The order of lithium ion affinities for the 20 common α-amino acids. Calculation of energy-well depth of ion-bound dimers

Abstract

In an earlier publication it was shown that the kinetic method for determination of proton affinities can be satisfactorily explained when the critical energies for decomposition of the proton-bound dimers are calculated from the Marcus equation. In this work it is shown that the critical energies for decomposition of alkali metal ion-bound dimers also seem to follow the Marcus equation. This supports the application of the kinetic method for measurements of alkali metal-ion affinities of organic molecules. Based on unimolecular decompositions of Li⁺-bound dimers, the order of lithium ion affinity of the common α-amino acids has been established as: Arg > His > Gln > As n > Lys > Trp > Glu > Asp > Tyr > Met > Phe > Thr > Pro > Ser > Ile > Leu > Val > Cys > Ala > Gly.