Quantitative Study of Metachromasy. The Analysis of the Dye–Polyphosphate Multiequilibrium System by the Principal Component Analysis Method

Abstract

Abstract The absorption spectra of three dyes, 9-aminoacridine (AA), Crystal Violet (CV), and Trypaflavine (TF), were measured in the presence of sodium polyphosphate (NaPP). The optical titrations were performed at phosphate residue-to-dye ratios between 26.6 and 2130 for AA, between 42.6 and 788 for CV, and between 53.9 and 1120 for TF. Using a model in which the condensation of dyes to a poly electrolyte and the bound monomer\ightleftharpoons bound aggregate equilibrium in the vicinity of the polymer are assumed, the extended principal component analysis was applied to the observed spectra of each dye–NaPP system. The equilibrium constants and the pure spectra of bound dye species were determined. Both the bound monomer and the bound dimer were present in the AA–NaPP system, while the bound monomer, bound dimer, and bound tetramer were present in both CV– and TF–NaPP systems. In all the cases, the absorption spectrum of the bound monomer showed a slight bathochromic shift. The absorption spectrum of the bound dimer of AA showed a considerable bathochromic shift without any new band, while the spectrum of the bound dimer and bound tetramer of CV and TF showed metachromasy bands in wavelength ranges both shorter and longer than the peak wavelength of free CV and TF.