ABSTRACT
Thiazole dyes contain one or more benzothiazole units conjugated with various acceptor/donor moieties. Thiazole orange has an N-methylated thiazole ring with the other nitrogen being in a quinoline system, hence it is a cyanine. Coumarin dyes have benzo-2-pyrone fluorophores containing carbonyl groups as electron acceptors. Most coumarins used histochemically have electron donor 7-amino or 7-hydroxy groups, and so are neutrocyanines. Flavonoids are derivatives of benzo-4-pyrone (i.e. flavone), and the acceptor/donor pairs of dyes discussed here are hydroxy/carbonyl; hence they are neutrocyanines. The colorless precursors of two flavonoids, brazilin and hematoxylin, are also described. The FM styryl dyes, for instance, correspond to page numbers in the laboratory notebook of Fei Mao, who first synthesized them. In the biological literature it is often suggested that styryl dyes have distinct lipophilic and hydrophilic domains, and hence are strongly amphiphilic. Some of the coumarins described here react with proteins; they may give rise to hypersensitivity responses, although there are currently no reports of such.
