Search for: All records

Methane and cyclopropane (c-C3H6) were reacted with Ru+ ions in a room temperature ion trap and the resulting products were identified using a combination of mass spectrometry, IR action spectroscopy, and density functional theory calculations. In the reaction with methane, no products with odd numbers of carbon atoms were located, whereas significant amounts of products with even numbers of carbon atoms were observed. We identified [Ru,2C,4H]+ as the Ru+ ion with an ethene ligand attached, and [Ru,4C,6H]+ as a Ru(η4-cis-1,3-butadiene)+ complex. The barrier toward formation of Ru(C2H4)+ + 2 H2 was calculated at the B3LYP/def2-TZVPPD level to be 0.80 eV above the energy of the ground state Ru+ (4F) + 2 CH4 reactants. In the reaction of c-C3H6 with Ru+, we identified the dehydrogenation product [Ru,3C,4H]+ as Ru(η2-propyne)+, [Ru,2C,2H]+ as Ru+ with an ethyne ligand, and [Ru,5C,5H]+ as Ru(η5-c-C5H5)+ having a cyclopentadienyl ligand. 

Using light generated by an infrared free electron laser, action spectroscopy was performed on doubly charged complexes of the metalated dipeptide histidyl-histidine (HisHis). Metal cations used were zinc, cadmium, and copper. Molecular dynamics and quantum-chemical calculations were used to screen a large number of conformers, whose theoretical infrared spectra were compared to the recorded action spectra of these metalated complexes. The zinc and cadmium spectra display dominant features associated with an iminol binding motif of the HisHis ligand, where the metal ion coordinates with both pros () nitrogens of the imidazole sidechains, the terminal carbonyl oxygen, and the backbone nitrogen for which the hydrogen ordinarily bound here has migrated to a carbonyl. The copper complex was difficult to assign to a single species, because a few predicted bands are absent from the experimental spectrum. The theoretical single point energies were also calculated for all structures examined, and DFT methods were found to describe the ion conformer populations in the case of the zinc and cadmium chelates better than the MP2 prediction. 

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.