Study of the intercalation equilibrium between the polynucleotide poly(adenylic)-poly(uridylic) acid and the ethidium bromide dye by means of multivariate curve resolution and the multivariate extension of the continuous variation and mole ratio methods

The intercalation equilibrium between the polynucleotide poly(adenylic)-poly(uridylic) acid and the dye ethidium bromide was studied using molecular absorption spectrophotometry, spectrofluorimetry, and circular dichroism. The presence of an intercalation complex, its pure spectrum, and its concentration profile were clearly deduced using Multivariate Curve Resolution and a multivariate extension of the classical continuous variation and mole-ratio methods. The value of the polynucleotide/dye ratio (r(poly/dye)) in the intercalation complex and of its apparent formation log constant were estimated to be 4 and 6.2, respectively. The proposed multivariate methodology allowed an accurate qualitative and quantitative description of the intercalation process.