Theoretical studies of infrared signatures of proton‐bound amino acid dimers with homochiral and heterochiral moieties

Proton-bound homochiral and heterochiral dimers, X-H(+) -X, of five amino acids (X = Ser, Ala, Thr, Phe, and Arg) are investigated theoretically using quantum chemical density functional theory (DFT) calculations and molecular dynamics simulations with the aim to unveil diastereomer-specific mid-infrared (mid-IR) absorption bands in the spectral range of 1000 to 1800 cm(-1) . The theoretical calculations performed in this work imply that all systems, except Ala2 H(+) , have distinct mid-IR absorption bands in homochiral and heterochiral configurations, which make them appropriate systems to be studied experimentally with mid-IR spectroscopy. We show that intermolecular interaction with the side chain, in the form of hydrogen bonding or cation-pi interaction, is necessary for chiral effects to be present in the mid-IR spectra of proton-bound dimers of amino acids. We also report new conformers for Ala2 H(+) , Thr2 H(+) , Phe2 H(+) , and Arg2 H(+) , which were not found in earlier studies of these dimers.