a special property among carotenoids and depends not only on the number of sulphate groups present, but on the total carotenoid structure. The following water solubilities in mg/ml have been reported r,2 -dihydro-( ), /-caroten-T-ol (88) sulphate 0.01, astaxanthin (406) disulphate 0.02, zeaxanthin (119) disulphate 0.05, capsorubin (413) disulphate 0.14, fucoxanthin (369) sulphate 0.20 and peridinin (558) sulphate 0.36 [12]. It should be noted that the water solubility is drastically reduced in the presence of inorganic salts, as expected from solubility product considerations. 

In a dry 50 ml four-necked flatbottomed flask equipped with mechanical stirrer, thermometer and argon inlet, 0.5 ml of a freshly prepared solution of 10% ZnCl2 in ethyl acetate and 2 drops of freshly distilled Bp3 OEt2 were added to 12.8 g (72.7 mmol) fumaraldehyde bis(dimethylacetal) (2) (b.p. 100-103X (20 mbar), 95 %, Aldrich No. 36820-2). To the 

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