Ion-binding of glycine zwitterion with inorganic ions in biologically relevant aqueous electrolyte solutions

The ion-binding between inorganic ions and charged functional groups of glycine zwitter-ion in NaCl(aq), KCl(aq), MgCl2(aq), and CaCl2(aq) has been investigated over a wide salt concentration range by using integral equation theory in the 3D-RISM approach. These systems mimic biological systems where binding of ions to charged residues at protein surfaces is relevant. It has been found that the stability of ion pairs formed by the carboxylate group and added inorganic cations decreases in the sequence Mg2+ > Ca2+ > Na+ > K+. However, all formed ion pairs are weak and decrease in stability with increasing salt concentration. On the other hand, at a given salt concentration the stability of ( -NH3+:Cl-)(aq) ion pairs is similar in all studied systems. The features of ion-binding and the salt concentration effect on this process are discussed. (C) 2014 Elsevier B.V. All rights reserved.