Proton and potassium affinities of aliphatic and N-methylated aliphatic α-amino acids: Effect of alkyl chain length on relative stabilities of K+ bound zwitterionic complexes

► ZW1/CS1 K+ affinities and proton affinities linearly correlated (r2 ≥ 0.95). ► For ZW1, greater deformation energy, Edef, found for smaller glycine/alanine. ► ZW1 K+ affinities for Val, Leu and Ile found within a narrow 2 kJ mol−1 range. ► Leveling off of molecular polarizability contributions in Val, Leu and Ile. ► Similar ZW1/CS1 K+ affinity trends in N-methylated aliphatic amino aids.