ABSTRACT
Dyes contain a planar dibenzothiazine heterocyclic chromophore. Most dyes with the cationic thiazine, more precisely thiazinium, chromophore carry conjugated amino substituents. All the thiazine dyes used in biology and medicine are small, with small conjugated systems. They are cationic, or in one case neutral, under usage conditions. The cationic thiazines are hydrophilic, albeit some only weakly; the neutral ketothiazine is lipophilic. This group of dyes illustrates rather neatly the distinction between hydrophilicity and water solubility, the latter having no simple relationship to former. Thiazine dyes can often be reduced by various components of biological systems. This involves disruption of electronic structure of chromophore, with reduced species being colorless. Azure B is diaminothiazine whose planar conjugated system is small, as is dye’s overall size. Azure B is used, directly and indirectly, to stain living cells, for instance to visualize enzyme-labeled axonal tracer, and to image neurons in the ganglion cell layer of the living retina using an infrared sensitive camera.
