Modelling triazolophane–halide binding equilibria using Sivvu analysis of UV–vis titration data recorded under medium binding conditions

Abstract

Two different models that calculate association constants from UV–vis titration data have been evaluated for the 1:1 binding between triazolophane receptor ([Host] = 1–13 μM) and various halides F− , Cl− , Br− and I− in CH2Cl2 (K a ≈ 103–106 M− 1). The Drago model fits the ΔA values at a single wavelength as a function of the added guest concentration. The new computer program Sivvu performs equilibrium-restricted factor analysis using all the wavelengths of the dataset simultaneously. Both models generate comparable K a values, and both provide a means to assess the accuracy of the binding constant determination: K a [host] < 12. Analysis with Sivvu (1) allows the number of unique chemical absorbers to be identified in an unbiased manner. This analysis allowed for a 2:1, triazolophane:F− intermediate to be identified and included in the model. Sivvu also (2) allows alternate models to be quickly evaluated, (3) generates more accurate binding constants, and (4) generates the extinction profiles for each absorbing species in solution.