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Glutathione is a biologically abundant and redox active tripeptide that coordinates with metals. This study examines the change in binding conformation with relevant dications; Zn²⁺, Cu²⁺, and Fe²⁺. 

Threshold collision-induced dissociation (TCID) and infrared multiple photon dissociation (IRMPD) spectroscopy are used to examine complexes of metal mono- and dications with amino acids and peptides. Trends in the results are elucidated. 

A combination of infrared multiple-photon dissociation (IRMPD) action spectroscopy and quantum chemical calculations was employed to investigate the [M,C,2H]⁺(M = Ru and Rh) species. 

Cesiated complexes of the aliphatic amino acids (Gly, Ala, hAla, Val, Leu, and Ile) were examined by infrared multiple photon dissociation (IRMPD) action spectroscopy utilizing light from a free-electron laser (FEL). To identify structures, the experimental spectra were compared to linear spectra calculated at the B3LYP-GD3BJ/def2-TZVP level of theory. Relative energies at 0 and 298 K for various possible conformers of all complexes were calculated at B3LYP, B3LYP-GD3BJ, and MP2(full) levels using the def2-TZVP basis set. Spectral comparison for all complexes indicates that the dominant conformation has the cesium cation binding to the carbonyl and hydroxyl oxygens, [CO,OH]. This conclusion contrasts with previous work for Cs+(Gly), which suggested that the [CO] binding motif was prevalent. This dichotomy is explored theoretically in detail using coupled-cluster calculations with single, double, and perturbative triple excitations, CCSD(T), as well as advanced density functional theory (DFT) approaches. The comparisons show that the [CO,OH] – [CO] double-well potential found for most DFT approaches disappears at the higher level of theory with only the [CO,OH] well remaining. An exploration of this effect indicates that electron correlation is critically important and that DFT approaches incorrectly handle the internal hydrogen bonding in these molecules, thereby over-delocalizing the charges on the amino acid ligands.