Microcalorimetric studies of solvent-induced conformational change of sodium and cesium salts of poly(L-glutamic acid) in aqueous media

✍ Scribed by Hubert Daoust; Daniel St-Cyr

• Publisher: Wiley (John Wiley & Sons)
• Year: 1988
• Tongue: English
• Weight: 827 KB
• Volume: 27
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.360270807

✦ Synopsis

Organic solvent-induced coil + helix conformational change of poly(sodium L-glutamate (NaPLG) and poly(cesium L-glutamate) (CsPLG) in solution in aqueous mixed solvents have been studied at 25°C. H e a t s of dilution of NaPLG in the water-dioxane pair have been measured as a function of polymer concentration and solvent composition. The results indicate that the overall chain conformation in the disordered form is not too different from that in the a-helical form.

Heat capacity measurements by flow microcalorimetry have also been done. The apparent monomolar heat capacity at constant pressure of the polymer, Cp,+, decreases with dilution similarly to other strong polyelectrolytes in aqueous media. In the water-dioxane pair, Cp,+ increases with the dioxane content due to partial desolvation of ionic species resulting from increasing ionic association. In the case of the water-2-chloroethanol (CE) pair, the transition takes place at low CE content and results show a fast decrease in Cp,+ when the a-helical conformation predominates. I t is believed carboxylate groups and CE molecules associate themselves into a complex formation responsible for the transition. The size of the cation plays a significant role in the thermodynamic properties of these polyelectrolytes in solution since sodium ions are more strongly bound to the chain than cesium ions.