Interactions between acridines and triphenyl methane dyes: Their possible role in therapeutic interference

The interaction of trypaflavine, or its N-ethyl analog, with the triphenyl methane dyes, Crystal Violet and parafuchsin, has been investigated. Molecular orbital calculations indicate that interaction between the two species is feasible and likely. Experimental evidence from X-ray diffraction determination, spectrophotometry in the visible region and fluorescence quenching confirms the existence of a complex between the species, with a 1:1 ratio of dyes, and the lack of fluorescence quenching with the model quencher methylene blue indicate that this 1:1 complex forms only when both molecules are flat. The formation of this complex is discussed as a possible explanation of the therapeutic interference by triphenyl methane dyes on the action of the acridines.