A study of the binding between polymers and peptides, using affinity capillary electrophoresis, applied to polymeric drug delivery systems

We have investigated the potential of affinity capillary electrophoresis (ACE) to evaluate binding constants between an anionic polydispersed polymer and four peptides. Nonlinear regression and three current linearization methods, the y-reciprocal, the x-reciprocal and the double-reciprocal, were employed for the estimation of the binding constants. The x-reciprocal and the double-reciprocal plots indicated the presence of two portions of straight lines for angiopeptin, triptorelin and the thyrotropin releasing hormone (TRH), and therefore the probable existence of a second-order interaction which causes the deviation from the 1:1 model. Peptide 1 exhibited a unique binding constant of 2.4 x 10(6)M(-1). In contrast, angiopeptin, triptorelin and TRH exhibited a K(1) of 4.0 x 10(6), 5.3 x 10(6) and 20.2 x 10(6)M(-1), respectively, and a K(2) of 0.4 x 10(6), 0.5 x 10(6) and 1.4 x 10(6)M(-1), respectively. The origin of the high scattering of the data points was further investigated. Neither the viscosity, nor the adsorption of the peptides to the capillary wall appeared to be the determining factor of data scattering. Finally, a possible adsorption of the polymer leading to the electroosmotic flow instability was supposed.