Preferential and absolute adsorption to poly[N5-(3-hydroxypropyl)-L-glutamine] in water/2-chloroethanol solvent mixtures.

Preferential adsorption to poly[N5-(3-hydroxypropyl)-L-glutamine] (PHPG) in water/2-chloroethanol solvent mixtures has been determined by measuring density increments at constant concentration and at constant chemical potential. At low alcohol concentrations, decreasing preferential adsorption of 2-chloroethanol is observed. When the organic solvent content is increased, an inversion of preferential adsorption occurs, water being preferentially adsorbed. The inversion zone parallels the conformational transition curve. As an explanation it is proposed that a competition occurs between noninteracting helicogenic 2-chloroethanol, which stabilizes hydrophobic interactions, and the hydrophilic interactions of water with PHPG. The former retains a helical structure, whereas the latter induces a helix-to-coil transition.