Figure 17.

(a) Relative concentration (ξ_l,i) of the glycine zwitterion (continuous black curve), the cation (long-dashed red curve), and the anion (short-dashed blue curve) at 298.15 K and 1 bar, as a function of pH. The pK_A and pI values¹⁷⁴ are denoted by the vertical black dotted lines. (b) The solubility of glycine in water at 298.15 K (black), 318.15 K (blue), and 348.15 K (orange) and at 1 bar as a function of pH. The continuous curves represent SAFT-γ Mie calculations and symbols represent experimental solubility data; circles denote pH-dependent data of Needham et al.¹⁶⁷ and triangles solubility data at the isoelectric point (pI) of Dalton and Schmidt.⁸⁰ The filled circle represents the data point used in optimizing the NH₃⁺–COO^– interaction, while empty symbols denote data not used in the parameter estimation.