New Insights into Buffer-Ionic Salt Interactions: Solubilities, Transfer Gibbs Energies, and Transfer Molar Volumes of TAPS and TAPSO from Water to Aqueous Electrolyte Solutions

The solubilities of N-[tris(hydroxymethyl)methyl]-3-aminopropanesulfonic acid (TAPS) or N-[tris(hydroxymethyl)methyl]-3-amino-2-hydroxypropanesulfonic acid (TAPSO) in water and in aqueous solutions of CH(3)COOK (KAc), KBr, KCl, or NaCl were determined from density measurements at 298.15 K. The solubilities of TAPS in aqueous solution decrease with increasing concentration of the salts (salting-out effect), whereas those of TAPSO increase with increasing concentration of the salts (salting-in effect). The solubility and density data were further used to calculate the apparent transfer Gibbs energies, Delta(tr)V(phi)(0) , of these buffers from water to aqueous electrolyte solutions at 298.15 K. The contributions of various functional groups of TAPS, TAPSO, and the related buffers ( tris( hydroxymethyl) aminomethane, TRIS, and N-tris[hydroxymethyl]-4-amino-butanesulfonic acid, TABS) to the transfer properties were systematically estimated from the calculated Delta(tr)G and Delta(tr)V(phi)(o).G, and transfer molar volumes,