Electrical conductance and volumetric studies in aqueous solutions of DL-pyroglutamic acid

Conductivity measurements of DL-pyroglutamic acid and sodium pyroglutamate in dilute aqueous solutions were performed in the 288.15-323.15 K temperature range. The limiting molar conductances of pyroglutamate anion, λ^o(pGlu^-, T) and the dissociation constants of pyroglutamic acid, K(T) were derived from the Onsager, and the Quint and Viallard conductivity equations. Densities of aqueous solutions with molalities lower than 0.5 mol-kg^-1 were determined at 5 K intervals from T = 288.15 K to 333.15 K. Densities served to evaluate the apparent molar volumes, V _2,φ(m, T), the cubic expansion coefficients, α (m,T) and the changes of the isobaric heat capacities with respect to pressure, (∂C_P/∂ P)_T,m . They were correlated qualitatively with the changes in the structure of water when pyroglumatic acid is dissolved in it.