Surface chemistry of carotenoids. 1. Astacene

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Abstract
Astacene in light petroleum is yellow: on emulsification with water the colour changes to pink. This change is not affected to any marked degree by pH or salt cone. It is suppressed by other surface active substances, with the exception of the anions of fatty acids. The position of the absorption band of astacene in the yellow-red region of the spectrum was measured in different solvents. In more polar solvents the band is further towards the red. The position of this band, in light petroleum soln. and in emulsified light petroleum soln., was measured for astacene, [beta]-carotene and zeaxanthin. In all cases the band is shifted to longer wavelengths by emulsification, the effect being least with carotene, greatest with astacene. Surface pressure and surface potential measurements are given for monolayers of astacene, and of astacene mixed with oleic acid. On acid soln. there is little interaction in the mono-layers between the 2 sets of molecules: on alkaline soln. there is a pronounced interaction. The color change on emulsification is attributed mainly to the more polar character of the interface compared with light petroleum, but in the case of astacene enolisation may also be involved.

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