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Determination of Preferential Interaction Parameters by Multicomponent Diffusion. Applications to Poly(ethylene glycol)-Salt-Water Ternary Mixtures
 

Summary: Determination of Preferential Interaction Parameters by Multicomponent Diffusion.
Applications to Poly(ethylene glycol)-Salt-Water Ternary Mixtures
Cong Tan, John G. Albright, and Onofrio Annunziata*
Department of Chemistry, Texas Christian UniVersity, Fort Worth, Texas 76129
ReceiVed: December 13, 2007; In Final Form: February 13, 2008
Poly(ethylene glycol) (PEG) is a hydrophilic nonionic polymer used in many biochemical and pharmaceutical
applications. We report the four diffusion coefficients for the PEG-KCl-water ternary system at 25 C
using precision Rayleigh interferometry. Here, the molecular weight of PEG is 20 kg mol-1
, which is
comparable to that of proteins. The four diffusion coefficients are examined and used to determine
thermodynamic preferential interaction coefficients. We find that the PEG preferential hydration in the presence
of KCl is 1 order of magnitude larger than that previously obtained under the same conditions for lysozyme,
a protein of similar molecular weight. In correspondence, the coupled diffusion in the PEG case was greater
than that observed in the lysozyme case. We attribute this difference to the greater exposure of polymer coils
to the surrounding fluid compared to that of globular compact proteins. Moreover, we observe that the PEG
preferential hydration significantly decreases as salt concentration increases and attribute this behavior to the
polymer collapse. Finally, we have also employed the equilibrium isopiestic method to validate the accuracy
of the preferential interaction coefficients extracted from the diffusion coefficients. This experimental
comparison represents an important contribution to the relation between diffusion and equilibrium
thermodynamics.

  

Source: Annunziata, Onofrio - Department of Chemistry, Texas Christian University

 

Collections: Chemistry