An Investigation of the Structures of [(Glycine)(1‐Methyluracil)]M⁺ Complexes (M=H, Li, Na, K) in the Gas Phase by IRMPD Spectroscopy and Theoretical Methods

The presence of ions in the complexation of molecules can profoundly affect the structure, resulting in changes to functionality and stability. These non-covalent interactions drive many biological processes both necessary and inimical and require extensive research to understand and predict their effects. Protonated and alkali metalated complexes of glycine (Gly) and 1-methyluracil (1-mUra) were studied using infrared multiphoton dissociation (IRMPD) spectroscopy and density functional theory (DFT) calculations. The experimental and simulated vibrational spectra were compared to help elucidate the structure of each complex. The lowest energy structure for [(Gly)(1-mUra)]H⁺ consists of amine protonated Gly bound to O4 of canonical 1-mUra through a single ionic hydrogen bond with another, intraglycine ionic hydrogen bond between the protonated amine group and the carbonyl oxygen. For [(Gly)(1-mUra)]Li⁺, [(Gly)(1-mUra)]Na⁺ and [(Gly)(1-mUra)]K⁺, the experimental spectra are most consistent with the metal cations binding in a trigonal planar geometry with 1-mUra bound to the metal cation via the O4 carbonyl. In [(Gly)(1-mUra)]Li⁺ and [(Gly)(1-mUra)]Na⁺, the metal cation is bound to canonical Gly via the carbonyl oxygen and amine nitrogen, but in [(Gly)(1-mUra)]K⁺, Gly is bound through both oxygens and contains an intraglycine hydrogen bond from the hydroxyl to the amine nitrogen. It was found that the B3LYP/6-31+G(d,p) vibrational spectra are most consistent with the experimental spectra, but M062X was better than B3LYP at determining the lowest-energy structures.