Interaction of povidone with aromatic compounds IV: effects of macromolecule molecular weight, solvent dielectric constant, and ligand solubility on complex formation.

Complex formation of ligand molecules with povidone was investigated to elucidate the effect of the molecular weights of the macromolecule and the influence of the solvent dielectric constant on the complexing tendency. The higher molecular weight polymers were more effective complexing agents than those with lower degrees of polymerization. When studying complex formation as a function of the dielectric constant (D), a linear relationship was noted between D and log B/F (B/F representing the ratio of bound to free ligand); the use of solvent mixtures to achieve a range of solvent dielectric constants enabled changes of the pH of the solvent, ligand dissociation, and solubility of the ligand and macromolecule. Of the variables under investigation, only the change in ligand solubility seemed to play an important role: a linear relationship was noted between the complexing tendency (log B/F) and the logarithm of the inverse of the ligand molecule solubility in the solvent mixtures (log 1/S). It was concluded that the change in solubility of the ligand was the predominant factor in the decrease of the complexing tendency with decreasing dielectric constant.