Metachromasy. II. Interaction between Sodium Polyphosphates and Crystal Violet with Special Emphasis on the Effect of Chain Lengths of the Polymer on the Metachromasy Band

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Abstract
The interaction of crystal violet with sodium polyphosphate in aqueous solutions at neutral pH has been investigated by means of visible absorption spectroscopy and electric conductivity. The mixing ratio of polymer residue to dye was varied from 0.1 to 10000. The metachromasy band at 506 nm was found to fully develop between 3 and 10, whereas conductometric titration showed that crystal violet saturates the polymer site. Emphasis was placed on the effect of the polymer chain length on the metachromasy band. To study this effect, 17 fractionated and 13 refractionated polymer samples with degrees of polymerization extending from 4 to 300 were utilized. A critical range of the degree of polymerization from the metachromasy band exists between 7 and 20. The effect of small ions on metachromasy was also studied using sodium phosphates. An increase in Na+ ions tends to suppress the metachromasy band. This effect is more pronounced with shorter polymer lengths. In order to explain the observed metachromasy phenomena, two mechanisms were postulated; one attributes metachromasy to the flexibility of the polymer backbone when dye is present, and the other deals with specific interaction of dye and polymer site.