Density functional theory methods with the B3LYP and B97D functionals with triple-zeta 6-311++G(d,p) basis set have been used to study the acidity, basicity and metal affinity of L-gamma-carboxyglutamic acid (GLA) and its peptide derivative [2-acetylamino-3-(methylamino)-3-oxopropyllmalonic acid (AMD-GLA). The Gibbs interaction energies of the GLA(2-)center dot center dot center dot M2+ and AMD-GLA(2-)center dot center dot center dot M2+ (M = Mg, Ca, Zn) complexes show an increasing binding affinity in the order Ca2+ < Mg2+ < Zn2+ The transition metal Zn2+ is most effectively recognized by the dianions of GLA and AMD-GLA. Of the dianions studied the AMD-GLA dianion is the strongest Lewis base. Computations that include the effect of solvation showed that in water the relative stability of GLA(2-)center dot center dot center dot M2+ and AMD-GLA(2-)center dot center dot center dot M2+ ionic bonds is rapidly diminished. The computed interaction Gibbs energy in water is small and negative. (C) 2014 Elsevier B.V. All rights reserved.