STUDIES ON AQUEOUS SOLUTIONS OF SODIUM POLY-L-GLUTAMATES - DETERMINATIONS OF MEAN ACTIVITY COEFFICIENT, OSMOTIC COEFFICIENT, TRANSFERENCE NUMBER, AND PARTIAL MOLAL VOLUME

The mean activity coefficient of sodium poly-L-glutamate, NaPGA, in the two-component system water-NaPGA was investigated by the isopiestic vapor pressure and/or emf measurements. The transference and related measurements were also carried out for the determination of the net valency and the transference number of PGA ions. The degrees of neutralization of PGA with NaOH were 0.3, 0.6, and 1.0, and the solution temperature studied was between 25 and 50°. The fraction of free geganions and the transference number of PGA ions were concentration insensitive, and dependent on the degree of neutralization and solution temperature, being 0.6~0.95 and 0.2~0.4, respectively. The osmotic coefficient was between 0.5 and 1.3, varying with the degree of neutralization, polymer concentration, and temperature, and increased sharply by the helix-coil transition induced by rising temperature. The mean activity coefficient decreased with concentration at low concentrations; the decreasing tendency was more remarkable for the helical structure than for the coiled state. The two coefficients indicated the strong water structure-forming tendency of the PGA ions. The partial molal volume was further measured for various salts of PGA. The individual molal volume of PGA ions was calculated to be 85.7 ml/monomol; the electro-strictional hydration effect and the hydrophobic structural effect were – 7.7 and –11.7 ml/monomol, respectively. From this, it is concluded that the monomer unit of PGA is hydrated electrostrictionally by three water molecules. © 1969, American Chemical Society. All rights reserved.