Metachromasy. IV. The Simultaneous Determination of the Bound Dye Spectra and the Equilibrium Constants between Metachromatic Dyes and Various Polyelectrolytes by the Extended Principal Component Analysis Method

Fourteen sets of visible absorption spectra of two metachromatic dyes, Crystal Violet (CV) and Trypaflavine (TF), were measured in the presence of seven widely different polyelectrolytes—sodium polyphosphate, polyacrylate, and poly(ethylenesulfonate), sodium and potassium poly(p-styrenesulfonate)s, and native and denatured calf thymus DNA–in polymer residue-to-dye ratios between 0 : 1 and about 1 : 1. The optical titration curves of these dye-polyanion systems showed either of two changes, sigmoidal or monotonous. The method of principal component analysis was applied to the observed spectra of each dye-polyanion system in order to determine both the equilibrium constant of the binding reaction and the pure spectrum of the bound dye. An empirical parameter a was introduced into the expression for the equilibrium constant in such a way that K=[complex]/[free dye][unoccupied binding site]α, by which the sigmoidal titration curves could be reproduced only with α>1 and the monotonous ones, with α≤1. The spectra of bound CV and TF showed metachromasy bands, which depend on the functional group and the conformation of the polyanions, in wavelength regions both shorter and longer than the peak wavelength of the free dyes.