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Pure Appl. Chem. Vol. 74, No. 8, pp. 1391-1396 (2002)

Pure and Applied Chemistry

Vol. 74, Issue 8

Photoisomerization by Hula-twist. Photoactive biopigments*

Robert S. H. Liu

Department of Chemistry, University of Hawaii, Honolulu, HI 96822, USA

Abstract: A review of literature on photoisomerization of bilirubin and photoactive yellow protein suggests possible involvement of the volume-conserving Hula-twist (HT) reaction mechanism in their primary photochemical processes. Additional definitive experiments to verify their involvement are proposed. Information related to photoproducts of bacteriorhodopsin, rhodopsin, and phytochrome are reviewed. For carotenoids, because of participation of the longer lived triplet state in, for example, the photosynthetic apparatus, the involvement of HT is probably less likely.

With the aim of extending the color fan of nature-identical food colorants offered by Roche and therefore offering a less critical colorant to the food industry, a project was initiated at Roche. The goal was to find a safer, naturally occurring pigment with a color hue similar to tartrazine.

This paper discusses the process of how such a project is addressed in industry, as well as how promising candidates were selected from the wide variety of the naturally occurring carotenoids. The syntheses of some of these carotenoids will also be described.

*Lecture presented at the 13 th International Symposium on Carotenoids, Honolulu, Hawaii, USA, 6-11 January 2002.
Other lectures are published in this issue, pp. 1369-1477

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