Characterization and thermodynamic studies of the interactions of two chiral polymeric surfactants with model substances: Phenylthiohydantoin amino acids

Analytical ultracentrifugation is used for determination of the molecular w eights and the sedimentation coefficients of poly(sodium undecanoyl-L-valin ate) (PSUV) and poly(sodium undecanoyl-L-threoninate) (PSUT) at different t emperatures. Plots of absorbance as a function of radius indicates that bot h PSUV and PSUT are highly monodispersed. A method for evaluating the parti al specific volumes using density measurements is presented. The partial sp ecific volumes of PSUV are slightly higher than those of PSUT. In addition, the temperature dependence of the retention factor in electrokinetic chrom atography was used to estimate the enthalpy, the entropy, and the Gibbs fre e energy of the surfactant/analyte complexes. Five phenylthiohydantoin-DL-a mino acids were separated and each enantiomeric pair was completely resolve d. Comparison of the thermodynamic values obtained with PSUV vs PSUT using a van't Hoff relationship suggests that PSUT, with a less favorable free en ergy change (i.e., less negative Delta(Delta G)), generates a more positive entropy change, hence slightly less chiral resolution.