Absolute potassium cation affinities (PCAs) in the gas phase.

The potassium cation affinities (PCAs) of 136 ligands (20 classes) in the gas phase were established by hybrid density functional theory calculations (B3-LYP with the 6-311+G(3df,2p) basis set). For these 136 ligands, 70 experimental values are available for comparison. Except for five specific PCA values-those of phenylalanine, cytosine, guanine, adenine (kinetic-method measurement), and Me(2)SO (by high-pressure mass spectrometric equilibrium measurement)-our theoretical estimates and the experimental affinities are in excellent agreement (mean absolute deviation (MAD) of 4.

A theoretical study of potassium cation binding to glycylglycine (GG) and alanylalanine (AA) dipeptides.

By combining Monte Carlo conformational search technique with high-level density functional calculations, the geometry and energetics of K(+) interaction with glycylglycine (GG) and alanylalanine (AA) were obtained for the first time. The most stable K(+)-GG and K(+)-AA complexes are in the charge-solvated (CS) form with K(+) bound to the carbonyl oxygens of the peptide backbone, and the estimated 0 K binding affinities (DeltaH(0)) are 152 and 157 kJ mol(-1), respectively. The K(+) ion is in close alignment with the molecular dipole moment vector of the bound ligand, that is, electrostatic ion-dipole interaction is the key stabilizing factor in these complexes.