ABSTRACT
Carotenes are simple polyenes with conjugated double bonds as their only functional groups. Their chemistry is quickly summed up: they absorb light, cis-trans isomerize, polymerize, and take up oxidants in allylic positions. Nevertheless, there are more open questions in carotene chemistry than anywhere else in bioorganic chemistry. Some examples of such questions are as follows:
1. Carotenes are water insoluble. Nevertheless ~-carotene, C40HS6' occurs in large amounts in carrots, which consist almost exclusively of water (80%) and cellulose (20%). ~-Carotene is, therefore, not part of a functional membrane or enzyme system in these roots and occurs in the form of dead microcrystals. Also, carrots grow in the earth in total darkness. Why should there be a crystalline dye and how can it be formed? Can crystals playa biological role that would justify the pain it takes to synthesize them?
