Induction of metachromasia and circular dichroism in the dye 1,9-dimethyl methylene blue by ATP.

The theoretical prediction of induction of metachromasia [V Czikkely, H D Foersterling & H Kuhn (1970), Chem Phys Lett, 6,207] in a dye by a polyanion having only four to six anionic sites is proved experimentally, for the first time, in ATP--1.9-dimethyl methylene blue system. The findings show that ATP induces metachromasia in the dye at neutral pH, when ATP molecule remains fully charged providing four anionic sites to the dye cations. Conductometric titration shows that the dye molecules bind stoichiometrically to ATP (four dyes/ATP). However ATP at acidic pH and ADP and AMP at any pH fail to induce metachromasia. This is also the first report of induction of circular dichroism in bound dyes by ATP. Though the chiral moiety of ribose sugar in ATP may induce dichroism in the bound achiral dyes, the observed high molar ellipticity values indicate aggregation of bound dyes with twist in one sense initiated by the twisted conformation of the triphosphate chain in ATP. This inference on the state of conformation of ATP in its native environment is in agreement with that derived from PMR and spin lattice relaxation technique. It is thus interesting that the conformation of crystalline disodium ATP, as concluded from X-ray crystallography, is maintained by tetrasodium ATP in dilute aqueous solution--the native environment of ATP.