Thermodynamic study of the second-stage dissociation of N,N-bis-(2-hydroxyethyl)glycine (bicine) in water at different ionic strength and different solvent mixtures.

The second stage dissociation constant pK2 of N,N-bis-(2-hydroxyethyl)glycine (bicine) has been determined in aqueous solution at different ionic strengths and different temperatures, using pH-metric technique. The thermodynamic quantities (deltaG(o), deltaH(o), and deltaS(o)) have been studied and discussed. Evaluation of the effect of organic solvent of the medium on the dissociation processes have also been reported and discussed. The organic solvents used were methanol, dimethylsulfoxide (DMSO), and dioxane. The pK2 for the ionization in water +10, +20, +30, +40, and +50 wt % dioxane has been determined at five different temperatures from 15 to 35 degrees C at intervals of 5 degrees C. The thermodynamic quantities were calculated. The implications of the results with regard to specific solute-solvent interactions (particularly stabilization of zwitterionic species) are also discussed.