Studies of the Interaction of Sodium Polyphosphates with Acridine Orange

Abstract

Abstract The interaction of sodium polyphosphates with acridine orange has been studied by means of absorption spectra, fluorescence, and viscosity measurements. Polyphosphates with a variety of molecular weights were used in order to investigate the effect of the degree of polymerization (\barn) on the interaction. No spectral change was observed in the case of polyphosphates with \barn<5. In the case of \barn=9, an absorption band corresponding to the dye dimer was observed, whereas in the case of larger \barn values those corresponding to higher aggregates were also found. The maximum metachromasy occurred at P⁄D=3–6. Fluorescence quenching was observed, accompanied by an absorption change. Such behavior may be considered to be characteristic of the dye molecules bound to the long-chain polyphosphates; the bound-dye molecules seem to exhibit almost no fluorescence. The quenching constants of the fluorescence increased with the increase in \barn values. The binding energies were estimated to be 5–6 kcal/mol independent of the \barn values. In the presence of acridine orange, the reduced viscosity of Kurrol’s salt decreased remarkably, probably as a result of the neutralization of the charged phosphate groups. Further, its reduced viscosity decreased remarkably with time; this may be attributed to the catalytic action of the dye on the hydrolytic degradation of polyphosphates.