Cooperative complexation of α-cyclodextrin with alternating copolymers of sodium maleate and dodecyl vinyl ether with varying molecular weights

In this study, we investigated the effect of the polymer molecular weight on the cooperative complexation of α-cyclodextrin (α-CD) with alternating copolymers of sodium maleate and dodecyl vinyl ether (pC ₁₂M) by ¹H NMR measurements. It was confirmed that the pC₁₂M prepared formed micelle-like aggregates in aqueous media by steady state fluorescence and sedimentation equilibrium experiments. Using the NMR data, the concentrations of free and complexed α-CD (C_CD,f and C_CD,c, respectively) were calculated and the C_CD,c values were plotted as a function of C_CD,f to prepare binding isotherms. The binding isotherms exhibited sigmoidal curves for all the polymers examined, indicative of cooperative complexation. The binding isotherms also indicated that the complexation was more cooperative for pC₁₂M of a higher molecular weight. Analysis of the binding isotherms using a model proposed based on the one-dimensional lattice theory indicated that the molecular weight dependency of the cooperative complexation was due to molecular dependent attractive interactions between free dodecyl groups and between complexed α-CD molecules.