UV absorption data analysis has been used to evaluate equilibrium constants of the pH-induced interaction of 2,2′-Bipy with polyadenylnic-polyuridylic acid in aqueous solution. The conditional probabilities hard model has been adopted in treatment of concentration diagrams calculated by the soft modelling-based Multivariate Curve Resolution-Alternating Least Squares approach. Intrinsic binding constant (lgKg = 1.93), and the cooperativity parameter (ω = 340), were calculated as the best fit. The plot of the experimental binding constant versus 2,2′-Bipy equilibrium concentration shows two modes of ligand with polymer interactions. The equilibrium hard model correctly reproduced the binding constant variations observed in the experiment. The results indicated that ligand binding in two steps is governed by a cooperative process, that is, the enhancement of deprotonated structure stability. It would appear that proposed calculation approach can be used in future combined hard modelling theoretical and soft modelling experimental works. © 2013 Wiley Periodicals, Inc. Biopolymers 99:621–627, 2013.