Acridities and phenanthridines

The acridine and phenanthridine chromophores both contain a central six-membered aromatic nitrogen heterocycle, with benzo rings fused onto each side. Although sulfonated and hydroxylated acridines have been synthesized, none are used as stains. The hydrophilic/lipophilic properties of the dyes under usage conditions are varied. Acridine and phenanthridine chromophores are small and planar, and can intercalate into DNA helices. Overall the aromatic units in the common phenyl derivatives of both acridines and phenanthridines (e.g. phosphine and ethidium bromide respectively) are nonplanar, with phenyl units rotated out of the plane of the chromophore. Acridine and phenanthridium dyes used in biology and medicine vary markedly in size, with formula weights between 249 and 857. Quinacrine is used to stain platelets to permit subsequent assessment of their adhesion and aggregation; and to assess the dense granule content of platelets using flow cytometry. Quinacrine has a long history of use as an antimalarial drug, and is still so used where newer drugs cannot be afforded.