Dialysis Monitoring of Ionic Strength and Denaturant Effects, and Their Reversibility, for Various Classes of Macromolecules.

Monitoring membrane-mediated dialysis in real time with static and dynamic light scattering revealed distinctive differences, including reversibility/irreversibility, in the effects of ionic strength (NaCl) and the denaturant guanidine-HCl (Gd) on a synthetic polyelectrolyte and several types of biomacromolecules: protein, polysaccharide, and polyampholyte. Dialysis cycles against aqueous NaCl and Gd, and reverse back to the original aqueous solution, were monitored. The behavior of Na-polystyrenesulfonate was reversible and yielded a detailed polymer physics description. The biomacromolecules additionally showed hydrogen-bonding/hydrophobic (HP) interactions. An interpretive model was developed that considers the interplay among polyelectrolyte, polyampholyte, and HP potential energies in determining the different associative, aggregative, and dissociative behaviors. NaCl isolated purely electrostatic effects, whereas Gd combined electrostatic and HP effects. Some macromolecules showed partially reversible behavior, and others were completely irreversible. The dialysis monitoring method should prove useful for investigating fundamental macromolecular and colloid properties and for drug formulation and stability optimization.