Small molecules as chromotropes in metachromasia

Summary Interactions of cationic dye methylene blue with small polyanions like inositol hexasulfate, adenosine-triphosphate, ammonium molybdate, potassium ferro- and ferricyanide have been studied spectrophotometrically and conductometrically to ascertain the chromotropic characters of these polyanions. Results show that while almost all of them bind the dye stoichiometrically, none of them except ammonium molybdate is a chromotrope in the sense in which heparin, chondroitin sulfate etc. are. Inositol hexasulfate induces an intermediate spectra, though not perfectly metachromatic as is the case with inositol hexaphosphate. It is concluded that a chromotrope need not be a macromolecule to induce metachromasia in a dye solution, but the minimum number of charges per polyanion to give it a chromotropic character will vary with the nature of the polyanion.University Research Scholar.