An Evaluation of the Metachromasy of Anionic Dyes. II. Visual and Spectral Observations on Solutions

The reactions of 13 anionic dyes in solution with a basic protein (protamine), a cationic detergent, guanidine, histamine, procaine, quinine, and strychnine were examined visually and spectrophotometrically in order to distinguish metachromatic changes of the dyes. Disazo dyes (Congo red, benzopurpurin, but not trypan blue) were metachromatic; indigoid, triphenylmethane and xanthene dyes were not. The magnitude of metachromasy in this series of dyes was not great compared with cationic dyes, the shifts of absorbance maxima being only about 15 mμ against 90 mμ or more for some cationic metachromatic dyes. The most effective chromotropes were protamine and a cationic detergent. Agreement between visual observations on tissue sections, visual observations on solutions, and spectral observations on solutions was generally good.