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Structure of Proton-Bound Methionine and Tryptophan Dimers in the Gas Phase Investigated with IRMPD Spectroscopy and Quantum Chemical Calculations
journal contribution
posted on 2020-03-11, 12:19 authored by Åke Andersson, Mathias Poline, Meena Kodambattil, Oleksii Rebrov, Estelle Loire, Philippe Maître, Vitali ZhaunerchykThe
structures of three proton-bound dimers (Met2H+, MetTrpH+, and Trp2H+) are
investigated in the gas phase with infrared multiple photon disassociation
(IRMPD) spectroscopy in combination with quantum chemical calculations.
Their IRMPD spectra in the range of 600–1850 cm–1 are obtained experimentally using an FT-ICR mass spectrometer and
the CLIO free electron laser as an IR light source. The most abundant
conformers are elucidated by comparing the IRMPD spectra with harmonic
frequencies obtained at the B3LYP-GD3BJ/6-311++G** level of theory.
Discrepancies between the experimental and theoretical data in the
region of 1500–1700 cm–1 are attributed to
the anharmonicity of the amino bending modes. We confirm the result
of a previous IRMPD study that the structure of gas-phase Trp2H+ is charge-solvated but find that there are more
stable structures than originally reported (Feng, R.; Yin, H.; Kong,
X. Rapid Commun. Mass Spectrom. 2016, 30, 24–28). In addition, gas-phase Met2H+ and MetTrpH+ have been revealed to
have charge-solvated structures. For all three dimers, the most stable
conformer is found to be of type A. The spectrum of Met2H+, however, cannot be explained without some abundance
of type B charge-solvated conformers as well as salt-bridged structures.